Potato germplasm resistant to corky ringspot disease

Potato germplasm was assessed for resistance to corky ringspot disease (CRS ) incited by transmission of tobacco rattle virus (TRV), TRV is transmitted by the stubby root nematode, Paratrichodorus allius, in the Pacific Northw est, and characterized by necrotic areas in the tuber. Four tests were cond ucted at two different problem fields in Umatilla, OR and Pasco, WA. The fi elds differed in the virulence of the virus isolates. Some clones and named varieties showed resistance only in the field with the relatively mild Uma tilla isolate, while others remained symptomless at both sites. The host su itability of test potatoes to three P, allius populations from the region w as determined in greenhouse pot tests, and expressed as reproductive values [R-f = (final population of nematode at 55 days) / (initial population)]. The Rf values for the nematodes were not correlated with resistance ratings based on visual scoring of CRS symptoms in field grown potatoes. Thus, it appears that CRS resistance is based on reaction of potato genotypes to vir us and not the vector, The availability of resistant clones in in vitro for m is indicated.