Yeast Soft Rot of Onion in the Walla Walla Valley of Washington and Oregon. Dennis A. Johnson, Extension and Associate Plant Pathologist, Irrigated Agriculture Research and Extension Center, Prosser, WA 99350. K. M. Regner, and J. D. Lunden. Research Associate, Department of Plant Pathology, Washington State University, Pullman 99164; and Research Technician, Irrigated Agriculture Research and Extension Center, Prosser, WA 99350. Plant Dis. 73:686-688. Accepted for publication 10 April 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0686.

Soft rot of onion disks inoculated with the yeast Kluyveromyces marxianus var. marxianus increased significantly (P = 0.01) as temperature increased from 10 to 30 C. Rot was not evident in onion disks inoculated with the yeast and incubated for 12 days at 2 C. A temperature of 2 C or less during transit and storage of bulbs will reduce damage caused by the yeast. The amount of soft rot caused by seven isolates of K. m. var. marxianus from the Walla Walla Valley of southeastern Washington and northeastern Oregon did not vary significantly (P = 0.05) when tested on onion disks. A strain of the bacterium Erwinia carotovora subsp. carotovora from onion produced significantly (P = 0.01) more soft rot in onion than K. m. var. marxianus at 25 and 15 C, whereas K. m. var. marxianus produced significantly more soft rot in onion than a strain of E. c. subsp. carotovora from potato. Resistance to K. m. var. marxianus was not evident in 25 onion cultivars grown in the Pacific Northwest.