- Vegetables: greens (leafy)
- Pest Management: cultural control, prevention
The USA produces ≤20% of the world’s spinach seed, with western Washington and Oregon the only region of the USA suitable climatically for spinach seed crops. Pathogen-free, high quality seed is needed to meet the demand for fresh and processing spinach crops, particularly baby leaf crops planted at 3-4 million seed/acre. Stemphylium leaf spot of spinach, caused by the fungi Stemphylium vesicarium and S. beticola, has become difficult to manage following widespread development of fungicide resistance in populations of S. vesicarium. This study will use population genetics to clarify the relative contribution of infected seed lots as inoculum for disease outbreaks. Populations of S. vesicarium from seed lots grown in major spinach seed production regions of the world, including the USA, will be compared to assess the probability that S. vesicarium isolates are moved among regions of seed production and sales through global seed trade. Populations of S. vesicarium from baby leafy crops with Stemphylium leaf spot will be compared with populations from seed lots planted in these fields. The results and knowledge generated recently on fungicide resistance, spinach cultivar resistance, and epidemiology of the disease will be updated online resources, including the PNW Plant Disease Management Handbook and the PNW Vegetable Extension Group. An extension bulletin will be published and results shared at the Western Washington Seed Workshop, Texas Spinach Field Day, and WSU Mount Vernon Field Day in 2023. Reports will be shared with seed growers, companies, and at the 2023 American Phytopathological Society Annual Meeting.
Project objectives from proposal:
- Quantify the relative abundance of Stemphylium species pathogenic on spinach that occur on spinach seed lots.
- Asses the role of global spinach seed trade in moving isolates of vesicarium, causal agent of Stemphylium leaf spot of spinach, by characterizing populations of S. vesicarium genetically from seed lots grown in the five major spinach seed-producing countries of the world.
- Determine the relative significance of seedborne S. vesicarium as an inoculum source for outbreaks of Stemphylium leaf spot by comparing isolates of the fungus from leaves of baby leaf spinach crops symptomatic with the disease to isolates from seed lots used to plant these spinach crops.
- Disseminate results of this study and other recent knowledge generated on this disease at WSU to spinach seed producers, fresh market and processing producers, vegetable seed companies, other scientists that work with spinach, and the general public through oral, poster, and written presentations at fields days, a seed grower workshop, and an academic conference, and by updating the information on this disease available in the online Pacific Northwest Plant Disease Management Handbook (https://pnwhandbooks.org/plantdisease/host-disease/spinach-spinacia-oleracea-stemphylium-leaf-spot) and the spinach photo gallery of the Pacific Northwest Vegetable Extension Group