Seed Transmission and Management of White Leaf Spot and Light Leaf Spot Pathogens in Brassicas in the Pacific Northwest

View the project final report

• 2016 annual report

Commodities

• Agronomic: canola, mustard, radish (oilseed, daikon, forage), rapeseed, Turnip cover crops
• Vegetables: broccoli, brussel sprouts, cabbages, cauliflower, radishes (culinary), rutabagas, turnips
• Additional Plants: Brassica weeds, brassica cover crops

Practices

• Crop Production: cover crops, cropping systems, postharvest treatment, plant diseases, seed pathology
• Education and Training: extension, workshop
• Pest Management: chemical control, economic threshold, eradication, field monitoring/scouting, integrated pest management, physical control
• Production Systems: organic agriculture

This Western SARE funded project explores an emerging plant pathology issue in the Pacific Northwest. In 2014, an outbreak of two brassica diseases new to the Pacific Northwest were documented in the Willamette Valley, Oregon: white leaf spot (Pseudocercosporella capsellae, teleomorph Mycosphorella capsellae), and light leaf spot (Cylindrosporium concentricum, teleomorph Pyrenopeziza brassicae. In addition, black leg (Phoma lingam, teleomorph Leptosphaeria maculans and L. biglobosa), was detected in >43 of 61 field sites in the Willamette Valley in 2014. Not only had white leaf spot (WLS) and light leaf spot (LLS) not previously been documented to occur in the Pacific Northwest, but LLS had not previously been reported in North America. All three pathogens can be seedborne in brassicas. In early 2015, black leg also was detected in >18 dryland canola fields in west-central Idaho and in two irrigated canola fields in northeastern Oregon. Brassica crops are important in Washington State. Based on 2012 USDA Agricultural Census data, there were >21,520 acres of brassicas planted in Washington that year. The many types of species within the Brassicaceae, including crops and numerous weed species, are almost all susceptible to the three fungal diseases in the 2014 Willamette Valley epidemic. Inglis et al. (2013) reported >1,500 acres of 15 brassica species for seed production annually. The value of these seed crops ranges from $1,500 to >$6,500 per acre, and the crops provide an estimated 50% of the U.S. supply of seed and 25% or more of the world’s seed supply of these species (Schreiber and Ritchie, 1995) because of the unique climatic requirements for seed production. This research will explore how the WLS and LLS pathogens, which are new to the Pacific Northwest, are transmitted as seedborne pathogens on several brassica species important to this region. I will develop a seed health assay(s) for these pathogens. I will generate infected seed lots to assess seed transmission rates and test seed treatments for organic and conventional production systems. I will assist in monitoring the distribution of these pathogens in Washington, e.g., suspect symptoms were observed in two hybrid cabbage seed crops in northwestern Washington in spring 2015 that were planted with seedlings produced in the Willamette Valley in 2014. I will provide outreach to brassicas growers via workshops and a field guide or extension bulletin on identifying and managing brassica leaf spot pathogens. If the presence of these new pathogens is documented in Washington State, the information will be published as a Disease Notes in Plant Disease. I anticipate two additional research papers will be published in peer-reviewed scientific journals from this project.

The overarching goal of this research is to provide farmers and seed companies that produce brassica crops in this region with the tools and awareness to detect and manage LLS and WLS in brassica fields and seed lots. Specific objectives include:

1. 1. Produce brassica seed lots infected with the LLS and WLS fungi by inoculating developing pods on plants of several types of brassica to facilitate natural mode(s) of infection of seed that will be harvested from these plants (summer and fall of 2015).

1. 1. Use these seed lots to develop a seed health assay(S) to detect the presence of the LLS and WLS pathogens in infected seed lots (winter and spring 2015-16).

1. 1. Assess rate(s) of seed transmission of the LLS and WLS pathogens from these seed lots planted under conditions conducive to the two diseases (spring 2016).

1. 1. Assess organic and conventional seed treatments to prevent or reduce seed transmission of the LLS and WLS fungi (2016).

1. 1. Provide farmers, seed company representatives, consultants, extension educators, and other relevant stakeholders with educational materials and training opportunities on detection and management of the LLS and WLS pathogens, including the importance of purchasing high quality seed (2016):
      2016. 2016. Present information at the WSU Mount Vernon NWREC Field Day in July 2016.
      2016. 2016. Present workshops to various brassica stakeholders, e.g., Puget Sound Seed Growers’ Association, Western Washington Small-Seed Advisory Committee, Columbia Basin Vegetable Seed Association, Pacific Northwest Vegetable Association, Washington Oilseed Cropping Systems (http://css.wsu.edu/biofuels), etc. (2016).

1. 1. Create an extension bulletin or field guide on brassica diseases for diverse stakeholders (2016).

1. 1. Publish in scientific journals research results on seed transmission and seed treatments for LLS and WLS (winter 2016-17).

1. 1. Complete field research in the Willamette Valley of Oregon and any areas in Washington where LLS and WLS are detected (e.g., crops, volunteer brassicas, or brassicas weeds) to further our understanding of pathogen spread, survival, population diversity, and other aspects of the epidemiology and management of these fungi (2015-2017).

Timeline: This project work will span late 2015 through early 2017.