Sensitivity and resistance of Sclerotinia minor to fungicides for control of Sclerotinia blight of peanut

dc.contributor.authorBrenneman, Timothy Branneren
dc.contributor.committeecochairPhipps, Patricken
dc.contributor.committeecochairStipes, R. Jayen
dc.contributor.committeememberMoore, Laurence D.en
dc.contributor.committeememberPorter, Duncan M.en
dc.contributor.committeememberYoder, Keith S.en
dc.contributor.departmentPlant Pathology, Physiology and Weed Scienceen
dc.description.abstractSclerotinia blight, caused by <i>Sclerotinia minor</i>, is a severe disease of peanut in Virginia. Vinclozolin (V), iprodione (I), dicloran (D), and pentachloronitrobenzene (PCNB) were evaluated for their fungitoxicity to <i>S. minor</i>. The mean ED₅₈ values for five isolates were found to be 0.07, 0.11, 0.91, and 1.27 μg/ml, for V, I, D, and PCNB, respectively, on fungicide-amended glucose yeast-extract agar (GYEA). Fungicide-resistant growth sectors developed on media amended with I or V. Nine such strains occurred; they were capable of growth on GYEA amended with up to 1000 μg/ml of I or V, and were cross-resistant to D or PCNB. Resistance was maintained in all but two strains after repeated culture in the absence of fungicide for 3 yr. In field microplots, two resistant strains were pathogenic to peanut and survived as well as a fungicide-sensitive field isolate. D, I and V were applied to peanuts in the microplots for 3 yr at total annual rates of 8.41, 3.36, and 2.52 kg/ha, respectively. Disease severity caused by the resistant strains was suppressed 19, 33, and 87% by D, I, and V, respectively, as compared to 15, 24, and 76% for the sensitive isolate. Isolates recovered from tissue biopsies still grew on fungicide-amended GYEA indicating that <i>in vitro</i> and <i>in vivo</i> resistance are not equivalent in this case. Fungicide treatments reduced sclerotial populations of all strains, and reduced the viability of sclerotia from sensitive but not resistant strains. Fungicide-resistant strains were capable of surviving and competing pathogenically in microplots infested with equal numbers of sclerotia from a sensitive and a resistant strain; this trend was enhanced by fungicide applications. A survey of 763 isolates from fields treated with these fungicides failed to detect resistant strains. One fungicide-resistant isolate was recovered from an iprodione-treated microplot originally infested with a sensitive field isolate. A technique utilizing excised peanut stems was devised to evaluate isolate pathogenicity, cultivar resistance to the disease, susceptibility of different age peanut tissues, and fungicide persistence on peanut stems in the field. The method was also used to screen fungicides; results verified previous findings which indicated that <i>in vitro</i> resistance is not equivalent to <i>in vivo</i> resistance. Resistance to these fungicides may eventually become a field problem, but with correct management they should provide years of disease control.en
dc.description.degreePh. D.en
dc.format.extentxi, 103 leavesen
dc.publisherVirginia Polytechnic Institute and State Universityen
dc.relation.isformatofOCLC# 14816879en
dc.rightsIn Copyrighten
dc.subject.lccLD5655.V856 1986.B736en
dc.subject.lcshPeanuts -- Diseases and pestsen
dc.subject.lcshFungicides -- Testingen
dc.subject.lcshSclerotium (Mycelium) -- Controlen
dc.titleSensitivity and resistance of Sclerotinia minor to fungicides for control of Sclerotinia blight of peanuten
dc.type.dcmitypeTexten Pathology, Physiology and Weed Scienceen Polytechnic Institute and State Universityen D.en


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