There is an increasing interest among Plant Pathologists to explore, more fully, the nature of parasitism. This interest lies in obtaining a clear understanding of the host-parasite relationship. The emphasis is placed on the physiological mechanisms involved which enables the plant pathogenic organisms to effect entry into the host body and to assimilate the available nutrients, to tolerate or overcome the resistance of the host and to induce disease in the host by their metabolic products or toxins. The host-parasite relationship of the common scab disease of potatoes, caused by Streptomyces scabies (Thaxt.) Waksman and Henrici, presents many features of parasitism which would be interesting to explore as far as the physiological mechanisms are concerned.

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Disease resistance in plants is an attribute which ensures the survival of the species against the agents of disease. It is evolved in nature in the course of natural selection and is genetically controlled. Extensive use of this property is made in breeding resistance into susceptible but otherwise desirable varieties. The nature of resistance, however, is but little understood; although, on the basis of numerous morphological, anatomical, chemical and physiological studies, several theories of resistance have been offered.

Hoodia gordonii has been used by the San people for centuries as an appetite suppressant while they were on long hunting trips. These succulents are globally known as an important component in diet supplements and products which assist in weight-loss. Together with other plants these contribute towards a multimillion US dollar market, as many pharmaceutical and nutritional companies have made significant financial investments in the research and development for people who suffer from weight problems and obesity. In South Africa, H. gordonii is classified as being endangered, because so many pharmaceutical companies cashed-in on the dietary characteristics of these succulents. The plant is found in the South Western parts of Southern Africa mainly in the Karoo, Kalahari and Namib deserts. Plants were also grown in cultivated nurseries under favourable conditions for commercial use. However, diseases have dramatically hampered production in nurseries with almost total loss of crop. Although not many diseases have been documented on this plant, Fusarium wilt, a devastating fungal disease of H. gordonii, caused by F. oxysporum had been identified. This disease is not only responsible for economic losses, but also contaminates the soils with spores, which remain dormant until the next season as inoculum. This study concentrated on the morphological characterisation and molecular identification of the Fusarium wilt causing pathogen present in four areas (Kakamas, Klein Pella, Pofadder and Prieska) as well as the morphological evaluation of the host. Fusarium oxysporum was identified as the causal agent of Fusarium wilt on H.gordonii plants. The AFLP analysis and DNA sequences resulted in two distinct groups. Those that clustered in the AFLP cluster B were also grouped in a TEF cluster B, however some isolates from AFLP cluster A also grouped together with the TEF cluster B. The low genetic variation revealed by the AFLP analysis indicated that differences amongst the pathogen isolates occur, but the DNA sequences confirmed that these isolates share a common ancestor. DNA sequencing analysis was used to place 44 South African F. oxysporum isolates into the phylogenetic groups as described by OâDonnell and associates. South African F. oxysporum isolates clustered into two groups. The observed genetic variation amongst individual isolates was lower than the genetic variation between out-group isolates. Two clusters were identified; within each cluster isolates had a relatively high frequency of clones. These clones confirm that these pathogen isolates share similar allele frequencies. Results from sequencing data showed that the isolates fall within the FOSC, however there was no isolates identified that show 100% similarities when compared with all three genes sequences with recorded genetic sequences of F. oxysporum isolates in other parts of the world. Therefore, based on the current taxonomic system, of host specificity the fungus only infects H. gordonii, so the study has proved that a possible new formae specialis has been identified. New preventative measures must be applied to the host when planting in nurseries. Knowledge gained from analyses of the genetic fingerprinting, DNA sequencing of these isolates and the mporphological evaluation of the host might assist with the development of effective control strategies, i.e. resistance breeding against Fusarium wilt. This will provide an incentive to potential farmers to plant H. gordonii, thus improving production of this succulent for pharmaceutical companies and nurseries in South Africa.

