INDIVIDUAL SELECTION IN COMBINATION WITH SELF-POLLINATION

ABSTRACT

To more quickly stabilize the economically valuable traits of the line and increase its homogeneity, we used the technique of artificial self-pollination of flowers, followed by testing of the generation, culling of unwanted individuals and selection. All inbred lines of the studied cotton varieties generally retained their typicality. However, compared to cross-pollinated lines, their heterogeneity in individual quantitative traits was greater. It was revealed that the depressive effect of self-pollination affects primarily the fruit set and a decrease in the weight of the boll in the year of self-pollination. With self-pollination, the number of sterile styles increases noticeably. Noticeable deviations were observed in individual varieties in terms of boll weight, yield and fiber length.

АННОТАЦИЯ

Для более быстрой стабилизации хозяйственно ценных признаков линии и повышения их однородности нами был использован прием искусственного самоопыления цветков с последующим испытанием поколения, выбраковкой нежелательных особей и отбором. Все инбредные линии изучаемых сортов хлопчатника в целом сохранили типичность. Однако по сравнению с перекрестноопыленными линиями их гетерогенность по отдельным количественным признакам была больше. Выявлено, что депрессивное действие самоопыления сказывается в первую очередь на завязываемости плодов и снижении массы коробочки в год самоопыления. При самоопылении заметно увеличивается количество бесплодных столбиков. Заметные отклонения наблюдались у отдельных сортов по массе коробочки, урожайности и длине волокна.

Keywords: Cotton plant, variety, population, individual selection, self-pollination, homogeneity.

Ключевые слова: Хлопчатник, сорт, популяция, индивидуальный отбор, самоопыление, однородность.

Introduction. A plant variety can be considered as a self-reproducing, relatively stable discrete biological, namely genetic system. Deterioration of a variety is the process of reducing its economic and biological qualities based on hereditary variability due to splitting, the appearance of mutations, mechanical and biological contamination and a decrease in resistance to diseases transmitted through seeds. Cotton can self-pollinate or cross-pollinate with the help of bees that transfer pollen between flowers of different plants. If conditions are favorable, the pollen grain will germinate after it adheres to the stigma and form a pollen tube that passes through the tissues of the pistil (Gelbart, Aderkas, 2002; Jorge Lora, José I. Hormaza, María Herrero, 2016).

The degree of uniformity of plants is determined by the constancy of the pollination method of plants and the level of modification variability. One of the main reasons for the decrease in the varietal purity of varieties and the loss of cotton fiber quality is that distant hybridization is used in cotton breeding, involving wild and semi-wild forms of cotton (Mamarakhimov, 2015; Iksanov et al., 2001, Shodieva et al., 2021). The remoteness of genomes disrupts the general recombination process and the balance of the genetic system, splitting occurs at many loci, stabilization of polygenic traits occurs in very late generations. Therefore, varieties, especially polyploid ones, based on distant hybridization should be refined for a long time and not introduced into production until the homogeneity of economically valuable traits reaches a certain limit (Kozubaev, 2004; Shodieva et al., 2019). Self-pollination helps to identify recessive alleles hidden in heterozygotes, as a result of which it is possible to isolate new forms that are homozygous for many traits (Mamarakhimov, Khalikova, 2015). Considering that most economically useful traits are controlled by recessive genes, this method is naturally of great value.

The inheritance of traits in cotton largely depends on genetic homogeneity and the degree of paratypic variability of traits. Cotton is a non-strict self-pollinator and, in the presence of pollinating insects and other specific conditions, is subject to natural cross-fertilization. When pollinating without castration of plant flowers, the percentage of cross-fertilization reaches 40-80% depending on the variety (Mamarakhimov, Khalikova, 2015). In the practice of seed production, biological contamination of varieties is possible. All these issues are important for the methodology of cotton seed production. In this regard, we set the task of studying the degree of variability of traits in cotton varieties under conditions of self-fertilization, cross-pollination and open flowering.

Materials and methods. The study was conducted in 2019-2021 in the experimental plots of the Research Institute of Breeding, Seed Production and Agrotechnologiyes. The varieties Sultan, Jarkurgan, S-6524 and Namangan 77, belonging to the species G.hirsutum, were sown as the object of research (Table 1).

Table 1.

List of cotton varieties, participating as an object of research

The plant placement scheme is a single-row plot of 6 l/m, plant placement every 15 cm with a row spacing of 60 cm. Elite seeds of the varieties included in the experiment were sown in 50-hole plots and self-pollination and cross-pollination were carried out for each variety for 10 days from the beginning of flowering. In the fall, all ripe capsules of self-pollinated and cross-pollinated flowers were collected for each variety separately. The weight of the raw material, the number of seeds, the yield and the length of the fiber were determined for each capsule. To study the offspring, the seeds from each capsule were sown separately as a line. For each variety, 30 self-pollinated and 30 cross-pollinated lines were sown. Self-pollination was repeated annually for the same lines during 2019-2021. For each variety that had self-pollinated in previous years, forced self-pollination was again carried out by isolating the buds with paper bags on the eve of flowering. To ensure normal flower development, the isolator bag was made of thin, highly translucent tissue paper. The size of the bag ensured free opening of the flower. In addition, to ensure that the pollen germination conditions were the same during self-pollination and cross-pollination of the studied cotton varieties in the "intra-varietal cross-pollination" option, the pollinated flowers were also covered with paper bags.

