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ARS Home » Pacific West Area » Pullman, Washington » WHGQ » Research » Publications at this Location » Publication #308176
Title: Stunted patches in onion bulb crops in Oregon and Washington: Etiology and yield loss

Author
item POUDYAL, DIPAK SHARMA - Washington State University
item Paulitz, Timothy
item DU TOIT, LINDSEY - Washington State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2014
Publication Date: 5/1/2015
Citation: Poudyal, D., Paulitz, T.C., Du Toit, L.J. 2015. Stunted patches in onion bulb crops in Oregon and Washington: Etiology and yield loss. Plant Disease. 99:648-658.

Interpretive Summary: Onion stunting caused by Rhizoctonia spp. is an important soilborne disease in the Columbia Basin of Oregon and Washington. From 2010 to 2013, 251 isolates of Rhizoctonia or Rhizoctonia-like spp. were obtained from soil and onion plant samples collected from Oregon and Washington. Rhizoctonia solani AG-8 was the most important pathogen associated with onion patches. Onion stunting reduced the average marketable bulb yield by 25 to 60% among the six cultivars. In general, stunting did not reduce onion plant stand but consistently reduced the size of bulbs. Yield reduction increased with increasing disease severity.

Technical Abstract: Onion stunting caused by Rhizoctonia spp. is an important soilborne disease in the Columbia Basin of Oregon and Washington. From 2010 to 2013, 251 isolates of Rhizoctonia or Rhizoctonia-like spp. were obtained from soil and onion plant samples collected from Oregon and Washington. Sequence analysis of the internal transcribed spacer (ITS) region was used to identify the isolates. The most frequent subgroup was Waitea circinata var. circinata (25%), followed by Rhizoctonia solani AG 3 (17%), R. solani AG 4 (14%), Ceratobasidium sp. AG A (10%), R. solani AG 8 (7%), Ceratobasidium sp. AG K (6%), R. solani AG 2-1 (6%), W. circinata var. zeae (6%), R. solani AG 5 (4%), Ceratobasidium sp. AG G (2%), R. solani AG 11 (2%), and R. solani AG 1-1B and AG 10 (each <1%). DNA concentrations of AG 2-1, AG 3, AG 4, and AG 8 quantified from bulk soil samples before onion sowing in 2012 did not show a significant association disease during the growing season. However, the frequency of isolation and DNA concentration of R. solani AG 8 were greater for samples collected during the growing season from inside patches of stunted plants than samples collected from adjacent healthy areas of the crop in 2012. For a similar symptomatic onion crop sampled in 2013, however, neither the frequency of isolation of various AGs nor the amount of DNA detected for the AGs was significantly associated with the incidence or severity of onion stunting. Relationships between number of bulbs or bulb weight vs. severity of stunting were defined using correlation and regression analyses from onion fields surveyed in 2012 and 2013. Onion stunting reduced the average marketable bulb yield by 25 to 60% among the six cultivars. In general, stunting did not reduce onion plant stand but consistently reduced the size of bulbs. Yield reduction increased with increasing disease severity.