Development of the theory of heterosis in plants

The phenomenon of heterosis is widely used in the breeding of most crops. The article presents historical data on the discovery of this phenomenon and a number of theories explaining its origin. The most important of these, on which modern genetics and breeding are based, are the theories of dominance, overdominance, genetic balance, epistatic interaction of genes, ecological heterosis, mutation theory of heterosis, and hypotheses of physiological heterosis and formation of combining ability. Heterosis in hy-brids usually manifests itself in the first generation. Unfortunately, to date, none of the hypotheses can fully explain the nature of the phenomenon of heter-osis. The occurrence of heterosis in hybrids of the first generation is caused by both allelic and interallelic gene interactions. The problem of heterosis fixation is solved by vegetative reproduction and apomixis; in autopoliploids of the second and subsequent genera-tions, segregation is slower than in diploids.