Aggressiveness of Phaeoisariopsis griseola isolates and reaction of common bean varieties to the isolates under greenhouse conditions

Angular leaf spot caused by Phaeoisariopsis griseola is one of the most destructive diseases on common bean in Southern and Southwestern parts of Ethiopia. However, systematic and focus studies were lacking to this important disease. Therefore, greenhouse study was conducted to test aggressiveness of P. griseola isolates and evaluate resistance reactions of bean varieties to pathogenic isolates. 55 leaf samples were collected and seven isolates were recovered, but three isolates namely Dolla1, Dolla2 and Dorebafano1 were successfully multiplied and tested to evaluate their pathogenicity and aggressiveness on susceptible variety Dinknesh. Dolla1 and Dolla2 isolates were collected from Bolloso Sore district, while Dorebafano was from Hawassa Zuria. 21 days old plants were inoculated with spore concentration of 2 × 104 conidia ml-1. The study was factorial arranged in a completely randomized design in four replications. All tested isolates were found aggressive to susceptible check with PSI value ranging from 83.34 to 93.52%. 75% of tested varieties showed susceptible reaction to isolates, but overall aggressiveness was higher on varieties Dimtu, Babile, KATB1, KATB69 and Dinknesh. PSI values ranged from 87.96 to 100% in most varieties. The apparent infection rate was faster on susceptible varieties. The disease progress curve attained sigmoid shape in most varieties. Varieties SER125, SER119 and Nasir were identified as a good source of resistant gene to develop ALS resistance. However, further studies on identification of genes and genetic diversity of the pathogen should capture research priority. Varieties evaluated under greenhouse conditions should also be tested under field conditions. Key words: Aggressiveness, angular leaf spot, common bean, incidence, reaction, severity.