GENETIC-RELATIONSHIPS AND CROSS PATHOGENICITIES OF VERTICILLIUM-DAHLIAE ISOLATES FROM CAULIFLOWER AND OTHER CROPS

Morphologies, genetic relationships, and host specificities of Vertici llium dahliae isolates from artichoke, cabbage, cauliflower, cotton, p epper, potato, strawberry,tomato, and watermelon were evaluated. Tempe rature optima for mycelial growth were evaluated at 10, 15, 20, 25, 30 , and 35 degrees C. Depending on the isolate, temperature optimum was either 20 or 25 degrees C. The length and width of conidia in isolates from crucifer crops were significantly greater than the dimensions of conidia in other isolates. Isolates from artichoke, cabbage, cotton, pepper, potato, strawberry, tomato, and watermelon were tested for the ir pathogenicity on their host of origin, as well as on cauliflower. I n addition, two V. dahliae isolates from cauliflower were tested for t heir pathogenicity on all the above crops, lettuce, and other crucifer crops such as bok choi, broccoli, Brussels sprouts, napa cabbage, rad ish, and rapini. All isolates caused wilt on cauliflower. The cauliflo wer isolates caused various degrees of wilt on all crops except lettuc e, but their virulence depended on the host inoculated. Cauliflower is olates were highly virulent on other crucifer crops except broccoli an d Brussels sprouts, on which they were only weakly virulent. None of t he isolates tested were host specific. Seventeen isolates of V. dahlia e from noncruciferous hosts were associated with one of two vegetative compatibility groups. Twelve V. dahliae isolates from cruciferous cro ps could not be assigned to a vegetative compatibility group because t hey did not produce nitrate nonutilizing mutants when cultured on chlo rate-containing media. This observation may reflect diploidy in the cr uciferous isolates, an interpretation which was supported by conidial size and in situ measurements of conidial DNA content. Based on polymo rphisms in the intergenic spacer region of the nuclear rDNA, the V. da hliae isolates from cauliflower were unlike isolates from other hosts.