Dylan Short

Verticillium wilt caused by V. dahliae is a devastating disease of lettuce in California (CA). The disease is currently restricted to a small geographic area in central coastal CA, even though cropping patterns in other coastal lettuce production regions in the state are similar. Infested spinach seed has been implicated in the introduction of V. dahliae into lettuce fields but direct evidence linking this inoculum to wilt epidemics in lettuce is lacking. In this study, 100 commercial spinach fields in four coastal CA counties were surveyed to evaluate the frequency of Verticillium species recovered from spinach seedlings and the area under spinach production in each county was assessed. Regardless of the county, V. isaacii was the most frequently isolated species from spinach followed by V. dahliae and, less frequently, V. klebahnii. The frequency of recovery of Verticillium species was unrelated to the occurrence of Verticillium wilt on lettuce in the four counties but was related...

Verticillium dahliae is a soilborne, economically significant fungal plant pathogen that persists in the soil for up to 14 years as melanized microsclerotia (ms). Similarly, V. longisporum is a very significant production constraint on members of Brassicaceae. Management of Verticillium wilt has relied on methods that reduce ms below crop-specific thresholds at which little or no disease develops. Methyl bromide, a broad-spectrum biocide has been used as a pre-plant soil fumigant for over 50 years to reduce V. dahliae ms. However, reductions in the number of ms in the vertical and horizontal soil profiles, and the rate at which soil recolonization occurs has not been studied. The dynamics of ms in soil pre- and post- methyl bromide + chloropicrin fumigation were followed over three years in three 8 × 8-m sites each in two fields. In separate fields, the dynamics of ms in the 60-cm deep vertical soil profile in 5-cm increments pre- and post-fumigation with methyl bromide + chloropicrin followed by various cropping patterns were studied over four years. Finally, ms densities were assessed in six 8 × 8-m sites in a separate field prior to and following a natural 6-week flood. Methyl bromide + chloripicrin significantly reduced but not eliminate V. dahliae ms either in the vertical or horizontal soil profiles. In both field studies, increases in the recolonization levels of ms was highly dependent upon the crop rotation pattern followed post-fumigation. In the vertical soil profile, densities of ms were highest in the top 5-20 cm of soil but were consistently detected at 60-cm depths. Six-weeks of natural flooding significantly reduced (on average ~65% in the total viable counts of ms), but did not eliminate viable ms of V. longisporum.

The spread of aggressive fungal pathogens into previously non-endemic regions is a major threat to plant health and food security. Analyses of the spatial and genetic structure of plant pathogens offer valuable insights into their origin, dispersal mechanisms and evolution, and have been useful to develop successful disease management strategies. Here, we elucidated the genetic diversity, population structure, and demographic history of worldwide invasion of the ascomycete Verticillium dahliae, a soil-borne pathogen, using a global collection of 1100 isolates from multiple plant hosts and countries. Seven well-differentiated genetic clusters were revealed through discriminant analysis of principal components (DAPC), but no strong associations between these clusters and host/geographic origin of isolates were found. Analyses of clonal evolutionary relationships among multilocus genotypes with the eBURST algorithm and analyses of genetic distances revealed that genetic clusters repres...

In this letter, we advocate recognizing the genus Fusarium as the sole name for a group that includes virtually all Fusarium species of importance in plant pathology, mycotoxicology, medicine, and basic research. This phylogenetically guided circumscription will free scientists from any obligation to use other genus names, including teleomorphs, for species nested within this clade, and preserve the application of the name Fusarium in the way it has been used for almost a century. Due to recent changes in the International Code of Nomenclature for algae, fungi, and plants, this is an urgent matter that requires community attention. The alternative is to break the longstanding concept of Fusarium into nine or more genera, and remove important taxa such as those in the F. solani species complex from the genus, a move we believe is unnecessary. Here we present taxonomic and nomenclatural proposals that will preserve established research connections and facilitate communication within and between research communities, and at the same time support strong scientific principles and good taxonomic practice.