Wheat is one of the most important food crops and consumption in the past year was higher than production worldwide, which indicates improved wheat cultivars need to be developed to maintain the demand for wheat. One of the biggest threats of wheat is ever-evolving pathogens that overcome resistance. To overcome threatening diseases, breeders need to incorporate new resistant genes/QTL into improved cultivars. Incorporating different resistant genes/QTL into a single line using gene-pyramiding and MAS can enhance the breeding process. However, pyramiding of genes for resistance can lead to a decrease in baking quality characteristics, which are important for the milling and baking industry as well as for consumers. To overcome this problem, lines should also be tested for bread-making quality characteristics such as HMW-GS and the LUPP% which are directly linked to protein quality. The aim of the study was to identify rust and FHB resistant lines with good protein content. Rust and FHB resistant wheat lines were developed during previous studies. The best rust and FHB resistant lines were planted and self-pollinated. Lines were evaluated for the presence of five rust resistant genes/QTL (Lr19, Lr34/Yr18/Sr57, QYr.sgi.2B-1, Sr2 and Sr26) and four FHB resistant genes/QTL (Fhb1, Qfhs.ifa-5A-1, Qfhs.ifa-5A-2 and Fhb2) for two consecutive years. These selected rust and FHB resistant lines were also subjected to three biochemical tests namely SDS-PAGE, SEHPLC and RP-HPLC. PCR-based markers linked to HMW-GS alleles and the IBL.1RS translocation, associated with weak dough strength, were also tested. Since the breeding programme was still in an early stage, only few seeds per line were available and therefore biochemical tests that can be performed using single seeds were selected. Results from SDS-PAGE and molecular markers linked to HMW-GS were similar and therefore lines were further evaluated using only molecular markers. No correlations were detected for the RP-HPLC data of lines therefore it was excluded during further analysis. The rust and FHB resistant genes/QTL co-segregated based on their related parental lines. An additional round of self-pollination either led to higher levels of homozygosity for the selected traits or to the loss of traits due to recombination. MAS enabled the selection and enhancement of homozygous lines. Only a few offspring of one of the rust resistant lines contained the Sr26 gene, while the Lr34/Yr18/Sr57 gene was present in all tested lines. None of the rust resistant lines contained the Sr2 gene which is a major gene for resistance against stem rust and especially effective against the threatening Ug99 race. The top ten rust resistant lines all had the same rust resistant gene/QTL present (Lr19, Lr34/Yr18/Sr57 and QYr.sgi.2B-1) as well as the same protein quality alleles (Ax2*, Bx7+By8 and Dx5+Dy10). The LUPP% of these lines showed high levels of variation and was optimal (40% to 50%) for only one line. High levels of variation were detected for the FHB resistant markers in the FHB resistant populations. The top ten lines contained all six markers although the level of homozygosity varied. Four of these lines expressed both the Bx7+By8 and Bx17+By18 alleles and only one line did not express the Bx7OE allele. None of these lines expressed the 1BL.1RS translocation. Two of these lines showed a desirable LUPP%. Results indicated the preference towards rust or FHB resistance selection followed by selection for protein quality alleles and lastly the LUPP%. The top ten rust and FHB lines can serve as resistance sources in further breeding programmes.

Quality protein maize (QPM) which is nutritionally enhanced, has the potential to alleviate malnutrition and related diseases in communities where maize is a dietary staple and often the only source of proteins. The wide dissemination and utilisation of QPM in Africa depends on the competitiveness of cultivars for grain yield and other agronomic traits compared to normal maize. This study was conducted to (i) evaluate the grain yield performance and stability of newly developed early maturing QPM hybrids under stress and non-stress environments of ESA (ii) analyse mega-environments of SSA based on the primary and secondary traits of QPM (iii) asses the adaptation pattern of QPM in SSA based on multivariate analysis techniques (iv) identify and recommend best performing and widely adapted early maturing open pollinated QPM varieties for large scale production in the region and (v) enhance the role of QPM in combating protein energy malnutrition and attendant diseases in SSA. The result of the evaluation of 96 single cross hybrids (95 QPM and one normal maize) for grain yield and stability showed that the candidate varieties out yielded the normal check based on combined ANOVA across 15 environments. Nine parametric and non-parametric measures were used to analyse grain yield stability. The parameters ranked the entries differently mainly due to the inclusion of extreme (stress) environments in the analysis and the less stable nature of single cross hybrids. Most of the stability parameters were significantly and positively correlated. AMMI and GGE biplots were effective for the analysis of the multi environment data set. The models were used to identify stable genotypes, discriminating environments and adaptation patterns of the entries in ESA. Entries 40 and 37 were the highest yielding while entry 60 was the most stable. The optimum environments in Harare, Zimbabwe were the most discriminating and representative. Mega-environment analysis using the GGE biplot grouped the environments into four groups, with each having more than one site except Chisumbanje, Zimbabwe which was identified as a separate mega-environment. AMMI2 explained 60% of the G x E interaction which was higher than the GGE2 (50%) which in turn was higher than the AMMI1 (35.73%) model. The GGE biplot options allow better visualisation of the complex multi-environment data than the AMMI model. Candidate QPM OPVs out yielded the normal maize commercial variety, Katumani in 37 environments of ECA based on two sets of trials conducted during 2006-2008. However, Katumani was earliest maturing in all the environments. The environments were grouped into different mega-environments based on grain yield and days to anthesis. The classification of environments into similar mega-environments will facilitate germplasm exchange among environments and will assist the large scale production of QPM in similar environments. It was found that recycling of QPM OPVs for more than three years or seasons will result in significant yield reduction. Hence, seeds should be renewed after three generations of recycling. Although this study should significantly contribute to the role of QPM in reducing malnutrition and related diseases in SSA through best performing genotypes, the fast-track deployment of QPM in the region, however, depends upon the presence of a functional maize seed system. A viable maize seed system will improve access and availability of QPM seeds, particularly OPV seeds, to resource poor farmers who are the most vulnerable to food and nutritional insecurity. Future research can also deal with the effect of diverse growing conditions of SSA on the nutritional quality of QPM and how farmers can maintain the seed and protein quality of OPVs.

