1a.Objectives (from AD-416):
Identify spinach germplasm with resistance to Verticillium wilt disease.
1b.Approach (from AD-416):
Screen spinach germplasm collections for source of resistance against Verticillium wilt under inoculated conditions.
This project contributes directly to the objective 3 of the parent project, genetic improvement of spinach. This report documents research conducted under a Reimbursable Agreement between ARS and the University of California, Davis. Although Verticillium wilt has not been a problem for spinach production in California due to the late appearance of disease symptoms, spinach seeds may bring large amount of pathogen inoculums into fields, which pose a threat to other rotational crops in Salinas Valley such as lettuce and strawberry. No spinach cultivar resistant to Verticillium wilt is available on the market at present. In collaboration with University of California-Davis, we retested the 23 putative resistant accessions of the USDA spinach germplasm collection that were identified in preliminary screening experiments from 2009 to 2011, along with eight susceptible and nine cultivar controls, to confirm their resistance to Verticillium dahliae Race 2 and test their resistance to Race 1 in inoculated tests in greenhouse with nine replications. Twelve accessions showed resistance to one or two isolates of Race 1 and Race 2, respectively, of Verticilliun dahliae from spinach, but not to all three isolates. It seems that the two isolates of Race 2 pathogen had different virulence against these spinach accessions. Some accessions had no disease incidence, seed infection, and/or pathogen in seeds. The susceptible control and commercial cultivars exhibited high levels of disease incidence, severity, and seed infection on NP-10 plates, and pathogen copy numbers. These results are consistent with the results from previous preliminary screening experiments using a Race 2 isolate. These accessions are being tested again this year against the Race 1 and Race 2 isolates of the pathogen.