The influence of potato variety on the cyst of the potato‐root eelworm, Heterodera rostochiensis Wollenweber

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Abstract
Experiments are described with eelworm cysts obtained from the roots of four potato varieties, Doon Star, Arran Banner, Redskin and Kerr's Pink. In a cyst‐type: excretion‐type hatching trial carried out in autumn, each group of cysts was stimulated by root excretions derived from the four types of plants. There were significant differences in the response to the root excretions from the different sources, and in the number of larvae emerging from the different cyst types, the number being highest for Arran Banner and practically nil for Doon Star cysts; but there was no correlation between cyst type and excretion type.In experiments the following spring with the same cysts, emergence was heavy for all cyst types; but it began considerably later for Doon Star than for the other cyst types. The lack of emergence from Doon Star cysts in the previous autumn was, therefore, not due to the death of the contents of these cysts.Fewer larvae emerged from Doon Star cysts than from either Arran Banner or Redskin (experiments with Kerr's Pink were discontinued). Doon Star cysts were smaller; however, comparing values for larval emergence and cyst volume for the different cyst types by the method of covariance, the larval emergence was found to be significantly lower for Doon Star cysts than for cysts of the other types, even after adjustment for cyst size.The number of eggs in each cyst was determined. Analysis by the method of covariance showed that, after adjustment for cyst size, there were significantly fewer eggs in Doon Star cysts than in cysts of the other types.A similar analysis was carried out of the relationship of larval emergence and egg number. The regression coefficients show that for each cyst type a constant proportion of eggs hatched; but the proportion is smaller in Doon Star cysts, for, after adjustment foreggnumber, the value for larval emergence is still significantly lower. Fewer larvae therefore emerged from Doon Star cysts partly because the cysts are smaller, partly because, for the same volume, they contain fewer eggs, and partly because a smaller proportion of these eggs hatched during the course of the experiments.The results are discussed in relation to a recent paper by Gemmell (1943). While the differences may be due to resistance on the part of the host plant, as claimed by this worker, there are other possibilities; it is considered that these should be investigated before the hypothesis of ‘resistance’ is accepted. In particular, it is suggested that the differences in cyst size and egg number may be due to differences in the seasonal behaviour of the different potato varieties; differences in the hatching response of the cysts may then be due to the fact that the eelworm cyst responds to root excretions as a unit and that egg concentration is a factor affecting the nature of the unit.