Differential susceptibility of pumpkins to bacterial wilt related to plant growth stage and cultivar

Abstract

Fifteen jack-o'-lantern and three processing-pie pumpkin ( Cucurbita pepo L.) cultivars were tested in the greenhouse and field for their susceptibility at different growth stages to Erwinia tracheiphila, the causal agent of bacterial wilt. The bacterium is vectored by cucumber beetles ( Acalymma vittatum (F) and Diabrotica undecimpunctata howardi Barber). Each variety was artificially inoculated with E. tracheiphila in the greenhouse at cotyledon, first, second, third, fourth and fifth true leaf, first flower and first female flower growth stages to discern if maturity confers tolerance to the disease. Field experiments compared the sublethal effects of E. tracheiphila inoculated plants with water-inoculated plants on pumpkin fruit yield and quality. The cotyledon stage was most susceptible to infection (22% of plants killed). At the 3–4 leaf stage, no plants died owing to bacterial wilt. Howden, Baby Boo, and Happy Jack inoculated at the cotyledon stage were the most susceptible jack-o'-lantern cultivars, with 18%, 15% and 13%, respectively, of the inoculated plants dying. Only 5% of all the processing pumpkins inoculated at any stage died from bacterial wilt. Eighteen percent, 90% and 100% of infected plants that started to wilt 2 weeks after inoculation at the cotyledon, first true leaf and second true leaf stages, respectively, recovered and continued to grow. None of the most susceptible cultivars recovered from initial wilting. Infected plants that survived did not have significantly different yields or quality of pumpkin fruit compared with plants inoculated with water.