Para-crinkle: a potato disease of the virus group

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Abstract
The presence of virus diseases in potato plants of the King Edward variety, which appear to be in perfect health, is demonstrated. One such latent disease is due to a pathogene which produces in the variety Arran Victory a violent crinkle. This disease is termed para-crinkle. No support is found for the existence of viruses in really healthy potatoes. The variable reaction of different varieties to the same pathogene is described, and the practical importance of the absence of reaction to infection is shown. The problem of the effect of environment on the seed tuber is touched on, and the opinion put forward that this effect is in reality due to the reaction of the environment on a latent or partially suppressed virus disease, and that completely healthy virus-free potatoes may prove physiologically stable within very wide fluctuations of environmental conditions. The para-crinkle latent in the varieties King Edward and President is compared and occasional differences between their behavior in the glasshouse and in the field pointed out. Arran Victory plants are as readily and as severely diseased by infecting from a carrier plant as from a visibly diseased plant of its own variety. The symptoms of para-crinkle in Arran Victory are described, both in the seasonal infection and in the tuber-born plant, and compared with those of crinkle "A" (see preceding abstract). The reaction of several other varietips to para-crinkle is described. They fall into 4 classes; those which react like Arran Victory, with a crinkle; those which react with a mosaic; those which carry the virus but do not react visibly to it; and those which neither react to nor carry the virus. In all these experiments infection was attempted by means of grafts. Eleven varieties were inoculated by needle with the juice of para-crinkle infected plants with no result, whether the infective source was derived from a plant infected recently or from King Edward where it was from infected mother plants. When Arran Victory, several seasons old, was itself the source an infection was effected. Inoculation of para-crinkle by needle to Datura is without effect, nor is there any evidence that it exists in a latent condition in Datura. However, the virus succeeds in entering under certain conditions. Thus, when it is derived from a diseased mother plant of Arran Victory a reaction occurs; again, when the virus has been passed by grafting through Datura and then through potatoes, and again by needle to Datura, a reaction was obtained. The reactions thus obtained are distinct from those following needle inoculations with crinkle "A" as well as from those obtained by grafting para-crinkle-infected scions. Datura can be infected with para-crinkle by grafting scions of infected and visibly diseased plants, and equally by grafting scions of carriers. The symptoms induced are characteristic and distinct. Double grafts made by grafting Datura, with and without leaves attached, to Arran Victory, and a para-crinkle scion to the Datura, demonstrate that passage through the tissue of a solid Datura stem, 2 inches long, has no effect on the virus, but that the presence of the leaves and the mixture of their metabolic products in the stem tissue with the virus passing through it destroys the virus. Neither inoculation of juice nor grafting of para-crinkle scions has any effect on tobacco plants of the 2 varieties tried.