Host range specificity in Verticillium dahliae

Verticillium dahliae isolates from artichoke, bell pepper, cabbage, caulifl ower, chili pepper, cotton, eggplant, lettuce, mint, potato, strawberry, to mato, and watermelon and V. albo-atrum from alfalfa were evaluated for thei r pathogenicity on all 14 hosts. One-month-old seedlings were inoculated wi th a spore suspension of about 10(7) conidia per mi using a root-dip techni que and incubated in the greenhouse. Disease incidence and severity, plant height, and root and shoot dry weights were recorded 6 weeks after inoculat ion. Bell pepper, cabbage, cauliflower, cotton, eggplant, and mint isolates exhibited host specificity and differential pathogenicity on other hosts. whereas isolates from artichoke, lettuce, potato, strawberry tomato, and wa termelon did not. Bell pepper was resistant to all Verticillium isolates ex cept isolates from bell pepper and eggplant. Thus, host specificity exists in some isolates of V. dahliae. The same isolates were characterized for ve getative compatibility groups (VCGs) through complementation of nitrate non utilizing (nit) mutants. Cabbage and cauliflower isolates did not produce n it mutants. The isolate from cotton belonged to VCG 1; isolates from bell p epper, eggplant, potato, and tomato, to VCG 4; and the remaining isolates, to VCG 2. These isolates were also analyzed using the random amplified poly morphic DNA (RAPD) method. Forty random primers were screened, and eighteen of them amplified DNA from Verticillium. Based on RAPD banding patterns, c abbage and cauliflower isolates formed a unique group, distinct from other V. dahliae and V. albo-atrum groups. Minor genetic variations were observed among V. dahliae isolates from other hosts, regardless of whether they wer e host specific or not. There was no correlation among pathogenicity, VCGs, and RAPD banding patterns. Even though the isolates belonged to different VCGs, they shared similar RAPD profiles. These results suggest that managem ent of Verticillium wilt in some crops through crop rotation is a distinct possibility.