The effect of resistant solanaceous plants on the sex ratio of Heterodera rostochiensis and the use of the sex ratio to assess the frequency and genetic constitution of pathotypes

SUMMARY The sex ratios of two Heterodera rostochiensis populations were compared on fifteen solanaceous plants. Larvae did not mature in the roots of Atropa belladona, Datura stramonium or Nicotiana tabacum but adults were produced on the other plants, on some only males and on others, males and females. With two other populations, but not with a third, the percentage of larvae that became female on a potato hybrid with a dominant gene for resistance derived from Solanum tuberosum ssp. andigena increased during successive generations on the hybrid in accordance with the hypothesis that such larvae are double recessives (aa). Fewer larvae became adult in plants with two dominant genes for resistance than in plants with one, and such plants probably exerted selection of both males and females. A population from St Brelades (Jersey) produced fewer females and more males on the susceptible variety Arran Banner than did either the Thorney (Cambs.) or Aberystwyth populations. A much greater percentage of larvae from the St Brelades population became female on an ex andigena hybrid derived from CPC 1690 than on one derived from CPC 1685.