THE METHOD OF APOMICTIC SEEDS CULTIVATION OF SELECTIVE-VALUABLE GENOTYPES OF CUCUMBER (CUCUMIS SATIVUS L.).

Abstract

 Introduction. At present, in the varietal and hybrid selection of cucumber, the method of genetic stabilization of the selection material is used, which is quite labor-consuming in terms of the number of operations and time-period, the method is based on the forced self-pollination of sorto-linear populations and their subsequent genetic analysis on homozygosity. As the cucumber is a cross-breeding crop, it is practically impossible to achieve absolute leveling of the lines in the above-mentioned way. In order to increase the efficiency of the breeding process, there is an urgent need to develop more effective and accelerated methods of genetic stabilization of selection-valuable material. One of the alternative ways of accelerated genetic stabilization is the use of the method of induced apomixis, which makes it possible to receive diploid homozygotes in the first generation. In our studies conducted during the 2016-2017 years, the various options of obtaining apomictic cucumber seeds, proposed in the literature for other plant species, were tested. In particular, experiments, which involve the processing of unfertilized female flowers by aqueous mixture of growth regulators (gibberellin and cytokinin) according to Kurbatov's recommendations, were carried out. However, this treatment option stimulated exclusively parthenocarpic growth of the fruits without the formation of apomictic seeds in all studied genotypes of cucumber.

Methods. To obtain apomictic seeds in hermaphrodite or gynomonogenic forms of cucumber plants, in advance, one day before the disclosure, female flowers were isolated by parchment insulators. On the following day, women's flowers were removed from parchment isolates and subjected to apomictic treatment according to the methodology developed by the authors. The proposed method of obtaining apomictic seeds has been tested on cucumber lines of the parthenocarpic type of selection of the Institute of Vegetable and Melons Growing NAAS during 2016-2017. As objects of research, the lines of the parthenocarpic type were used – [F₅I₅ Golubchik], [F₆I₅ Kuznechik], [F₁₀I₅ Marinda] and F₈I₆N₁₁.

At the end of the reproductive phase of the development of plants, the accounting of seed productivity of the plants of the above lines was performed for different variants of the formation of the seed material - by means of apomictic treatment and insugnification (control version). The experiment was conducted in a glass greenhouse without heating. Experimental samples of cucumber plants were obtained by seedling method according to the generally accepted method.

Results and Discussion. Among the 4 linear genotypes in which the apomictic treatment was carried out, fully developed seeds were found in the fruits of plants derived from 3 lines F₈I₆N₁₁ (156 fully formed seeds, collected from 14 fruits), [F₁₀I₅ Marinda] (166 seeds, collected from 10 fruits) and [F₅I₅ Golubchik] (130 seeds, collected from 10 fruits) (Table 1). According to the obtained data, the formed apomictic seeds are always essentially, statistically significant, inferior to the amount of seeds that was formed as a result of inquisition. In particular, according to the "average number of fully formed seeds ", this advantage for the line [F₅I₅ Golubchik] was 22.08 times, for the line [F₁₀I₅ Marinda] - 11.95 times, and the line F₈I₆N₁₁ - 20.57 times. Attracted attention, also, is an experimental fact of the quantity of defective seeds, which was obtained by different methods of reproduction. Specifically, in the experimental version using the apomagic method of reproduction, this percentage is much higher and the component for the line [F₅I₅ Golubchik] - 74.51%, the line [F₁₀I₅ Marinda] - 57.11% and the line F₈I₆N₁₁ - 59.06%. But despite this, a smaller amount of well-formed apomictic seeds has a much more valuable genetic material for breeding work, since the plants grown from them are potential diploid homozygotes with the maximum manifestation of genetic stabilization of the source material obtained during one generation.

The results of the biotestes of the proposed method for the production of apomictic seeds were subjected to statistical processing using two-factor dispersion analysis. At the same time, as effective signs, consistently used three characteristics: "number of fully formed seeds "; "number of defective seeds"; "the weight of 1000 seeds". Accordingly, factor A reflected the reaction of cucumber lines, which managed to get apomictic seeds (3 gradations), factor B - different methods of reproduction (2 gradations). The main results of the dispersion analysis are summarized in Tables 2-4, where the calculations of the impact of each of the investigated factors on the performance characteristics are reflected.

On the manifestation of the sign "average number of fully formed seeds" is statistically significant (at the significance level of p <0.05) was the effect of all investigated factors and their interaction. The most significant factor was factor B (85.74%), i.e. breeding methods were used. At the same time factor A, in its influence was significantly inferior (1.78%). At the development of the signs, "number of defective seeds " statistically significant (at the significance level of p <0,05) were all the investigated factors, but the most significant was their interaction (30,07%). The influence of the factor B, that is the method of reproduction, also proved to be significant (27.61%). Analysis of the factors on the manifestation of the sign "the weight of 1000 seeds" has shown statistically significant only the interaction of factors A and B (14,58%). Separate factors did not have significant significance.

The cultivated apomagic seed from all studied linear cucumber genotypes was characterized by a high similarity at the level of 84-92% in case of germination in potted seedlings. The obtained plants-apomicts of each line showed a friendliness ripening and did not have abnormal deviations in the process of organogenesis during the period of vegetative and reproductive stages of development at the plant level, which multiplied by the traditional method of insuching. Thus, in the conducted studies the high efficiency of the proposed method of growing apomictic seeds has been confirmed, the wide introduction of which in the breeding practice will allow to accelerate in 2-4 times the genetic stabilization of the initial material by replacing the method of inrushing with apomictic reproduction.