Assessment of vegetative compatibility of race-2 tomato wilt isolates of Verticillium dahliae in Japan.

Verticillium dahliae race-2 can invade the resistant cultivars of tomato possessing theVe gene. This new race was recently found in several regions in Japan, and 10 isolates ofV. dahliae race-2 from these regions were used in our study. Pathogenicity tests identified these isolates as the tomato pathotype (B). We examined the vegetative compatibility of 8 of these 10 Japanese isolates ofV. dahliae race-2 to estimate their genetic relatedness with the testers of Japanese vegetative compatibility group previously proposed (VCGJ) usingnit mutants. Compatiblenit1 and NitM mutants were obtained from allV. dahliae race-2 isolates. Selected representativenit1 and NitM mutants of eachV. dahliae race-2 isolates were paired with VCGJ testers. All isolates ofV. dahliae race-2 showed a strong reaction with VCGJ2, i.e., tomato pathotype. All isolates ofV. dahliae race-2 except for isolate To22 reacted weakly to VCGJ1 and J3. Japanese isolates ofV. dahliae race-2 were assigned as VCGJ2 and were hence vegetatively closely related with those ofV. dahliae race-1. The origin of Japanese isolates ofV. dahliae race-2 was discussed.