HERITABILITY OF RESISTANCE TO WEB BLIGHT IN 5 COMMON BEAN POPULATIONS

Common bean (Phaseolus vulgaris L.) production in the humid tropics wo uld benefit from the selection of cultivars with greater levels of res istance to web blight, a devastating disease caused by Rhizoctonia sol ani Kuhn. This will require screening techniques that are sensitive en ough to detect moderate levels of resistance. Greenhouse experiments e valuated the effectiveness of a droplet inoculation technique for scre ening five F-5:6 segregating populations for resistance to web blight. Another objective was to estimate the heritability of resistance to w eb blight in five common bean populations. Significant differences in Lesion size were detected among Fs lines within each population. Lines with less web blight infection than the resistant parent MUS83 were o bserved in each population. This suggests that both parents contribute d to the resistance of the progeny. Narrow sense heritability estimate s for web blight reaction ranged from 0.61 to 0.79. These relatively h igh heritabilities suggest that selection for smaller lesion size may be effective in earlier generations when MUS83 is used as a source of resistance to web blight. Physiological resistance to web blight, as m easured by lesion size by means of the droplet inoculation technique, will need to be combined with disease avoidance traits such as erect a rchitecture to obtain effective resistance in the field. Five lines fr om the MUS83 x DOR483 population with smaller lesion sizes in the gree nhouse had moderate to low levels of web blight infection in field exp eriments conducted in Puerto Rico and the Dominican Republic.