THE ROLE OF VOLUNTEER-POTATOES IN THE SPREAD OF POTATO-VIRUS-Y-N IN WARE-CROPS OF CV-RECORD

Surveys were made for the presence of potato virus Y (PVY) in the plan ted seed and harvested tubers in ware potato crops of cv. Record grown at three sites in England in 1994 (survey 1) and seven sites in 1995 (survey 2). PVY was not found in samples of planted seed, but high lev els of infection were found in many, but not all, harvested crops. How ever, plants of volunteer potatoes (VP) (i.e. plants arising from tube rs or true seed derived from previous crops and surviving in the soil) were frequently found to be infected. Infection in tubers harvested f rom crops in the first survey ranged from 2-52%. In 1995, VP were coll ected from two of the three English sites where potato crops had been grown the previous season and also from a site in Scotland where PVY i nfection in an experimental crop of cv. Record had been monitored in 1 994. The percentages of infected VP ranged from 2-54%. PVYN was the pr edominant strain found in sampled VP, with only two plants (out of 300 infected) containing PVYO. In the second survey, VP were assessed wit hin the 1995 ware crops and were found at four sites, at which they co mprised between 4-8% of emerged potato plants. Between 31-93% of VP we re infected. Again PVYN was the predominant strain with one plant cont aining PVYO and another PVYC (out of 189 infected). A sample of harves ted tubers from each site was also tested for PVY. At those sites whic h had many infected VP, the harvested crop contained a large percentag e of infected tubers, ranging from 60-97%. Two sites which had not pre viously been used for cropping potatoes had no VP and a very low incid ence of PVY infection in the harvested tubers (1% and 2%). However, al though no VP were found at one site, 31% of harvested tubers were infe cted, suggesting that alternative inoculum sources may be important.