Association Between Angular Leaf Spot (Phaeoisariopsis griseola (Sacc.) Ferraris) and Common Bean (Phaseolus vulgaris L.) Yield Loss at Jimma, Southwestern Ethiopia

Common bean (Phaseolus vulgaris) production in the tropics is usually limited by damage due to Angular Leaf Spot (ALS) caused by Phaeoisariopsis grisola. Field experiments were conducted in 2005, 2006 and 2007 at Jimma, Ethiopia, to determine the amount of yield loss due to ALS and to investigate the relationship between ALS and bean yield. Different levels of disease severity were created on two common bean varieties (GLPX-92 and ICA15541) using natural epidemics by spraying the fungicide benomyl at 7-14- 21 and 28-day intervals and by seed dressing. Generally, all fungicide sprays significantly reduced ALS severity and increased yield and seed weight but seed dressing did not affect significantly. The relative yield and seed weight losses to ALS ranged from 2 to 47 and 15 to 33%, respectively. Single-point regression models predicted that for each per cent increase in ALS severity, there was a seed yield loss of 18 to 124.5 kg ha-1 in GLPX and 12.9 to 103.9 kg ha-1 for ICA15541 and 100-seed weight loss per sample of 100 seeds of 10 to 13 g for GLPX-92 and 13 to 22 mg for ICA15541. The study suggests that fungicide sprays affect ALS epidemics and influence the amount of loss in yield attributable to ALS permitting the crop to reach physiological maturity without being under severe infection. Thus fungicide sprays can be used as a means to reduce ALS severity and increase common bean yield.