Doctoral Degrees (Plant Sciences)

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Open Access
'n Morfologiese studie van die genus Acacia Miller in Suid-Afrika
(University of the Free State, 1971-07) Robbertse, Petrus Johannes; Van der Schijff, H. P.
English: The genus Acacia is an extensive one with representatives in Africa, America, Asia and Australia. When Bentham revised the subfamily Mimosoideae in 1875 he divided the taxon into six subgenera. All the South African representatives of the genus were placed in the two subgenera Vulgares and Gummiferae. Bentham distinguished between the two subgenera by the differences in morphology of the stipules. Bentham's classification of the subgenera differs from that of Oliver (1871), whose grouping of the South African Acacia species is based on the morphology of the inflorescence. Species which are affected by this difference are A.albida, A.schweinfurthii and A.kraussiana. Because of this problem and the fact that, judging from the literature, there is some uncertainty regarding the application of taxonomic criteria, it is necessary that the whole genus be revised. Due to the extent of such a project it was decided to limit this investigation to the South African species with the main emphasis on characters which could be of taxonomic importance. Where it was deemed necessary a few species from other geographical areas were included in the investigation. Various characters were found which were valuable for considerations of phylozenetic history of the genus and for delimitation of taxa. On the basis of the presence of starch grains in the cotyledons and the morphology of the seedlings, A.albida, A.kraussiana and A.schweinfurthii were placed in a new subgenus, Farinosae. On the basis of these characters the subgenus Farinosae shows affinity with the subgenera Phyllodinae, Bothryocephalae and Pulchellae of Australia and certain Vulgares species of America. The subgenus Farinosae can possibly be phylogenetically regarded as the oldest extant taxon of the genus Acacia. With the species A.albida, A.krau8siana and A.schweinfurthii in a separate subgenus, the remaining South African members of the subgenera Vulgares and Gummiferae can be separated on the basis of classical features such as the morphology of the stipules and inflorescences. Other clear differences which were found between these two subgenera are as follows: (a)The flower of the Vulgares (and Farinosae) species contains a cup-like disc to which the filaments are adnate, and the ovary has a prominent pedicel (gynophore). In the flower of the Gummiferae species the disc is lacking and the ovary is almost sessile. A disc and pedicelled ovary are also found in the flower of A.albida and the name Feidherbia albida which Chevalier proposed for this taxon in 1934 is therefore not justified. The origin of the cup-like disc on which the stamens are found can probably be regarded as a relict of an ancient branched system on which stamens were borne and which later became reduced. (b) In the pods of the Vulgares (and Farinosae) species the fibre zone consists of both cross and longtitudinally arranged fibres, while the pods of the Gummiferae species have only longtitudinally arranged fibres, or none at all. (c) In the pinnules of the Vulgares (and Farinosae) species a few layers of spongy parenchymatous cells are found between the abaxial and adaxial palisade parenchyma cells. In the pinnules of the Gummiferae species the abaxial and adaxial palisade cells are continuous. (d) The seedlings of the Vulgares species have membranous or leaf-like stipules while the stipules of the Gummiferae species are spinescent. Hooked spines are absent on the Gummiferae seedlings but appear on the Vulgares seedlings either dispersed on the internodes or arranged in groups of two or three directly below the nodes. On the basis of the morphology of the flower, the anatomy of the pod and the morphology of the seedlings, the Vulgares and Gummiferae species can be divided into smaller groups and, in certain cases, into definite species. Keys have been compiled to facilitate the classification. Interesting differences between the Vulgares and Gummiferae species were noted with regard to the nocturnal movements of the leaves. These differences were, however, not very clear in all cases. In the case of certain species such as A.polyacantha and A.robusta the nocturnal movements are very conspicuous and specific (see Fig. 125). A hypothesis was postulated concerning the evolution of the inflorescence systems and inflorescences of the genus Acacia. The hypothesis includes a theory concerning the development of the involucel (cupula). Flowering dates of the different Acacia species are determined to a large extent by the morphology of the inflorescence system. Date of flowering can therefore be considered as a genetic character which nevertheless can be influenced to a certain extent by ecological conditions. The development of the ovule and the ontogeny of the seed was investigated. Ideas were put forward as to the possible homology of the ovule. A study of seed ontogeny produced information concerning the presence of endosperm in mature seeds of A.kirkii, A.tortilis and A.xanthophloea. This characteristic cannot be used as a criterium to remove these three species, as well as other exotic species containing endosperm in the seed, out of the genus Acacia (cf. Vassal, 1968). The arrangement of vascular tissue in the seedling, leaves and young shoots are discussed. Judging from the arrangement of the primary vascular bundles in the seedling there is probably a relationship between a monolacunar node with two leaf traces, a trilacunar node and a node which is called the "fifth type" by Takhtajan (1969). It may be concluded that the extant South African taxa of the genus Acacia can be distinguished from each other on a specific level. By using variable characters such as degree of pubescence and numerical taxonomic characters such as seed and leaf size it is possible to carry the subdivision of species too far. It is therefore recommended that the taxa with an extensive distribution, manifesting considerable variation, such as A.karroo Hayne, A.caffra Willd., A.reficiena Wawra (= A.luederitzii Engl.) and A.robusta Burch., should not be divided into smaller taxa until more information is available concerning the abovementioned characteristics. As a final summary, a key has been composed in which as many characters as possible have been used to distinguish between the South African Acacia species.
Open Access
Studies on the survival of Verticillium dahliae in soil
(University of the Free State, 1979-12) Baard, Schalk Willem; Pauer, G. D. C.
Various aspects concerning the survival of Verticillium dahliae Kleb. in soil, in the field, green-house, and laboratory were studied. 'With biological control in mind, attention was paid to factors affecting antagonists of V. dahliae and to colonization of microsclerotia (MS) in soil. Possible activation of antagonists during the period of absence of host plants was considered. Regression analysis of survival data indicated that individual MS are capable of surviving up to 43 months in soil in the absence of host plants. Soil moisture and temperature could not be related to the attrition of the pathogen. However, microbial colonization of the MS could have had an effect. Pathogen propagules were released into rhizosphere soil after the plants had been killed. Antagonistic fungi did not appreciably increase in the rhizosphere soil after the release of pathogen propagules. Bacteria and actinomycetes antagonistic to V. dahliae could be stimulated to increase in high pH soil by the addition of MS and fertilizers containing phosphate. In low pH soil, which favoured fungal antagonists, these tendencies were less obvious. The largest numbers of bacterial and actinomycetous antagonists occurred in high pH soil in which V. dahliae survived best. The attrition rate of MS was fastest in low pH (c. pH 4,5) soil. However, it was established that fungal antagonists were not mainly responsible for the attrition. Active microbial invasion of MS in soil was established by electron microscopic studies. Apparently lysed cell walls and eroded areas in the immediate vicinity of bacteria indicated that enzymes may be involved in the deterioration of the cell walls. It is concluded that antagonists are capable of actively destroying MS in soil, but this probably is a much slower process than that which was observed in acidified soil. Various techniques were used to establish the fact that attrition was much faster in acidified than in alkaline soil. The use of several techniques demonstrated that the effect of ·low pH on the attrition of the pathogen was real and not a reflection of the inadequacy of a single technique. It was also evident that the effect of low pH was fungitoxic and not fungistatic to the pathogen. Experiments to test the validity of the claim that the Al-ion is toxic to V. dahliae at very low concentrations indicated that the attrition of V. dahliae was as fast in low pH soil devoid of aluminium salts as in aluminium-amended soil. Soil acidification may be considered as a control measure. However, practical and economic considerations will prohibit its implementation. Apart from the cost factor, most plants do not tolerate such a low soil pH. Liming of the soil would be necessary, with the result that favourable conditions are again created for renewed increase in pathogen numbers. In a green-house study it was found that varying the moisture content of the soil and incorporating N and P, were ineffective as measures to reduce Verticillium populations. However, in flooded and air-dried soils, significant decreases occurred. The addition of urea at 0,25% or higher to the soil, reduced Verticillium populations appreciably. Various organic soil amendments gave diverse results. Maize residues, followed by soyabean pods caused the fastest attrition of NS in the soil. The addition of urea to soil at high rates would not be practical as a control measure. In situations where cotton can be produced in rotation with paddy rice, flooding may be of practical use.,Air-drying of the soil will depend on weather conditions, but it may be possible to devise agronomic practices to speed up the drying-out process and thereby reduce pathogen populations. This 'finding should, however, be studied under field conditions to verify the results obtained in the laboratory. The reduction of MS in the soil after amendment with plant residues holds promise as a control measure. Various crops could effectively be used in rotation with cotton and when the residues are incorporated into the soil, a significant attrition rate could be expected. However, the large quantity (1%) of residues required to effectively reduce the population of V. dahliae suggests that attrition would not be as fast under field conditions as it was under laboratory conditions. A long term rotation might thus be necessary. Electron microscopic studies on the fine structure of the MS indicated that they are composed of numerous thin- and thickwalled cells. The cell walls varied in thickness and were impregnated with melanin which also occurred in the matrix between the individual cells. These properties confer resistance to attrition to the MS. In the soil they apparently germinate over extended periods and give rise to limited hyphal growth which exhausts the reserves of the less resistant cells. However, some of the more resistant cells may remain· dormant and retain the viability of the MS. This may explain the survival of some propagules even under the adverse conditions to which they were subjected in the present study. It also explains why V. dahliae is such a difficult pathogen to eradicate under normal agronomic conditions.
Open Access
Die plantekologie van die Waterberg Platopark
(University of the Free State, 1983-03) Jankowitz, Willem Jacobus; Venter, H. J. T.; Van Rensburg, W. L. J.
