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Title: EFFECT OF INSECT EXCLUSION ON THE INCIDENCE OF YELLOW VINE DISEASE AND OF THE ASSOCIATED BACTERIUM IN SQUASH

Author
item BEXTINE, BLAKE - OKLAHOMA STATE UNIVERSITY
item WAYADANDE, ASTRI - OKLAHOMA STATE UNIVERSITY
item Bruton, Benny
item Pair, Sammy
item MITCHELL, FORREST - TAES, STEPHENVILLE, TX
item FLETCHER, JACQUELINE - OKLAHOMA STATE UNIVERSITY

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2001
Publication Date: 8/1/2001
Citation: Bextine, B., Wayadande, A., Bruton, B.D., Pair, S.D., Mitchell, F., Fletcher, J. 2001. Effect of insect exclusion on the incidence of yellow vine disease and of the associated bacterium in squash. Plant Disease. 85:875-878.

Interpretive Summary: Yellow vine disease of cucurbits, caused by a phloem-limited bacterium, causes rapid wilting and death in affected watermelon, squash, cantaloupe, and pumpkin. Presently there arre no effective control strategies for this serious disease, primarily because the way yellow vine is acquired has been in question. In a previous study, fields treated with insecticides had lower incidence of yellow vine than untreated fields, suggesting that insects are involved in the transmission of the bacterium. In the study reported here, we compared occurrence of the yellow vine bacterium in uncovered squash plants either covered or not covered with fine mesh fabric to exclude insects. The row cover was removed after either 40 or 50 days, at which time all plants were destructively sampled by harvesting the crown and root. Three percent of uncovered plants and 0% of covered plants had foliar symptoms. Using a molecular test (Polymerase Chain Reaction) specific for the bacteria associated with yellow vine, we found that 25% o uncovered plants and 0% of covered plants were positive. These data strongly suggest that insects were involved in the transmission of the bacterium and will allow us effectively screen insect populations to determine the vector(s) and devise control tactics for yellow vine disease.

Technical Abstract: Yellow vine disease of cucurbits, associated with a phloem-limited bacterium, causes rapid wilting and death in affected plants. In a previous study, fields treated with insecticides had lower incidence of yellow vine than did untreated fields, suggesting that insects are involved in the transmission of the bacterium. In the study reported here, we compared occurrence of the yellow vine bacterium in uncovered squash plants (Cucurbita pepo var. melopepo) either covered or not covered with fine mesh fabric secured such that insects were excluded. Seeds of yellow squash were planted at 0.45-meter intervals, and within 24 hours the row mesh cover was stretched over flexible PVC hoops and anchored in the soil. The row cover was removed after either 40 or 50 days, at which time all plants were destructively sampled by harvesting the crown and root. Three percent of uncovered plants and 0% of covered plants had foliar symptoms. Seven percent of uncovered plants and 0% of covered plants were positive using Dienes' stain, which highlights callose deposits in phloem of plants in an advanced stage of disease. Using primers specific for the bacteria associated with yellow vine, 25% of uncovered plants and 0% of covered plants were positive when analyzed by polymerase chain reaction. These data support the hypothesis that insects were involved in the transmission of the bacterium.