Evaluation of breeding strategies for resistance to potato cyst nematodes using a population dynamic model

Abstract

Strategies for breeding for resistance to potato cyst nematodes were evaluated by a simulation model. The model describes the annual changes in nematode density, the yield reduction of the crop, and the selection for genes enabling the nematodes to circumvent the resistance genes in the host. This selection of virulent pathotypes is responsible for the breakdown of the resistance. With respect to the durability of resistance genes, the simulations showed, or reassured, the following principles. a) Combination of two resistance genes (A and B) in one variety is much more effective than alternating A-resistant and B-resistant varieties, which is in its turn more effective than cultivating only a single resistant variety. b) The higher the level of partial resistance, the more the population growth is retarded. However, when the resistance is pathotypespecific, it is broken earlier at higher resistance levels. c) A low resistance level offers in itself an effective protection against the selection of virulent pathotypes, so that pathotype non-specificity becomes an advantage only at high levels of resistance. d) Monogeneous, complete resistance is much more durable when incorporated in a genetic background of partial resistance. e) Breakdown of resistance will in general proceed more rapidly in mixtures of two nematode species than in populations of virulent and avirulent pathotypes of the same species.