English: The object of this study is to provide a foundation for management based on sound scientific procedures. To classify the vegetation into different homogenous plant communities, the wellknown Braun-Blanquet-technique was used. A monitorsystem was applied to determine baseline data to evaluate future changes in the plant composition. The basal cover and relative frequency of the grasses were determined by using an altered wheelpoint method. The production of the standing crop was obtained by using the tuft-clipping method and quadrat clipping method. The production of the available browsing of the trees and shrubs was also calculated. The key fodder plants of the most numerous animal, the eland, was obtained through a feed preference study. The standing crop of these key plants was used to provide a system which could be utilized to classify the plant communities according to the feeding preferences of animals. The vegetation of the Waterberg~plateau Park can be described as a homogenous deciduous tree savanna where the shrub layer has become closed thicket Acacia atxacantha,. The vegetation of the Waterberg-plateau Park was classified into six major communities which were divided into a further 23 smaller units. The absence of well defined ecotones was apparent especially between the TerminaZia sericea-plant communities. These deep sand communities cover the greatest (29 000 ha) part of the game park, followed by the PeZtophorum africanum-rock communities which cover more or less 10 000 ha. According to the results obtained from the monitoring project, certain palatable grass species, for example Anthephora pubescens and Digitaria polevansii did benefit by the veld fires while SporoboZus fimbriatus was adversely affected. Similar observations which are important for management were made 1n the tree and shrub layers where the unpalatable Ochna pulchra proved to be sensitive to fire. This species is also partly responsible for the scrub encroachment. For the rest very few changes were observed in the plant composition. According to results determined by other workers and the quadrat-clipping method, the standing crop values obtained by the tuft-clipping method was too high. The highest standing crop (946 kg ha-1) is furnished by the Anthephora pubescens - Eragrostis superba-plant community. According to the carrying capacity determinations the Terminalia sericea - Melhania acuminata-plant community can sustain the highest number of animals, while the gamepark as a whole can carry more or less 2000 grazers. The results acquired from food preference study has indicated that although the eland is a selective feeder, it utilizes a wide range (42 species) of plant species. It was observed that during winter the eland ate herbs and a great amount of dry leaves off the ground. Terminalia sericea and Lonchocarpus nelsii proved to be very high on the preference list of these animals. With the help of the standing crop of the key fodder plant species of the eland, it was determined that the woody Terminalia sericea - Melhania acuminata-plant community is the best eland habitat in the game park. The available knowledge, obtained from this project, was used to provide the park with the necessary recommendations to place the future management on a sound scientific basis.
Open Access
Genetic variability for yield and quality characteristics in South African cotton germplasm (Gossypium hirsutum L.)
(University of the Free State, 1999) Emeetai-Areke, Thomas Edison; Van Deventer, C. S.
English: The objective of this research was to study the genetic variability in South African cotton germplasm and to identify superior parental lines for the improvement of yield and quality characteristics. 2 Six parental lines (Irco, Palala, OR27, 2131-2-5, DPAc90 and Sicala) were crossed in diallel fashion. The parents and their F1-offspring were planted in four experiments at two locations, Rustenburg and Loskop, in two successive years, 1997/1998 and 1998/1999. Twenty agronomic and yield characteristics were measured. The data for each characteristic were subjected to a diallel analysis, using the computer program "Agrobase". 3 Significant mean differences were found among the parental lines and their F1-offspring for most of the characteristics measured at both locations, during the two successive years. The only exceptions were SI and LB. On average, Palala and Sicala proved to be the best yielders at Rustenburg, while Irco yielded the best at Loskop. Sicala proved to be the best for FL in both environments, while OR27 was on average the best for FS at both Rustenburg and Loskop. Palala was the best for FU at Loskop, while bath Irco and 2131-2-5 ranked the best at Rustenburg. For the character MC, all the parents were within the acceptable range of 3.5 - 4.5. 4 OR27 proved to be the best combiner for yield and most of the yield components, at both Rustenburg and Loskop. The parental line Sicala proved to be the best general combiner for fibre length, while OR27 was the best general combiner for fibre strength and fibre uniformity at both locations. Parental lines DPAc90 and Irco were the best general combiners for MC at Rustenburg and Loskop respectively. 5 The G.C.A.:S.C.A. ratios were close to unity for most of the characteristics, including yield. Some of the characteristics, such as HC (31.6 - 46.8), GOT2 (1.7 - 17.3), FS (4.6 - 15.7) and FL (2.9 - 14.4) had relatively high G.C.A.:S.C.A. ratios. 6 Extremely high broad sense heritabilities were found for HC (0.92 - 0.98), FL (0.92 - 0.95) and GOT2 (0.77 - 0.93). Extremely high narrow sense heritability was found for HC (0.88 - 0.92), and relatively high values were also computed for FL (0.32 - 0.77), GOT2 (0.42 - 0.87), and FS (0.48 - 0.63). 7 Extremely high significant genetic correlations were computed between SCYP and LYP (0.97), SCYPLT and LYP (0.97), SCYPLT and LYPLT (0.98), SCYP and HC (0.98), LYP and HC (0.97), SCYP and TBF (0.96), SI and U (0.98) and FL and FS (0.97). 8 Relatively high positive correlated response was found between SCYPL Tand GOT2, U, LB, TBF and UHB in bath trials at Rustenburg. In the trials planted at Loskop characteristics like SCYP, SCYPL T, LYP and HC, had relatively high, positive correlated response with most of the other characteristics. High negative correlated response was found between SCYP and GOT, BS, HC and FL in the Loskop trials, while LYP had a negative response with GOT and BS. 9 Mid-parent as well as high or best parent heterosis were highly positive for SCYP and LYP, in most of the crosses. The cross Sicalaxlrco, showed on average the highest amount of heterosis at Rustenburg and Loskop during 1997/98 season. The amount of heterosis for SCYPL Tand LYPL T varies from large negative to large positive values.
Open Access
Fusarium dry rot of potatoes: etiology, epidemiology, toxicity and control
(University of the Free State, 1999-05) Theron, Daniël Jacobus; Marasas, W. F. O; Wingfield, M. J.
English: Eighteen Fusarium species were isolated from dry- and stem-end-rotted potato tubers in South Africa. Samples with dry-rot lesions were easily obtained, even though samples were taken directly after harvest and Fusarium dry rot is a post-harvest disease, highlighting the importance of this disease in South Africa. Nine species (F. oxysporum, F. so/ani, F. sambucinum, F. acuminatum, F. crookwellense, F. graminearum. F. culmorum, F. scirpi and F. equiseti) caused typical dry-rot lesions on artificially inoculated potato tubers. Fusarium oxysporum and F. solani were predominantly isolated and the most virulent. These results differ from those obtained in other parts of the world, especially the northern hemisphere, where F. sambucinum and F. solani are mainly associated with Fusarium dry rot. Control of Fusarium dry rot with mancozeb or thiabendazole, the only fungicides registered for control of this disease in South Africa, was unsatisfactory. This was especially evident when F. oxysporum was the cause of the rotting. It is recommended that effective fungicides against F. solani and F. oxysporum, e.g. prochloraz, should be applied as soon as possible after harvest and that potatoes should be stored at 5°C. Thiabendazole resistance, which is a problem in North America and Europe, appears to be absent in local isolates of F. solani, F. oxysporum and F sambucinum. The use of seed pieces under local conditions is risky. When used due to scarcity of seed tubers or economic reasons, good quality seed tubers should be used and treated with carbendazim on the day prior to a spring planting under irrigation in soils with a temperature <18°C. Fusarium solani [= F. solani var. coeruleum and F. coeruleumi is commonly associated with dry rot of potatoes world wide. The local F. solani isolates were compared to foreign F. solani, F. solani var. coeruleum and F. coeruleum isolates. Local and foreign F solani isolates did not differ morphologically and with respect to their optimum growth temperatures and matched the description of F. solani. However, foreign isolates referred to as F. solani var. coeruleum and F. coeruleum differed from the F. solani isolates. Grouping these isolates together under one species (F. solani) is thus disputable. In contrast to other countries, Fusarium sambucinum [= F. sulphureum and F. roseum var. sambucinum J, is not commonly associated with dry rot of potatoes in South Africa. The local isolates were compared with foreign isolates because they appeared to be atypical of F. sambucinum sensu lata. Moreover F. sambucinum sensu lato has been divided into three species i.e. F. sambucinum sensu srticto, F. torulosum and F. venenatum. Morphologically and on the basis of optimum temperature for growth and dry-rot development, the local isolates could not be differentiated from the foreign isolates, but no vegetative compatibility occurred between them. Local and foreign isolates could be assigned to six and three vegetative compatibility groups, respectively. Sexual crosses between the local isolates and the Gibberella pulicaris strains, were unsuccessful. However, crossing some local isolates with each other resulted in fertile crosses, producing ascospores significantly larger than those produced when the G. pulicaris strains were crossed. This is the first report of South African F. sambucinum isolates from potatoes producing a teleomorph. Five of the local F. sambucinum isolates generated bands of the expected size with F. venenatum primers, indicating that these isolates are conspecific with F. venenatum. However, morphologically these isolates did not agree with the description of F. venenatum and their growth rates were faster. It appears that these South African isolates are members of a new species of Fusarium with a newly discovered Gibberella. The genus Fusarium contains important mycotoxin-producing species which have been implicated in human and animal diseases. Diseased or damaged tubers are often fed to cattle, stressing the urgency to determine the possible threat posed to the industry. Except for F. graminearum Gr. 1, isolates of the other 17 Fusarium species tested, caused death in one-day-old Pekin ducklings, indicating the involvement of mycotoxins. Differences in the toxicity of the various Fusarium spp., as well as within isolates of the same species, were evident. Fusarium nygamai appeared to be the most toxic, followed by F. acuminatum and F. moniliforme. The fact that South African dry-rot isolates proved to be toxic to ducklings emphasizes the need to determine the identity of toxins produced, particularly if these mycotoxins can be produced in colonized potato tubers. This dissertation has made a contribution towards the better understanding of, and the development of an integrated control strategy for Fusarium dry rot of potatoes in South Africa.
