[The problem of durable resistance of plants to different pests]

Different hypotheses concerning durable plant resistance against different pest were tested: 1) resistance is weak and polygenetically controlled; 2) resistance depends on "residual effect" of oligogenes that were overcome by pests. Contrast pair of plants and pests were used in experiments: wheat, barley--facultative parasite Bipolaris sorokiniana Shoem., wheat--obligate parasite Puccinia recondita Rob. ex Desm., sorghum--greenbug Schizaphis graminum Rond. Differential interaction between parasite and host plant resulted in their increased compatibility under long reproduction of parasite on resistant varieties were regarded as criteria of quick overcoming of resistance. The results did not support any hypothesis. The rate of adaptation of B. sorokiniana to the resistant varieties of wheat and barley did not depend on the level of resistance expression (weak, moderate or strong) and genetic control (oligogenic, polygenic or cytoplasmatic). It was shown by hybridological analysis that "residual effect" of oligogenes of sorghum resistance against greenbug depended on small resistance genes, that can be independent or weakly connected with marker oligogene. These data allows to doubt in phenomenon of "residual effect" of oligogenes. It was shown that non specific pathogenicity of parasitic fungi increased during their reproductions on sensitive varieties of plants. Thus, cultivation of sensitive varieties causes damage of crop culture non only because of their own losses, but also by increasing the infection of moderately resistant varieties.