Verticillium dahliae interactions with V-albo-atrum 'Group 2' and V-tricorpus and their effects on Verticillium wilt disease development in potato

Verticillium dahliae is a strong soil-borne pathogen that causes early dying of potato plants. Pathogen population dynamics were studied during disease development following combined inoculations of potato with V dahliae and various other Verticillium species. In greenhouse and field studies, three Verticillium species were examined: V dahliae, V. albo-atrum 'group 2' and V. tricorpus. Potato plants were inoculated with two out of the three species in various combinations of an aggressive (V dahliae) and weak (V albo-atrum 'group 2' or V tricorpus) pathogen either on the same date or with a weak species followed by an aggressive species four days later. Plant and soil samples were collected and relative population levels (RPLs) of each pathogen were determined using polymerase chain reaction (PCR) techniques. In combinations where pathogens were inoculated at the same time, RPLs of the weaker species did not exceed those of the aggressive species. In combinations where the weaker species were inoculated first, followed by V. dahliae four days later, the two weaker species were still not able to exceed RPLs of V dahliae. Visual wilt symptoms, however, were significantly lower than co-inoculations at the same time and the single inoculation studies. Implications of these findings on epidemiological aspects of these host-pathogen interactions are discussed.