First Report of Soilborne wheat mosaic virus on Wheat (Triticum aestivum) in the Columbia Basin of Oregon.

Abstract

The Columbia Basin of Oregon consists of six counties (Gilliam, Hood River, Morrow, Sherman, Wasco, and Umatilla) and is the major wheat-producing region in the state. In 2005, these counties produced 300,277 ha of mostly fall-planted wheat. While primarily a dryland production area, wheat (approximately 8,094 ha) is also grown as a rotational crop under irrigation. Stunted and chlorotic winter wheat plants with leaves exhibiting a mosaic pattern consistent with that caused by Soilborne wheat mosaic virus (SBWMV) were observed in March 2005. These plants originated from four center-pivot irrigated fields in Umatilla County with each field approximately 50.6 ha. One-half of one field was planted with cv. Western Breeders 470 (WB470) and the other half with cv. Tubbs, while the three other fields were planted to Tubbs. In the split-planted field, symptoms were widespread in the WB470 half but only observed in low-lying areas planted with Tubbs. ELISA with a monoclonal antibody (Agdia Inc., Elkhart, IN) confirmed the presence of SBWMV, which is transmitted by the soilborne organism Polymyxa graminis. Electron microscopy confirmed rigid, rod-shaped particles that were 19 nm wide and of two size classes, 138 to 222 and 416 to 471 nm long. Presence of SBWMV was further verified by reverse transcription (RT)-PCR using SBWMV RNA-2 specific primers (sense 5'-AAAGAGTCTIGCGTRTARCAYTC-3' and antisense 5'-AACGGTGTTAGTAARYTRGGKGA-3'), which amplified the predicted 338-bp product from the coat protein gene (1). Additional positive samples were found in 2006 from fall-planted wheat cvs. WB 528 and MJ9 from two additional 50.6-ha fields in Umatilla County. In 2005, yield of WB470 in the split-planted field was reduced by approximately 15% compared with yields obtained in similar fields planted with WB470 not exhibiting symptoms. SBWMV has been reported previously in Oregon (2) but nearly 322 km to the west in an area that is not the major wheat-producing region in Oregon. Because of the apparent reduced susceptibility of Tubbs, which is an older cultivar, as compared with WB470, WB528, and MJ9, which are three new high-yielding cultivars, additional research is needed to identify the reaction to SBWMV of cultivars adapted for production in the Pacific Northwest, particularly if this disease becomes widely distributed in both irrigated and dryland production areas.