Open Access
Inheritance of agronomic and quality characteristics in sweet potato (Ipomoea batatas (L.) Lam.)
(University of the Free State, 2000-03) Kanju, Edward Eneah; Van Deventer, C. S.
English: 1. The study was undertaken to estimate genetic parameters like variance components, general and specific combining ability effects, phenotypic and genetic correlation coefficients, heritability coefficients, heterosis, genotype by environment interaction and genotypic stability for various characteristics of sweet potato. 2. Four male parents (Kenia, Brondal, Impala and Mafutha) were crossed in a factorial fashion with three female parents (Bosbok, Koedoe and Ribbok). The offspring and their parents were planted in three different environments at Roodeplaat, near Pretoria. One trial was planted under irrigation in 1998. The other two were planted in 1999 under irrigation and rainfed conditions, respectively. Twenty-five different agronomic and quality characteristics were measured. The computer program AGROBASE (1997) was used to perform the different analyses of variance such as the Line x Tester and additive main effects and multiplicative interaction, and correlations. 3. Significant differences were found among the averages of the parents and their offspring for nearly all characteristics except NMRW. The G x E interactions were significant for TRW, MRN, TSS, Hl, Pl, VC, lO, llT and Nl. Kenia and Mafutha were outstanding with regard to their high dry matter content. 4. The male parent Mafutha had the largest GCA effect for TRN (0.65), RFC (0.46), OMC (0.01) and HI (0.04). Impala had the largest GCA effect for TRN (0.75), Bosbok for RSC (1.55) and Kenia for OMC (0.02). No significant SCA effects were found between the crosses for economic important characteristics. 5. GCA: SCA ratios across environments for all root yield characteristics of economic importance were close to unity except for TRN with a ratio of 8.6. Extremely high GCA: SCA ratios were found for LLT (81.65), VC (61.56), La (54.12), PL (44.72) and VIL (39.25). 6. The VAIVG ratios were relatively high for most of the characteristics except for MRW (0.59) and TRW (0.68). 7. Larger heritability coefficients were found from the female parents for RSC, RO, LVP and PP. Combined narrow and broad-sense heritabilities estimated over both parents (h2 M+F) were negative for most economic important characteristics. Relatively high narrow-sense heritabilities were found for RFC (0.47), VL (0.46), VIL (0.46), LVP (0.45), La (0.48) and LLT (0.49). Narrow-sense heritability estimates by the parent-offspring regression method ranged from negative for NMRW and TRW, to 1.44 for PL. Among the characteristics of economic importance, OMC had the highest estimate (0.66) followed by RSC (0.57) and TRN (0.54). 8. Highly significant phenotypic correlation coefficients were found between OMC and TSS (0.75), TRN and MRN (0.86), VIL and VL (0.90), LLT and LO (0.84), NL and LO (0.83), NL and LLT (0.78), MRN and TRN (0.79), Hl and FW (-0.93) and HI and VL (-0.77). Extremely high and significant genetic correlations were found between TRW and MRW (0.92), LVP and NMRW (0.94), TRN and NMRN (0.88), Hl and TSS (0.94), TSS and VIL (0.91), TSS and NL (0.96), OMC and Hl (0.91), OMC and PP (0.93), OMC and LLT (0.97), FW and Hl (-0.91), Hl and LL (-0.95), VL and VIL (0.94), PL and FW (0.91), TRW and LL (0.91), VC and PP (0.93), LO and LLT (0.92) and between FW and LL (0.93). 9. Correlated response to selection indicates that selection for high HI is likely to increase MRW (0.02) and MRN (0.07 - 0.08). Furthermore, selection for long vines is likely to increase TSS (0.12 - 0.22), MRW (0.06), MRN (0.11), and TRW (0.08). 10.When combined across parents and environments, mid-parent heterosis was negative for all root yield and quality characteristics of economic importance except RO, which showed a positive heterosis of 12.9%. However, positive heterosis was found for individual crosses at some of the environments. 11.The AMMI stability value (ASV) showed that the parents were less stable than their crosses. The cross Koedoe x Impala was ranked first for MRN, Ribbok x Brondal for TRN, Ribbok x Kenia for MRW and Ribbok x Impala for TRW. The cross Koedoe x Impala showed significant levels of mid-parent heterosis for stability for MRN (-98.3%), Ribbok x Brondal (-89.5%) for TRN, Ribbok x Impala (-89.4%) for MRW and Ribbok x Impala (-95.4%) for TRW.
Open Access
Genetic variation among land races of Cucurbita moschata and inheritance of its fruit yield and quality
(University of the Free State, 2000-07) Gwanama, Cousins; Labuschagne, M. T.; Botha, A. M.
English: Tropical pumpkin (Cucurbita moschata Duchsne) is one of the most important vegetable crops in Africa. Apart from its phylogenetic relationships with other members of the genus, little information is available for this species. This study explored the amount of genetic variation in Zambia and Malawi for possible use in breeding. UPGMA cluster analysis from 3~) polymorphic and 105 monomorphic DNA fragments amplified by 16 RAPD markers showed four clusters, with genotypes from Malawi mainly clustering in three clusters while all genotypes from Zambia and three from Malawi clustered in one cluster. Six land races from this classification were mated in a daillel fashion and parents and progeny evaluated for fruit yield and quality. Variety effects were significant for the time to female anthesis and first fruit maturity, the weight of the first fruit, mean fruit weight and soluble solids. These characters could be improved by selection. Only for soluble solids were the progeny as a set different from the set of parents. Both variety and specific heterosis were significant FOR some of these traits, offering opportunities for heterosis breeding.
Open Access
Control of foliar rusts of wheat in South Africa with special emphasis on Puccinia striiformis f. sp.Tritici
(University of the Free State, 2000-11) Boshoff, Willem Hendrik Petrus; Pretorius, Z. A.
English: Stripe rust, caused by Puccinia striiformis Westend. f. sp. tritici Eriks., has become an endemic disease of wheat (Triticum aestivum L.) in South Africa after being observed for the first time near Moorreesburg, Western Cape, during August 1996. Pathotypes (pts.) detected in surveys were 6E16A- with virulence to Yr2,6,7,8,11,14,17 and Yr19, and 6E22A- with added virulence to Yr25. Stripe rust isolates found on Hordeum murinum L. in the Western Cape were identified as pt. 6E 16A- whereas both pts. 6E 16A- and 6E22A- were collected from Bromus catharticus Vahl in the eastern Free Sate. The possible role that grass species may play in the over-summering of the stripe rust pathogen has not yet been fully established. However, stripe rust infections have been found on summer-sown wheat in the south Western Cape during 1998, volunteer wheat growing in the summer and autumn months in the eastern Free State from 1998 to 2000, and on summer-sown wheat in Lesotho. The reaction of 55 South African and 18 foreign wheat cultivars was determined to pts. 6E16A- and 6E22A- in both the seedling and adult plant stage. The occurrence of stripe rust head infections was studied using 16 spring wheat cultivars and 17 supplemental lines. Six of the 55 local wheat cultivars expressed seedling resistance, 18 appeared heterogeneous and 31 were susceptible. The mean area under the disease progress curve (AUDPC) determined in the field for 42 cultivars over a three year period showed that 11 cultivars expressed high levels of complete or adult plant resistance (AUDPC <200). Twelve cultivars expressed intermediate levels of resistance (AUDPC 200 to 500) and 19 displayed AUDPC values of 500 to 1598. The percentage head infection was positively correlated to stripe rust severity on flag leaves. Of the 18 foreign cultivars evaluated 10 were resistant in both seedling and adult plant stages. The remaining eight cultivars were susceptible as seedlings but showed high levels of adult plant resistance in the field. Field trials were conducted from 1997 to 1999 to determine the effect of stripe and leaf rust (P. triticina Eriks.) epidemics on yield and quality of wheat. Five triazole fungicides, applied at two growth stages on three cultivars in the south Western Cape during 1997, resulted in a mean decrease of 31% in the AUDPC calculated for stripe rust infection. The application of fungicides closely to, or just after head emergence, resulted in a 65 to 74% decrease in the occurrence of stripe rust head infections. In contrast, head infection was reduced by only 8% when fungicides were applied at the seven leaf stage. Combined seven and flag leaf treatments with propiconazole, averaged over the three cultivars, resulted in a 56% yield increase, followed by increases of 49%, 44%, 39% and 25% with tebuconazole, flutriafol, bromuconazole, and flusllazole, respectively. In the absence of disease during 1998 no fungicide treatment resulted in a significant yield or hectolitre mass increase in any of the trials. The application of eight fungicides at both seven and flag leaf stages at Langgewens in the Western Cape during 1999, resulted in a mean decrease of 65% in the AUDPC, calculated for leaf rust severity. Combined seven and flag leaf treatments resulted in a mean yield increase of 56%, followed by 50 and 15% for the flag leaf and seven leaf treatments, respectively. Over treatments applied, yield increases varied from 24% for bromuconazole to 53% for epoxiconazole/carbendazim. Furthermore, the application of a flag leaf, and combined seven and flag leaf treatments, resulted in a significant increase in hectolitre mass. During 1999 the combination of triticonazole seed treatment with a propiconazole flag leaf spray on the cultivar Gariep in the eastern Free State resulted in a 91% decrease in the stripe rust AUDPC, and an associated 36% yield increase. Hectolitre mass increased by 3% and protein content decreased by 4% for the latter treatment. Triticonazole seed treatment had a 54% decrease in the AUDPC resulting in 16 and 2% yield and hectolitre mass increase, respectively. The best control of stripe rust was obtained with a combined seven and flag leaf treatment with propiconazole, as well as triticonazole seed treatment combined with a seven and flag leaf treatment of propiconazole. The latter two treatments resulted in a 49% yield increase. The results obtained in yield loss studies emphasise the importance of research aimed at the genetic control of rust diseases of wheat in South Africa. Effective and longlasting genetic control can only be obtained by coordinating future research, continuous monitoring of changes in the pathotype population, the regular collection of germ plasm carrying new or unused sources of resistance, characterising current sources of resistance, and by deploying available sources of resistance in a responsible manner. The result of successful genetic control is not only aimed at preventing the repeated application of fungicides, but also at reducing risk in wheat production, thereby ensuring more stable yields of high quality.
