Survival and chemical control of Cylindrocladium spp. inciting root rot of black walnut seedlings.
Roth, Don Allen
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Cylindrocladium spp. are soil-borne pathogens of many economically important plants, including black walnut (Juglans nigra L.) and peanut (Arachis hypogaea L.). Black walnut is an important lumber and nut tree in Indiana, Illinois, and the southeastern U.S. Production of black walnut seedlings in forest nurseries in these areas is limited by Cylindrocladium root rot, incited by f.· scoparium Morgan and C. floridanum Sobers and Seymour. Further, f.· crotalariae (Loos) Bell and Sobers, incitant of Cylindrocladium black rot of peanut, has been isolated from black walnut seed-bed soils and pathogenicity on black walnut seedlings has been demonstrated. Control of Cylindrocladium root rot has been typically inadequate with standard rates of currently employed chemical fumigants. Thick-walled, dark pigmented microsclerotia are the principal survival and infective propagules of Cylindrocladium spp. These propagules are produced in large numbers in colonized root tissues and released upon root decomposition. Microsclerotia are capable of long-term survival in non-sterile soils and initiating infection at low inoculum densities. The influence of soil physical factors on survival of microsclerotium populations is of potential importance in disease management. Decreased germinability and survival of Cylindrocladium microsclerotium populations due to soil physical factors may result in decreased disease incidence. In addition to microsclerotia, hyaline conidia may be produced. Conidia are believed to be of minimal importance in the life cycle of Cylindrocladium spp. although the ecology of conidium populations in non-sterile, non-amended soils is poorly understood. The objectives of the present studies were to determine the influence of low soil temperature and soil air drying on survival and germinability of Cylindrocladium microsclerotium populations, to elucidate the response of Cylindrocladium conidia to soil fungistasis, to determine the survival of conidia in artificially infested soils, to determine the distribution of inoculum of Cylindrocladium spp. in a forest nursery and to evaluate the effect of chemical fumigants on control of Cylindrocladium root rot of black walnut seedlings.
- Doctoral Dissertations