Recent progress in understanding relationships between Verticillium species and subspecific groups

Improved understanding of the genetic diversity within fungi in the genus Verticillium has resulted from recent studies based on vegetative compatibility analysis and several techniques of molecular biology. Although the method used to identify vegetative compatibility groups (VCGs) does affect the results, vegetative compatibility appears to be a stable characteristic among isolates. Fairly low VCG diversity has been detected within V. dahliae and V. albo-atrum using nitrate non-utilizing mutants. VCGs do not appear to be related to pathogenicity to particular host species, with the exception of V. albo-atrum on alfalfa. However, there is some correlation with virulence on certain hosts and with the ability of V. dahliae to interact with root-lesion nematodes. Studies based on DNA analysis indicate that V. dahliae and V. albo-atrum are closely related but separate species. Restriction fragment length polymorphism (RFLP) studies have identified several subspecific groups within V. dahliae, including two non-host-adapted groups and two that are host-adapted. They also have confirmed that alfalfa strains of V. albo-atrum are a distinct subgroup that is probably a separate population of clonal origin. Using polymerase chain reaction (PCR), a second non-host-adapted subgroup within V. albo-atrum was identified that was previously unknown.