Phylogenetics of the genus sorghum, genetic diversity and nutritional value of its cultivated species

Sorghum (Sorghum bicolor (L.) Moench) ranks fifth among cereal crops and second highest in production after maize in Africa particularly in the semi arid regions where it is a food security crop. This study assessed phylogenetic relationships of the species within the genus Sorghum, genetic diversity and the nutritional value of cultivated sorghum for its use for breeding and conservation. The phylogenetic analyses based on sequence data from four chloroplast DNA (cpDNA) regions and the internal transcribed spacer (ITS) revealed that S. laxiflorum and S. macrospermum were more closely related to Eu-sorghum species than to any other section and that the former two species are best merged into one section. Assessment of 27 Zambian sorghum accessions and 14 accessions from Malawi, Tanzania and Zambia for genetic diversity based on microsatellite markers revealed a significant genetic variation within and largely among (>80%; p < 0.001) sorghum accessions. Bioassay for grain mineral contents of 27 farmer varieties of sorghum from southern Africa and 13 improved varieties showed that improved sorghum varieties were superior in macronutrients while farmer varieties showed superiority for grain Fe and Zn contents. Morphological characterization of 17 accessions from southern Africa revealed considerable variation among accessions and plant height, days to 50% flowering and inflorescence length were more important discriminating traits. The studies in this thesis provide insights into the extent and pattern of genetic relationships within the genus Sorghum and reveal significant genetic variation for nutritional value improvement