Theor Appl Genet (1994) 88:838-844 9 Springer-Verlag 1994 M. Deu 9 D. Gonzalez-de-Leon 9 J.-C. Glaszmann I. Degremont 9 J. Chantereau - C. Lanaud 9 R Hamon RFLP diversity in cultivated sorghum in relation to racial differentiation Received: l April 1993 / Accepted: 10 November 1993 Abstraet Careful assessment of the comparative diver- sity for molecular markers and for potentially-useful mor- pho-agronomic traits is paramount to the analysis of a ge- nome 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 panicle and grain traits. Isozyme diver- sity has provided a new insight into genetic diversity, and showed a marked geographic structure. We performed RFLP analysis on 94 varieties, chosen to represent the main cross combinations (race x geographic origin), using 35 maize probes that detect polymorphism with at least one of the two restriction enzymes HindIII and XbaI. A total of 50 polymorphic probe-enzyme combinations yielded 158 polymorphic bands. The bicolor race appeared highly variable and included many rare markers. Among the other races multivariate analysis of the data differentiated six clusters corresponding, by decreasing magnitude of diver- gence, to: the margaritiferum types (a sub-race of race guinea); the guinea forms from western Africa; race cau- datum; race durra; race kafir; and the guinea forms from southern Africa.The apparent geographic differentiation was related to the contrasting distribution of these races and to a higher similarity between races localized in south- ern Africa. The data agree with the current hypotheses on sorghum domestication but reveal associations between neutral markers and traits probably highly subjected to hu- man selection. Whether such associations will be observed with other useful traits, and to what extent they are main- tained by genetic linkage, is worth exploring. Communicated by G. E. Hart M. Deu - D. Gonzalez-de-Leon 1 - J.-C. Glaszmann 9 I. Degremont 9 J. Chantereau - C. Lanaud. R Hamon (~) Centre de Cooperation Internationale en Recherche Agronomique pour le D6veloppement, BP 5035, 34032 Montpellier Cedex, France Present address: I Centro Internacional de Mejoramiento de Maiz y Trigo, Lisboa 27, Apdo. Postal 6-640, Mexico D.F. 06600, Mexico Key words Sorghum 9 RFLP 9 Genetic diversity Cultivated 9 Racial differentiation Introduction Information about genetic diversity and relationships among landraces is essential for the improvement of agri- cultural plants and the management of their genetic re- sources. Various markers, essentially morphological and isozymic markers, are traditionally used for that purpose. Despite the relatively-small number of loci involved, they have allowed efficient varietal classification for a large ar- ray of crops. In sorghum (Sorghum bicolor ssp. bicoIor), traditional cultivars were classified by Harlan and De Wet (1972) into five main races (bicolor, caudatum, durra, guinea, kafir) and ten intermediates (e.g., bicolor-caudatum, durra-kafir), mainly on the basis of spikelet and grain morphological criteria. This differentiation was documented with quanti- tative data by Chantereau et al. (1989). Numerical analyses of isozyme diversity were recently performed (Morden et al. 1989; Ollitrault et al. 1989; Al- drich et al. 1992; Ddgremont 1992) and compared to the scheme based on morphology. No evident congruence was found between the classical racial classification of Harlan and De Wet (1972) and the distribution of allele frequen- cies. At the most, concordance between the enzymatic dif- ferentiation and the racial classification appeared in par- ticular geographic areas. A recent study (Aldrich and Doebley 1992) evaluated RFLP diversity in the nuclear and chloroplast genomes of sorghum using 56 accessions. This study confirmed the earlier hypothesis that central-northeastern Africa is the most likely principal area of domestication of sorghum. Comparison of the nuclear and cytoplasmic genomes sug- gested that introgression between wild and cultivated forms occurs. The aim of the research reported here is to study nu- clear RFLP diversity in cultivated sorghum, using a sam-