Isozyme variability among isolates of Phaeoisariopsis griseola in southern Africa

Angular leaf spot caused by Phaeoisariopsis griseola is an economically important disease of beans (Phaseolus vulgaris) in southern Africa. The success of local programmes breeding for resistance to this disease depends to a large extent on the genetic variation within the pathogen population. To assess variability within the pathogen, 28 isolates of P. griseola from various localities were compared using isozyme analysis by means of starch gel electrophoresis. Thirteen loci were identified in 10 enzyme systems. Using UPGMA, three electrophoretic types were detected. The most common type included the South African isolates, namely seven from the Mpumalanga and KwaZulu-Natal provinces, respectively, 10 from Malawi, and one from Portugal. Two isolates from Bembeke in Malawi, and one from the Netherlands, differed from the rest. An isolate of Phaeoramularia angolensis, used as an outgroup, differed from the P. griseola isolates in all enzyme systems tested. The high homology of banding patterns among isolates of P. griseola from southern Africa suggests the local population to be uniform.