Grafting eggplant, tomato, and watermelon to manage verticillium wilt caused by Verticillium dahliae

Sacha J. Johnson

Verticillium wilt, predominantly caused by V. dahliae, is a significant soilborne disease on cucurbit and solanaceous crops in Washington State. This study evaluated grafting to manage Verticillium wilt in eggplant, tomato and watermelon. Grafted plants are placed in a healing chamber to facilitate graft union formation. However little is known about impact of healing chamber design on survival of grafted plants. The effect of three healing chamber designs on the survival of grafted eggplant, tomato, and watermelon was evaluated. A humidifier did not increase relative humidity or graft survival, and smaller healing chamber dimensions maintained consistently higher relative humidity. Grafted tomato survival was not affected by healing chamber design, indicating that grafted tomato is tolerant of lower relative humidity during graft union formation. Grafted eggplant, tomato, and watermelon were also evaluated for yield, fruit quality, and disease resistance in open field production with confirmed V. dahliae soil populations at two locations: an irrigated dryland area in the Columbia Basin and a high annual rainfall area in western Washington. Each crop was non-grafted, self-grafted and grafted onto two commercially available rootstocks chosen for possible V. dahliae resistance as available. Eggplant was grafted onto ‘Beaufort’ interspecific tomato hybrid and S. aethiopicum, tomato was grafted onto ‘Beaufort’ and ‘Maxifort’ interspecific tomato hybrids, and watermelon was grafted onto ‘Emphasis’ bottle gourd and ‘Strong Tosa’ interspecific squash hybrid. Rootstock-grafted, non-grafted, and self-grafted plants had equivalent yield, fruit size, and fruit quality for all three crops. ‘Beaufort’-grafted eggplant had reduced Verticillium wilt severity as compared to nongrafted, self-grafted, and S. aethiopicum-grafted eggplant. V. dahliae was isolated from all treatments including ‘Beaufort’-grafted eggplant. Verticillium wilt symptoms were not observed in any tomato treatments at either location in either year. Non-grafted and self-grafted watermelon plants had significantly greater Verticillium wilt severity than ‘Emphasis’ and ‘Strong Tosa’-grafted watermelon in western Washington both years; but again, V. dahliae was isolated from all treatments. Plant growth was increased and Verticillium wilt severity was reduced in ‘Beaufort’-grafted eggplant and ‘Emphasis’ and ‘Strong Tosa’-grafted watermelon, indicating these rootstocks may be partially resistant to V. dahliae and may effectively control Verticillium wilt.

Grafting eggplant, tomato, and watermelon to manage verticillium wilt caused by Verticillium dahliae

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