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Managing F1heterosis is one of the major objectives in hybrid crop breeding programs. The classical theory considers the heterozygosity in F1hybrids to be the main factor contributing to heterosis and therefore presumes a linear relationship between the value of genetic polymorphisms in parental lines and the heterotic response of their F1offspring. Therefore, the genetic diversity information is viewed as a tool for selection of promising cross-combinations, but results published by different researchers are inconsistent. In this work, we studied the contributions of structural and nonstructural DNA polymorphisms to F1heterosis manifestation. We used SSR and methyl-sensitive AFLP (MSAP with HpaII and MspI izoshisomers) protocols for obtaining specific patterns for heterotic and nonheterotic F1hybrids of sweet pepper (Capsicum annuum L.) from a Belarusian breeding program. We found out that a certain portion of heterosis for yield-related traits might be explained by the polymorphism revealed by SSR analysis. According to our data, the total number of polymorphic SSR loci and the ratio of polymorphic and nonpolymorphic loci demonstrate a significant predictive value and can serve as additional prognostic criteria for the selection of promising cross-combinations. From the MSAP assay, we found a relationship between heterosis and the numbers of methylated and nonmethylated DNA loci for yield traits. Our results indicate that cross-hybridization may favor epiallelic modifications in F1hybrids, presumably responsible for heterosis. Thus, epigenetic DNA variation may explain the absence of a linear relationship between the level of structural DNA divergence and F1heterosis, as well as the manifestation of heterosis in crosses of related (genetically similar) accessions.

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S u m m a r yThe creation of heterotic hybrids by means of conjunction of necessary alleles as result of recombination -is one of the most promising ways of adaptive selection. The raising of frequency of recombination in tomato as self-pollinator, therefore, has large value. In the present article the authors study a model efficiency of intra-and interpopulation breeding in connection with degree of genetic variability in Licopersicon esculentum Mill. tomato lines for protected soil. The Start (24-Е × 12-В) and Nadezhda (24-Е × 21-17) indeterminant hybrids and their parents forms were used as initial material. The 24-E and 21-17 parental forms, obtained by 2-year inbreeding from the Vezha local variety and the Matra Holland variety, respectively, have high combination ability on main components of productivity. The 12-B form from collection of N.I. Vavilov All-Russian Scientific Research Institute of Plant Growing, St. Petersburg has complex resistance to cladosporium and TMV. The crossing during obtaining F1 hybrids were made by hand. The results, obtained on F1 hybrids of Start and Nadezhda forms, were shown that used optimal schemes for periodical breeding with minimal inbreeding and regular hybridization increase the practical frequency of combination of necessary genes, influenced on productivity and resistance to diseases, and may be used for improvement of parental forms and rising of heterosis effect in hybrids. The isolated in two cycles periodical selection the F1 hybrids excelled the initial hybrids in productivity of 6-10 % and kept the complex resistance to TMV and cladosporium, that suggests about an efficiency of present models in tomato breeding for heterosis.Keywords: heterosis, tomato, green house, recurrent selection.Creation of heterotic hybrids is a promising approach currently used in the adaptive breeding of various crops including tomato (1). In the literature data, mechanisms of heterosis are primarily associated with genetically determined additive effects and domination, and in some cases -overdominance and epistasis (2-5). In this regard, breeding program result in viable forms with balanced genetic systems and broad adaptivity if the initial population has desirable alleles that can be recombined in subsequent generations to provide a desired result.Increasing the frequency of recombination is especially important in tomato, a self-pollinator with low probability of crosspollination. The frequency of recombination can be significantly improved by re-hybridization of selected genotypes. This cyclical scheme of breeding is called periodic selection, when each cycle includes selection, the assessment of best individuals and subsequent hybridization of them (6-8). Periodic selection causes small repeated changes in the frequency of genes in population as a result of selection pressure and it is considered as effective if hybrids derived from improved secondary populations exceed hybrids of the initial population. Periodic selection uses intra-and interpopulational methods (9) that, in t...

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