Pathogenic variability among Colletotrichum kahawae Waller & Bridge population from major coffee growing regions of Ethiopia

Aggressiveness variation among the population of Colletotrichum kahawae representing seven major coffee-growing administrative zones of Ethiopia was studied under greenhouse conditions. The experiment was conducted through cross inoculation of eight Arabica coffee cultivars with seven C. kahawae isolates. The results revealed the presence of significant (p < 0.05) differences among coffee cultivars, isolates and their interactions. However, the large proportion of the variation was due to the main effects of the cultivars and the isolates. The interaction effect between cultivars × isolates was minimal, indicating that variation for virulence within C. kahawae is unlikely to occur. Although all of the isolates were pathogenic to the coffee cultivars tested, isolate CBD07 and CBD68 were the most aggressive followed by CBD184 and CBD156. On the other hand, except the coffee cultivar 741 and 971, the remaining coffee cultivars showed higher susceptibility reactions under greenhouse conditions. Moreover, cultivar 74110 and 1377 were extremely susceptible showing comparable disease reaction with the standard coffee berry disease (CBD) susceptible check ‘cv 370’. The study also showed that the mean disease incidence and severity of 72.5% and 56.2%, 70.7% and 56.2%, 69.6% and 54.4% were obtained with pathogen strains isolated from forest, semi-forest and garden coffee, respectively. Thus, the current variation in pathogenicity among the C. kahawae population is important in the development of disease resistant cultivars by considering the most aggressive isolates for successful screening of coffee germplasms for coffee berry disease resistance.