Masters Degrees (Plant Sciences)

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Open Access
Die transpirasie van 'n aantal Karoobossoorte
(University of the Free State, 1964-12) Du Preez, Charles Matthias Rowe; Van Zinderen Bakker, E. M.
Afrikaans: Die Karoobossies speel 'n belangrike rol as dierevoedsel in die Karoogebied en tree ook op as indringerplante na die noorde en die ooste. Aangesien hierdie unieke dwergstruike meesalonder droogtetoestande groei en water n beperkende faktor is, is besluit om 'n studie te maak van die transpirasie van 'n aantal bossiesoorte. Hierdeur kan 'n bydrae gelewer word tot die fisiologies-ekologiese kennis van hierdie gebied. 'n Oorsig word gegee van die verskillende transpirasiebepalingsmetodes. Dit blyk dat die "Momentele weegmetode" van Stocker die mees praktiese metode is om die transpirasie van Karoobossies onder veldtoestande te meet. Die vernaamste beswaar teen hierdie metode is die feit dat van afgesnyde plantdele gebruik gemaak word. 'n Kritiese beskouing van die metode, die proefterrein en die proefmateriaal, oorbrug hierdie beswaar in 'n groot mate. Die proefterrein is geleë aan die voet van 'n reeks dolerietrante en bestaan uit 'n uniforme bossiebedekking. Die Karoobossies is houtagtige xeromorfe dwergstruike. 'n Beskrywing word gegee van die blare, stingels en wortels van die bossies. Die suigkrag van die wortels van 'n aantal bossiesoorte is bepaal. Dit blyk dat die stadige transpireerders hoër suigkragte het as die vinnige transpireerders. Gereelde waarnemings van die fenologiese stadium waarin die bossies verkeer, is gemaak. Dit blyk dat hul aktiefste groei in die herfs en in die winter plaasvind, terwyl die meeste bossies in die voorsomer blom. Gegewens oor die verloop van die vernaamste klimatologiese faktore gedurende die proeftydperk, asook vir die dae waarop die transpirasiobepalings uitgevoer is, is verskaf. Proewe is met Medicago sativa uitgevoer ten einde die waterhuishouding van n mesomorfe plant met dié van die Karoobossies te vergelyk. 1. Na afsnyding van die takkies neem die waterverliestempo van M. sativa heelwat gouer af, as wat dit in die geval met die afgesnyde bossietakkies was. 2. In albei gevalle neem die transpirasietempo skerp toe in die oggend. Die bossies se transpirasie neem egter gou weer af, wat waarskynlik toegeskryf kan word aan die vroeë sluiting van die stomata. 3. Phymaspermum parvifolium en Lycium arenicolum se maksimum transpirasiewaardes verskil nie veel van die maksimum waarde van M. sativa nie. Hierdie gegewens bevestig die bevindinge van vorige navorsers dat, onder gunstige grondvogtoestande, xeromorfe plante net so vinnig kan transpireer as mesomorfe plante. Die verloop van die waterverlies van afgesnyde bossietakkies is gemeet en die volgende gevolgtrekkings is uit die resultate gemaak: 1. By lae grondvogtoestande neem die transpirasie baie gouer af as by hoër grondvogtoestande. 2. Aanvanklik het stomatêre transpirasie plaasgevind, maar nadat die stomata hidroaktief gesluit het, vind slegs kutikulêre transpirasie plaas. 3. Oor die algemeen sal dit veilig wees om die transpirasie van afgesnyde takkies binne tien minute na die afsnyding te bepaal. 'n Eksperiment is met Pentzia incana uitgevoer, waarin die transpirasie gedurende die loop van n dag in vyfvoud bepaal is. Die resultaat het daarop gedui dat betroubare transpirasiewaardes verkry sou word, indien slegs een bepaling per tydstip per bossiesoort gedurende die loop van 'n dag uitgevoer sou word. Die transpirasie en die relatiewe turgessensie van Penzia incana en pteronia tricephala is gelyktydig gedurende die loop van twee dae bepaal. Dit blyk dat die transpirasie en die relatiewe turgessensie teenoorgestelde neigings vertoon en ook in 'n groot mate die hidratuur van die plant beheer. Die verloop van die transpirasie van agt Karoobossoorte is gelyktydig gedurende 'n dag in die somer, 'n dag in die herfs, 'n dag in die winter en 'n dag in die voorsomer bepaal. Die volgende inligting is uit die resultate verkry: 1. Die maksimum transpirasiewaardes van Phymaspermum permum parvifolium en Lycium arenicolum is oor die algemeen hoër as die ander bossiesoorte s'n. 2. Die stadig transpirerende bossies se wortels het skynbaar laer suigkragte as die wortels van P. parvifolium en L. arenicolum. 3. Die daaglikse transpirasiekurwes volg waarskynlik dieselfde neiging as die daaglikse evaporasiekurwes, maar wyk dikwels af van die evaporasiekurwe a.g.v. interne watertekorte en die werking van die stomata. 4. Met sonop neem die transpirasie skerp toe en bereik gewoonlik gedurende die oggend 'n maksimum waarde, waarna die transpirasie weer afneem. In die namiddag kom daar dikwels 'n toename in die transpirasie voor, maar neem dan later in die middag saam met die evaporasie af.
Open Access
Ultrastruktuur en konidiogenese in Fusarium crookwellense
(University of the Free State, 1986-11) Venter, Elrita; Van Wyk, P. S.
Afrikaans: Die ultrastruktuur, sporulasie en sitologie van Fusarium spp. het wye aandag geniet, maar sekere basiese inligting hieromtrent is nie beskikbaar nie. Tydens die huidige bestudering van die toetsorganisme, Fusarium crookwel lense is bevind dat daar oor die algemeen ooreenstemming is tussen die huidige resultate en resultate wat aangemeld is ten opsigte van sitoplasmiese insluitsels. Verskille in hife-, konidium- en chlamydospoorwandinterpretasie het egter voorgekom en daar is bevind dat die hifewand soortgelyk aan die makrokonidiumwand is. Laasgenoemde wande bestaan uit twee lae, naamlik'n fibrillêre of fraaiingagtige buitewandlaag en binnewandlaag wat in sommige geval le as twee sones waarneembaar is. Die verskynsel van sones in die binnewandlaag kan toegeskryf word aan proteien of lipied impregnering in die wand saam met die effek van fiksering- en kleuringstegnieke. Die dikker chlamydospoorwand bestaan basies ook net uit twee lae, naamlik 'n buite disintegrerende elektrondigte laag wat die oorspronklik buitewandlaag van die hife (konidium) verteenwoordig en 'n binnewandIaag wat, aan die buitekant die oorspronkIike hife (konidium) binnewandlaag en, aan die binnekant die nuwe sekondêre wandmateriaal bevat. Verskille in elektrondigtheid in hierdie lae kan moontlik toegeskryf word aan die onderbrekingsperiode in die neerlegging van wandmateriaal en teenwoordigheid van osmofiliese materiaal in 'n gedeelte van die wand. Die wyse waarop konidiogeneselle en konidia gevorm word, word algemeen deur mikoloë as die basis van die klassifikasie van Deuteromisete aanvaar. Tydens die huidige ondersoek is twee wyses waarvolgens die eerste konidium geproduseer kan word, waargeneem. In die eerste geval is 'n septum in die konidiogenesel, weg van die apeks af, neergelê. Breuke ontstaan in die buite selwandlae net bokant die posisie waar die septum neergelê is en as gevolg van verdere ontwikkel ing van die konidium, skei die buitelae van die ou konidiogenesel op die posisie van die breuk en gee dit oorsprong aan 'n kollaret. Tydens die tweede tipe ontwikkeling is geen afsnydingseptum in die konidiogenesel neergelê nie en konidiumontwikkeling is voorafgegaan deur disintegrasie van die apikale wandarea van die konidiogenesel. 