Pathogenicity of Washington and Oregon isolates of tobacco rattle virus onpotato

Soil samples from corky ringspot (CRS) problem fields of potato in the stat es of Washington and Oregon were collected and planted with Nicotiana tabac um 'Samsun NN' tobacco to bait tobacco rattle virus (TRV) and to increase P aratrichodorus allius populations, the vector of TRV. Pathogenicity of thre e isolates of TRV was assessed on Russet Burbank and Russet Norkotah plants using P. allius as the vector. The most severe CRS tuber symptoms were wit h TRV from Pasco, WA, followed by Umatilla, OR, and Mattawa, WA, indicating a distinct variation in virulence among virus isolates. The lowest number of P. allius that transmitted TRV resulting in CRS symptoms on Russet Norko tah mas three nematodes per 250 cm(3) soil. When potato plants mere exposed to P. allius at different times in their growth, tubers on older plants we re more resistant than younger tubers to CRS. Severity of CRS tuber symptom s mas correlated with age of potato plants in pot culture. Reproduction of P. allius on potato roots did not influence the incidence and severity of t ubers symptoms. Under similar conditions, Bintje, a variety known to be res istant to CRS, served as a host for P. allius, yet remained asymptomatic. T he protocol employed in these studies is appropriate for testing potato ger mplasm for resistance to CRS.