Genetic diversity of Verticillium dahliae populations from oats (asymptomatic host) is lower than in populations from potato (symptomatic host)

Background/Question/Methods

Verticillium dahliae is a soil-borne pathogen that causes Verticillium wilt in hundreds of dicotyledonous crop plants.  Control of the disease is difficult because after colonizing the roots of plants, invading the vascular tissue, and causing subsequent death, the pathogen forms microsclerotia in the dying plant tissue.  Microsclerotia act as the fungal inoculum that can persist in the soil for up to ten years.  Farmers have attempted, with varying rates of success, to manage this disease by rotating cereal crops with host crops.  Variation in success may result because cereal crops, and other monocotyledons, have been considered as non-hosts, while evidence suggests that they may be asymptomatic hosts.  We lack much biological information on V. dahliae associated with asymptomatic hosts since most research has focused on V. dahliae associated with symptomatic hosts. Our overall goal was to assess whether V. dahliae populations that are found colonizing asymptomatic hosts are the same that cause disease on symptomatic hosts.  Specifically, we asked whether the genetic diversity of V. dahliae populations associated with oats (asymptomatic host) is different than those found in potato cultivars (symptomatic host) of varying disease susceptibility.  We used several hypervariable microsatellite markers to assess genetic diversity of fungal populations with two different indices.

Results/Conclusions

Both Nei’s Gene Diversity Index and the Shannon-Wiener Genotypic Diversity Index agreed that the asymptomatic host, oats, was colonized by a fungal population with significantly lower genetic diversity, while the symptomatic host, potato, was colonized by a fungal population with greater genetic diversity that also increased with susceptibility to the disease.  Whether or not asymptomatic host plants might contribute to changes in the genetic diversity of V. dahliae populations in the soil in is just one of many questions that might be asked in the future about the biology, persistence, and spread of populations of V. dahliae colonizing asymptomatic host plants.  Since farmers use cereals in crop rotations to reduce Verticillium wilt in subsequent crops, more research is needed to understand the relationships of the pathogen with this and other asymptomatic hosts.