'n Kollaret het ook in laasgenoemde geval ontstaan, maar die morfologie daarvan verskiI van dié van die kollaret soos vir die eerste tipe ontwikkeling vermeld. Beide tipes ontwikkeling van die eerste konidium sal/kan tot gevolg hê dat selwandoorblyfsels op die ontwikkelende konidium aanwesig is, alhoewel die hoeveelheid materiaal wat betrokke is, kan verskiI. Hierdie twee tipes van eerste konidium ontwikkeling versoen die teenstrydige resultate wat in die literatuur aangemeld is en dui op 'n kontinuum van ontwikkeling vir die eerste konidium vanaf 'n geheel thalliese tot 'n geheel enteroblastiese wyse. Alle konidia wat na die eerste konidium gevorm word, in beide tipes van eerste konidiumontwikkeling, word holoblasties gevorm. Waar uitgebreide perikliniese verdikking in die konidiofoornek voorkom, kan konidiogenesel le regenereer en prolifereer om 'n nuwe konidiogenesel wat konidia op 'n hóêr vlak produseer, te vorm. Sitologie binne die genus Fusarium het hoofsaaklik aandag op die gebied van aantal kerne per sel, kerndeling en aantal chromosome by die onderskeie spesies geniet en slegs 'n enkele verwysing is na die voorkoms van kerne en neerlegging van septa in makrokonidia gemaak. Jong ontwikkelende konidia is sonder kerne totdat die konidium die finale grootte bereik het. Op hierdie stadium beweeg 'n dogterkern uit die konidiofoor in die konidium in en konidiumafgrensing vind waarskynlik net hierna plaas. Kerndeling vind in die konidium plaas en 'n septurn (primêre septurn) word in die middel van die konidium tussen die twee dogterkerne neergelê. Gesinchroniseerde verdeling van die twee dogterkerne vind dan plaas en septa (sekondêre septa) word neergelê om die apikale en basisselle af te grens. Hierna volg 'n tweede gesinchroniseerde kernverdeling en septa (tersiêre septa) word neergelê om beide hierdie langsliggende selle te verdeel. Volgens hierdie proses het die "normale", volwasse makrokonidium dus vyf septa en elke sel bevat een kern. Alternatiewelik is gevind dat, nadat die kern die konidium binnebeweeg het, voordat kernverdeling plaasgevind het, septa neergelê word wat die kernlose apikale- en basissellé afgrens. Volgens hierdie wyse van kerndeling en septasie ontstaan 'n konidium met ses selle, maar vier kerne. Gesinchroniseerde kerndeling kan ook tot gevolg hê dat een van die twee septa langs die primêre septurn nie neergelê word nie en 'n tweekernige sel sal dus in 'n makrokonidium met vier of ses septa in een van die selposisies langs die primêre septum geleë wees. Septumneerlegging in makrokonidia geskied dus volgens 'n definitiewe patroon en word normaalweg deur kernverdelings voorafgegaan.
Open Access
Plantsosiologie van die Bloemfontein-Wes-Distrik
(University of the Free State, 1992-11) Malan, Pieter Willem; Venter, H. J. T.; Du Preez, P. J.
English: The aim of this study was to identify, characterize and interpret, ecologically, by using hahitat properties, the major vegetation units and their variations. The study area covers approximately 350 000 hectares. Most of the area is intensively utilized for farming practice. The western parts of Bloemfontein are, geologically underlied by the Ecca group. The hilly appearance of this area is caused mainly by dolerite intrusions. Bloemfontein is situated in a semiarid region, having dry, cold winters with frost and warm summers accompanied by a low, irregular rainfall. The mean annual rainfall is 564 mm, but it varies greatly. As far as the biotic environmental factors are concerned, man, especially, plays a great part by affecting the composition of the vegetation and the condition of the habitat. A total of 254 sample plots were used to survey the area. A combination of classification techniques was used to interpret the vegetation, ecologically, and to identify and classify plant communities. The study area was stratified according to land types. The number of sample plots was chosen subjectively and pro rata according to the size of each land type within each land type. Five separate plant sociological tables were compiled, and the results of each of these are discussed separately. Because the Bloemfontein area was previously studied by different authors no survey was made in the Ea-land type. Thirty five plant communities were identified and described. These communities are summarized in a synoptic table for the entire study area. In the synoptic table four vegetation units could be identified. These units are: (1) Communities of the other Rhoetalia ciliato-erosae (2) Communities of the lowland areas (3) and (4) Disturbed communities of the lowland areas The most important tree species are Acacia karroo, Buddleja saligna, Celtis africana, Cussonia paniculata, Ehretia rigida, Grewia occidentalis, Heteromorpha trifoliata, Olea europaea subsp. africana, Rhus lancea and Ziziphus mucronata. The dominant shrubs include: Euclea crispa, Euphorbia mauri tanica, Rhigozum obovatum, Rhus burchellii, R. ciliata en R. erosa. The dominant grass species are Aristida congesta, A. diffusa, Chloris virgata, Digitaria eriantha, Eragrostis curvula, E. lehmanniana, E. obtusa, E. superba, Heteropogon contortus, Themeda triandra and Triraphis andropogonoides. Among the dwarf shrubs and herbs Asclepias fruticosa, Berkheya onopordifolia, B. pinnatifida, Chenopodium album, Felicia filifolia, Lactuca dregeana, Chrysocoma ciliata, Cirsium vulgare, Hermannia bryoniifolia, Hertia pallens, Lantana rugosa, Melolobium candicans, Nenax microphylla, Nidorella resedifolia, Protasparagus laricinus, P. striatus, P. suaveolens, Rumex crispus, R. lanceolatus, Salsola kali, Salvia stenophylla, S. verbenaca, Solanum coccineum, S. incanum, Stachys rugosa, Tagetes minuta en Walafrida saxatilis are the most important. The stratification of the study area into land types and the compilation of a separate plant sociological table for each land type resulted in the successful identification of ecologically sound plant communities.
Open Access
The expression of leaf rust resistance in wheat lines containing Lr12 and Lr13
(University of the Free State, 1995-11-30) Bender, Cornelia Magrietha; Pretorius, Zacharias A.; Spies, Johannes J.
