Using a subsample of the core collection to identify new sources of resistance to white mold in common bean

Pew sources of physiological resistance to the fungal pathogen Sclerotinia sclerotiorum (Lib.) de Bary, causal organism of white mold disease in commo n bean (Phaseolus vulgris L.), have been found and exploited by breeders. O ur objective was to screen a subsample of the core collection of P. vulgris accessions representing the active USDA National Plant Germplasm System co llection of 1698 accessions from Central and South America for reaction to white mold using a greenhouse straw test. White mold reactions were rated f or 89 accessions from 1 = no disease symptoms to 9 = total plant collapse. Eleven core accessions, PIs (plant introductions) 152311, 207136, 207154, 2 90990, 290995, 293353, 313850, 415886, 415906, 415913, and 415936, with sco res <5 were identified as having putative physiological resistance to white mold. An expanded screening among 35 accessions from the active collection which had similar passport data to the resistant core PIs 207136, 290990, and 313850 revealed 20 resistant accessions with disease scores <5. A simil ar expanded screening of 18 accessions with similar passport data to core P Is 310674, 313608, and 415954 that had scores >6, revealed only four access ions with scores <5. These results indicated that a subsample of the core c ollection was useful for identifying ranges of accessions within the active Phaseolus collection that possessed a high incidence of putative physiolog ical resistance to white mold.