Comparative Aggressiveness of Verticillium dahliae, V. albo- atrum and V. tricorpus on Potato as Measured by their Effects on Wilt Severity, Plant Growth and Subsequent Yield Loss

Verticillium wilt is among the most serious diseases of potato in Tunisia. Three Verticillium species are involved in potato vascular wilt symptoms. The present study evaluated the pathogenic abilities of different Verticillium spp. isolates on the basis of their effects on wilt severity, plant growth and subsequent yield loss. Artificial inoculation of potato cv. ‘Spunta’ plants showed, 60 days post-inoculation (DPI), that all the Verticillium spp. isolates adversely affected the inoculated plants compared to the non-inoculated control. A high degree of pathogenic variability among Verticillium spp. isolates, and especially those of V. dahliae was detected, according to their differential ability to cause wilt and browning of the vascular system together with a reduction in plant height, aerial part weight and tuber yield. Although, V. dahliae isolates were the most aggressive on potato plants, some V. albo-atrum and V. tricorpus isolates were found to be as aggressive as some V. dahliae isolates, according to our experiment conditions. All three Verticillium spp. seem to contribute, to variable degrees, to the potato Verticillium wilt complex in Tunisia. To our knowledge this is the first report of V. albo-atrum and V. tricorpus with comparable aggressiveness as some V. dahliae isolates on potato in Tunisia. _____________________________________________________________________________________________________________