Monogenic resistance in wheat (Triticum aestivum L.) to leaf rust, caused by Puccinia recondita Rob. ex. Desm. f. sp. tritici, has generally not been durable. One strategy of attaining durable resistance to rust diseases of wheat is the combination of several resistance genes in a single genotype. Interactions among Lr genes have been defined as the combination of two or more genes resulting in higher resistance levels than that conferred by the genes individually. It has been suggested that Lr12 and Lr13, both adult-plant resistance genes, in combination with other genes, form the basis of durable resistance in several cultivars. In this study, the assumption that Lr12 and Lr13 may interact to condition improved resistance to leaf rust, was investigated. Four Thatcher (Tc) F3 lines (13/12-3, 13112-9, 13/12-19 and 13/12-40), homozygous for both Lr13 and Lr12, were selected and compared with the parents (CT263 [=TcLr13] and RL6011 [=TcLr12]), the single gene lines Tc/13-22 and Tc/12- 16, and Thatcher. In addition to infection type studies in seedlings and adult plants, lines were compared according to several histological and macroscopic components of resistance, as well as disease ratings in the field. Flag leaf infection type studies showed that Lr12 is effective against most pathotypes of P. recondita f. sp. tritici occurring in South Africa. Conversely, Lr13 is ineffective against the dominant pathotypes, implying that the gene has no value as a monogenic source of resistance. Both Lr12 and Lr13 were inherited dominantly. Based on the fact that several pathotypes are avirulent to these genes, they should be manipulated with relative ease in local breeding programmes directed at utilising these sources in combination with other Lr genes. Considering the microscopic components, effects of Lr12 and/or Lr13 resistance on the prepenetration stages were not determined. Results of aborted penetration, consisting of nonpenetrating appressoria and aborted substomatal vesicles, showed that inhibition of fungal growth in wheat lines containing Lr12 and/or Lr13, was activated, to a certain degree, before haustoria were formed. Determination of colony size 240 hours after inoculation indicated that fungal colonies in the combination lines were generally smaller than in the parents, but not necessarily smaller than those in the monogenic line Tc/13-22. Host cell necrosis was more frequently associated with infection sites, specifically of UVPrt2, in the combination lines than in the parents. Hypersensitivity index values (calculated by dividing the area of leaf necrosis with the area of the respective colony), indicated that host cell necrosis was more severe following infection of the combination lines with UVPrt2. Quantification of cell wall appositions showed that fewer papillae occurred in Thatcher than in the other host genotypes. The number of haustoria observed per colony did not indicate any clear, repeatable differences between lines. The common occurrence of host cell necrosis observed during histological examinations was also reflected in the macroscopic components. Infection types on the flag leaves of lines carrying both Lr12 and Lr13 often displayed chlorosis and necrosis. These ratings on primary and flag leaves, as well as the quantitative components including latent period, uredium density and uredium size, did not indicate clear differences between the digenic lines and the most resistant parent. In the absence of a pathotype virulent to both genes, the combination lines were resistant in the field. Field tests with a pathotype virulent to both Lr12 and Lr13 would have been more valid in evaluating whether the genes interacted. Data obtained were not conclusive in suggesting pronounced resistance enhancement due to combining Lr12 with Lr13. Therefore, the assumption of durability, resulting from a novel resistance mechanism conditioned by this combination, was not confirmed.
Open Access
Inheritance of yield and quality characteristics in processing tomatoes
(University of the Free State, 1998-09) Blokpoel, Ian Hendrik Christiaan; Van Deventer, C. S.
English: The main objective of this study was to determine the combining ability of several tomato genotypes, the heritability of various yield and quality characteristics and the expression of heterosis in the F1 hybrids. 2. Six inbred tomato genotypes were used as parental lines in the diallel cross. Crosses were made in glasshouses at the University of the Orange Free State. The F1 hybrids and their parental lines were planted at the ARC - Roodeplaat Vegetable and Ornamental Plant Institute. Various yield and quality characteristics were analysed. 3. Significant differences among the six parental lines were recorded for total yield, marketable yield, green yield and average fruit mass. The 15 F1 hybrids showed significant differences for total yield, marketable yield, unmarketable yield, green yield and average fruit mass. 4. Significant genetic variation among the SIX parental genotypes was recorded for fruit pH. The 15 F1 hybrids show no significant differences for soluble solid content and fruit pH. 5. A significant positive phenotypic correlation (r=0.95) was found between total yield and marketable yield. 6. Inbred line p88/120 was the best general combiner for most of the yield characteristics while p88/120 and p88/192 is the best general combiners for most of the quality characteristics. Crosses p881l40 x UC82B, P881l20 x p88/192 and p881l40 x p881l92 were the best specific combiners for total and marketable yield. The best specific combination was the cross between p88/164 and UC82B, which had 7 positive SCA values. 8. A GCA:SCA ratio of 85:1 was recorded for average fruit mass indicating that additive genes are involved. 9. Narrow sense heritability were relatively high for average fruit mass (H2n= 74.38%), green yield (H2n=55.01 %) and fruit colour (H2n= 50.04%). The breeder can select effectively for larger fruited genotypes as well as selecting against green yield to increase the total yield. 10. The average level of heterosis over the best parent exceeds 10% for total and marketable yield between all the F1 hybrids. Heterosis of the F1 hybrids over mid-parent value (Hmp), heterosis over the better parent (Hbp) and superiority over the best parent (Scm) was mostly negative for all the quality characteristics.
Open Access
Water quality of the Modder River
(University of the Free State, 1998-11) Koning, Nadene; Grobbelaar, J. U.; Roos, J. C.
English: The Modder River is a relatively small river which drains an area of 7 960 km² , in the central region of the Free State Province, South Africa and has a mean annual runoff of 184 x 10⁶ m³ . Botshabelo is a city which was developed in the catchment area of the river and its sewage outflows are discharged into the Klein Modder River, a tributary of the Modder River. This study was conducted in order to determine seasonal and spatial patterns in the system, the influence of Botshabelo's sewage outflow on the water quality of the river, as well as the presence of any toxic compounds. It was determined that the Modder and Klein Modder Rivers do not follow distinctive seasonal patterns in terms of chemical parameters, however, N0₃-N and P0₄-P concentrations usually increased with increasing flow in the river. Physical parameters such as turbidity, flow and temperaturefollowed distinctive seasonal patterns. Turbidity and flow was high during the rainy season and temperature followed the air temperature. The Modder River is a very turbid system, influenced by physical (flow, turbidity and temperature) as well as chemical factors (high nutrient availability). The Modder River showed similarities with other South African rivers, such as the Vaal and Orange Rivers, in terms of turbidity/conductivity relationships and the range of physical and chemical parameters. Phytoplankton growth also showed distinctive seasonal patterns, with low chlorophylla concentrations in the winter and higher chlorophyll-a concentrations when temperatures became more favourable. Diatoms (especially Cyclotella sp., Stephanodiscus sp. and Nitzchia sp.) dominated the algal community in both the Klein Modder and Modder Rivers for most of the time, with the euglenophyte, Trachelomonas dominating occasionally. In the Klein Modder River, algal blooms occurred more frequently, as well as with higher concentrations than in the Modder River. This could be ascribed to the higher nutrient concentrations in the Klein Modder River, which, together with low flow conditions, provide favourable conditions for algal growth. There were periods when the nutrient concentrations in the waters of the Modder and Klein Modder Rivers were low, however, Botshabelo has an enrichment effect on the water quality, in terms of the nutrient concentrations. The inflow of the Klein Modder River into the Modder River caused on average, a 112 % increase in P0₄-P₃, a 171 % increase in N0-N nitrates and a 50 % increase in chlorophyll-a concentration. However,the Modder River showed a self-purification capacity and nutrient concentrations decreased significantly downstream to Mazelspoort, restoring the water to almost the quality of the "unpolluted" reference point. Based on toxicity tests performed with Selenasfrum capricornufum and Daphnia pulex, no high concentrations of potentially toxic compounds were found in either the Klein Modder or Modder River. However, the occasional presence of heavy metals can not be excluded. Bacteria concentrations were high in both rivers and may pose a threat to human and animal health. The use of a water quality model (PC-QUASAR) on the Modder River system, showed no results to predict the conditions in the rivers and for planning and management purposes, since the model could not be calibrated with the available data. The parameters of the model also showed great insensitivities regarding manipulation of important parameters. Because the Modder River is a very turbid system, it is also important that light availability be taken into account in any forecasting procedures m³ . Botshabelo is a city which was developed in the catchment area of the river and its sewage outflows are discharged into the Klein Modder River, a tributary of the Modder River. This study was conducted in order to determine seasonal and spatial patterns in the system, the influence of Botshabelo's sewage outflow on the water quality of the river, as well as the presence of any toxic compounds. It was determined that the Madder and Klein Modder Rivers do not follow distinctive seasonal patterns in terms of chemical parameters, however, N0₃-N and P0₄ -P concentrations usually increased with increasing flow in the river. Physical parameters such as turbidity, flow and temperaturefollowed distinctive seasonal patterns. Turbidity and flow was high during the rainy season and temperature followed the air temperature. The Modder River is a very turbid system, influenced by physical (flow, turbidity and temperature) as well as chemical factors (high nutrient availability). The Modder River showed similarities with other South African rivers, such as the Vaal and Orange Rivers, in terms of turbidity/conductivity relationships and the range of physical and chemical parameters. Phytoplankton growth also showed distinctive seasonal patterns, with low chlorophylla concentrations in the winter and higher chlorophyll-a concentrations when temperatures became more favourable. Diatoms (especially Cyclotella sp., Stephanodiscus sp. and Nitzchia sp.) dominated the algal community in both the Klein Modder and Modder Rivers for most of the time, with the euglenophyte, Trachelomonas dominating occasionally. In the Klein Modder River, algal blooms occurred more frequently, as well as with higher concentrations than in the Modder River. This could be ascribed to the higher nutrient concentrations in the Klein Modder River, which, together with low flow conditions, provide favourable conditions for algal growth. There were periods when the nutrient concentrations in the waters of the Madder and Klein Modder Rivers were low, however, Botshabelo has an enrichment effect on the water quality, in terms of the nutrient concentrations. The inflow of the Klein Modder River into the Modder River caused on average, a 112 % increase in P04-P, a 171 % increase in N0₃ -N nitrates and a 50 % increase in chlorophyll-a concentration. However,the Modder River showed a self-purification capacity and nutrient concentrations decreased significantly downstream to Mazelspoort, restoring the water to almost the quality of the "unpolluted" reference point. Based on toxicity tests performed with Selenasfrum capricornufum and Daphnia pulex, no high concentrations of potentially toxic compounds were found in either the Klein Madder or Modder River. However, the occasional presence of heavy metals can not be excluded. Bacteria concentrations were high in both rivers and may pose a threat to human and animal health. The use of a water quality model (PC-QUASAR) on the Modder River system, showed no results to predict the conditions in the rivers and for planning and management purposes, since the model could not be calibrated with the available data. The parameters of the model also showed great insensitivities regarding manipulation of important parameters. Because the Modder River is a very turbid system, it is also important that light availability be taken into account in any forecasting procedures
Open Access
Micropropagation of Pinus species
(University of the Free State, 1999) Jacoby, Angeline; Van der Westhuizen, A. J.; Botha-Oberholster, A. M.
