THE USE OF TISSUE CULTURES TO PRODUCE VIRUS-FREE CLONES FROM INFECTED POTATO VARIETIES

By growing the excised apical meristems of sprouts from the potato varieties King Edward and Arran Victory, infected respectively with potato paracrinkle virus and potato virus S, virus-free plants were obtained. Although the method failed to produce virus-free plants from varieties infected with potato virus X, this virus also seems not to be present in apical meristems, for no virus could be demonstrated in callus tissue that developed from excised meristems less than 200 mu across. The concentration of tobacco mosaic virus in tomato roots and tobacco stems is also much less near the growing point than in older cells, but there is no evidence that the meristematic region is virus-free.