Genetic improvement of QPM can assist to better the livelihoods of resource poor communities and farmers in SA who rely on maize. QPM germplasm from the ARC-GCI was evaluated to generate information to assist breeders in improving the breeding programme through designing efficient selection procedures that will reduce the time and cost required to develop lines with improved nutritional quality; in the process benefiting small-scale farmers. Pollen parent effect was determined by selfing and cross-pollinating 12 QPM inbred lines for tryptophan content. The two pollination methods did not differ significantly for tryptophan content. Single ANOVAs detected genotypic differences for grain quality traits, while combined ANOVAs across eight environments detected highly significant genotype, environment and GEI effects for all traits except endosperm hardness. The AMMI and GGE biplot analyses explained more than 60% of GEI variation. GGE biplots were the best for visualisation of environments and cultivar performance. AMMI and GGE biplots were similar in identifying high performing genotypes for all traits except for oil content, and the most stable genotypes except for starch and tryptophan content. The GGE biplots identified the ideal genotypes as KO54W, KO54W, Hans Male, SO503W and CML144 for QI, tryptophan, protein, oil and starch content respectively. GGE biplots identified Cedara optimum N as the most representative and discriminating environment for QI, tryptophan and starch content, Tshiombo optimum N for protein and Potchefstroom optimum N for oil content. Twenty QPM and non-QPM genotypes were evaluated under low and optimum N conditions in two locations and highly significant environment effects were observed for all traits, whilst significant genotypic differences and GEI were observed for tryptophan content and QI. Most of the traits improved with increased N level. QPM varieties performed significantly better than non-QPM varieties for tryptophan content and QI in all environments. Tryptophan content was highly significantly correlated with QI (r = 0.95, 0.98 and 0.97), while starch content was significantly negatively correlated with oil content (r = -0.72, -0.65 and -0.67) in low, optimum and across N environments. Line x tester analyses of QPM inbred lines showed highly significant GCA mean squares of lines and testers for most traits and highly significant SCA mean squares for all traits except endosperm hardness. Contribution of SCA (lines x testers), was higher than that of GCA for lines and testers for most traits, with contribution of between 29-83% to the sum of squares; except for endosperm hardness. For endosperm hardness GCA for tester was the highest contributor to total sum of squares by 50%. Larger GCA of females than males showed the importance of maternal effects in most of the traits. Among the testers CML144, SO607W and SO503W had the best GCA for the majority of the traits. Four crosses viz., K64R x SO503W, T1162W x RO452W, K64R x RO452W and K64R x SO713W were promising for endosperm hardness, tryptophan content, QI and protein content, respectively. In general RO452W was the best specific combiner. The present study provides novel results on pollination methods, GEI, AMMI and GGE analyses, line x tester analysis, and correlation of grain quality traits of QPM germplasm in SA.

