Effect of primary inoculum sources of bean common bacterial blight on early epidemics, seed yield and quality aspects

The effect of primary inoculum sources of Xanthomonas campestris pv. phaseoli from infected seed, infested debris and soil on common bean (Phaseolus vulgaris) was studied in Ethiopia during the 1997 and 1998 cropping seasons. The inoculum sources initiated common bacterial blight (CBB) and influenced incidence and severity during early epidemics. The incidence, assessed at flowering in 1997 from beans grown on infested debris-inoculated plots, was higher by 59%. than on beans from the treated seed plots. CBB on beans from untreated seed-planted and infested debris-noculated plots was more severe than on beans from infested soil-inoculated plots. Bean seed yield and quality aspects were also influenced by the inoculum sources. Lower seedling emergence, stand count and seed yield were obtained from infested debris- and soil-inoculated plots. Seeds harvested from plots planted with treated seeds had the lowest proportion of discoloured seeds. Discoloured seeds were on average 5.3-26.4% lighter than normal seeds. Management options that highly reduce CBB primary inoculum should be promoted.