Annually during 2019-2021. Self- and cross-pollination were repeated on the same lines. Self-pollination of flowers was carried out on typical well-developed plants obtained from seeds of self-pollinated bolls. During the harvest period, raw cotton from bolls obtained by self-pollination was collected within each family. At the same time, hybrid (F₀) bolls were collected for each hybrid combination separately. The selected typical plants were marked with tags before self-pollination. After the bolls (self-pollinated) opened, raw cotton was collected in a row bag. During the growing season, and especially from the moment of boll ripening, families were viewed, and then the best plants.

All data were processed using Microsoft Excel 2016. according to B.A. Dospekhov (Dospekhov, 1985). The reliability of the results was assessed at p≤ 0.05.

Results. The results of our studies showed that heterogeneity of varieties in qualitative dominant traits is revealed in the first two years of self-pollination. Heterogeneous plants were rejected. All self-pollinated lines of the studied cotton varieties generally retained the typicality of the variety. However, compared to cross-pollinated lines, heterogeneity in individual quantitative traits was more significant. It was revealed that the depressive effect of self-pollination affects primarily the setting, reducing the weight of the boll in the year of self-pollination (Table 2).  In all varieties, seed set deteriorates equally depending on the variety. The decrease in the number of set seeds in the capsules of self-pollinated lines, as already noted, is the result of insufficient fertilization. In self-pollination and cross-pollination, an important role is played by the incompatibility between the pollen grains and the pistil of self-pollinated lines.

Table 2.

Setting of seeds of cotton varieties with self- and cross-pollination

The number of sterile styles and pollen tubes that did not pass through the base of the latter were recorded (table 3).

Table 3.

Growth of pollen tubes

Note: s.p. – self-pollination; c.p. – cross-pollination

The styles of pollinated and self-pollinated flowers were fixed in a 90% ethanol solution 24 hours after self- and cross-pollination, and then the number of pollen tubes that passed through the bases of the styles in the ovary was determined in cross sections stained with potassium iodide.

It is evident from the data in Table 3 that self-pollination significantly increases the number of sterile styles; none were found in three varieties, while only three styles were sterile in the C-6524 variety.

Along with the high variability of such traits as the number of capsules per plant, the number of seeds per capsule, and the weight of the capsule, self-pollinated lines differ in the degree of pubescence (pubescent, slightly pubescent), bush habitus (wider, relatively compact), but do not lose varietal typicality. Cross-pollinated lines are uniform and do not show any deviations from the original variety.

The variability coefficients for fiber yield and length in self-pollinated and cross-pollinated lines do not differ particularly, indicating the relative stability of these traits. No deterioration was observed under the influence of self-pollination.

In 2020, varieties in the second year and propagation nursery were studied. Both variants were sown in parallel rows, and on the right and left - varieties: self-pollinated and non-self-pollinated. Plant productivity was determined by taking into account the number of bolls set on the bush on October 1. It was found that there was no difference between self-pollinated and non-self-pollinated varieties. Both absolute indicators and the coefficient of variability for the trait were identical.

In 2021, plants in the seed propagation nursery were studied for yield, boll weight, yield and fiber length. The results confirmed the conclusion of 2020. However, noticeable deviations were observed in individual varieties in boll weight, yield and fiber length. For example, the Sultan variety has a higher boll weight in the non-self-pollinated version - 7.0 g versus 6.7 in the self-pollinated one. On the contrary, self-pollinated plants of the C-6524 variety have a larger boll. However, there is no pattern: in one case, the self-pollinated variant is better, and in the other, the non-self-pollinated variant. A similar picture is observed for the fiber length, although in most cases, plants of self-pollinated varieties and hybrids are better than non-self-pollinated ones. Perhaps these deviations are random.

Environmental conditions can significantly affect the success of pollination, as pollen grains can evaporate under conditions of low relative humidity (Gelbart, Aderkas, 2002). Numerous studies show that the percentage of cotton seed set is directly dependent on the number of germinating pollen grains and pollen tube growth (Jorge Lora et al., 2016). We have also established a similar dependence. Some breeders and seed growers believe that the main reason for the deterioration of self-pollinating varieties in production is their long-term self-pollination, so with each reproduction they supposedly progressively lose their yield qualities (Altukhov, 2003; Nagylaki, 1992). For a more rapid stabilization of economically valuable traits of the line and increasing its homogeneity, we used the method of artificial self-pollination (inbreeding) of flowers on typical early-ripening, productive, high-quality and white-colored fiber individuals with subsequent testing of the offspring, rejection of undesirable plants and selection in families of forms. Based on our research work, it is clear that in self-pollinating crops, significant depression of degeneration or deterioration under the influence of self-pollination does not occur.

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