The phylogeny and biogeography of Raphionacme were investigated in this first comprehensive study which included virtually all the species. Raphionacme is the largest genus in the subfamily Periplocoideae (Apocynaceae sensu lato) and consists of 36 species and two subspecies. Sequence data from the nuclear ITS gene region and 45 morphological characters were used to determine relationships between 30 Raphionacme species. Raphionacme is an African genus and widely distributed throughout this continent with the highest concentration of species in southern Africa, the Cape Floristic Region excluded. Only one species, R. arabica, is found outside Africa on the Arabian Peninsula. The most common habitat in which members of this genus occur is grassland or savanna. The majority of species are herbaceous geophytes, with four species that have a climbing habit. Four areas of species richness were identified. These are the Tongaland-Pondoland Mosaic in northeastern South Africa, which includes the Maputaland Centre of Endemism, the Zambezian Region, the Karoo-Namib Region and Kalahari-Highveld Transitional Zone both in the west of southern Africa. Nine endemic species were identified of which seven occur south of the Equator. These are R. chimanimaniana, R. elsana, R. haeneliae, R. namibiana, R. sylvicola, R. villicorona and R. zeyheri, with only R. moyalica occurring in the north of Kenya and R. arabica in Oman. The cladistic results of this investigation indicated that the first and therefore oldest clade to diverge contain species from southern Africa, leading to the assumption that Raphionacme originated in this region. The geophytic habit of the species would probably be an indication that this coincided with the aridification of this region. Thereafter diversification and radiation may have occurred northwards following the savanna that developed east and north of the remaining Equatorial rain forest. Some taxonomic implications, based on the phylogenetic results, have been included. The outgroup Schlechterella abyssinica was found to be nested in the Raphionacme clade, in both the molecular and combined cladograms. The removal of Raphionacme abyssinica to the genus Schlechterella would seem to have been incorrect and the species S. abyssinica may have to be returned to Raphionacme. Three Raphionacme species, R. bingeri, R. excisa and R. splendens were combined under the name R. splendens. Subsequently R. splendens was subdivided into two subspecies. The cladistical results of this study support the creation of Raphionacme splendens subsp. splendens and R. splendens subsp. bingeri.

The aim of this study is to provide a taxonomic revision and molecular phylogenetic analysis of the eight Garuleum Cass. (Asteraceae) species of southern Africa. The taxonomic revision resulted in the construction of an identification key to the species, a revision of all type literature and nomenclature, clarification and designation of type specimens, compilation of morphological and micromorphological descriptions, distribution maps and ecological data for all Garuleum species. The molecular phylogenetic investigation resulted in the first complete phylogeny for the genus Garuleum, based on the nuclear gene region ITS and the chloroplast intergenic spacers trnTâtrnF and psbAâtrnH. All available type specimens related to Garuleum in southern Africa were studied. Where holotype specimens could not be located; lectotypes were designated from available isotypes or syntypes. In cases where only syntypes had been given by authors of species names, lectotypes were designated. Additional herbarium specimens on loan from several South African and European herbaria were investigated and additional material was collected in the field. These specimens were used to compile morphological descriptions and distribution maps. Micromorphological investigation of leaf surfaces, fruit, flowers and pollen was also completed. Garuleum species are aromatic, herbaceous shrubs with the inflorescence arranged in a capitulum composed of white or mauve coloured ray florets and yellow disc florets. The abaxial and adaxial leaf surfaces, leaf structure and involucral bract sizes are important for species identification. Garuleum is widely distributed over southern Africa, with the majority of the species found in the Eastern Cape. Some species, such as G. album, have restricted distribution ranges while others, such as G. bipinnatum, are very common and widely distributed. The annual precipitation of a specific region, in addition to altitude are possibly important factors influencing the biogeography and evolution of the eight species. Heterocarpy has evolved in G. bipinnatum, providing this species with an ability to survive in frequently disturbed areas and to distribute widely. Garuleum schinzii also has a wide distribution and may have the ability to reproduce through heterocarpy. The rest of the Garuleum species have more restricted distribution ranges and only reproduce through homocarpy. The micromorphological characters of the leaves of Garuleum are not taxonomically informative, due to their intraspecific variability. Micromorphological analysis of the flowers of the different species indicated that trichome complement on ray- and disc floret corollas may be taxonomically important. The micromorphology of the epidermal surfaces of achenes from different species is informative for species identification. The micromorphology of the pollen is not sufficiently variable for species level identification, but does support the monophyly of the genus. The phylogeny obtained from the combined nuclear and chloroplast regions revealed that G. latifolium may belong to the earliest diverging lineage within the genus. The rest of the species are divided into two sister clades. Clade A consists of G. album, G. sonchifolium, G. schinzii and G. woodii. Clade B consists of G. bipinnatum, G. pinnatifidum and G. tanacetifolium. The position of G. schinzii in clade A is poorly supported, while the morphology and geographic proximity of this species to the species in clade B, suggests that G. schinzii belongs in clade B. This phylogeny, in combination with geographical, micromorphological and morphological data provided insight into a possible point of origin for the genus in Kwazulu-Natal or the northern parts of the Eastern Cape. The topography of the Drakensberg may have influenced the distribution routes of the different species, forcing distribution either along the coast or into the interior of Southern Africa by acting as a barrier.