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Infection of Bean by Ascospores of Whetzelinia sclerotiorum. G. S. Abawi, Assistant Professor, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456; F. J. Polach(2), and W. T. Molin(3). (2)(3)Assistant Professor, and Research Assistant, respectively, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456. Phytopathology 65:673-678. Accepted for publication 20 January 1975. DOI: 10.1094/Phyto-65-673.

Bean blossoms serve as an energy source to support infection of beans by Whetzelinia sclerotiorum; hence, under New York conditions, an epidemic of white mold occurs only after flowering. On bean petals, ascospores germinated by forming one or two germ tubes within 6 hours after inoculation. Simple, club-shaped appressoria were formed, and direct penetration of the host cuticle by infection pegs occurred within 24 hours. A vesicle was produced under the cuticle layer which eventually produced hyphae of different diameters that grew intercellularly and intracellularly in blossom tissues. By 72 hours the infected blossoms were completely invaded and disintegrated by the fungus. Hyphal strands protruding from infected blossoms produced multicellular, cushion-shaped appressoria when contact was made with other host tissues. A depression in the host tissue was first observed beneath the appressorium. Infection pegs were produced by the flattened ends of the appressoria, and penetrated the cuticle directly. Once beneath the cuticle, the fungus grew rapidly throughout the leaf tissue. Appressorial development of W. sclerotiorum on dialysis tubing segments was positively correlated with the nutrient level in the agar medium used. These results further substantiate the role of blossoms as an energy source in the epidemiology of white mold of beans in New York State.