Abstract:

Colletotrichum lindemuthianum is a highly variable pathogen of common beans that easily defeats resistance in
cultivars bred with single-gene resistance. To determine virulence variability of the pathogen in Uganda,
samples of common bean tissues with anthracnose symptoms were collected in eight districts of Uganda,
namely Kabarole, Sironko, Mbale, Oyam, Lira, Kapchorwa, Maracha and Kisoro. 51 isolates sporulated
successfully on potato dextrose agar and Mathur’s media and were used to inoculate 12 differential cultivars
under controlled conditions. Five plants per isolate for each cultivar were inoculated and then evaluated for
their reaction using the 1 – 5 severity scale of Drifjhout and Davis (1989). Data was subjected to analysis of
variance and races were classified using the binary nomenclature system proposed by Pastor Corrales (1991).
Variation due to cultivar and isolate effects was highly significant (P = 0.001) for severity. The 51 isolates from
eight districts grouped into 27 different races. Sironko district had the highest number of races followed by
Mbale and Kabarole. Races 2047 and 4095 were the most frequently found, each with 10 isolates grouped under
them. Race 4095 had the broadest spectrum of virulence since it caused a susceptible (S) reaction on all 12
differential cultivars and the susceptible check. This was followed by races 2479, 2047 and 2045 respectively.
Two races, 4094 and 2479, caused a susceptible reaction on the highly resistant differential cultivar G2333,
which nevertheless, showed the broadest resistance followed by Cornell, TU, and AB136 respectively. These
cultivars are recommended for use in breeding programs aimed at breeding for broad resistance to bean
anthracnose in Uganda.