RFLP DIVERSITY IN CULTIVATED SORGHUM IN RELATION TO RACIAL DIFFERENTIATION

Careful assessment of the comparative diversity for molecular markers and for potentially-useful morpho-agronomic traits is paramount to the analysis of a genome through the mapping of favorable genes. Sorghum (Sorghum bicolor ssp. bicolor) varieties are traditionally classified into five races on the basis of morphological traits, especially panic le and grain traits. Isozyme diversity has provided a new insight into genetic diversity, and showed a marked geographic structure. We perfo rmed RFLP analysis on 94 varieties, chosen to represent the main cross combinations (race x geographic origin), using 35 maize probes that d etect polymorphism with at least one of the two restriction enzymes Hi ndIII and XbaI. A total of 50 polymorphic probe-enzyme combinations yi elded 158 polymorphic bands. The bicolor race appeared highly variable and included many rare markers. Among the other races multivariate an alysis of the data differentiated six clusters corresponding, by decre asing magnitude of divergence, to: the margaritiferum types (a sub-rac e of race guinea); the guinea forms from western Africa; race caudatum ; race durra; race kafir; and the guinea forms from southern Africa. T he apparent geographic differentiation was related to the contrasting distribution of these races and to a higher similarity between races l ocalized in southern Africa. The data agree with the current hypothese s on sorghum domestication but reveal associations between neutral mar kers and traits probably highly subjected to human selection. Whether such associations will be observed with other useful traits, and to wh at extent they are maintained by genetic linkage, is worth exploring.