|POUDYAL, DIPAK SHARMA - Washington State University|
|DU TOIT, LINDSEY - Washington State University|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/2014
Publication Date: 5/1/2015
Citation: Poudyal, D., Paulitz, T.C., Porter, L., Du Toit, L.J. 2015. Characterization and pathogenicity of Rhizoctonia and Rhizoctonia-like spp. from pea crops in the Columbia Basin of Oregon and Washington. Plant Disease. 99:604-613.
Interpretive Summary: Processing peas for canning and freezing are produced in irrigated circles in the Columbia Basin of Washington. Patches of stunted peas have appeared in fields in recent years, and may be caused by Rhizoctonia spp. The purpose of this research was to do surveys to isolate from soil and plant samples over a two year period. 179 isolates were characterized, identified, and the groups were tested for pathogenicity in the greenhouse. The most virulent were Rhizoctonia solani AG 2-1, 4, and 8. Each caused a different set of symptoms, and are involved in this disease complex.
Technical Abstract: A total of 179 isolates of Rhizoctonia and Rhizoctonia-like species were obtained from soil and plant samples collected from irrigated pea crops in the semi-arid Columbia Basin of Oregon and Washington from 2011 to 2013, and characterized to species, subspecies, and anastomosis groups (AG) based on sequences of the internal transcribed spacer region of ribosomal DNA. R. solani comprised 77% of all isolates, and included isolates of AG 4 (31% of all isolates), AG 2-1 (18%), AG 3 (10%), AG 8 (8%), AG 5 (5%), AG 10 (3%), and AG 9 (1%). The isolates of Ceratobasidium spp. (19%) comprised four AGs: AG K (11%), AG A (6%), AG I (2%), and AG I-like (1%). Waitea circinata isolates (4%) comprised two subspecies, W. circinata var. circinata (4%) and W. circinata var. zeae (<1%). Repeated pathogenicity tests of isolates of the 10 most frequently detected AGs and subspecies were carried out on the pea cv. Serge at 15 ± 1oC. R. solani AG 2-1 isolates caused the greatest reduction in pea emergence, followed by R. solani AG 4 isolates. R. solani AG 4 isolates caused the most severe root rot, stunting, and reduction in pea seedling biomass, followed by isolates of AG 2-1. R. solani AG 8 isolates did not affect emergence, plant height, and total biomass compared to non-inoculated control plants, but root rot caused by isolates of AG 8 was ranked the third most severe among isolates of the 10 Rhizoctonia subgroups, after that caused by isolates of AG 4 and AG 2-1. Isolates of the other AGs and subspecies were either weakly virulent or non-pathogenic on pea. The most dominant AGs, AG 4 and AG 2-1, detected in pea fields in the Columbia Basin were also the most pathogenic at causing pea root rot. In one pea field in which a winter wheat crop was sprayed with herbicide and incorporated into the soil 5 days prior to planting the pea crop, a much greater frequency of R. solani AG 8 was detected than AG 2-1 and AG 4 from within patches of stunted pea plants, indicating that isolates of AG 8 may also be associated with the root rot complex in some pea crops in the Columbia Basin.