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Drought stress is a major limiting factor in soybean production in South Africa. The development of soybean varieties with enhanced tolerance to soil waterlimited induced stress (WLIS) is one sustainable way to deal with drought. Root traits have shown strong potential for improvement of drought tolerance through breeding. The objectives of this study were to evaluate seedling shoot- and root growth responses under WLIS in order to study root morphology as a mechanism to cope with drought stress and to determine if there were genotypic differences in shoot- and root morphology between drought tolerant and -sensitive soybean genotypes. Seedlings of three drought tolerant and one sensitive genotype were subjected to soil WLIS in deep-root-pots for 21 days. Results suggested significant genotypic differences for shoot length, number of leaves, tap root length and root-to-shoot length ratio. Soybean tolerant genotypes were associated with moderate shoot biomass, deep rooting abilities and maintained a large root-to-shoot ratio under WLIS conditions. In contrast, the sensitive genotype was associated with a reduced root-to-shoot ratio and shallower root system. Soybean genotypes showed varying seedling root growth responses to soil WLIS, while shoot biomass characteristics were similar.

Use of an efficient selection tool in breeding for complex traits such as soil water-limitedinduced- stress (WLIS) tolerance is of paramount importance in order to reduce the genotype by environment interaction effects that affect the heritability of the trait and reduce the associated cost implications of testing in multiple environments. Hence this study was carried out in order to determine the response of drought tolerant and -sensitive soybean genotypes to soil WLIS conditions at different growth stages. Furthermore, the study evaluated seedling root properties and proline accumulation as possible selection criteria for soil WLIS in soybean. The association between proline accumulation and yield-based drought tolerance indices was investigated. Results showed that different soil WLIS levels had varied effects on the morphological traits measured. The severe (30% deficit irrigation) and moderate (50% deficit irrigation) soil WLIS treatments drastically affected the morphological traits. Soil WLIS stress imposed during poddevelopment growth stage affected the seed yield of soybeans much more than drought stress imposed during the flowering and vegetative growth stages. Soil WLIS reduced soybean seed yield, 100-seed mass, seed mass, seed number per plant, number and mass of pods per plant, plant height, node number and plant biomass among the morphological traits measured. Significant differences were observed among genotypes for seed yield and seed mass per plant in response to soil WLIS. Seed mass mean difference is the relative performance of a genotype in a soil WLIS in contrast to a non-stress environment. Seed mass mean difference proved to be a useful index for soil WLIS tolerance, as tolerant genotypes were discriminated from the sensitive ones. Tolerant genotypes showed lower reduction in seed mass per plant after severe WLIS, compared with that of sensitive genotypes. Soybean genotypes showed varied seedling shoot- and root morphology in response to soil, National Research Foundation (NRF)

English: Cocoyam (C. esculenta (L.) Schott and X. sagittifolium (L.) Schott) belongs to the family Araceae. Cocoyam has the potential to contribute significantly to world agriculture in terms of food, nutrition and crop diversification. Despite this the crop remains neglected in terms of research focus. Limited or no information exists on the prevalence, preference and utilisation as well as the pattern and level of diversity that exists in cocoyam germplasm found in Malawi. This study determined the level and pattern of genetic diversity of cocoyam from Malawi using ethno-botany, morphological characters and AFLP markers. Mineral composition of selected genotypes was also determined. The ethno-botanical survey showed that farmers in Malawi maintain a large amount of cocoyam germplasm. These farmers have rich ethno-botanical and ecological knowledge of the cocoyam cultivars they conserve. Farmer’s preferences regarding cocoyam cultivars included uses of plant parts, adaptation and eating quality. Morphological characters showed high levels of variation among accessions. Two main species of cocoyam, Colocasia and Xanthosoma were identified based on leaf base shapes (petiole attachment). AFLP markers showed low levels of genetic diversity between accessions as opposed to the high morphological diversity. A combined (morphological characters and AFLP data) analysis using UPGMA clustering, PCA and AMOVA further alluded to the presence of the two cocoyam species within the germplasm. High levels of variation were detected between the two species and low levels of variation were observed within each of the two species (Colocasia and Xanthosoma). The PCA exhibited a better representation of the genetic diversity pattern than the hierarchical clustering. Accessions showed high levels of mineral composition. Potassium was identified as the major mineral component. Accessions also exhibited high levels of essential minerals (Ca, Fe and Zn). Incorporating cocoyam into the diet, Afrikaans: Amadumbie (C. esculenta (L.) Schott en X. sagittifolium (L.) Schott) behoort aan die Araceae familie. Amadumbie het die potensiaal om betekenisvol tot wêreldlandbou in terme van voedsel, voedingswaarde en gewasdiversifikasie by te dra. Ten spyte hiervan word die gewas nog steeds in terme van navorsing afgeskeep. Beperkte of geen inligting is oor die voorkoms, voorkeure en gebruik van die gewas sowel as die patroon en vlak van diversiteit wat voorkom in kiemplasma van Malawi beskikbaar. In hierdie studie is die patroon en vlak van genetiese diversiteit in amadumbie kiemplasma van Malawi met behulp van etnobotanie, morfologiese eienskappe en AFLP merkers bepaal. Minerale inhoud van geselekteerde genotipes is ook bepaal. Die etno-botaniese opname het getoon dat boere in Malawi ‘n groot hoeveelheid genotipes onderhou. Die boere wat die kiemplasma aanplant het ‘n ryk etno-botaniese en ekologiese kennis van die genotipes wat hulle bewaar. Die boere se voorkeur in terme van amadumbie cultivars sluit in die potensiële gebruik van plantdele, aanpassing en eetbaarheid. Morfologiese eienskappe het hoë vlakke van variasie tussen genotipes getoon. Die twee hoof spesies van amadumbie, Colocasia en Xanthosoma, is op grond van blaarbasis vorms (petiool aanhegting) geïdentifiseer. AFLP merkers het lae vlakke van diversiteit tussen genotipes getoon, wat teenstrydig was met die hoë morfologiese diversiteit. Gekombineerde analises (morfologiese eienskappe en AFLP data) met UPGMA groepering, PCA en AMOVA het die teenwoordigheid van twee amadumbie spesies in die kiemplasma bevestig. Hoë vlakke van variasie tussen die spesies en lae vlakke binne die twee spesies (Colocasia en Xanthosoma) is waargeneem. Die PCA het ‘n beter verteenwoordiging van die genetiese diversiteitspatrone as hierargale groepering gegee. Genotipes het hoë mineraalinhoudvlakke getoon. Kalium was die belangrikste minerale komponent. Genotipes het ook hoë vlakke van noodsaaklike minerale (Ca, Fe en Zn) gehad.