Open Access
Isolation and characterization of a possible polygalacturonase: inhibiting protein from wheat
(University of the Free State, 2001) Kemp, Gabré; Pretorius, Z. A.; Van der Westhuizen, A. J.; Bergmann, C. W.
English: The presence and possible role of polygalacturonase-inhibiting protein (PGIP) in wheat (Triticum aestivum) as part of the plant's defense reaction following leaf rust (Puccinia triticina) infection were investigated. Through its ability to inhibit fungal endopolygalacturonase (EPG) that breaks down the plant cell wall during colonization, this protein is known to play an important role in the natural defense arsenal of dicotyledonous plants. The presence of PGIP in monocotyledonous cereals has never before been conclusively proved. A preliminary investigation using a polyclonal antibody raised against a purified bean PGIP (PGIP-I) revealed the induction of a possible PGIP of ±37.0 kDa following fungal infection, while an inhibition assay of EPG from AsperglÏ/us niger showed a decrease in PGIP activity. Through ion-exchange and size exclusion chromatography the presence of wheat PGIP was subsequently confirmed by the purification of a ±36.0 kDa inhibitor, which proved specific for the EPG of Coch/iobo/us sativus and not A. niger. Using a more specific anti-PGIP antibody (PGIP-II) the presence of this protein in wheat was also confirmed through immunoblotting. The expression of PGIP in wheat following salicylic acid (SA) treatment and fungal infection in terms of C sativus EPG inhibition was recorded. While SA treatment showed an induction of PGIP at protein and activity levels, fungal infection repeated the reduction in PGIP activity as previously observed. Using PGIP-II in immunogold localization the expression of PGIP in wheat leaves was confined to the plant cell wall and the periphery of the haustorium in the cytosol. Attempts to clone the wheat pgip gene through the polymerase chain reaction (peR) using degenerate primers were inconclusive, as fragments amplified did not exhibit significant similarity to PGIP from dicotyledonous plants. These results therefore indicate that wheat expresses a ±36.0 kDa PGIP in reaction to fungal and SA treatment, but fungus-related factors originating from either the plant or the fungus apparently induce the EPG activity to higher levels, or suppress the PGIP activity to lower levels, both recordable as a decrease in PGIP activity and having the potential to enhance plant disease.
Open Access
Biology and control of Sclerotium rolfsii on groundnut in South Africa
(University of the Free State, 2001-05) Cilliers, André John; Pretorius, Z. A.; Van Wyk, P. S.
English: Information gleaned from this study has stimulated new questions regarding the genetic structure, population dynamics and control of Sclerotium rolfsii. This work can hopefully serve as a foundation for the further study of this fungus in South Africa and elsewhere in the world. The population of the fungus in South Africa was studied and the 121 isolates collected were found to belong to 13 different mycelial compatibility groups (MCG), occurring on various crop and other plants in different geographic localities. Vague associations between MCG, host plant and geographical area could be observed. The genetic fingerprinting technique of amplified fragment length polymorph isms was found to be an effective tool to distinguish between MCGs of S. rolfsii. This technique has never before been used for this purpose, even though other genetic techniques have been used in other studies. No previous study, however, was able to distinguish isolates within MCGs, as this study was able to do. The hypothesis was also made that isolates within a MCG are not clonally derived, based on the differences observed between isolates in the same MCG, the different host plants and the different geographic areas from which the isolates originated. The pathogenicity of MCGs of S. rolfsii to groundnut appeared to be significantly different from group to group, but the results of field trials suggested that isolates were not fixed into specific MCGs, even though a controlled glasshouse experiment did not support this. The phenomenon of MCG switching has never been reported for this fungus, even though it has been recorded for other fungi. Certain isolates also appeared to be more pathogenic to groundnut than others. Mycelial compatibility group E consistently emerged as a virulent pathogen of groundnut. No groups were found to e specific to any of three other crop plants tested. The control of the fungus in groundnut fields was found to be possible with the use of an inversion plough in trials conducted over two consecutive seasons. A fungicide was identified that suppressed S. folfsii but not Trichoderma harzianum, a naturally occurring biological antagonist of the pathogen in the soil. The application of the fungicide difenoconazole at 12.5% of the registered concentration for groundnuts did not reduce disease in the field. The application of T. harzianum and difenoconazole in the early stages of groundnut plant development had no effect on yield or disease incidence. levels of disease in the field were found to increase with a decreased plant density. This observation was attributed to increased soil erosion in the field as a result of the sparser plant density. Sclerotium roltsii is a virulent pathogen of numerous crop plants in South Africa and this study has provided some answers to questions regarding the biology and control of this fungus. However, much still has to be discovered and may future scientists find some inspiration from what was done here. Key words: Sclerotium faItsii, southern stem rot, population, mycelial compatibility groups, AFlP analysis, pathogenicity, control, inversion plough, integrated pest management.
Open Access
Inheritance of stem borer resistance in maize (Zea Mays L.)
(University of the Free State, 2001-05) Andre, Adriano Muiocoto; Labuschagne, M. T.; Van Rensburg, J. B. J.
English: The stem borer Busseala fusca (Lepidoptera: Noctuidae) is an important pest in maize production in South Africa and many other countries South of the Sahara. The mean goal of the present study was to gather information about the genetic and phenotypic characteristics of B. fusca resistance in maize as a help to understand the nature of the resistance in order to overcome the difficulties standing in the way of transfer of the resistance from available sources to the local and adapted cultivars. The inheritance was studied through assessment of the resistance on basis of phenotypic expression after artificial infestation with first instar larvae of B. fusca of 36 crosses of 18 susceptible inbred lines with two sources of resistance, CML 139 and Mp706. Plants were evaluated for characters like leaf feeding, larval mass gain, internal damage and yield losses. A scaling test was used to analyse the data. Results indicated that additive, dominant and non-heritable parameters were all important for B. fusca resistance. GCA and SCA values indicated good performance of the crosses for additive and dominant gene effects (heterosis). The correlation coefficient was used to evaluate the relatedness of three parameters of assessment of the resistance and the result indicated that there are significant correlations between leaf feeding, larval mass gain and internal damages caused by the insect. Different levels of inheritance from the two sources were seen in each cross indicating that the resistance is inherited differently, depending on the source used. F2:3 lines were obtained from selected crosses (CML 139 xP608) and (Mp706 xP608) for AFLP analysis. The analysis of the 10 categories of phenotypic assessment evaluated for the fragment segregation indicated that additive gene contribution from the parents was present at several loci. This was in agreement with negligible one locus non allelic interaction found by the scaling test for absence of epistasis. Different fragments were found to be specific for resistant parents and the progeny, which indicated that dominance was again present in the inheritance of the resistance. In this study we have concluded that despite attempts to improve the varieties' resistance by transfer of the resistance from resistant sources to more adapted varieties, the polygenic nature of the resistance and the presence of high levels of non-inherited parameters are still the most important cause of ineffective use of conventional methods of breeding. The use of markers to tag the genetic information about the inheritance of the resistance in cross progenies of resistant and susceptible varieties is seen as one of the ways to overcome this barrier. Unfortunately the use of this important tool is still not perfected for use in this particular area of science. Until the perfection of molecular marker technology, the recurrent selection approach will have to be used for insect resistance improvement in maize cultivars.
Open Access
Inheritance of nitrogen use efficiency components in maize
(University of the Free State, 2001-12) Ranthamane, Matla Martin; Van Deventer, C. S.
