Growth, Yield, Fruit Quality, and Verticillium Wilt Tolerance of Grafted Watermelon and Tomato in Field Production in the Pacific Northwest

Growth, yield, fruit quality, and potential tolerance to Verticillium wilt were compared among non-grafted, self-grafted, and grafted triploid watermelon ‘Crisp’n Sweet’, and heirloom tomato ‘Cherokee Purple’. Watermelon rootstocks were bottle gourd and ‘Strong Tosa’ while tomato rootstocks were ‘Beaufort’ and ‘Maxifort’. Field trials were carried out in 2010 and 2011 at Hermiston and Eltopia (eastern Oregon and Washington, respectively), and Mount Vernon (western Washington). At Mount Vernon, watermelon grafted onto ‘Emphasis’ and ‘Strong Tosa’ had significantly larger stem diameter than non-grafted and self-grafted plants both years, while there were no differences at Hermiston or Eltopia. In 2011, ‘Cherokee Purple’ tomato grafted onto ‘Beaufort’ and ‘Maxifort’ had significantly larger stem diameter than non-grafted and self-grafted tomato at Eltopia and Mount Vernon, and ‘Beaufort’-grafted plants were significantly taller than other treatment plants at Mount Vernon. Grafting did not impact watermelon or tomato fruit yield or quality at any location either year. Foliar symptoms of Verticillium wilt were not observed on ‘Crisp’n Sweet’ watermelon at the Columbia Basin locations either year, however at Mount Vernon, ‘Emphasis’ and ‘Strong Tosa’-grafted watermelon had significantly lower Verticillium wilt severity than non-grafted and self-grafted watermelon both years. Microsclerotia were observed in all recovered watermelon stems sampled at Eltopia and Mount Vernon. V. dahliae was isolated from non-grafted and ‘Emphasis’-grafted ‘Crisp’n Sweet’ stems at Eltopia, and non-grafted, self-grafted, and ‘Strong Tosa’-grafted stems at Mount Vernon. Foliar symptoms of Verticillium wilt and microsclerotia in stems were not observed on ‘Cherokee Purple’ tomato at either location both years.