The Estimation of the Cyst Contents of the Potato-root Eelworm H. rostochiensis

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Abstract
Research on the potato-root eelworm Heterodera rostochiensis has been severely handicapped by the fact that it is virtually impossible to estimate the infectivity of individual cysts. Since the infectivity of an individual cyst is determined by the number of viable larvae present within it, the problem can be settled in one of two ways—either by means of a technique which recovers all the viable larvae and rejects the non-viable or by estimating firstly the total contents and then the proportion of them which is viable. Techniques for the recovery of larvae from cysts have been described by Fenwick (1941) and Fenwick and Franklin (1940). The former of these sought to express soil infectivity directly in terms of available larvae per gm. of soil while the latter was concerned merely with obtaining a representative sample of larvae from a given batch of cysts. Neither claimed to estimate viability of the contents. A further technique (Bracey, 1946) which was described in a paper circulated among interested workers was a modification of that described by Fenwick and Franklin (loc. cit.) and claimed to express viability of cyst contents directly as a percentage.