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Studies on the pathogenicity and biological control of the white mold pathogen Sclerotinia sclerotiorum (Lib.) De Bary
Abstract
Mutants of Sclerotinia sclerotiorum, derived from UV-irradiation of ascospores, were used to elucidate the role of oxalic acid (OA) in pathogenesis of white mold of dry beans. A simple and quick plate assay was developed to isolate the OA minus mutants. The assay medium consists of potato dextrose agar containing 50 mg/l of the indicator bromophenol blue and adjusted to pH of 7. Determinations by gas and high performance liquid chromatography as well as the oxalate enzymatic method indicated that the selected mutants do not produce OA in carbohydrate-rich media or common bean blossoms. In growth chamber experiments using stem and leaves and in laboratory tests using detached leaves and pods, these OA-mutants remained non-pathogenic, while the OA-producing wild type and revertant remained pathogenic. Although the mutants and wild type were phenotypically alike, none of the mutants produced sclerotia. Reversion to oxalic acid production was induced by growing the mutants on PD media containing 1.5% sodium succinate. Mutants with restored ability to produce OA were able to infect leaves and induce lesions under 2.0 cm in diameter. Other research was undertaken on the biological control of S. sclerotiorum by antagonistic bacteria. Two bacterial strains, Erwinia herbicola and Bacillus polymyxa, isolated from bean blossoms in Western Nebraska, were antagonistic to S. sclerotiorum in vitro. Pre-treatment of blossoms with either bacteria prevented ascospore germination and growth of mycelia and thus, subsequent infection of stem and pods of bean plants in the growth chamber. Field bean plots inoculated with E. herbicola had a significantly lower incidence of white mold than untreated plots. High populations of E. herbicola persisted in the inoculated bean plots throughout the study. Disease severity in plots inoculated with B. polymyxa was not significantly different from that in untreated plots. The decline of B. polymyxa populations after each application may account for its failure to control white mold.
Subject Area
Plant pathology|Agricultural engineering
Recommended Citation
Godoy Manana, Graciela Antonia, "Studies on the pathogenicity and biological control of the white mold pathogen Sclerotinia sclerotiorum (Lib.) De Bary" (1989). ETD collection for University of Nebraska-Lincoln. AAI9019570.
https://digitalcommons.unl.edu/dissertations/AAI9019570