FIRST REPORT OF DAMPING-OFF OF CANOLA CAUSED BY RHIZOCTONIA SOLANI AG 2-1 IN WASHINGTON STATE

Authors: Paulitz, Timothy; Okubara, Patricia; SCHILLINGER, W - WASHINGTON STATE UNIV.

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2006
Publication Date: 5/20/2006
Citation: Paulitz, T.C., Okubara, P.A., Schillinger, W.F. 2006. First report of damping-off of canola caused by rhizoctonia solani ag 2-1 in washington state. Plant Disease. Vol. 90: 829.

Interpretive Summary: Rhizoctonia solani AG 2-1 has been implicated in damping-off, girdling, and seedling death in canola at two locations in eastern Washington. This is the first report of this pathogen on canola in the dryland cereal production areas of the Pacific Northwest. This pathogen could reduce stands of both winter and spring canola, which are becoming important rotation crops in these areas.

Technical Abstract: In early Sept. 2003, winter canola (Brassica napus) cv. Inca was direct-seeded into plots previously cropped with spring barley, as part of a long-term irrigated cropping systems experiment at the WSU Dryland Research Station at Lind, WA. Before planting, the plots received 80 mm of water by sprinkler irrigation and, two weeks later, volunteer barley was killed with paraquat contact herbicide. In late September, three weeks after planting, canola seedlings exhibited post-emergence damping-off and lesions on the hypocotyls, resulting in significant stand reductions, especially in plots where residue was not removed or burned off. Rhizoctonia solani was isolated from infected hypocotyls, using water agar amended with chloramphenicol (100 µg/ml). Cultures on PDA produced dark-brown colonies with dark-brown microsclerotia. Three isolates were grown on autoclaved oat seed for 3 weeks in 1-liter Erlenmeyer flasks, and colonized seed was air-dried in a laminar flow hood, ground in a coffee grinder and added to a Thatuna silt loam at 1% (w/w). The infested soil was placed into 4- × 20.5-cm plastic tubes and planted with 5 canola seeds/tube, 5 tubes per isolate. In the control treatment, soil was not infested. Plants were grown in a temperature controlled room in a greenhouse at 16 C, 12 hr light/dark Isolates caused pre-and post-emergence damping-off after 1 week and the surviving seedlings had significantly less plant height and dry weight. Isolates were identified as AG 2-1, by pairing cultures with AG 8, 2-1, and 10 on agar-coated slides (1). Selected isolates were also identified as AG 2-1 by sequencing of the ITS 1 and 2 regions of the rDNA, and matching them to sequences in GenBank. In a pathogen mapping experiment on a farm north of Pullman, WA in 2004, R. solani was isolated from soil in spring and winter wheat fields, using a toothpick baiting method (2). R. solani was found primarily from sites previously cropped with winter and spring canola. These isolates were identified as AG 2-1 and five isolates were tested in the greenhouse as described above, on canola (cv Inca), lentil (cv. Merrit), wheat (cv Madsen), barley (cv. Baronesse), pea (cv. Stirling) and chickpea (cv. Sierra). Three out of 5 isolates significantly reduced emergence of canola and all isolates significantly reduced dry weight of canola seedlings and caused lesions on hypocotyls. None of the isolates reduced emergence of the other crops. All isolates reduced the dry weight of pea and three isolates reduced plant height. None of the isolates reduced the dry weight of lentil, chickpea, wheat, or barley. One of the isolates was also tested on Arabidopsis thaliana and found to be pathogenic. R. solani AG 2-1 has been reported as an important pathogen on canola in Canada and Australia, but has not been reported from the Pacific Northwest of the US. Canola is a minor rotation crop in cereal-based cropping systems in eastern Washington and northern Idaho, but there is increasing interest in this oilseed crop for biodiesel production. However, R. solani AG 2-1 may reduce stands and yield of canola.