1a.Objectives (from AD-416):
To screen public spinach germplasm for new sources of resistance to downy mildew race 10.
1b.Approach (from AD-416):
The entire USDA spinach germplasm collection will be screened for downy mildew resistance in inoculated greenhouse tests.
This project contributes directly to the Objective 3 of the in-house project, genetic improvement of spinach. This report documents research conducted under a cooperative agreement with California Leafy Greens Research Program. Downy mildew (DM) caused by Peronospora farinose f. sp. Spinaciae is the most important disease for California spinach growers. Many new downy mildew races have emerged including the latest Races 10, 11, 12, and 13. We have conducted several increases of pathogen isolates and identified their races through differential host tests. We are making crosses to develop near isogenic lines of different DM resistant genes. Crosses were made among ten cultivars with different DM resistant genes to combine their resistances.
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 Lab, 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.