Genetic variation in blast resistance in rice germplasm from West Africa.

The genetic variation in resistance to blast ( Cavara) in 195 rice accessions comprising 3 species of the AA genome complex (Asian rice [ L.], African rice [ Steud.] and wild rice []) was investigated based on their patterns of reaction to standard differential blast isolates (SDBIs) and SSR marker polymorphism data. Cluster analysis of the polymorphism data of 61 SSR markers identified 3 major clusters: cluster A (mainly Japonica Group or upland accessions), cluster B (mainly Indica Group or lowland accessions) and cluster C ( and ). The accessions were classified again into 3 resistance groups based on reactions to SDBIs: group Ia (susceptible), group Ib (middle resistance) and group II (high resistance). Group Ia included only a few differential varieties, susceptible controls and the Japonica Group cultivar Nipponbare. Accessions in clusters A and B included all 3 resistance groups and showed a wide variation in blast resistance, but cluster C contained only group Ib. These results demonstrated that variations in Asian rice () accessions in West Africa were skewed toward high resistance and that variations in and were limited and lower than the Asian rice accessions.