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2007 Plant Management Network.
Accepted for publication 19 May 2007. Published 17 September 2007.


Delayed Emergence, Stem Distortion, Stunting, and Foliar Symptoms Associated with Tobacco Rattle Virus and Paratrichodorus Allius in Potatoes Grown in the Pacific Northwest


Stacy L. Gieck, Nicholas L. David, and Philip B. Hamm, Hermiston Agricultural Research and Extension Center, Oregon State University, Hermiston 97838; James M. Crosslin, USDA-ARS Vegetable and Forage Crops Research Unit, Prosser, WA 99350; and Russell E. Ingham, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331


Corresponding author: Stacy L. Gieck.  stacy.gieck@oregonstate.edu


Gieck, S. L., David, N. L., Hamm, P. B., Crosslin, J. M., and Ingham, R. E. 2007. Delayed emergence, stem distortion, stunting, and foliar symptoms associated with Tobacco rattle virus and Paratrichodorus allius in potatoes grown in the Pacific Northwest. Online. Plant Health Progress doi:10.1094/PHP-2007-0917-01-BR.


Symptoms previously unreported in the Pacific Northwest in potato (Solanum tuberosum) were observed in small circular areas in May 2005, representing less than 5% of a 50-ha, center-pivot irrigated, commercial field in Morrow Co., OR. Half of the field was planted with cv. Russet Norkotah (RN) and half with cv. Ranger Russet (RR). Stems of plants that had not emerged were thickened and twisted. Several stunted plants of both cultivars near these poorly emerged areas exhibited foliar symptoms of leaf chlorosis and yellow rings or chevrons (Fig. 1). Foliar symptoms were more severe in RN, while larger areas of delayed emergence and stunting were present in RR (Fig. 2). Similar early-season symptoms have been reported in RN and cv. Russet Nugget in Colorado (3) and found to be associated with Tobacco rattle virus (TRV), vectored by the stubby-root nematode Paratrichodorus allius. Corky ringspot (CRS) disease, a resulting symptom in tubers from TRV infection, has been reported previously in the Pacific Northwest (2).


 

Fig. 1. Foliar symptoms associated with TRV infection of potato cv. Russet Norkotah.

 

Fig. 2. Impact of TRV and/or early nematode feeding on potato cv. Ranger Russet; healthy plant on left.


Two paired soil samples collected near plants with and without symptoms contained an average P. allius population of 148 and 12 per 250 grams of dry soil, respectively. No other plant-parasitic nematodes were consistently present. Leaves, stems, stolons and daughter tubers of both cultivars from 18 symptomatic plants in 12 randomly selected locations tested positive for TRV, but healthy plants from the same locations were negative when analyzed by reverse transcription polymerase chain reaction (RT-PCR) using primers specific to the RNA1 region (1). RT-PCR products were cloned and sequenced and comparisons with known TRV isolates showed 99% or greater homology. Symptomatic leaves and daughter tubers with internal discoloration were negative for other tuber necrotic viruses when evaluated by RT-PCR. In 2006, four additional fields, one in Umatilla Co., OR (cv. RR) and three in Franklin Co., WA (cv. RN), were observed to have plants with distorted stems and delayed emergence and were confirmed to have TRV by RT-PCR (Fig. 3). However, none of these fields had plants with foliar symptoms, which may be related to nematode density. The field with foliar symptoms in 2005 had 148 P. allius while the Oregon field without foliar symptoms in 2006 had only 5 P. allius per 250 grams of soil. RT-PCR determined that pooled samples of P. allius associated with affected plants from three areas within the 2006 Oregon field were viruliferous with TRV, whereas nematodes from soils near unaffected plants were not. Seed pieces from symptomatic plants from all four fields were negative for TRV, indicating seed was not the inoculum source. At full emergence (30 days post-planting), oxamyl was applied by chemigation every two weeks for the duration of the growing season to the Oregon fields and few tuber symptoms of CRS were observed. Oxamyl was not applied as recommended to the fields in Washington and severe tuber damage resulted.


 

Fig. 3. Areas of delayed emergence associated with Tobacco rattle virus and/or early stubbyroot feeding of cv. Russet Norkotah in Franklin Co., WA in 2006.

 

Delayed emergence, stem twisting, and foliar symptoms have not been reported in the Pacific Northwest in fields fumigated prior to planting with 1,3-dichloropropene, an effective method for controlling CRS (2). Post-emergence applications of oxamyl for nematode suppression on potato have increased since its registration in 1993 and may have contributed to the development of these symptoms since virus transmission may occur before the first application. Adding an in-furrow oxamyl application may have reduced symptom expression in the fields described in this report since it has prevented CRS symptoms in tubers grown in the Klamath Basin of Oregon (R. E. Ingham et al., unpublished data), where above ground symptoms have not been seen. This is the first report of stunting, stem distortion, delayed emergence and foliar TRV symptoms on potato in the Pacific Northwest where approximately 50% of the US potato crop is grown. The shift in use from 1,3 dichloropropene to oxamyl may suggest these symptoms will be more frequently observed in the future.


Literature Cited

1. Crosslin, J. M., and Thomas, P. E. 1995. Detection of tobacco rattle virus in tubers exhibiting symptoms of corky ringspot by polymerase chain reaction. Am. Potato J. 72:605-609.

2. Ingham, R. E., Hamm, P. B., Williams, R. E., and Swanson, W. H. 2000. Control of Paratrichodorus allius and corky ringspot disease of potato in the Columbia Basin of Oregon. J. Nematol. 32:566-575.

3. Thomas, P. E., Thompson, K., Ingham, R. E., and Crosslin, J. M. 2001. An apparent new strain of Tobacco rattle virus that causes systemic symptoms in potatoes. Am. J. of Potato Research. 78:486-487.