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Poster: Biology & Disease Mgmt: Cultural Control


Evaluation of disinfectant treatments to reduce transmission of Didymella bryoniae during watermelon grafting
A. KEINATH (1), V. DuBose (2), C. Conrad (2) (1) Clemson University, U.S.A.; (2) Clemson University, U.S.A.

Gummy stem blight can develop in greenhouses on watermelon seedlings grown as transplants or as scions and on cucurbit rootstock seedings used in grafting. When diseased seedlings are cut during grafting, the pathogen, Didymella bryoniae (Stagonosporopsis sp.), may be transferred to healthy seedlings. The objective of this study was to evaluate disinfectant treatments to prevent or reduce transmission. In a first experiment, Kleengro (didecyl dimethyl ammonium chloride), Physan 20 (benzyl ammonium chloride) and Virkon S (potassium peroxymonosulfate) were ineffective when sprayed onto entire watermelon seedlings before or after cutting hypocotyls with a blade contaminated with mycelium or conidia. In a second experiment, applying 0.6% sodium hypochlorite, 0.4% Physan 20 or 70% and 95% ethanol to a contaminated blade or heating it before cutting watermelon hypocotyls reduced incidence of gummy stem blight (P=0.01); water, 3% hydrogen peroxide, 1% Virkon S and 7.5% Kleengro were ineffective. In a third experiment, both the watermelon scion and the interspecific hybrid squash rootstock were cut with contaminated and treated blades before grafting. After 7 days in a humid healing chamber, heating the contaminated blade reduced incidence (11%) more than ethanol (45%), and both treatments reduced incidence compared to Physan 20 (100%) and water (100%) (P=0.01). Using heat or ethanol to disinfest cutting tools may reduce transmission of D. bryoniae during grafting.