Role of Verticillium dahliae and V. tricorpus naturally infected tubers in causing Verticillium wilt disease, contribution of soil pathogen inoculum and subsequent progeny tuber infection

Abstract

Colonization of stems, symptom development, yield, progeny tuber infection, quantification of soil inoculum and contribution of soil inoculum on subsequent disease development by Verticillium dahliae, causal agent of Verticillium wilt of potato was evaluated in the glasshouse using naturally infected and non-infected seed tubers of seven cultivars in two trials. Internal seed tuber infection of seven potato cultivars did not contribute to severe disease development although the pathogen was isolated from symptomless plants. Susceptible cultivars Atlantic, Trent and Russet Burbank had the highest incidence of petiole infection while the moderate resistant cv Ranger Russet had the lowest incidence at 65 days after planting. Progeny tuber infection in various cultivars after harvest ranged from 0 (cv Ranger Russet) to 13 % (cv Atlantic). Planting infected tubers contributed to V. dahliae inoculum in the potting soil. Mean levels were highest from cv Russet Burbank (70 pg DNA/g of soil; range from 6 to 149) while the least was recorded in cv Ranger Russet planted soil (11 pg DNA/g of soil; range from 3 to 31). Soil inoculum originating from naturally infected tubers did not contribute to subsequent foliar disease development in Russet Burbank and Shepody cultivars that were grown in this infected soil. However, V. dahliae was isolated from the petiole of some symptomless plants. Progeny tubers were completely free from V. dahliae. Tubers of cv Nicola, infected with Verticillium tricorpus, produced very few Verticillium wilt symptoms but the fungus was re-isolated from the petiole of symptomless plants. Only 4 % of progeny tubers were infected by the pathogen and the level of V. tricorpus inoculum in the soil at maturity was only 1 cfu/g of dry soil. There was no significant difference in the yield of tubers between plants originating from infected and non-infected tubers.