English: The general objectives of this research were to study the genetic variability for nitrogen use efficiency components, to identify suitable inbred parental lines with out standing nitrogen efficiency characteristics, to calculate the inheritance of nitrogen use efficiency (NUE) components and to develop a strategy for the development of nitrogen efficient maize hybrids. Four parental lines (AC8342, CML394, K64R and M162W) were individually crossed to each tester (CML351, CML202 and CML216) in a Line x Tester fashion to produce FI hybrids seed. The FI hybrids were evaluated in two different environments each under two different nitrogen levels. Six agronomic and yield characteristics and three nitrogen use efficiency components were measured. The data were analysed using the computer program' AGROBASE 2000'. Analyses such as Line x Tester, additive main effects and genetic correlations were performed. In the combined ANOVA, significant differences between locations were found for all characters measured. The nitrogen levels differed significantly for PLHT and GNC. The FI hybrids differed significantly for PLHT, GY, SDW, SDN and GNC. Significant differences were also found among the FI hybrids for PLHT, GY, SDW, SDN, HI, GNC and SNC at Doompan. Similar significant differences were observed at Bethlehem except for HI and SNC. Significant variability between FI hybrids was observed for yield efficiency, recovery efficiency and physiological efficiency. There was a large'" environmental difference between locations for the nitrogen use efficiency components. In the simple ANOVA, significant differences between FI hybrids were observed for yield efficiency, recovery efficiency and physiological efficiency at Doompan. Significant differences were also . found between the FI hybrids for yield efficiency and recovery efficiency at Bethlehem. With a few exceptions in the Bethlehem trial, the selection indices of the F, hybrids for PLHT were less than one. The selection index for GY exceeds the value of one in three and nine of the F, hybrids in the Doornpan and Bethlehem trials respectively. For SOW three of the F, hybrids in the Doornpan trial had values above one and nine of the F, hybrids in the Bethlehem trial. The selection index values for SDN were lower than one in the Doornpan trial. In the Bethlehem trial the values of three of the crosses were larger than one. The selection indices for HI in both trials were relatively high. At Ooornpan the F, hybrids responded significantly different to the two N-Ievels for PLHT, GY, SDW, SDN, HI and GNC. Significant differences between the F, hybrids at the low N-Ievel were found for all characters measured except for SNC. At the high N-level the F, hybrids differed significantly for PLHT, GY, SDW, SDN, HI and GNC. At Bethlehem, FI hybrids responded significantly different to the two N-levels for GY, SON and HI. Significant differences were found between the F, hybrids at both N-levels for PLHT, GY, SDW, SDN and GNC. At Doornpan significant differences existed between the F, hybrids for yield efficiency, recovery efficiency and physiological efficiency. At Bethlehem significant variability was found between the FI hybrids for all three nitrogen use efficiency components. The two N-Ievels had a significant effect on the GCA-values of the lines and testers for PLHT and SDN in the Doornpan trial. Significant variability was also found between the GCA-values for PLHT, GY and SDN at both N-levels. The GCA-values of the inbred lines in the Bethlehem trial responded differently to the two N-Ievels for GY and SON. Significant differences were found between the GCA-values of the inbred lines for PLHT at both N-Ievels and for GY only between the testers at the high N-Ievel. At Doornpan significant differences between the GCA-values of the lines were found only for physiological efficiency and between the testers for yield efficiency and recovery efficiency. At Bethlehem the GCA-values for testers differed significantly for yield efficiency and recovery efficiency. No significant differences were found between. the GCA-values of the lines for nitrogen use efficiency components at Bethlehem. The FI hybrids responded differently with regard to their SCA-values for GY, SOW. HI, GNC and SNC in the Doornpan trial. Significant differences for SCA-values were found for PLHT, GY, SOW, SON and SNC at both N-Ievels. In the Bethlehem trial the two N-levels had only an effect on the SCA-values of a few of the hybrids for SON and GNC. Significant differences were found between the SCA-values of the FI hybrids for PLHT, GY, SOW, SON and GNC at both the low and the high N-Ievels. The F I hybrids showed significant differences between the SCA-values for all three nitrogen use efficiency components in the Doornpan trial and only for yield efficiency and recovery efficiency in the Bethlehem trial. The GCA:SCA ratios differed significantly at the two N-levels for PLHT in the Doornpan trial. With the exception of SON the additive variance components of SOW, GNC and SNC were higher at the high N-level. In the Bethlehem trial the GCA:SCA ratios for PLHT, SDW and GNC were higher at the high N-level. SOW had the largest GCA:SCA ratios under both N-levels. The GCA:SCA ratios for recovery efficiency was larger than that of yield efficiency. In the Doornpan trial the narrow-sense heritabilities for PLHT and GNC were the largest under the high N-level. The narrow-sense heritabilities for nitrogen use efficiency components were very low. The narrow-sense heritabilities of PLHT, GY, SOW, GNC and SNC were much larger at the high N-Ievel at Bethlehem. Again the heritabilities obtained for nitrogen use efficiency components were very low. Significant phenotypic correlation coefficients were found between GY and PLHT at the high N-Ievel in the Doompan trial. Significant correlation coefficients were also found between GY and SDN at both N-Ievels. In the Bethlehem trail significant correlation coefficients existed between GY and PLHT and between GY and SON at both N-levels. GNC was significant but negatively correlated with GY at the high N-level. The genotypic correlation coefficients in the Doompan trial were significant between GY . and SDN and between GY and SNC at both N-Ievels. HI and GY were significantly correlated at the high N-Ievel. In the Bethlehem trial SDN was highly correlated with GY at both N-levels. GY was significantly correlated with PLHT at the high N-level, negatively correlated with SDW at the low N-Ievel and negatively correlated with GNC at the high N-Ievel. In the Doompan trial GY at the low arid the high N-levels was significantly correlated with yield efficiency. It was also significantly correlated with recovery efficiency at the high N-level. In the Bethlehem trial GY was significantly correlated with the three nitrogen use efficiency components at the high N-level. Recovery efficiency was significantly correlated with GY at the low N-level.
Open Access
Organically based strategies used by small-scale farmers in Lesotho for the sustainable management of soilborne diseases
(University of the Free State, 2002-11) Kena, Mapotso Anna; Swart, W. J.; Ralitsoele, S.
English: Damping-off of vegetable seedlings caused by Rhizoctonia solani Kuhn., Pythium ultimum Trow. and Fusarium oxysporum Schlecht. cause serious losses in seedbeds in Lesotho. Composts prepared from poultry, cattle, pig and sheep manure and commonly used by Lesotho farmers were shown to decrease disease severity and increase plant biomass. Cattle, pig and poultry manure composts gave the best disease suppression and stimulated the growth of vegetable seedlings. Composted sheep manure however, did not suppress damping-off nor increase seedling biomass. Seed germination was also significantly suppressed in this compost. High concentrations of phytotoxic elements were possibly responsible for this phenomenon. Disease suppression was also investigated in field studies. Composted cattle, pig and poultry manures significantly suppressed seedling damping-off. Sheep manure compost was also able to reduce damping-off severity under field conditions but to a lesser extent than the other three composts. General microbial activity in field soil including fungal populations present in the four tested composts was evaluated in the laboratory using FOA. Composted cattle, pig and poultry manure displayed a significantly higher level of microbial activity and consequently yielded more fungal colonies. The lowest microbial activity was observed in composted sheep manure. Research conducted on the suppression of R. so/ani, P. ultimum and F. oxysporum with crude extracts of Rhamnus prinoides L. Herit, Artemisia afra Jacg. ex Willd., Leucosidea sericea Eckl. & Zeyh and Melia azedarach L, confirmed their ability to suppress these pathogens. Mycelial growth of R. so/ani, F. oxysporum and P. ultimum was inhibited in vitro by extracts of R. prinoides, L. sericea and A. afra. The growth of these pathogens was however not significantly suppressed by extract of M. azedarach. The plant extracts were also able to suppress damping-off of seedlings when added to soil. Populations of R. solani, F. oxysporum and P. ultimum in soils treated with these extracts were also significantly reduced. Disease reduction was highest 7 and 14 days after treatment with the extracts. The combination of composted animal manures with plant extracts resulted in a reduction of general soil microbial activity, especially fungi. Microbial activity was most reduced in cattle, pig and poultry manure composts while the microbial activity in composted sheep manure was not affected by plant extracts. In fact in some cases, the application of plant extracts resulted in an increased microbial activity in sheep manure. Disease suppression in greenhouse studies was not negatively or positively affected by the addition of plant extracts. The present study confirms that composted manure of cattle, poultry and pig as used by Lesotho farmers, can be effectively used to control damping-off of vegetable seedlings in seedbeds. The use of sheep manure is however still questionable due to its negative effect on seed germination and general plant growth. Extracts of L. sericea, A. afra, R. prinoides and M. azedarach as used by Lesotho farmers, also have the potential to suppress soilborne pathogens. They can be used to control soilborne diseases either individually or in combination with animal manure composts.
Open Access
Epidemiology of grain mould of sorghum in South Africa and Ethiopia
(University of the Free State, 2002-11) Terefe, Tarekegn Geleta; Swart, W. J.; McLaren, N. W.
