Greenhouse and field assessments of resistance in soybean inoculated with sclerotia, mycelium, and ascospores of Sclerotinia sclerotiorum
2004
Rousseau, G. | Huynh Thanh, T. | Dostaler, D. | Rioux, S.
Thirty-five soybean lines were evaluated for sclerotinia stem rot (SSR) resistance using stem inoculations with mycelium in the field and greenhouse, flower inoculations with mycelium or ascospores in the field and greenhouse, and soil infestation with sclerotia in the field, between 1997 and 2000. Symptoms were evaluated by stem lesion length (SLL, mm) and lesion extension (LE, mm) after stem inoculations; infected flowers (IF, %) and a disease severity index (DSI, %) after flower inoculations with ascospores and mycelium; and a DSI after soil infestation with sclerotia. Results show significant differences among lines for SLL and LE in the greenhouse and for IF and DSI in the field and greenhouse. Significant correlations were found between stem inoculation and sclerotia method and between all trials with flower inoculation using either ascospores or mycelium. Maple Donovan and Frisquet were the least susceptible genotypes after flower inoculations with ascospores, whereas OAC Bayfield was the most susceptible. Maple Donovan was also the least susceptible genotype after mycelium stem inoculation in the trials in 2000, while OAC Bayfield was again the most susceptible. Nattosan was the most susceptible genotype in trials conducted in the fields infested with sclerotia. In this study, flower inoculations provided better discrimination than stem inoculations in the assessment of soybean genotypes for SSR resistance, and the results suggested two phenotypes of partial or incomplete resistance, one occurring in the flower, and the other in the stem. Key words: Sclerotinia sclerotiorum, soybean, mycelium, ascospores, inoculation, resistance
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