THE RED QUEEN HYPOTHESIS AND PLANT PATHOGEN INTERACTIONS/

The Red Queen Hypothesis (RQH) explains how pathogens may maintain sex ual reproduction in hosts. It assumes that parasites become specialize d on common host genotypes, reducing their fitness. Such frequency-dep endent selection favors sexual reproduction in host populations. Neces sary conditions are that resistance and virulence are genotype specifi c so that host genotype frequencies respond to changes in pathogen gen otype frequencies, and vice versa. Empirical evidence on the genetic b asis of disease, variation in resistance and virulence, and patterns o f infection in sexual acid asexual plants support certain features of the hypothesis. However, gene-for-gene interactions are generally not consistent with the RQH because they do not result in cycling of gene frequencies, unlike a matching allele mechanism. A conclusion of wheth er the RQH can explain the maintenance of sexual reproduction cannot b e reached at present. Nevertheless, the RQH theory has shed light on m any aspects of plant/pathogen interactions important for reducing path ogen damage in agricultural systems.