Seed tuber incidence, identification and pathogenicity of Verticillium species infecting potatoes in South East Australia

Verticillium wilt, caused by the soilborne fungi Verticillium dahliae and Verticillium albo-atrum , is a serious disease of potato as well as many other crops. Potato seed tuber surveys (2010 to 2012) from Victoria and Tasmania, Australia identified V. dahliae , V. albo-atrum and V. tricorpus infecting the stem end vascular tissue of seed tubers. The species were identified by traditional morphology and phylogenetic analysis of the ITS region. Isolation of V. dahliae within a seed lot varied greatly and ranged from 0 to 55%. Verticillium spp. were isolated from the stem-end vascular tissue of tubers from seed lots from Victoria and Tasmania with an overall percent infection of 27.7 ( V. dahliae ), 8.4 ( V. albo-atrum ) and 4.8 ( V. tricorpus ). Verticillium dahliae was isolated from 11% of tubers with discoloured stem-end vascular tissue and 3.3% of tubers without stem-end vascular decolourisation suggesting that tuber stem end vascular discolouration symptoms were not a reliable indication of Verticillium wilt infection. In glasshouse trials, V. dahliae isolates from different geographical locations varied in pathogenicity during infection of susceptible potato cv Shepody, moderately resistant cv Ranger Russet and eggplant cv Black Beauty. The majority of V. dahliae isolates were highly aggressive in potato and eggplant, especially the Tasmanian V. dahliae isolates. Infected plants of cv Shepody inoculated with V. albo-atrum and V. tricorpus showed typical wilt symptoms however, the severity of infection caused by V. tricorpus was substantially lower compared to highly aggressive isolates of V. dahliae . In eggplant, V. dahliae isolates also varied in pathogenicity in terms of disease severity but all isolates significantly ( p ≤ 0.05) reduced eggplant growth.