RAPD Based Assessment of Genetic Diversity in Cultivated Races of Sorghum

Analysis of the extent and distribution of genetic diversity in crop plants is essential for optimizing sampling and breeding strategies. We used random amplified polymorphic DNA (RAPD) markers to assess genetic diversity and taxonomic relationships in 190 accessions sampled to represent the cultivated races of sorghum [Sorghum bicolor (L.) Moench], A high level of variation was detected among cultivated genotypes. Partitioning the genetic variation in cultivated sorghum with Shannon's diversity index revealed that 86% of the total genetic variation occurred among accessions and 14% among races. We also examined the degree of association of accessions with their geographic areas of origin by using Shannon's diversity index. The results indicated that only 13% of the total genetic variation was attributable to divergence among regions. Further tests using principal component analysis also failed to show separation of accessions into discrete racial or geographic groups. Despite such limited differentiation among races or regions, RAPD markers successfully identified races and regions with maximum genetic diversity. For example, accessions within races bicolor and guinea had greater genetic diversity than accessions from race kafir. Accessions from southern Africa had a lower level of genetic diversity than accessions from Far and Middle East, Central and Eastern Africa, and Western Africa. Thus, use of RAPD markers may optimize sampling of genetically divergent accessions for introgression into breeding pools.