The influence of Pratylenchus penetrans on the incidence and severity of verticillium wilt of potato.

The influence of Pratylenchus penetrans on the incidence and severity of Verticillium wilt was examined in the potato cultivars 'Kennebec', 'Katahdin', and 'Abnaki'. Single-stem plants were grown in soil maintained at a temperature of 22 +/- 1 C. Axenically cultured nematodes were suspended in water and introduced to the soil, at a rate of ca 5,000/25.4-cm pot, through holes made around each stem. Ten days after infestation with nematodes, conidial suspensions of Verticillium albo-atrum were introduced into the soil at a rate of ca 1,000,000/pot. Among Katahdin plants, the severity of foliar symptoms was increased in the presence of both pathogens 2 and 3 weeks after soil intestation. During the remaining 5 weeks, severity of foliar symptoms was not different between plants infected by both pathogens and those infected by Verticillium alone. Within the wilt-susceptible cultivar Kennebec and the resistant eultivar Abnaki, no effects on foliar symptom severity were observed. When plant heights, shoot weights, and tuber yields were analyzed, a Pratylenchus-Verticillium interaction was not evident within any of the cultivars tested. Nematode populations in roots and rhizosphere were suppressed in Kennebec and Katahdin plants in the presence of Verticillium.