English: The aim of this study was to develop an effective protocol for the micropropagation of Pinus patuIa and P. radiata. Micropropagation procedures by means of somatic embryogenesis on solidified medium and in cell suspension cultures as well as organogenesis were investigated. In addition the possible relationship between phenolic, auxin and cytokinin content within cuttings and the tendency of these cuttings to root, were to be investigated. The cones of P. patuIa and P. radjata were collected for the somatic embryogenesis study, on a two weekly basis during the summer months of 1995 to 1997. Somatic embryonic cultures were initiated from the immature female gametophytes containing zygotic embryos. The embryonal suspensor mass (ESM) formed, was used as starting material for cell suspension cultures. Organogenesis included axillary and adventitious budding on hypocotyls and cotyledons respectively of young germlings deriving from seeds of open pollinated cones. Various techniques to sterilize the seeds were evaluated and it was found that 30% H202 (10 min.) proved most effective for P. patuIa, and 10% H202 (5 min.) was most effective for P. radiata. The initiation of somatic embryonic cultures was attempted on solidified modified Murashige and Skoog medium (MSG), Schenk and Hildebrandt (SH), Gresshof and Day (GO), Quoirin and Lepoivre (LP) and variations of the Douglas-fir Cotyledon Revised (OCR) media, each differing with regard to nitrogen sources and growth regulator composition. It was concluded that the most effective initiation media for P. patuIa were DCR1 and DCR5, and that DCR2 was most effective for P. radiata. Maintainance of the embryonic cultures was most successfully achieved for both species on ½ LP medium containing 3% maltose and no growth regulators. Maturation of P. radiata somatic embryos was achieved on solidified OCR2 medium supplemented with 1.3 rnql-¹ ABA, 30 gl-¹ glucose and 1% (mIv) activated charcoal. Attempts to mature P. patuIa embryos were unsuccessful. Embryonic cell suspension cultures were established in liquid GO, OCR, SH and ½ LP media. The best culture growth was achieved on ½ LP medium supplemented with 0,5 mql-¹ 2,4-0 and maltose as carbon source. Re-establishment of these cultures onto solidified ½ LP medium, supplemented with ABA, for further development and maturation was successful. Adventitious buds were induced on young (14 day old) cotyledons on nutrient (OCR) medium containing cytokinins (2 rnql-¹ BAP and 0.5 rnql-¹ Kin). In addition axillary buds were initiated on hypocotyls. A better success rate was obtained by axillary budding on hypocotyls than adventitious budding on cotyledons. Best elongation of the axillary buds was recorded on OCR medium containing no growth regulators. Rooting of these elongated shoots was subsequently successfully conducted on a GO medium supplemented with 0.5 rnql-¹ NMand 2 mgI-¹l IBA. An investigation on possible chemical markers of the rooting potential of cuttings was conducted on softwood cuttings of P. elliottii hybrids. The rooting percentage correlated inversely with the total phenolic content of the cuttings. According to TLC chromatograms for the separation of phenolic acids no special phenolic acid could be related to high or low rooting potential. Immunoassays were used to determine the endogenous auxin and cytokinin levels of cuttings. The rooting percentage correlated positively with the auxin concentration and negatively with the cytokinin concentration as expected. Results obtained in this study showed that the micropropagation of P. patuIa and P. radiata is feasible. These results contribute to a better understanding of micropropagation of Pinus species which has great potential for mass propagation demanded by forestry.
Open Access
A phylogenetic study of some South African representatives of the tribe Arundineae
(University of the Free State, 1999-05) Roodt, Rouvay; Spies, J. J.
English: This study dealt with the phylogenetic history of some representatives of the South African Arundineae. Arundineae Durnort. is one of the tribes in the grass (Poaceae) subfamily Arundinoideae Tateoka. This is known to be a heterogeneous assemblage and a taxonomically difficult group. Three techniques were used to investigate the relationships within the tribe Arundineae, namely cytogenetics, DNA amplification fingerprinting and DNA sequencing of the ITS region of the nuclear DNA. The genera Pentameris P.Beauv., Pentaschistis (Nees) Spach. and Prionanthium Desv. are the only three genera in the tribe with seven as a basic chromosome number (excluding the genus Dregeochloa Conert, which was not investigated in this study). A close affinity between these genera is, thus, recognised. This relationship is corroborated by the DNA fmgerprinting and DNA sequencing data. One Prionanthium dentatum (L.f.) Hem. specimen was, however problematic. This specimen grouped with Tribolium Desv. Clayton and Renvoize (1986) proposed this relationship, but in the light of various studies, as in this study, Prionanthium is removed from this closely related genus. Therefore, the recognition of subtribes in Arundineae, is proposed. The genera Arundo L. and Phragmites Adans. were grouped together. This is unexpected, because according to Clayton and Renvoize (1986), these genera are not as closely related, as their similarity in habit would suggest. In this study these two genera, known as arundinoid genera, are a monophyletic grouping nested within the rest of the genera, known as danthonoid genera. The genera Karroochloa Conert & Turpe, Merxrnuellera Conert and Prionanthium were shown to be polyphyletic with the sequencing data. DNA amplification fingerprinting was helpful in resolving species relationships, but failed to elucidate most of the generic relationships in the study. DNA sequencing was the more informative of the two techniques. The combined analysis was helpful in that some resolution was gained, while other was lost. Due to large amounts of missing data and the inability of DNA fingerprinting to resolve generic relationships, the combined analysis could not be used to its fullest capacity. PAUP and HENNIG86 were both used and both software programs gave the same results. In general, the trees created with PAUP were usually shorter. Both software programs can be used, but the ease of PAUP makes it the preferred analysis package. Successive weighting usually resulted in a tree with better Cl and RI values, compared to a search conducted on the equally weighted data set. The topologies of the trees, however, remained the same. Adams consensus trees were the only consensus trees, which were usually the best (or most) resolved when compared to Strict and Semistrict consensus trees. The present tribal classification for the Arundineae seems justified. However, a subdivision of the tribe Arundineae, to accommodate the clustering of the genera Pentameris, Pentaschistis and Prionanthium into a subtribe, may be justified. The position of Arundo and Phragmites is monophyletic if only the South African representatives are investigated. Some confusion still exists within the tribe and DNA sequencing studies of more specimens per species and more species per genus is advised.
