The Degree of Heterodera Infectivity of Soil and its Determination

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Abstract
(1) A technique for measuring the infectivity of soil with Heterodera schachtii in terms of the number of larvae potentially capable of infecting plants per pound of soil is described.(2) The liberation of the larvae is accomplished by subjecting the cysts recovered from one half-pound sample of soil to a given strength of calcium hypochlorite solution for four hours. The loss of larvae due to solution during this time was found to be negligible.(3) It was shown that if the larvae liberated were made up to a suspension, then counts made on 0·15 cc. samples of this suspension fall into a Poisson distribution and hence the accuracy of the final determination is dependent only on the number of larvae counted.(4) It was found that provided the soil to be examined was thoroughly mixed that it was unnecessary to examine more than one half-pound sample as there was no significant difference between the means from different samples.(5) Figures of cyst counts tabulated alongside available larvae show the utter inadequacy of cyst counts as a measure of infectivity.(6) No attempt is made in this paper to determine how many of the larvae are alive and viable, further research into this matter being contemplated.