Search

This review considers the processes of morphogenesis used in the development of propagation methods and the creation of a new starting material for sugar beet. It has been demonstrated that methods of particulation, in vitro microcloning and cell breeding that reflect non-sexual forms of plant reproduction increase the effectiveness of breeding experiments. The review describes the in vitro culture methods maintaing a tendency in plants for vegetative propagation and stimulating increase in genetic variability of properties when mutagens such as ethyl methanesulfonate, alien genetic structures with mf2 and mf3 bacterial genes in Agrobacterium tumefaciens strains, and selective agents (Сd++ ions and abscisic acid) are incorporated into plant cells. It presents the results of using fluorescent microscopy, cytophotometry, biochemical analysis and determining the level of phytohormones and content of nucleic acids in nuclei for forecasting the seed setting ability. It has demonstrated that long self-pollination of plants causes decrease in fertility of pollen grains, resulting in the sterilization of male gametes and the appearance of pistillody flowers. Self-fertile plants isolated from these lines serve as sterility fixers, while the apomixis elements increased the ovule number, additional embryo sacs and embryos. A role of apomixis in contributing to variability in the ontoand phylogenetic development of plants have been substantiated. The review reflects the morphological features of the in vitro development of sexual and somatic cells in embryos during the formation of seedlings based on floral and vegetative embryoidogeny. Use of the SNP and SSR (Unigenes) molecular-genetic markers having a high polymorphism level has appeared effective to characterize the developed breeding material and hybrid components when carrying out crossings. The study of sugar beet starting materials for the presence of TRs mini-satellite loci making it possible to reveal O-type plants-pollinators (sterility fixing agent) and MS-form plants are of interest for breeding as well. The selected material can be widely used in breeding to produce hybrids, allowing for a 2–3-fold reduction of the development period. The review also discusses the prospects for the development and implementation of new methods and original schemes in sugar beet genetics, biotechnology and breeding.

In 1949 S. S. Khokhlov (one of the founders of the Russian scientifi c school on the problem of apomixes) proved the original conception of the progressive evolutionary role of apomixis. He contended that the basic direction of the reproductive system evolution in angiosperms is a gradual failure of sex reproduction and transition to apomixis. This hypothesis was heavily criticized and called a “scientist’s fantasy”. In the second half of the 20th century the discovery of recombination repair led to a reassessment of the role of meiosis in the evolution. Now meiosis is considered as the guarantor of genomic stability, and not only as a source of combinative variability. Various molecular-genetic mechanisms of genome transformation unrelated to the sexual process were described. There are gene duplications, horizontal gene transfers and mobile gene systems. All this creates grounds to assume that not only amphymixis but apomixis can solve the dilemma: (1) saving the genotypic structure of the species, (2) providing the genetic diversity of the progeny. Parthenogesis allows the copying of genotypes and the saving of the genotypic structure of the species. The dropping out of meiosis from the development cycle of apomicts, on the one hand, increases its mutability because there is no recombination repair, and, in the other hand, promotes polyploidyzation and consequently contributes to the evolution by gene duplication. The accumulated data about distribution and embryology features of apomicts indicate its signifi cant evolutionary potential. In the light of the modern data S. S. Khokhlov’s hypothesis of the beginning of “apomixis era” appears to be not so fantastic as before.

Exogenous factors affecting on the expression of apomixis in cabbage have been identified. Apomictic seeds developed into embryoids were observed in three cabbage varieties such as Jana, Lazurnaya and Lesia (Ukraine). Thus, it was possible to induce an incomplete organogenesis of parthenogenesis seeds originated from these four varieties of cabbage. The occurrence of apomixis was provoked by the synergitic effect of plant growth regulators and alien pollen applied simultaneously as an aqueous mixture of gibberellins and cytokinin applied on the base of the pistil, while the alien pollen (Chinese radish - Loba) was placed on the stigma of castrated cabbage buds 2-3 days before they disclose.

Genomic in situ hybridization (GISH) was used for a chromosomal composition study of the later generations of interspecific hybrids between A. cepa L. and A. fistulosum L., which are relatively resistant to downy mildew (peronosporosis). GISH revealed that F2 hybrids, which did not produce seeds, were triploids (2n = 3x = 24) with 24 chromosomes and possessed in their compliments 16 chromosomes of A. fistulosum L. and eight chromosomes of A. cepa L. or eight chromosomes of A. fistulosum L. and 16 chromosomes of A. cepa L. The advanced F5 hybrid, which produced few seeds, was amphidiploid with 32 chromosomes. BC1F5 hybrid was triploid with eight chromosomes of A. fistulosum L. and 16 chromosomes of A. cepa L., which did not produce seeds. BC2 (BC1F5) plant was amphidiploid that possessed 4 recombinant chromosomes and produced few seeds. GISH results point to 2n-gametes formation in macro- and microsporogenesis of the hybrids. The mechanism of 2n-gametes formation and the possibility of apomixes events in the backcrossing progeny are discussed.