Open Access
A phylogenetic study of some representatives of the genus Pentaschistis
(University of the Free State, 1999-05) Holder, Francisca; Spies, J. J.
English: The genus Pentaschistis (Nees) Spach consists of 68 species and is endemic to Africa, with 57 species being indigenous to South Africa and 40 species endemic (Gibbs RusseIl et al. 1990). To date, the chromosome number of 30 species have been reported, as well as the sequences of the rpoC2 gene of two species and the ITS region of one species. In this study, seventeen specimens were cytogenetically examined. The polyploid levels ranged from diploid (n = x = 7) to 14-ploid (n = 7x = 49). Two species were examined for the first time, namely: P. capensis (diploid) and P. veneta (tetraploid). New polyploid levels were also observed for P. viscidula (tetraploidy), P. densifolia (octaploidy), P. rupestris (decaploidy & 14-ploidy) and P. tortuosa (octaploidy). Due to the fact that no, or very few, multivalents were observed, we concluded that the species are alloploids or segmental alloploids tending towards alloploidy. The morphological groupings (Linder & Ellis 1990a) could unfortunately neither be supported nor rejected by cytogenetic evidence alone, therefore cytogenetics was used in conjunction with molecular data to determine the phylogeny. The fragment patterns obtained from RAPDs were used to calculate the genetic distances. A high degree of variation was observed within and between the morphological groups. Cladograms were obtained with the computer programs PAUP and Hennig86, and PAUP gave the most parsimonious cladogram. The resolutions of these cladograms were, however, not good, therefore DAFs was performed. Again PAUP and Hennig86 were used and again PAUP proved to give the most parsimonious clado gram. These cladograms gave a clearer indication of the phylogeny of Pentaschistis, but the genetic distances within and between the species again proved to be high. The ITS} region was sequenced and aligned separately with Clustal W and Malign. These cladograms indicated a close alliance between P. eriostoma and P. curvifolia. The three data sets were combined and a cladogram with much better resolution was obtained. The morphological data was included and had a minor influence on the phylogeny. This cladogram also indicated a sister relationship between P. eriostoma and P. curvifolia. Current data suggest that P. eriostoma could well have developed through the hybridisation of P. curvifolia and that both P. eriostoma are correctly grouped with Pentaschistis. The combined analysis also indicate that the morphological groupings of Linder & Ellis (1990a) is somewhat supported by phylogeny.
Open Access
Adult-plant resistance to Puccinia recondita f. sp. tritici in a collection of wild Triticum species
(University of the Free State, 1999-05) Barnard, Johanna Elizabeth; Pretorius, Z. A.; Kloppers, F. J.
English: The ability of rust pathogens to mutate and form new and virulent races, necessitates the broadening of the genetic base of resistance in common wheat to rust diseases. The wild relatives offer a rich reservoir of resistance genes. In an attempt to identify new sources of resistance to Puccinia recondita f. sp. tritici, 353 Triticum accessions, comprising diploid, tetraploid and hexaploid species were evaluated for seedling and adult-plant resistance to a mixture of pathotypes UVPrt2, 3, 9, and 13. In addition to infection type studies, plant height, growth habit and head type of adult plants were also recorded. One hundred and twenty six of the accessions were resistant to moderately resistant as seedlings to the pathotype mixture, whereas 180 were resistant or moderately resistant as adult plants. The number of days from planting to flag leaf stage varied from 54 to 187. High levels of resistance were observed in adult plants of T. longissimum, T. sharonense, T. searsii and T. turgidum ssp. compactum. Triticum kotschyi and T. ventricosum expressed hypersensitive infection types. Partial resistance (small pustules without any apparent chlorosis), was observed in T. turgidum ssp. durum, T. turgidum ssp. pyramidale and T. tauschii. In T. turgidum, which comprised 14 subspecies and 272 accessions, approximately 44% of the adult plants were resistant to moderately resistant compared to 24% of the seedlings. According to these results 13 accessions, producing smaller or fewer leaf rust pustules, without the characteristic chlorosis and necrosis associated with hypersensitive resistance, were selected. Adult plants were quantitatively inoculated with pathotype UVPrt13 of P. recondita f. sp. tritici. Palmiet, a bread wheat cultivar susceptible to UVPrt13, was included as a control. Latent period of leaf rust, uredium size and density, and infection type were determined in two experiments. In the first experiment latent period ranged from 309 h to 401 h compared to 258 h in the susceptible control, Palmiet. In the second experiment Palmiet had a latent period of 244 h whereas those in the Triticum accessions ranged between 175 hand 372 h. Most accessions supported more uredia per ern" flag leaf surface than Palmiet in the first, but not in the second experiment. However, pustules were significantly smaller on most of the lines. Based on these components, T. timopheevii ssp. araraticum v. tumanianii, T. turgidum ssp. durum v. obscurum, and T. turgidum ssp. persicum v. stramineum, showed high levels of partial resistance. Triticum turgidum and T. timopheevii accessions rated as potentially valuable sources of resistance were selected for histological studies on mechanisms of resistance. Penetration and establishment of the leaf rust pathogen were studied in flag leaves of T. timopheevii, T. turgidum ssp. dicoccum, T. turgidum ssp. durum and T. turgidum ssp. compactum. The T. aestivum wheats Thatcher (Tc) (susceptible common wheat control) and TcLr19 (resistant common wheat control) were included in the experiment. Using fluorescence microscopy, infection sites of pathotype UVPrt13 were examined for the percentage prestomatal exclusion (germtubes not forming appressoria and appressoria not forming over stomata), abortive penetration (non penetrating appressoria and aborted substomatal vesicles), early abortion (six or less haustorium mother cells per infection site) and infection sites successfully culminating in colonies. Flag leaf sections were prepared for phase-contrast microscopy by staining with either Trypan blue alone or in combination with a solution of picric acid in methyl salicylate. To confirm and expand light microscopy observations, upper and inner surfaces of epidermal tissue of T. timopheevii and T. turgidum ssp. dicoccum were fixed and prepared for scanning electron microscopy. Observations showed that resistance in T. timopheevii was typically hypersensitive and may thus not be durable. The prehaustorial resistance exhibited in T. turgidum ssp. durum and T. turgidum ssp. compactum, may be valuable sources of nonhypersensitive resistance when transferred to cultivated wheat.
Open Access
Grain yield and breadmaking quality of wheat lines with leaf rust resistance genes Lr29, Lr34, Lr35, and Lr37
(University of the Free State, 1999-06) Grobbelaar, Benida; Labuschagne, M. T.; Pretorius, Z. A.
English: 1. The aim of this study was to determine if the leaf rust resistance genes Lr2g, Lr34, Lr35 and Lr37 have an effect on the quality and yield characteristics of a cultivar it is incorporated into. 2. Near-isogenic lines (NIL's) of PalmietlLr2g and PalmietlLr34, as well as of Karee/Lr2g, Karee/Lr34, Karee/Lr35 and Karee/Lr37 as 'Neil as all relevant parents, were evaluated for four yield and nine quality characteristics in a field experiment in the central Free State. The experiment was conducted in a randomised block design. 3. Results and conclusions: • The HMW glutenin subunits indicated segregation in BC6, especially in the Palmiet lines. • Thatcher and Palmiet lines with Lr29 had significantly lower thousand-kernel 'Neight values compared to their recurrent parents. • Palmiet NIL's with Lr29 had significantly shorter mixograph mixing time compared to Palmiet. • Karee NIL's with the genes Lr34, Lr35 and Lr37 had significantly better PL-ratio's compared to Karee. • None of the leaf rust resistance genes used in this study had an influence on all the quality characteristics and yield components. • The results suggested that the introduction of foreign genes will not necessarily result in a yield reduction. The only reduction in yield was observed in Karee NIL's containing Lr34. • The two genetic backgrounds responded differently following to incorporation of the same Lr gene. • Some sister NIL's performed better than others, which emphasises the importance of sampling.
