Plant Sciences

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    ItemOpen 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.
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    ItemOpen 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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    '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.
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    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
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    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.