English: A study aimed to determine grain mould fungi associated with sorghum cultivars grown In two localities (Cedara and North West/Free State) in South Africa indicated Fusarium subglutinans and F. graminearum to be the predominant species. Fusarium proliferatum followed by F. thapsinum was however more commonly isolated from Ethiopian cultivars. Bipolaris sorghicola and Phoma sorghina were found in some cultivars from both countries. C.urvularia clavata was frequently isolated from South African sorghum cultivars. C. lunata was encountered occasionally although its prevalence was relatively high in Ethiopian cultivars. Alternaria alternata had the highest incidence in cultivars from both countries. Colletotrichum graminicola (Cl. Graminicola) occurred only in grains from Cedara. F. proliferatum and C. clavata were isolated from the embryos of many cultivars. F. graminearum, A. alternata, P. sorghina and Cl. graminicola were occasionally found in embryos of sorghum grains. Pathogenicity studies showed that F. subglutinans, Cl. graminicola and B. sorghicola were important in causing various kinds of grain damage (seed discolouration, 1000 grain mass and seed germination). Grain damage tends to increase when many species occurred together rather than separately. Most Fusarium spp., B. sorghicola and C. clavata had relatively higher transmission rates to seedlings and significantly reduced seedling vigour. Pathogens with embryo invading capacity had generally higher rates of transmission. During a three-year period (1999/2000 to 200112002), the relationship between weather variables and grain mould development was assessed in field trials at Cedara, South Africa. Significant positive correlations were observed between the incidence of A. alternata, Curvularia spp. (C. lunata and C. clavata), Fusarium spp. (F. proliferatum and F. graminearum), B. sorghicola and minimum temperature, total and frequency of rainfall (average during 4-6 or 5-8 weeks after flowering based on hybrid sorghum used). However, significant correlations could not be established between seed damage parameters such as seed germination and 1000-grain mass and incidence of different grain mould fungi. Linear models that described relationships between disease incidence and minimum temperature and between disease incidence and rainfall frequency were developed. Models that used minimum temperature as predictor explained 60 to 82% of variation in disease incidence. Frequency of rainfall explained 93% of the variation in disease incidence in one cultivar. The most susceptible grain development stage of major Ethiopian sorghum cultivars was determined in field trials. Higher infection incidences and damage to grains were associated mainly with dough stage of grain development. Significantly higher incidence of major mould fungi (Fusarium proliferatum, F. thapsinum and F. graminearum and B. sorghicola) consistently occurred during milk to dough stages. Incidences of C. lunata and P. sorghina were generally lower at all stages. Infection by P. sorghina increased at anthesis. Frequency of Alternaria spp. and Epicoccum spp. increased significantly after the dough growth stage. Grain colonisation by Cladosporium spp. was not affected significantly by growth stage. Differences in the incidence of fungi over growth stages were more evident in susceptible than resistant cultivars. The incidence of Fusarium spp. and B. sorghicola was negatively correlated with percentage germination but positively correlated with grain discolouration. A negative correlation was found between the incidence of B. sorghicola and 1000-grain mass. In the greenhouse, artificial inoculation at the soft dough growth stage with C. lunata, Fusarium moniliforme and P. sorghina, resulted in a greater reduction in seed germination than inoculation at anthesis. Sorghum cultivars from South Africa and Ethiopia were evaluated for resistance to grain mould and characterized for physical and chemical characteristics of grains. The objective was to determine resistance factors associated with grains. Resistant cultivars contained significantly greater amounts of phenols including glume proanthocyanidins, seed flavan-4-ols, apigeninidins and/or luteolinidins compared with susceptible cultivars. A highly significant negative correlation was observed between ergosterol content of grains and level of glume proanthocyanidins suggesting the role of glume proanthocyanidins in mould resistance. Cultivars containing diverse and increased concentrations of phenolic compounds had moderate to high resistance levels. Most of the resistant cultivars have coloured seed pericarps and glumes. Resistance was found in early, medium as well as late maturing cultivars. The present study revealed the widespread occurrence of grain mould pathogens among cultivars commonly grown in Ethiopia and South Africa. Hence, susceptible cultivars maturing during moist and warm conditions may suffer significant grain yield and quality losses. This dissertation provides important information mainly about the influence of meteorological factors and plant host growth stage on grain mould dynamics. It is hoped that these findings may motivate future studies particularly on the epidemiology of grain mould, to which little attention has been paid.
Open Access
Genetic diversity analysis of linseed (linum usitatissimum L.) in different environments
(University of the Free State, 2002-11) Gemelal, Adugna Wakjira; Labuschagne, M. T.; Osthoff, G.; Viljoen, C. D.
English: The study was carried out to assess the genetic diversity of 60 linseed accessions mainly collected from Ethiopia in different environments using morphological and amplified fragment length polymorphism (AFLP) markers from 2000 to 2002. AFLP and morphological characterization were conducted under glasshouse conditions at the University of the Free State in South Africa. Similarly, morphological evaluations were undertaken under field conditions at Holetta Research Centre in Ethiopia during 2000 and 2001 cropping seasons. The main objectives of the study were to determine the levels and patterns of genetic diversity along with other genetic parameters using both morphological descriptors and the AFLP markers, and to compare the usefulness and relationships of these two methods in discriminating the accessions of linseed by applying univariate, bivariate and multivariate statistical analyses. The analysis of variance for the glasshouse experiment showed highly significant difference (P < 0.01) among the accessions for Il quantitative traits measured, indicating the presence of high genetic diversity. This result was also confirmed by the principal component analysis (PCA) and cluster analysis (CA). PCA displayed that days to flowering, maturity and seeds/boil accounted for 20% of the total variability. CA grouped the accessions into Il main clusters, consisting one to 24 accessions each. No correspondence was found between clustering and geographic origins of the accessions. Estimation of broad sense heritability and predicted genetic gains (as percent of mean) were also computed to forecast the possible genetic advance in the future. Heritability ranged from 15.60% for seed yield/plant to 85.82% for initial days to flowering, whereas predicted genetic gains varied from 3.16% for days to maturity to 24.26% for plant height. The analysis of variance for the field experiments revealed highly significant differences (P < 0.01) among the accessions for Il characters. PCA and CA also denoted the same thing, showing the presence of a wide range of genetic variations between the accessions studied. CA clustered the accessions into nine classes, each consisting one to 39 accessions. The clustering was independent of collection areas. Phenotypic coefficient of variation ranged from 6.26% (days to maturity) to 54.97% (seed yield/plant), while genotypic coefficient of variation differed from 5.46% to 50.18% for the same characters. Heritability (broad sense) was in the range of 67.38% to 91.38%, whereas the predicted genetic gain varied from 9.38% to 94.37%. In both cases, the highest value was estimated for seeds/ball, while the lowest was for days to maturity. A combined analysis of variance of 10 quantative traits across four environments (two localities and two years) displayed highly significant differences (P < 0.01) among the accessions for all characters. There was also significant difference between the localities, years and their interactions for most characters, indicating the differential responses of the accessions across environments. PCA and CA also confirmed the differences between accessions and the prevalence of diversity among the accessions. PCA displayed that secondary branches/plant, plant height, days to flowering and seed yield/plant played major roles in differentiating the accessions. CA grouped the accessions into nine major clusters based on their mean performance rather than their geographic origins. Broad sense heritability and expected genetic advance were found higher across multi-environments than for the single one, indicating the importance of evaluating germplasm under different and appropriate environments. Both parameters were highest for plant height and days to flowering, indicating the effectiveness of selection for these traits. Diversity analyses for oil content, oil yield and fatty acid profiles generally indicated significant (P < 0.01) variations among the studied accessions. Oil content varied from about 29 to 36%, while oil yield ranged between 1443 and 3276 g/m2. The highest oil yield was obtained from Belay-96, followed by CDCVG (3212 g/m2), an introduction from Canada, which was identified as one the most promising genotypes in this study. Fatty acids that are principally grouped into two main groups (saturated and unsaturated) showed wide ranges of variation. Saturated fatty acids (palmitic and stearic) ranged from about 8 to 12%, whereas the unsaturated (oleic, linoleic and linolenic) ones significantly (P < 0.01) varied from 85 to 91%. The highest variation was recorded for oleic acid (14-29%), followed by linolenic (47-59%) and linoleic (10-16%) fatty acids. The accessions were grouped into six cluster based on their oil content, oil yield and linolenic acid, but into 10classes based on all their fatty acid profiles. Associations of characters were analysed across different environments to determine the extent and consistency of correlations and to identify major yield attributes of linseed. The degrees of correlation varied across years and locations due mainly to climatic factors, such as temperature, moisture regime and disease incidences. Seed yield was significantly (P < 0.01) and positively correlated with yield/plant, boils/plant and 1000-seed weight. These three traits were also strongly and positively related with plant height, branches/plant and days to maturity. Oil yield was significantly and positively associated with polyunsaturated (linoleic and linolenic) fatty acids, while it was negatively correlated with saturated (palmitic and stearic) fatty acids. The results generally showed tremendous variations in correlations of characters in response to the growing environments. The current accessions of linseed were assessed for their genetic variation by using AFLP markers. The estimated genetic distance for the entire pairwise accessions varied from 0.29 to 0.71. The top three pairs of accessions with the highest genetic distance were 22 and 57, 25 and 57 and 20 and 45. High levels of polymorphism were also observed for the analysed accessions, indicating the prevalence of genetic diversity in both exotic and local collections. Collections from central and northwest regions of Ethiopia revealed considerable variations, implying further explorations in these areas. Cluster analysis grouped the accessions into 13 classes, each consisting one to 14 accessions. AFLP was found effective in discriminating and grouping the accessions for more predictable breeding and efficient management of genetic resource in the future. Combining phenotypic and genotypic assessment of genetic diversity could help in acquiring more reliable genetic information for discriminating germplasm and cultivars. To this end, morphological and AFLP data were employed to investigate the levels and patterns of variation existing in linseed accessions and to compare the two methods. Analyses of ANOVA, PCA and CA revealed the existence of wide range of genetic diversity among the accessions. The average genetic distance of all pairwise accessions was 0.6684 for morphology and 0.5734 for AFLP markers. Higher level of variation was noted for morphology than for AFLP. Correlation between the two distances was very weak and their clustering patterns were also different. In fact, clustering patterns were variable based number of traits and environments tested. In spite of this disparity, however, both methods were found independently adequate and useful in germplasm characterization and/ or cultivar identification based on circumstances, like the availability of research facilities, fund and other essential resources.
Open Access
Genetic diversity analysis and genotpe x environment interaction in Ethiopian mustard (Brassica carinata A. Braun)
(University of the Free State, 2002-12) Kassa, Tsige Genet; Labuschagne, M. T.; Viljoen, C. D.
