An indirect test using oxalate to determine physiological resistance to white mold in common bean

In common bean (Phaseolus vulgaris L.), the detection of physiological resistance to white mold [Sclerotinia sclerotiorum (Lib.) de Bary] in the field is confounded by environmental factors and plant avoidance mechanisms. Development of a reliable screening procedure is needed to identify resistant bean germplasm and to develop resistant cultivars. The objective of this study was to determine if oxalate, a primary pathogenicity factor of S. scleroriorum, could be used to indirectly screen for physiological resistance to white mold in common bean. Cut bean seedlings were placed in a 20 mM oxalate solution in the greenhouse. Genotypes were rated based on differences in wilting response to oxalate, Oxalate ratings of the 27 genotypes were correlated with field ratings of a white mold disease severity index (r = 0.58**) and incidence (r = 0.57**), and negatively correlated with yield (r = -0.50**). The oxalate test is an efficient method to indirectly test for physiological resistance to white mold in common bean.