Genetic and phenotypic diversity in downy-mildew-resistant sorghum (Sorghum bicolor (L.) moench) germplasm

Genetic and phenotypic diversity among randomly selected 36 downy-mildew-resistant sorghum accessions were assessed, the former using 10 simple sequence repeat (SSR) marker loci and the latter using 20 phenotypic traits. The number of alleles (a(j)) at individual loci varied from five to 14 with an average of 8.8 alleles per locus. Nei's gene diversity (H-j) varied from 0.59 to 0.92 with an average of 0.81 per locus. High gene diversity and allelic richness were observed in races durra caudatum (H-j = 0.76, a(j) = 4.3) and guinea caudatum (H-j = 0.76, a(j) = 3.8) and in east Africa (H-j = 0.78, a(j) = 7.2). The regions were genetically more differentiated than the races as indicated by Wright's F-st. The pattern of SSR-based clustering of accessions was more in accordance with their geographic proximity than with their racial likeness. This clustering pattern matched little with that obtained from phenotypic traits. The inter-accession genetic distance varied from 0.30 to 1.00 with an average of 0.78. Inter-accession phenotypic distance varied from 0.01 to 0.55 with an average of 0.33. Eleven accession-pairs had phenotypic distance of more than 0.50 and genetic distance of more than 0.70. These could be used as potential parents in a sorghum downy mildew resistance-breeding program.