English: Ethiopian or Abyssinian mustard (Brassica carinata A. Braun) is one of the most important oil crops in Ethiopia. Apart from its phylogenetic relationships with other members of the genus Brassica, little information is available for this species. This study explored the genetic diversity and genotype x environment interaction for its possible use in genetic conservation and breeding. Geographical patterns of morphological variations were studied on 258 accessions of B. carinata randomly sampled from different parts of the country using Shannon Weaver diversity index ( H') to estimate the phenotypic diversity index for six morphological traits. The results revealed that the mean diversity index (H') across regions of the country was 0.72±0.06. Polymorphism was high for some of the traits. The mean diversity index (H') for the country across altitudinal classes was H' = 0.71 ± 0.07. Highest mean diversity index was recorded from areas ranging from 2600-280 masl. The centres of diversity appears to be Shewa, Bale and Arsi provinces with due consideration of altitudes. Further exploration and in situ conservation efforts should be undertaken in these regions. Brassica carinata possesses a number of agronomic advantages over other oil seed crops with similar ecological adaptation. However, the oil is considered low quality. Although efforts have been made to improve its quality, much has to be done to use natural variations that might exist within the species for fatty acid composition. The objectives of this study were to determine the oil content and fatty acid composition to determine the range of genetic diversity for these traits, and to select genotypes that can be used in crosses to improve these traits. Ninety-eight Ethiopian grown genotypes were analyzed by CGC to study the variability of fatty acid composition. The analysis revealed a wide variation in fatty acid composition; twenty-six fatty acids were identified. The predominant fatty acids were erucic (6.91-35.05%), linoleic (17.21-28.53%),α -linolenic (10.50-22.52%), and oleic (8.91-24.64%), followed by gadoleic (1.22-10.24%) and palmitic (3.38-16.42%). Palmitic acid had significant positive correlations with stearic acid. Erucic acid showed significant and negative linear correlations with palmitic, stearic, vaccinic, oleic, linoleic, α-linolenic acids and positive correlation with eicosenoic acid. The high oil yielding genotypes were relatively richer in erucic acid content. Oil content ranged from 25 to 48%. Genetic diversity analysis within B. carinata has not been examined with molecular markers. The objective of this study was to investigate the genetic relationships among 39 B. carinata genotypes by the AFLP markers. This study explored the amount of genetic variation for possible use in breeding. Thirty-nine genotypes of B. carinata were analysed using six AFLP primer combinations. A total of 189 polymorphic markers were scored, with an average of 32 markers per primer combination. GDE ranged from 0.346 to 0.639, with a mean of 0.504 ± 0.002. Polymorphism rates ranged from 50 to 80%. UPGMA cluster analysis revealed seven genetically distinct groups of genotypes. The GE interaction and the stability of 14 B. carinata genotypes for seed yield were evaluated at four rain-fed locations, over three years in north-western Ethiopia. The objectives were to estimate the component of variance associated with the first and second order interactions and to determine their effects and to measure the genotypes' stability using different stability statistics; and to compare the stability statistics. The analysis of variance test revealed that the main effects due to years, locations, and the first order interactions (year x location) as well as second order interactions (genotype x year x location) were highly significant. The genotype x location interaction was not significant. This suggests the necessity for increased emphasis on multiple years of testing than more locations. The estimates of variance components involving first order interaction of genotype x year, genotype x location and the error variance were very small. The variance components of the main effects of the genotype and second order interaction of genotype x location x year were very high. positive correlation with eicosenoic acid. The high oil yielding genotypes were relatively richer in erucic acid content. Oil content ranged from 25 to 48%. Genetic diversity analysis within B. carinata has not been examined with molecular markers. The objective of this study was to investigate the genetic relationships among 39 B. carinata genotypes by the AFLP markers. This study explored the amount of genetic variation for possible use in breeding. Thirty-nine genotypes of B. carinata were analysed using six AFLP primer combinations. A total of 189 polymorphic markers were scored, with an average of 32 markers per primer combination. GDE ranged from 0.346 to 0.639, with a mean of 0.504 ± 0.002. Polymorphism rates ranged from 50 to 80%. UPGMA cluster analysis revealed seven genetically distinct groups of genotypes. The GE interaction and the stability of 14 B. carinata genotypes for seed yield were evaluated at four rain-fed locations, over three years in north-western Ethiopia. The objectives were to estimate the component of variance associated with the first and second order interactions and to determine their effects and to measure the genotypes' stability using different stability statistics; and to compare the stability statistics. Mean yield over all locations and years ranged from 1304 to 1541 kg/ha by PGRCIE 210406 and PGRCIE 21163 respectively. The regression of yield on the environmental index resulted in a regression coefficient value ranging from 0.7488- 1.2288. The deviation from regression was non significant for all genotypes. The first two interaction principal component axes of the additive main effects and multiplicative interaction (AMMI) model together accounted between 35.7% and 54.3% of the total genotype x environment interaction of sum of squares for seed yield. The stability analyses identified PGRC/E 20017 and PGRC/E 20112 as more stable genotypes, while PGRC/E 21169 and (4DxZEM-1) x (ZEM-1-AD/88) were specifically adapted to some environments. Spearman's coefficient of rank correlation was performed for each of the possible pair wise comparisons of different stability statistics. Significant rank correlations were observed among some of the stability statistics. These significant rank correlations indicated their effectiveness in detecting stable genotypes over a range of environments. The hierarchical clustering of AMMI adjusted mean yield using UPGMA clustering method grouped the genotypes into five genetically distinct clusters and the environments into three heterogeneous clusters.
Open Access
Phylogeny of the genera Karroochloa, Merxmuellera and Schismus (Poaceae)
(University of the Free State, 2002-12) Malan, André Francois; Spies, J. J.; Venter, H. J. T.
English: In southern Africa, the Poaceae include 194 genera and 967 species and intraspecific taxa, of which 329 are endemic, 847 indigenous and 115 naturalised (Gibbs RusseIl 1985). The classification, at present, is based on non-Kranz leaf anatomy and morphology of the spikelet (Clayton & Renvoize 1986). The Arundinoideae are difficult to characterize because they are heterogeneous with numerous isolated or weakly linked genera, whose relationships are highly conjectural. Most of the species of Merxmuellera and Karroochloa were previously part of the genus Danthonia (Nees & Essenbeck 1841, Steudel 1855, Durand & Schinz 1895). A number of species of Danthonia were recently allocated to the new genera Karroochloa and Merxmuellera (Conert & Turpe 1969, Conert 1971). For a long time, the genus Schismus was regarded as very closely related to Danthonia and more recently to the genus Karroochloa. One Schsimus species was originally assigned to Danthonia (Conert & Turpe 1974). The genus Karroochloa consists of four species, two perennials and two annuals. At present, 20 species are recognised in Merxmuellera, 18 are from southern Africa and two species are from the mountains of Madagascar (Barker 1994). The type species of Schismus, namely S. barbatus grows in southern Africa as well as in northern Africa and Europe. The closely related species, S. arabicus also occurs in the Northern Hemisphere and the other three species in this genus are all endemic to South Africa. The high level of genetic variability allows the grasses to take advantage of new habitats (Ehrendorf 1980). In this investigation, the species M. stricta and M. disticha revealed wide distribution patterns which overlap and may indicate that these two species are of hybrid origin and, therefore, well adapted to a wide range of climatic conditions, soil types, rainfall and altitude. In the genus Merxmuellera, morphologically distinct groups of species can be identified. The genera Karroochloa and Schismus form monophyletic groupings and the distance data indicates that morphologically, Schismus lies between Merxmuellera and Karroochloa. Previous cytogenetic studies have indicated that the genus Merxmuellera has basic chromosome numbers of six and seven (Spies et al. 1990). In this investigation no indications of a basic chromosome number of seven was found and Merxmuellera is thus considered to have a basic chromosome number of six. This genus reveals high ploidy levels that indicate an old polyploid complex was dealt with. In the case of the other two genera Karroochloa and Schismus young polyploid complexes were dealt with. Only diploids were studied although there are reports on polyploids (Spies & Du Plessis 1986b, 1988). The chromosome behaviour indicates that M. stricta and M. disticha could be of hybrid origin. Embryo sac studies of nine species indicate that all these species are of the Polygonum-type and that Merxmuellera indicates a variety of embryo sac formations. Karroochloa, Merxmuellera and Schism us can be distinguished clearly on embryo sac structure. The peR based RAPD procedure was applied to resolve and investigate the three genera and their species. A strong relationship between the Merxmuellera species, M. ruie, M. decora and M. lupulina was clearly illustrated by the RAPD data. The ITS analysis indicated conflicting clustering of some species as well as expected clustering of other species. Ultimately the following argument is applicable: gene trees may not necessarily represent species trees (Doyle 1992). In this study the percentage lacking data in the combined analysis was too large to be used in the combined analysis. Therefore all the data sets were analysed separately and then compared to each other to make the final conclusions in this thesis. The close relationships between M. ruie, M. decora and M. lupulina are evident. Therefore, it is suggested that the three species should be combined into one species and be regarded as a polyploid complex, rather than three separate species. It is clear that all the summer rainfall Merxmuellera species are related and the most practical systematic treatment appears to be upholding only two species namely M. stricta and M. disticha. The validity of the species S. pleuropogon must be investigated because only one specimen, the type specimen, was collected and described by Stapf (1916) and no further specimens were found. Therefore, S. pleuropogon may have become extinct or it may have been a once-off hybrid. Although the genus Karroochloa consists of four species, the final analysis indicates that these species are very closely related and that the annual status of K. schismoides should be carefully investigated. Such an investigation will indicate whether Karroochloa includes four of three species.
Open Access
Genetic variability in the Solanum nigrum L. complex and related species in South Africa
(University of the Free State, 2003) Jacoby, Angeline; Labuschagne, M. T.