Open Access
An assessment of endophytic fungi in needles of three pinus spp. cultivated in South Africa
(University of the Free State, 1999-11) Kriel, Wilma-Marie; Swart, Wijnand J.; Crous, Pedro W.
English: Endophytes, in the strict sense, are organisms that cause symptom less infections in plants. As symptomless mutualists, they can act as biocontrol agents of herbivorous insects and plant diseases. They can also be indicative of host vitality and environmental pollution. Some endophytes, however, are latent pathogens with an endophytic phase. Pine needles are colonised by various species of endophytic fungi. It is well-known that the endophytic biota vary with host species, as well as with time. Therefore the aim of this study was to qualitatively and quantitatively compare endophyte populations within the canopies of Pinas patula, P. radiata and P. elliottii, during winter and summer, and within the canopies of two separate P. radiata trees, over different seasons. Endophytic fungi were isolated from pine needles, sampled in different seasons from various positions within the canopy, by plating surface-sterilised needle sections onto cornmeal agar supplemented with antibiotics. In the first study a significant difference (P < 0.05) in endophyte numbers between samples collected during winter and summer was observed. Pinus patula and P. elliottii were more intensively colonised during winter than summer. In P. radiata, however, the number of fungi isolated in summer was significantly higher than in winter, but the fungal species isolated were consistent. Cydsneusms minus and a sterile white yeast-like fungus were most commonly isolated. Cyclsneusms minus is a latent pathogen causing autumn needle cast, and sterile yeast-like fungus is suspected to be a true endophyte. Similar endophytic fungal species were isolated in the second study, performed on two eight-year-old P. radiata trees. Samples were taken during four seasons from an isolated, solitary tree and one growing in an even-aged, plantation nearby. Five needle fascicles of four different age groups were collected from each tree. One needle per fascicle, including the fascicle sheath, was cut into 12 sections and used for the isolations. In general, fewer endophytes were isolated from the solitary tree than the plantation tree. Qualitative and quantitative differences in endophyte populations were observed within needles as well as between needle age groups and seasons. The aim of the third study was to conduct a qualitative assay of enzyme production of 2 t predominant fungal endophytes isolated from the pine needles. The enzymes assayed included cellulase, pectinase, lipase, laccase, phenol oxidase, protease, B-glucosidase, cytochrome oxidase, and peroxidase. Results were consistent with attributes associated with leaf penetration and longterm residence of fungi within pine needles. All fungi screened produced at least two of the enzymes assayed. Different substrate utilisation patterns suggest biochemical partitioning of nutritional resources by endophytes. The ubiquitous presence of lipolytic activity in all isolates tested, suggests the ability to lyse cuticular waxes in order for penetration to occur. The tolerance of most tested fungi to tannic acid (phenol oxydase production) suggests low sensitivity to phenolic compounds (tannins etc.) normally present in pine needle tissue. Management practices in plantations that reduce or increase the environmental stress on individual trees, thereby influencing endophytic populations, could have distinct beneficial or negative effects on the general vitality of trees. The most important effects of certain practices would be the influence they have on latent pathogens such as C minus. Further investigation of foliar endophytic fungi of intensively managed pine plantations is therefore justified with a view to understand the effects management practices have on their ecology.
Open Access
'n Ondersoek na die antibakteriese eienskappe van Carpobrotus edulis L.
(University of the Free State, 1999-11) Van der Watt, Elmarie; Pretorius, J. C.; Kemp, K.
English: In the folk medicine of South Africa, many traditional medicinal plants are used by both the rural and a small percentage of the city population. One of these plants is Carpobrotus edulis L. An investigation of the chemical composition as well as the anti-microbial properties of this plant was the main objective of this study. Overviews on traditional medicine in South Africa and the family Mesembryanthemaceae are given. According to the available literature little is known about the chemical composition, active substances in as well as pharmacological properties of C. edulis, but most of the published information deals with the ecological importance of the plant. In this study the anti-bacterial properties of the plant were confirmed and three semipurified fractions were initially isolated by applying different chromatography techniques. During purification of active substances, with prior removal of tannins, six anti-bacterial compounds were isolated of which five were identified namely rutin, neohesperidin, hyperoside, cactecin, ferulic acid while one flavonoid remained unidentified. The conclusion from this study is that the anti-bacterial properties of the plant are related to the presence of the tlavonoids rutin, neohesperidin, hyperoside, cactecin and femlic acid as well as one unknown flavonoid. The most prormsmg observation during this study was the selective inhibition of gram negative bacteria, known to be more resistant than gram positive bacteria to antibioticums.
Open Access
Identification of genetic distances and heterotic groups of inbred maize (Zea mays) lines using DNA fingerprinting
(University of the Free State, 1999-12) Swanepoel, Ezanne; Labuschagne, M. T.; Viljoen, C. D.
English: AFLP (Amplified Fragment Length Polymorphism) analysis has found widespread use in DNA fingerprinting because of its relative simplicity, low cost and high marker output. AFLP analysis also does not have the limitations associated with morphological characterisation and the use of other molecular markers such as RFLP's (Restriction Fragment Length Polymorphisms) and RAPD's (Random Amplified Polymorphic DNA markers). Furthermore, the AFLP technique has found widespread use in the identification of cultivars, varieties and breeding lines. The accurate identification of breeding material is extremely important, not only for the protection of breeder's rights, but also to accelerate plant-breeding programmes. The aim of this study was to use AFLP fingerprinting for the identification and genetic distance analysis of a collection of maize inbred lines from the Advanta Africa genebanks. Fifty maize inbred lines from Africa (local), Argentina, Zimbabwe (CIMMYT), Garst (USA) and Thailand were fingerprinted using AFLP's. A total of 107 scored AFLP loci were used to calculate pairwise genetic distances. This revealed an average genetic distance of 4.38% between all lines studied. The trend of the clustering pattern was more variation in the major clusters with less variation between lines in subgroups and even less variation within the minor groups. It was also further illustrated that the local and foreign inbred lines were not grouped separately. Neighbour joining cluster analysis of the genetic distance data yielded a dendogram that indicated the absence of relation between geographic diversity and genetic diversity. The resulting knowledge of genetic distance and identification of maize inbred lines in this study will contribute towards maize breeding programmes in Advanta Africa Seeds. It permits an organisation of germplasm resources and identification of parents for crossing blocks. This will enable the breeder to make more scientific based choices, where both additive and non-additive sources of genetic variation contribute to the gain. Our results have shown that AFLP technology is a rapid, informative and precise technique for identification of maize inbred lines in this study
Open Access
Host-plant interactions and resistance mechanisms to banana weevil Cosmopolites sordidus (Germar) in Ugandan Musa germplasm
(University of the Free State, 2000-03) Kiggundu, Andrew; Labuschagne, M. T.; Louw, Schalk
English: Banana is an important subsistence crop in many tropical regions of the world. In the East African Great Lakes region it constitutes a staple food for more than 17 million people. Among many production constraints, banana weevil (Cosmopolites so rdidusi. is the most serious pest to the crop. The tunnels caused by the boring larvae interfere with water and mineral uptake, and provide entry for fungi and bacteria. Most importantly this weakens the corm, leading to toppling of plants even in slight winds. Host plant resistance is considered the basis of any successful integrated pest management plan, if the banana weevil problem is to be solved by the resource poor farmers. The screening trial of 45 Ugandan Musa germplasm accessions revealed that the plantain subgroup (AAB) was most susceptible to banana weevil followed by East African highland banana clones. The exotic bananas, especially Kayinja, Bluggoe (ABB), Kisubi and Ndiizi (AB) were resistant to banana weevil. Plantain derived tetraploid hybrids of the wild banana Calcutta-4 were also susceptible, indicating dosage effect of the susceptible gene. Mbwazirume, Tereza and Nakyetengu have been found to be relatively resistant local land races and they are recommended as possible resistant selections. Total inner damage was found to be the best criteria for screening, and selecting for weevil resistance, since it scored the highest heritability and was highly correlated with all other weevil damage indices. Significant phenotypic and genotypic correlations were found between corm hardness, dry matter content, sap/resin production, suckering ability and corm size and banana weevil damage. These were therefore considered important mechanisms of resistance in Musa and this indicated that banana weevil resistance is a complex polygenic trait. In agreement with the literature studied. antixenosis was not found to be important as a resistance mechanism in Musa. However. results from various no-choice experiments on hatchabil ity and development revealed significant differences. The previously observed resistance cultivars Kayinja. Yangambi-km5 and FHIA03, unlike the more susceptible plantains and EAHBs, significantly increased developmental time and in some cases caused mortality of immature weevil stages. Preliminary studies on the influence of secondary metabolites were undertaken. The results showed the presence of two or three compounds indicated by peaks on HPLC chromatograms of methanol extracts of corms from resistant cultivars (e.g. Kayinja and FHIA03) that were not present in susceptible cultivars (e.g. Atwalira and Gonja). These substances were also not present in some resistant cultivars like Yangambi-km5 and Cavendish, both of the AAA genome group. This was yet another indication that resistance is complex and these different factors are important in different groups of cultivars.
