Partial resistance to white mould in dry bean
White mould, caused by Sclerotinia sclerotiorum (Lib.) de Bary, is a constraint on dry bean (Phaseolus vulgaris L.) production across Canada. Under high disease pressure, dry bean cultivars succumb to the disease resulting in a severe loss of seed yield and quality. Disease development is highly influenced by environmental conditions. In the absence of complete resistance to white mould, dry bean cultivars with both field resistance (avoidance) and physiological resistance would be preferred by growers in order to reduce disease risk and production costs. The objective of this study was to characterize select dry bean genotypes for field resistance to white mould in inoculated disease nurseries, and physiological resistance in a controlled environment. White mould ratings ranged from moderately susceptible to susceptible. Dry bean cultivars lacked both field resistance and physiological resistance. Germplasm lines I9365-25, G122, A 195 and I9635-31 had low disease severity ratings (5.1 to 5.6 at 26 d after inoculation using a 1 to 9 visual disease rating scale) in controlled environment indicating physiological resistance. L 192, MO162, 92BG-7 and OAC Rico also had acceptable levels of physiological resistance (severity ratings of 5.8 to 6.2 at 26 d after inoculation). G122, A 195, L 192 and MO 162 had low white mould disease incidences (16 to 25%) in the field over 4 yr indicating field resistance to white mould. These genotypes may be used as parents in the development of dry bean cultivars with enhanced resistance to white mould.
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