English: Solanum nigrum L. and its related species can play a significant role in the food supply and nutrition of people in subsistence farming societies in Africa. - The objectives of this study were to conduct morphological trials on the parent material and progeny and to determine heterosis and correlation of the progeny to identify desirable characters that can be used in further breeding studies. The identification of the species was confirmed with the help of cytogenetics and. the crossability of five species was investigated. The genetic relationships between the different species and progeny were established. The total protein percentaqe, sugar content and pH of the different parental species was also determinate. - Seeds were obtained from several sources and seedlings were grown in a heatcontrolled glasshouse. Established plants were planted out in a glasshouse and two field locations, these plants were used in the various investigations. The experimental designs were complete randomized blocks with three or four replications. - The 15 morphological characters studied were subjected to an ANOVA. and significant differences were found between the accessions tested. - Cytological analyses were carried out and regard to the chromosome numbers the species seem to fit into the normal euploid series. - The ANOVA on the parents and progeny showed significant difference reflecting the extensive genetic differences between them. Solanum scabrum was an excellent parent and selections for characteristics like fruit per bunch and fruit size should lead to improved plants. - AFLP markers were used to distinguish polymorph isms between 14 species in this study. Three primer combinations between ECOR I and MSE, were used and multiple polymorph isms (62%) were detected. - Seven independent sequences and their reverse sequences were selected for use as primers in the SSR study. The genetic distance value amongst the species-and their progeny indicates the diversity but close relationship among the species tested. - The young leaves and fruit of the parental species used in the crossing study were used in the assessments of the protein percentage, sugar and acid content of the plants. - The protein percentages were in most cases higher in the fruit than the leaves except for Solanum scebrum; one of the species often used as leafy vegetable in Africa. - The TSS value in the fruit juice was inversely proportional to the size of the fruit. - The Solanum nigrum complex and related species is a rich, untapped source of characteristics and could be used to improve the crop and probably other species in the Solanaceae family.
Open Access
Analyses of drought tolerance in durum wheat (Triticum turgidum var. durum) genotypes
(University of the Free State, 2003-03) Fekybelu, Solomon Kebede; Labuschagne, M. T.; Viljoen, C. D.
English: In order to identify yield components associated with drought tolerance in durum wheat and evaluate the performace of Ethiopian durum wheat genotypes, 26 durum wheat genotypes, from different agro-ecologies of Ethiopia were evaluated under simulated moisture stress conditions. Stress caused dramatic reductions in grain yield and harvest index. Yield was significantly correlated primarily with number of kernels per spike and 100 kernel weight. Further decomposition of simple correlation coefficients into direct and indirect effects showed that number of kernels per spike and 100 kernel weight had the largest direct effects on grain yield, under both stressed and non-stressed conditions' The expression of drought tolerance in the F1generation obtained from all possible combinations among genotypes differing in their responses to moisture deficit stress was studied. Analysis of variance revealed significantly high variability among genotypes for yield, yield components and drought tolerance measurements due to the effects of treatments. Drought tolerance was expressed in the crosses involving tolerant parents. The diallel analysis showed that mean squares for both GCA and SCA were significantly high at both moisture regimes. GCA:SCA ratios indicated predominance of additive gene action for all characteristics positively correlated with grain yield under stress or negatively correlated with drought susceptibility index. Differences in water use and transpiration efficiencies and interrelationships among water use and transpiration efficiencies and associated traits were investigated among durum wheat genotypes with differing responses to moisture stress. Significantly high genotypic variability in the amount of cumulative water used before (ETba) and after (ETpa) anthesis was observed. Susceptible genotypes used higher amounts of water before anthesis and lower amounts after anthesis. In contrast, tolerant genotypes used a higher proportion of water during the post-anthesis period. Significantly high variability among the genotypes was observed for various measures of water use and transpiration efficiencies, total dry matter and harvest index. Ranking of cultivars for water use efficiency based on grain yield (WUEG) and transpiration efficiency based on grain yield, was consistent with ranking of cultivars for drought susceptibility indices. Drought susceptibility index was significantly but negatively correlated with harvest index, WUEG and grain yield. However, it was positively and significantly correlated with the ETba:ETpa ratio. A high positive correlation of WUEG with harvest index and grain yield with harvest index was found. Differences in flag leaf water potential were significant only for genotypes under stress treatments. Water potential declined with age under both treatment conditions, however, the fall was faster in stress sensitive types than in tolerant types in more advanced growth stages. Inheritance of water use and transpiration efficiencies was studied in a hybrid population obtained from six parents, selected for their different responses to moisture stress. GCA and SCA effects were significant at both the moisture levels. The interactions of GCA and SCA with moisture levels were also highly significant. Analysis of the genetic components of variation demonstrated that WU E and T were under the control of additive and dominance type of genes. Narrow sense heritability estimates for water use and transpiration efficiencies based on grain yield (WUEG) were higher at the moisture stress level. Measures of water use and transpiration efficiencies showed significantly high and positive genotypic and phenotypic correlations among them as well as with grain yield and harvest index. The impact of the effect of moisture stress on growth and phenological development was examined among durum wheat genotypes differing in their tolerance to moisture stress. Drought stress was found to delay major growth stages and shorten the grain filling period. Drought tolerant genotypes had fast early growth, whereas susceptible ones had slow RGR initially. Variation in RGR was associated with NAR and LAR. Differences in hybrid performance were due to significant GCA and SCA effects. Interactions of GCA and SCA with moisture level were also highly significant. Moderate to high levels of broad sense heritability estimates were found for most of the traits. Significantly high genetic and phenotypic correlations between NAR and RGR, and LAR and RGR were found. The genetic and phenotypic correlations of grain yield with total dry matter, harvest index, RGR and LAR were significant. The effect of moisture stress on the content of water soluble carbohydrate (sucrose and D-glucose) was investigated in durum wheat (Triticum turgidum L. var. durum) above ground organs to assess and characterise the responses of genotypes with differing responses to drought stress. In all organs examined, drought tolerant genotypes accumulated more glucose and sucrose, particularly, at an early age. Stress caused an overall increase in the level of these carbohydrates, but the levels were highest in the stems compared to other organs. Level of drought (drought susceptibility index, 'S') was strongly related with the level of carbohydrates in the various plant organs Genetic differences among genotypes with differing responses to drought stress and their progenies obtained from all possible cross combinations were assessed using AFLP markers. Moderate to high level polymorph isms were obtained with the primer combinations evaluated. Euclidean genetic distance estimates showed that there was considerable genetic diversity among the materials studied. The correlation coefficient for pair wise genetic distance estimates based on AFLP data and yield, yield components, and morphophysiological traits was significant and positive. Cluster analysis showed that grouping of genotypes on the basis of AFLP data and agro-morphological data fairly agreed. A number of AFLP fragments were significantly correlated with the various traits evaluated under stress conditions. AFLP fragments were observed to affect a number of traits that were strongly correlated with drought susceptibility index.
Open Access
Paleopolyploidy and molecular systematics of Southern African Chloridoideae
(University of the Free State, 2003-05) Roodt, Rouvay; Spies, J. J.
English: This study dealt with systematics of southern African representatives of the grass subfamily Chloridoideae. The group was studied on molecular and cytogenetic levels. Two main basic chromosome numbers in the Chloridoideae, namely x = 9 . and 10, were confirmed by this study. The basic chromosome number of x = 10 is the most prevalent and is seen as the original number from which other aneuploid deviations in the group arose. The basic chromosome number of x = 10 is, however, a paleopolyploid number as specimens with 2n == 2x = 10 have been found in the subfamily. Most of the chromosome numbers found in the Chloridoideae are derived from the original basic chromosome number, x = 5, or the paleopolyploid number, x = 10. Polyploidy is frequent in the grasses and subfamily Chloridoideae. In this study more than 70% of the southern African Chloridoideae was found to be polyploid. This polyploidy is largely attributed to hybridization, as many of the studied specimens were segmental allopolyploids or allopolyploids. This is facilitated by an effective asexual reproduction system in the form of apomixis. Two genomic regions were sequenced in this study, i.e. the nuclear ITS and chloroplast trnL-F regions. These two regions represent two different genomes and are inherited differently (maternal versus biparental), -which have phylogeneticimplications for studying hybridization, a frequent phenomenon in the Chloridoideae. The regions studied differed in the amount of resolution they provided. The ITS phylogeny was well resolved, but the trnL-F region had less variation and less resolution, especially at species level. Despite this no hard incongruence was found between the two phylogenies and they could be combined. The phylogenetié analyses indicated the monophyletic nature of the Chloridoideae. The two large -tribes, Cynodonteae and Eragrostideae were polyphyletic, although a general division into two separate groups was evident. The monophyly of all the generic groups in the subfamily was well supported, except for the two largest genera in the study, Eragrostis and Sporobolus. These two genera are very variable and taxonomically difficult groups, probably related to interspecific and -generic hybridization. The morphologically distinct tribe Pappophoi"eae was well supported in all analyses. The two genera Entoplocamia and Fingerhuthia was found basal in the combined analysis, a finding that supports the derivation of the Chloridoideae from arundinoid ancestors as these two genera are seen as a link to Spartochloa, Styppeiochloa and Tnbolium in the Arundinoideae and Danthonioideae. Despite the frequency of hybridization in the subfamily, hybrids could not be positively identified based on sequence polymorph isms or their phylogenetic· behavior. This is possibly related to the age of hybridization in the group or the close relationship of the groups ~etween which hybridization occurs. ' This study provides cytogenetic and molecular systematic support for paleopolyploidy in the Chloridoideae. This is based mainly on the occurrence of x = 5 in the subfamily and the close relationship of the Chloridoideae to the Arundinoideae and Danthonioideae which have a main basic chromosome number of x = 6 and from which x = 5 in the Chloridoideae was derived. This chromosome number was probably highly unstable and subsequent polyploidization lead to the now frequent x = 10 found in the majority of the subfamily.