Infection of Kennebec potato with Verticillium albo-atrum

Abstract

Infection of Kennebec potato plants by Verticillium albo-atrum (dark mycelium form) occurred when they were grown in soil samples collected after 4 years under perennial ryegrass-white clover pasture following an affected potato crop. Tuber transmission averaged 8 %, 13 % in the stolon half and 4% in the apical half. Infection readily spread from diseased to healthy plants that were growing in the same container of a peat-sand soil mix. Infection was detected in stems from the stage of early flowering; infection of a proportion of tubers had occurred by the stage of rapid tuber expansion. In some plants, tuber infection occurred in the absence of detectable stem infection. Latent infection was common and systemic movement was incomplete. The fungus was cultured from the above-ground stem more frequently than from other plant parts. In a field study, an infected potato crop produced soil-borne inoculum (which included infected dead haulms) that resulted in infection of 75 % of previously healthy plants of a subsequent crop. Current season spread was not detected in infector or bait crops by a runs test based on sequences of healthy and diseased plants. The use of pathogen-free stock and the removal of diseased plants from seed potato crops are unlikely to control the disease where V. albo-atrum is endemic.