The Effect of Initial Population Density On the Reproduction of Globodera Pallida On Partially Resistant Potato Clones Derived From Solanum Vernei

Abstract

The reproductive rates of two populations of Globodera pallida over a range of initial population densities (Pi) were compared on a non-resistant and two partially resistant potato clones derived from Solanum vernei. The final number of eggs/g soil (Pf) increased with Pi, as did the differences between clones. In contrast the reproductive rate (Pf/Pi) progressively decreased as Pi increased. The form of the curve relating Pf to Pi for the partially resistant clones was similar to that for the non-resistant clone but the rates of response to Pi and the final maximum densities were less on the partially resistant clones and related to their levels of resistance. Each population ranked the clones consistently for degree of resistance at all inoculation levels. This observation is related to other published results and it is concluded that Pf/Pi values are too sensitive to changes in initial nematode density and other environmental factors to be used either to define and separate categories of resistance in the plant or to identify pathotypes in the nematode. A new scheme for assessing the resistance of clones is proposed in which partially resistant clones are used as controls to delineate resistance classes.