Thomas R. Gordon – Full Professor
I am interested in the biology of plant associated fungi. Most projects in my lab are directed toward pathosystems involving species of Fusarium. This includes wilt diseases affecting strawberry, lettuce and blackberry caused by Fusarium oxysporum. Management of these diseases is achieved most effectively through genetic resistance, so we collaborate with plant breeders to identify and deploy genotypes that can sustain infections without significant reductions in yield. Another focus of activity is on pitch canker, a disease affecting pines that is caused by Fusarium circinatum. This includes studies of genetic variation in the capacity for F. circinatum to colonize corn and other species in the grass family.
Ana Maria Pastrana Leon – Post-Doctoral Researcher
As a PostDoc in the Gordon Lab in the Department of Plant Pathology at U.C. Davis, I work mainly with Fusarium oxysporum on blackberries and strawberries and Fusarium species on lupine. Fusarium oxysporum has recently been identified as the cause of a wilt disease affecting blackberry in California and Mexico. The Fusarium wilt of blackberry study aimed to characterize the structure of the population of F. oxysporum based on pathogenicity, somatic compatibility and phylogenetic analyses. We found that pathogenic isolates used in this study were comprised of nine three-locus sequence types, each of which corresponded to a somatic compatibility group. Based on the unique host range of isolates causing wilt of blackberry, we have proposed that they be designated as a new forma specialis. Currently, genomic regions linked to the pathogenicity of F. oxysporum isolates that cause Fusarium wilt of blackberry are being studied in order to identify diagnostic markers.
Fusarium wilt of strawberry, caused by the soil-borne fungal pathogen Fusarium oxysporum f. sp. fragariae (Fof), is a growing threat to the strawberry production industry worldwide. To delve into this disease, we are evaluating the effects of pH on growth of F. oxysporum f. sp. fragariae and infection of strawberry roots. We are also evaluating the ability of F. oxysporum f. sp. fragariae to colonize the stolons of infected mother plants and infect daughter plants without producing identifiable symptoms. Cryptically infected nursery plants would allow for introduction of the pathogen to previously un-infested fields. This study has been undertaken by Dean Watson, an undergraduate student working under my supervision.
Another objective of my research is evaluating Fusarium spp. as possible causal agents of disease on California native, Lupinus arboreus. All these studies are based on molecular techniques as well as traditional plant pathological assay methodologies. In collaboration with the QEB Lab (McRoberts Lab) at UC Davis, I am working on the spatial and temporal dynamics of angular leaf spot (caused by Xanthomonas fragariae) in strawberry nurseries. I also direct the work of undergraduate interns and serve as the Laboratory Safety Coordinator.
Kelley Paugh – Graduate Student Researcher
My research relates to the management of Fusarium wilt of lettuce, a soilborne disease caused by Fusarium oxysporum f. sp. lactucae. Fusarium wilt of lettuce causes yield losses in major lettuce-producing regions of California and Arizona, where symptoms include wilting, stunting, vascular discoloration, and necrosis. My objective is to develop information on approaches that will mitigate factors that are known to enhance severity of Fusarium wilt. This includes the effect of planting date on development of Fusarium wilt of lettuce, factors influencing survival of F. o. lactucae on crop residue, the efficacy of soil amendments for suppressing Fusarium wilt of lettuce, heritable variation in the colonization of roots by F. o. lactucae, and the population structure of F. o. lactucae in California and Arizona.
Previous work in the Gordon Lab has shown that severity of Fusarium wilt of lettuce is strongly influenced by ambient temperature, cultivar type, and inoculum density of the pathogen (Scott et al., 2010a, 2010b). For instance, more severe symptoms manifest at warmer temperatures, so it is expected that sowing susceptible cultivars in cooler planting windows and resistant cultivars in warmer planting windows will minimize the impact of Fusarium wilt. In investigating the efficacy of this strategy under California growing conditions, we have found that delaying planting – even as little as one or two weeks – can significantly reduce disease severity in moderately susceptible cultivars. Another factor that influences disease severity is inoculum density of F. o. lactucae in soil, which can be sustained by the incorporation of infested crop residue. For this reason, I have examined how drying and fragmentation of crop residue and the soil amendments affect survival of F. o. lactucae in soil.
I am also testing for heritable variation in the frequency of infection of roots by F. o. lactucae in recombinant inbred lines of lettuce. Genetic resistance is the single most important means for controlling wilt diseases, and deploying cultivars that sustain fewer cortical infections would further reduce the risk of disease. Another focus of my research is characterization of the population structure of F. o. lactucae in California and Arizona based on somatic compatibility groups and DNA sequence comparisons of translation elongation factor-1α and the intergenic spacer region of rDNA. Currently all isolates from the United States are associated with a single clonal lineage.
Jason Carter – Graduate Student Researcher
I am a Ph.D. candidate working with Fusarium circinatum, the causal agent of pitch canker disease in pines. My research focuses on the ability of F. circinatum to infect grasses without causing disease symptoms. I study the ability of F. circinatum to tolerate grass defense compounds, and I am determining if the ability to infect grasses correlates with virulence on Monterey pine (Pinus radiata). While I am primarily studying F. circinatum infecting corn, I also am interested in F. circinatum infecting native California grasses growing in proximity to naturally infected pines.
Peter Henry – Graduate Student Researcher
The foci of my research are: identifying factors leading to persistence of Fusarium oxysporum f. sp. fragariae (Fof, cause of Fusarium wilt of strawberries) in soil, characterizing the genomic diversity of globally collected Fof strains, and understanding the genetic mechanisms that are critical for Fof to cause disease on strawberry.
Past research suggests that non-host colonization by pathogenic forms of Fusarium oxysporum plays a significant role in long-term survival of this organism in the field. In the absence of reproductive hosts, pathogenic forms of Fusarium oxysporum have been found to rapidly decrease in abundance over time. Our research seeks to systematically investigate the link between reproduction on non-host plants and the ability to persist, with the goal of creating optimal crop rotation strategies.
Similarly, competition from non-pathogenic strains of Fusarium oxysporum has been implicated in general suppression of Fusarium wilt diseases. I am developing a high-throughput tool for characterizing inter- and intra-specific diversity of Fusarium spp. from plant and soil samples that will be used to explore the role of competition between closely related strains in non-host colonization.
Fusarium wilt of strawberry has been reported in many countries including Australia (where it was first observed), Japan, Korea, China, Serbia, Turkey, and others. Past research in our lab and others suggests that the pathogen could have travelled between these countries in asymptomatic transplants. We will compare whole genomes of, and test for somatic compatibility between, select isolates of Fof that are global in origin to identify the likelihood of common ancestry.