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Heritability of Resistance to Web Blight in Five Common Bean Populations

Dep. of Crop Protection, Univ. of Puerto Rico, Mayaguez, PR 00681
Dep. of Agronomy and Soils, Univ. of Puerto Rico, Mayaguez, PR 00681
USDA-ARS, Irrigated Agric. Res. and Ext. Center, Prosser, WA 99350
CIAS, San Juan de la Maguana, Dominican Republic

^* Corresponding author (J_BEAVER{at}RUMAC.UPR.CLU.EDU).

Common bean (Phaseolus vulgaris L.) production in the humid tropics would benefit from the selection of cultivars with greater levels of resistance to web blight, a devastating disease caused by Rhizoctonia solani Kühn. This will require screening techniques that are sensitive enough to detect moderate levels of resistance. Greenhouse experiments evaluated the effectiveness of a droplet inoculation technique for screening five F_5:6 segregating populations for resistance to web blight. Another objective was to estimate the heritability of resistance to web blight in five common bean populations. Significant differences in lesion size were detected among F₆ lines within each population. Lines with less web blight infection than the resistant parent MUS83 were observed in each population. This suggests that both parents contributed to the resistance of the progeny. Narrow sense heritability estimates for web blight reaction ranged from 0.61 to 0.79. These relatively high 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 measured by lesion size by means of the droplet inoculation technique, will need to be combined with disease avoidance traits such as erect architecture to obtain effective resistance in the field. Five lines from the MUS83 x DOR483 population with smaller lesion sizes in the greenhouse had moderate to low levels of web blight infection in field experiments conducted in Puerto Rico and the Dominican Republic.

Received for publication February 20, 1996.