A Rapid Method for Estimating the Density of White Cysts of Heterodera rostochiensis on Potato Roots

Abstract

ALTHOUGH there is little doubt that the best method of detecting and estimating infestations of Heterodera rostochiensis is by examining samples of air-dried soil, it is sometimes necessary to obtain an estimate of the density of white cysts present on growing roots. Chitwood and Feldmesser¹ describe a technique for this purpose using a ‘nematode index’, which is the number of white cysts which can be counted on a root in one minute. Although such a technique is interesting, we feel that when critical experiments are in progress it is unwise to confound true experimental effects with such personal factors as the varying rate at which different observers count. Moreover, it is important to be able to estimate the accuracy of any given technique so that the results can be analysed and significance-levels determined. The following method which we have used for obtaining a quantitative measure of numbers of cysts present on roots may, therefore, be of interest.