Inheritance of web blight resistance in common bean

Expanded production of common bean (Phaseolus vulgaris L.) in the humid tropics requires the development of cultivars with greater levels of resistance to web blight, a destructive disease caused by Thanatephorus cucumeris Frank Donk (anamorph: Rhizoctonia solani Kuhn). The objectives of this study were 1) to estimate the heritability of resistance to web blight in common bean and 2) to measure the effect of web blight on seed yield and quality. Sixty advanced lines from the cross 'MUS 83/DOR 483/Tio Canela 75' were evaluated in replicated field and laboratory tests for reaction to web blight. Heritability estimates for leaf damage (LD) scores, seed yield and percentage seed damage (SD) were intermediate in magnitude, ranging from 0.32 to 0.53. Although the LD on many lines was severe, the SD was less than 10% for most of the advanced lines, all of which suggests that resistance to LD and SD may be inherited separately. A simple field evaluation technique permitted a preliminary screening for resistance to web blight. The laboratory technique induced more severe symptoms and thus would be appropriate for identifying lines with high levels of physiological resistance expressed in the leaves.