Antagonism of white mold (Sclerotinia sclerotiorum) of bean by fungi from bean and rapeseed flowers

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Abstract
Filamentous fungi from white bean and rapeseed flowers were isolated, characterized, and evaluated for potential as antagonists to Sclerotinia sclerotiorum (Lib.) de Bary. Various fungi were isolated from surface-sterilized petals sampled from four developmental stages ranging from freshly opened flowers to petals that had lodged on plant surfaces. Alternaria and Cladosporium spp. were the dominant mycoflora and were isolated from 65–100% of the petals that developed fungal colonies. All isolates, except one, restricted ascospore germination by the pathogen on water agar by 16–66%, and 13 of 28 isolates restricted mycelial growth on potato dextrose agar by 29–46%. Bean flowers were inoculated with spore suspensions of S. sclerotiorum and of individual antagonists and were then placed on detached bean leaves, bean seedlings, and flowering bean plants. On detached leaves in a laboratory environment, 16 of 28 isolates suppressed white mold lesion diameter by 10–100%. On bean seedlings in a growth room, 8 isolates suppressed the percentage of flowers developing lesions by 42–100%, and 12 of 13 isolates reduced mean lesion diameter by 14–100%. On flowering bean plants in a greenhouse, 6 of 11 isolates suppressed the percentage of flowers developing lesions by 14–90 %. The most disease-suppressive fungi included isolates of Drechslera sp., Epicoccum purpurascens, Fusarium graminearum, and Fusarium heterosporum; isolates of Myrothecium verrucaria and Trichoderma viride were effective in some trials.