RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISMS (RFLPS) AND THE RELATIONSHIPS OF SOME HOST-ADAPTED ISOLATES OF VERTICILLIUM-DAHLIAE

The relationships of two host-adapted pathotypes of Verticillium dahli ae have been examined at the molecular level using restriction fragmen t length polymorphisms. Isolates obtained from and adapted to Men rha x piperita (peppermint), which were presumed to be haploid, formed a d istinct subspecific group (referred to as M) related to the previously described non-host-adapted subspecific group A of V. dahliae. The lim ited molecular variation found among the four group M isolates was not related to geographic origin. Isolates from several cruciferous hosts (and one from Beta vulgaris (sugar beet)), which are thought to be na tural, stable diploids, formed another distinct group (referred to as D) that was markedly different from all previously described subspecif ic groupings in both V. dahliae and V. alboatrum. This group of isolat es might better be regarded as a separate species. Again, only limited variation was found within the D group. Polymorphisms revealed by two probes distinguished two isolates derived from Brassica rapa (Chinese cabbage) from the six other isolates (four from Brassica napus (oilse ed rape) and one each from Raphanus raphanistrum (wild radish) and Bet a vulgaris).