The microflora of bean and rapeseed petals and the influence of the microflora of bean petals on white mold

Abstract

The number of colony-forming-units (cfu) of bacteria, yeasts, and filamentous fungi recovered from rapeseed and bean petals at four stages of development (stages A-D) was assessed with a wash/dilution-plating technique. The number of cfu of yeasts and filamentous fungi from freshly-opened bean and rapeseed petals (stage A) averaged 3.0 × 103 and 5.7 × 10² cfu/ mg corolla (dry weight) and increased 1700- and 263-fold, respectively, as petals aged. Bacteria on freshly-opened bean petals averaged 1.1 × 10⁴ cfu/ mg corolla and increased 446-fold as petals aged. Cladosporium cladosporioides and Alternaria alternata were the most prevalent filamentous fungi recovered from rapeseed petals but Epicoccum purpurascens was consistently isolated also. To elucidate the influence of the indigenous microflora of bean petals on white mold, field-collected flowers at four stages of development (stages A to D) were inoculated with ascospores of Sclerotinia sclerotiorum and placed on the primary leaves of bean seedlings in growth room and greenhouse conditions. Disease incidence and severity were compared between flowers previously sterilized with propylene oxide vs. nonsterilized flowers. Ascospores inoculated on sterilized flowers (stages A-C) initiated lesions of white mold 88-97% and 66-84% more frequently than ascospores inoculated on nonsterilized flowers under growth room and greenhouse conditions, respectively. Ascospores of S. sclerotiorum inoculated onto older, bleached flowers (stage D) produced significantly less disease in comparison to younger flowers, regardless of sterilization treatment. The indigenous microflora of bean petals from most stages of development was associated with a reduction in white mold. The term “anthoplane” is proposed to describe the microbial habitat on the surfaces of flowers.