Reactions of improved faba bean varieties to chocolate spot (Botrytis fabae Sard.) epidemics across contrasting altitudes in southwest Ethiopia

Abstract

Chocolate spot (Botrytis fabae Sard.) is one of the major diseases menacing faba bean (Vicia faba L.) production and restraining its productivity in Ethiopia and other African countries. The yield losses reach up to 100% on susceptible cultivars. Although a number of faba bean varieties with good yield potential have been released, their reaction to this major disease and yield performance are little understood in southwest Ethiopia. Thus, chocolate spot epidemics on 13 improved faba bean varieties were studied under natural infections at three sites varying in altitudes from 1805 to 2660 m in the Dawuro zone of southwest Ethiopia. The field experiments consisted of 14 treatments (13 varieties and a local cultivar) are laid out in a randomized complete block design (RCBD) with three replications (40 plants/plot) during the 2011/2012 crop season. The onset and progress of chocolate spot severity was assessed (with a 1-9 scale) every seven days until the epidemic attained peak and then grain yield and 100-seed weight were recorded and statistically analysed. The varieties varied significantly (P < 0.001) in disease severity index, AUDPC and infection rates (r) values, grain yield and 100-seed weight. CS20DK, Degaga, Nc-58, Bulga-70, Tesfa and Kasa exhibited high to moderate resistance to chocolate spot with consistently slow progression and terminal disease severity, AUDPC- and r-values at all testing sites. The yield performance of CS20DK and Degaga were also superior at Tocha and Turi while Nc-58 (2027 kg/ha) and Moti (1973 kg/ha) that showed susceptible reaction gave good yield only at Tocha. This study indicated that improved faba bean varieties reacted differently to chocolate spot infection and yield potentials across varying localities, and thus better performing varieties such as CS20DK, Degaga and Nc-58 are recommended for faba bean production in southwest Ethiopia.   Key words: Botrytis fabae, evaluation, improved varieties, Vicia faba.