Ecology of Paratrichodorus allius and its relationship to the corky ring-spot disease of potato in the Pacific Northwest

Paratrichodorus allius, a vector of the tobacco rattle virus which causes t he corky ringspot disease (CRS) in potato, was identified in soil samples f rom Oregon and Washington. Two populations from potato fields in Pasco, WA and Umatilla, OR reproduced successfully on alfalfa, wheat, and corn which are commonly rotated with potato, and most weeds associated with this crop in the Pacific Northwest. Greenhouse studies showed that P. allius was sens itive to low soil moisture, and increased 10 and 100 fold on Samsun NN toba cco in soil above field capacity compared to 1/2 and 1/3 field capacity, re spectively. Population dynamic studies for 1996 and 1997 on a potato-wheat cropping sequence showed that P. allius declined after the winter wheat cov er crop was disked in the spring of 1996, and remained low on potato at the 0-90 cm soil profile, with no evidence of downward migration. In 1997, P. allius declined early in the season on wheat, and remained low until June-J uly when it peaked before declining again. In soil columns, P. allius place d 30 cm below a confined tobacco root system was able to reach and transmit tobacco rattle virus. The nematodes below 30 cm transmitted the virus only when plant roots were allowed to grow to that depth.