Investigations of Black Leg and Light Leaf Spot on Brassicaceae Hosts in Oregon

Graduation date: 2017The Pacific Northwest is an internationally important region for the production of Brassica seed and other seed crops including grass seed. Oregon lawmakers mandated research into the co-existence of canola (Brassica napus) with other Brassica production in the Willamette Valley and House Bill 2427 was signed into law in 2013, providing funds for Oregon State University to research residue management, diseases, volunteer survival and insect pests associated with canola, turnip (B. rapa), and radish (Raphanus sativus) seed production. Outbreaks of black leg and light leaf spot diseases, the latter new to North America, were observed in Brassicaceae crop fields during March 2014. Black leg, caused by Leptosphaeria maculans and L. biglobosa, and light leaf spot, caused by Pyrenopeziza brassicae, are economically important fungal pathogens of Brassicaceae crops. Brassicaceae crops and weeds were surveyed in western Oregon for these two diseases. Weed host populations were mapped, diseased plant samples were collected, and pathogens characterized. Predominate weeds found along roadsides included birdsrape mustard species (B. rapa) and wild radish (Raphanus spp.). Both Leptosphaeria species were found throughout the Willamette Valley on both Brassicaceae crop and weeds but L. maculans was the most common and was observed close to Oregon’s borders with Washington and California. Two mating types of P. brassicae were detected on roadside weed populations, indicating potential for sexual reproduction and long-distance spore release on weed plants in Oregon. New hosts for black leg and light leaf spot were discovered, including Leptosphaeria on western yellowcress (Rorippa curvisiliqua (Hook.) Besser ex Britton). Information regarding the presence of these pathogens on weed hosts is useful for gauging the importance of weeds in the spread, persistence, and management of black leg and light leaf in Oregon