Screening Common Bean for Resistance to Four Sclerotinia sclerotiorum Isolates Collected in Northern Spain.

White mold, caused by the fungus Sclerotinia sclerotiorum, is a serious disease in common bean (Phaseolus vulgaris) causing significant yield loss. Few cultivars with high levels of physiological resistance to white mold have been described in common bean. The objectives of this study were to (i) determine variation in aggressiveness for the local S. sclerotiorum isolates and (ii) identify sources of resistance against local isolates using the greenhouse straw test. The evaluated materials included 199 accessions of a core collection established from the main bean gene bank in Spain and 29 known cultivars or lines, 5 of them described as resistant sources to white mold: G122, PC50, A195, Cornell 606, and MO162. Significant differences for aggressiveness among the four S. sclerotiorum isolates were detected. Generally, isolates 1 and 3 were more aggressive than isolates 2 and 4. In all, 19 genotypes exhibited a level of resistance equal to or significantly better than G122: 11 accessions from the core collection and 8 cultivars or lines from known materials, including the lines A195 and Cornell 606. To confirm resistance, 19 selected genotypes were tested using a more severe straw test with reactions evaluated 21 days after inoculation. Fifteen genotypes exhibited significantly less susceptibility than G122: eight accessions from the core collection and the known cultivars or lines AB136, Kaboon, BRB57, BRB130, Don Timoteo, and A195. The logical next step will be to evaluate the best genotypes for field reaction to white mold and conduct inheritance studies.