Open Access
Water quality of the upper Orange River
(University of the Free State, 2000-05) Venter, Gertruida C.; Roos, J. C.; Van Wyk, P. W. J.
English: The Upper Orange River is defined as the region between the source in the Drakensberg (Lesotho) and the Orange-Vaal confluence. Information on the water quality, phytoplankton composition and the influence of the dams on the Upper Orange River is limited. This study was conducted in order to determine seasonal and spatial patterns in the river system., as well as to determine the influence of the tributaries and the two major dams on the river system. Physical, chemical and biological factors were taken into account. Hypolimnetic water released from the Gariep and Vanderkloof Dams caused a significant decrease in the temperature downstream of the dams. The dams acted as sediment traps and caused the TSS and turbidity in the river system to decrease. A decrease in turbidity resulted in an increase in the light penetration. This created more favourable conditions for primary production and led to algal blooms in the dams. The dams are used for hydro-electric power generation and almost completely diminished seasonal flow patterns. This changed the Upper Orange River into a highly regulated system. The interference with seasonal flow patterns in the river is probably one of the main reasons for outbreaks of the pest blackfly, Simulium chutteri downstream of the dams. The oxygen-depth profile in the Gariep Dam during summer stratification indicated relatively high dissolved oxygen concentrations in the epilimnion (8.2 mg.l-1) and anoxic, near anaerobic, conditions (0.1 mg.l-1) in the hypolimnion. The oxygen decline in the hypolimnion was indirectly the cause of high algal production in the epilimnion during algal blooms. The average pH of the Upper Orange River system was mainly alkaline at 8.1, with an average total alkalinity of 95.2 mg CaC03.rl. This suggested that the Upper Orange River is a wellbuffered system. The average conductivity in the Upper Orange River was relatively low at 19.6 mS.m-1, but increased significantly since 1980. Major ions at Aliwal North occurred in the following proportions, i.e. Ca> Na > Mg > K for cations and CO3 > Cl> SO4 for anions. In the Gariep Dam and at Marksdrift the proportions were: Na > Ca > Mg > K for cations and CO3 > Cl > SO4 for anions. The average P04-P concentration was relatively low at 28.3 µg.l-1 and the average TP concentration was 107 µg.I-1. The average N03-N concentration was high at 312 µg.l-1 and increased in the dams and downstream probably due to agricultural fertilizers and nitrogen fixation by algae. The average chlorophyll a concentration ranged between 0.4 and 1084 µg.I-1, with and average concentration of 10.8 µg.l-1. The very high chlorophyll a concentration was due to a bloom of Microcystis sp. during February in the Gariep Dam. Phytoplankton dynamics manifested themselves in seasonal cycles. Cyanobacteria and Bacillariophyceae dominated during warmer months. The Chlorophyceae replaced cyanobacteria during cooler months. Light penetration in the Gariep Dam and the Vaal River had a major effect on the primary production. The maximum primary production in the Gariep Dam was 14.6 mg C. mg Chla-1 h-1 and in the Vaal River the maximum primary production was 76 mg C. mg Chla-l. h-1. According to the primary production in the Gariep Dam it can be classified as mesotrophic, while the high primary production in the Vaal River indicated eutrophic conditions. The dams exert major influences on the physical, chemical and biological parameters in the river. Low SASS4 scores were obtained and are an indication of poor water quality. This could be ascribed to disturbances by the dams. The serial discontinuity concept (SDC) is applicable in the Upper Orange River. It is likely that agricultural runoff, as well as urban and industrial pollution from the Vaal River catchment would mask the downstream recovery after the Orange- Vaal confluence.
Open Access
Drought, freezing, and nitrogen stress as factors predisposing pistachio trees to infection by Botryosphaeria obtusa and B. dothidea
(University of the Free State, 2000-05) Nieuwoudt, Tielman Daniel; Swart, Wijnand J.; Pretorius, J. C.
English: Drought, freezing and nitrogen stress are environmental factors known to predispose woody plants to infection by numerous fungal species. The main and ultimate objective of the present study was to identify possible stress factors that predispose commercially pistachio (Pistacia spp.) trees to infection and colonization by Botryosphaeria obtusa and B. dothidea in order to develop a sustainable disease control programme for South African pistachio producers. It was found that these stress conditions significantly affected the susceptibility of three genotypes of potted pistachio plants to infection and colonization by B. obtusa and B. dothidea. In the glasshouse, drought stress trials with potted Pistacia terebinthus plants artificially inoculated with B. dothidea showed significantly longer lesions than control treatments while P. integerrima displayed the greatest resistance to the pathogen. Although B. dothidea caused more severe cambial lesions in glasshouse trials, it showed a slower growth rate than B. obtusa under in vitro water stress conditions. In freezing stress trials performed in a growth chamber, there was a highly significant difference between the stressed and non-stressed plants of P. integerrima and Clone II (P. integerrima x P. atlantica). P. integerrima was the most susceptible rootstock and P. terebinthus the least susceptible. B. dothidea caused the most severe cambial lesions in all treatments. In nitrogen stress trials, most treatments showed a significant decrease in the length of cambial lesions at a higher level of applied nitrogen (28%). B dothidea was generally more pathogenic than B. obtusa for both levels of N applied. The most significant differences between nitrogen levels were recorded for P. terebinthus. From the above results it is clear that drought and freezing stress have a significant effect on the predisposition of pistachio plants to B. obtusa and B. dothidea. Drought stress occurs in pistachio orchards due to a very short hardening off period lasting two to three weeks. By postponing this period not only can drought stress be prevented but also freezing stress. Current nitrogen levels applied in the pistachio orchards are much lower than those applied in other parts of the world. Applying higher levels of nitrogen could thus possibly prevent the occurrence of Botryosphaeria diseases. The development of a selective medium for the pure isolation of B. obtusa and B. dothidea from diseased tissue and other sources enabled the isolation of B. dothidea from debri, bark, diseased and asymptomatic tissue without hindrance by extraneous fungi. B. obtusa, however, was only isolated from active cankers on the stems of pistachio trees. Isolation of B. dothidea from asymptomatic plant tissue suggests an endophytic or latent phase. Trials were conducted in vitro with different fungicides to determine other possible fungicides that could be employed for the control of the two Botryosphaeria species. Eria®, a mixture of carbendazim and difenoconazole displayed the highest inhibition. Benomylor the Eria® applied during bloom, and tebuconazole in combination with difenoconazole on a monthly basis throughout the season, should thus successfully control both Botryosphaeria diseases in South African orchards.
Open Access
A molecular systematic study of the genus Encephalartos
(University of the Free State, 2000-06) Coetzer, Maria Elizabeth; Spies, J. J.; Oberholster, A-M; Vorster, P.J.
English: The extant cycads (Cycadophyta) are divided into three families, with 11 genera (Johnson 1959, Stevenson 1990), and at least 210 species (Stevenson et al. 1995). In this study a molecular systematic study was done on the genus Stangeria T. Moore from the family Stangeriaceae, and the genus Encephalartos Lehm. from the family Zamiaceae. Fifty eight specimens representing 35 species of the genus Encephalartos, and one specimen from the genus Stangeria, Stangeria eriopus (Kunze) Nash were used. The effect and behaviour of hybrids in cladistic analysis were also investigated, such that they might be detectable during cladistic analysis. A pilot study of two molecular techniques, RAPD and DAF was done to determine the applicability, time effectiveness and most suitable primers for a molecular systematic study using these techniques. All the RAPD primers tested gave a high coefficient of similarity and adequate number of characters per specimen. The speed and simplicity of the RAPD technique, combined with the findings of the pilot study, made this an ideal method to generate a large amount of fingerprinting data for a phylogenetic assessment of the genus Encephalartos. Three variations of the DAF technique were tested in the pilot study i.e. simple DAFs, tecMAAP and multiplex DAFs. The coefficient of similarity was high in all the primers, with an increasing number of characters per specimen being generated. The multiplex DAF technique was the most successful, and most cost effective DAF variation. tecMAAP is also a very useful method in this study, but prior cleavage with restriction endonuclease, makes this a time consuming method. Multiplex DAFs combined with simple DAFs were, therefore, applied to more specimens in this study. Phylogenetic relationships were determined using the computer software PAUP, and the genetic distances between species were also determined, The RAPD and DAF cladograms show some correspondence, but also some discrepancies as expected because of the low resolution in the cladograms. Combining the data sets increased the resolution of the cladogram. The molecular results concur with morphological and biochemical studies that have been done on the species in this study, as observed in the close relationship between Encephalartos cupidus and E. eugene-maraisii, and E. umbeluziensis and E. villosus. The RAPD and DAF techniques were also successfully applied in hybrid analysis. An increase in hybrids to the cladistic analysis, do influence the tree topology, but not the cladogram resolution, with an increased tree length. Hybrids, therefore, are no more problematic cladistically than the increased inclusion of specimens. In this study the molecular techniques RAPD and DAF have proven to be a fast and cost effective method in successfully generating fingerprints for phylogenetic analysis.
Open Access
Identification of Ethiopian Triticum aestivum, T. turgidum, and Eragrostis tef using morphological, SDS-PAGE and AFLP characterisation
(University of the Free State, 2000-11) Hika, Yilma Amenu; Labuschagne, M. T.; Viljoen, C. D.
English: In this study, morphological, seed storage proteins, and AFLP markers were used to identify and determine the genetic divergence among 20 Ethiopian wheat varieties. In the same way, an attempt was also made to characterize 10 Ethiopian tef cultivars using morphological and AFLP markers. Seed storage proteins were not used to characterize the tef cultivars, because it was already reported that the low number of protein markers detected could not distinguish individual tef cultivars. The morphological traits have uniquely identified all the wheat and tef accessions, although it is found that morphological distances are not accurate estimate of genetic distances owing to their limited number and environmental interaction. Thus, results obtained from morphological data have to be confirmed by biochemical or DNA markers, depending on the need of identification. From the protein markers, the gliadins uniquely distinguished all the individual wheat accessions. Thus, gliadins can be effectively used to discriminate wheat cultivars. However, some of the wheat cultivars had the same HMW-GS banding patterns, and therefore, HMW -GS should not be used for cultivar identification. The HMW -GS can rather be used to determine quality characteristics. In general, compared to morphological markers, protein markers are more reliable as the effect of environmental influence is absent or minimal. The limitation with the protein markers is that only part of the genome that codes for a specific protein can be detected. With the AFLP markers, more variations were detected among the wheat entries, due to the potential of the AFLP markers to survey the entire genome and also due to the larger number of loci assayed. Thus, AFLP markers are more reliable and hence they can be used to supplement and refine morphological- and protein-based classifications.
Open Access
Pathogenic variability in Puccinia Sorghi on maize in South Africa
(University of the Free State, 2000-11) Fato, Pedro; Pretorius, Z. A.; Flett, B.; Van Deventer, C. S.
English: Common rust, caused by Puccinia sorghi Schw., is a major disease in maize (Zea mays L.) producing regions throughout the world and can result in high yield losses on susceptible genotypes when the environment is favourable for epidemic development. To understand the principal aspects related to P. sorghi, a literature survey concerning the biology of the pathogen, host range, host-pathogen interaction, and economic importance of the disease, was conducted. Furthermore, different methods of disease management are reviewed, with emphasis on genetic control. To determine pathogenic variability in Puccinia sorghi in South Africa, rustinfected maize leaves were collected during the 1999/2000 season. Isolates collected in the field were increased on susceptible plants and inoculated onto maize differential lines carrying different Rp genes for resistance to P. sorghi. Seven pathotypes, namely, A, B, C, D, E, F and G, were differentiated in the greenhouse. Pathotype B was the most virulent and occurred in Gauteng, KwaZulu-Natal, and Mpumalanga. Pathotype A, virulent only on Rp34 and Rp3B/ was widely distributed, occurring in six provinces. Pathotype C was detected in Mpumalanga and the Northern Province, D in the Northern Province whereas pathotype E was collected from North West, and F and G from KwaZulu-Natal. No virulence was detected for genes Rp1C, Rp1G,Rp1L, Rp3D and Rp3F. All isolates were virulent on Rp3B. The occurrence of virulence for most Rp genes suggests that monogenic resistance is of little value for future protection of maize cultivars against common rust in South Africa. One hundred maize inbred lines from Mozambique, South Africa and Zimbabwe, as well as 58 South African hybrids, were evaluated for resistance to common rust under field conditions over different localities in South Africa during the 1999/2000 season. Inbred lines were planted at Ermelo and Greytown and inoculated by a mixture of spores from previously identified P. sorghi pathotypes. Cultivars were tested under conditions of natural common rust infection at Greytown and Petit. Disease severity was assessed prior to anthesis, at anthesis, and after anthesis at all localities except the Greytown cultivar trial, which was assessed only once after anthesis. Disease was scored on a 0-9 scale converted to percentage leaf diseased area (0-96% scale). The percentage values were log-transformed using the natural logarithm function. Analyses of variance were carried out for each severity parameter (individual rating, mean, sum and AUDPC [area under the disease progress curve]) within, and (mean, sum and AUDPC) across localities. Significant genetic variation existed between genotypes for resistance to P. sorghi at each and across localities. Some inbred lines showed significant levels of partial resistance to the pathogen and may be used in resistance breeding programmes. Most hybrids showed susceptible reaction types to common rust and are thus potentially vulnerable to yield losses under conditions of epidemic occurrence of P. sorghi. In general, similar to other cereal rust pathosystems, it is apparent that monogenic rust resistance in maize will not be durable. Emphasis in breeding should therefore be placed on horizontal resistance, with particular attention to sources of resistance, screening procedures and heritability. This study will hopefully serve as an important source of information for future research of common maize rust in southern Africa.