Identification of the combining abilityof grain yield and its components in hybrid barley populations based on topcross analysis

The topcross method for assessing combining abilityis more economical and less laborious compared to diallel analysis, and also allows the breeder to obtain quite valuable information about the inbred material. In this research, the determination of the general (GCA) and specific (SCA) combining ability of barley (Hordeum vulgare L.) hybridsin two regions of Kazakhstan contrasting in soil and climatic conditions,the role of additive and non-additive genes in the determination of thetraits understudyhas beenrevealed. It is concluded thatthe predominance of additive gene interactions in the control of the traits understudyin theconditions of the Aral Sea region indicates the possibility of effective selection already in the F2 generation, and in the piedmontzone of the Almaty region, due to the high determination of these traits by dominant genes, it is necessary to differentiate the populations of hybrids, starting from the first generation and further selection shall be carried out in several cycles until the achievement of homozygosity of loci carrying dominant genes. Consequently, the genetic contribution of the additive and non-additive effects of genes to the determination and inheritance of the studied traits significantly depends on the conditions of growing the genotypes of spring barley. Of greatest practical interest are the varieties Rihane, WI2291/Roho/WI2269 from the International Center ICARDA and the variety-tester Odessa 100 (Odessa Selection and Genetic Institute, Ukraine) with high GCA and SCA effects, little dependent on growing conditions, which are recommended to be used as reliable donors in breeding programs.


Introduction
The Kyzylorda region of the Republic of Kazakhstan is geographically located in extremely unfavorable conditions for the implementation of crop production, where there is a decrease in the water resources of the transboundary Syrdarya River, which creates certain threats in ensuring guaranteed water supply to irrigated lands, causing intense desertification, salinization and soil blowing, which are the main obstacle to sustainable economic growth and social development of the region. In this regard, within the framework of the -green economy‖ and the diversification of crop production in the Kyzylorda region, the areas under low-water consumption agricultural crops are expanding, including the fodder-grain cropbarley, which is one of the leading crops in the world, due to its adaptive capabilities, high yield and versatile use [1,2]. However, the production of own fodder fails to meet the needs of the cattle breeding of the Kyzylorda region, it has to be purchased additionally, one of the reasons for which is the low yield of agricultural crops on saline soils. Therefore, one of the main tasks of selection work on barley in this region is to search for high yielding adaptive genotypes that are stable by year, and to determine their donor properties to attract them to hybridization programs.
The effectiveness of selection largely depends on the genetic analysis of the hereditary qualities of the source material. Genetic counseling, preservation of the genetic health of the population, protection of the existing gene pool are also ultimately based on genetic analysis. Therefore, further development and improvement of methodsof genetic analysis continue to be the most important task of modern genetics [3,4]. It is very important to identify from a variety of source material forms that not only combine a valuable complex oftraits, but also have the ability to breed true, to select combinations of crossing in which the desired transgressions can be obtained.
One of the methods of analysis that allows to evaluate the genetic properties of varieties is to identify the combining ability, which makes it possible to the researcher to anticipate the results of future crosses and focus on promising material, while avoiding unnecessary time and money outlays on re-obtaining and testing hybrids of no practical value. To determine the general (GCA) and specific combining ability (SCA) during cross-pollination, both the diallel scheme [5][6][7][8] and the system of topcrossbreeding [9][10][11] are used. The topcross method for assessing combining ability is more economical and less laboriouscompared todiallel analysis, and also allows the breeder to obtain quite valuable information about the inbred material.
Literature review has shown that different genes are involved in the determination of traits, sometimes they have a contradictory character in the limit of one agricultural crop, which, apparently, depends on the genotype of the parental lines involved in hybridization and, in the case of polygenic inheritance, can be also determined by the growth conditions of plants [12][13][14].

Materials and Methods
The research was carried out simultaneously in two zones of Kazakhstan, contrasting in soil and climatic conditions: -rice systems of the Kyzylorda region; -piedmont zone of the Almaty region.
The climate of the Kyzylorda region is sharply continental with hot dry summers and cold winters with unstable snow cover. The average annual air temperature is 9.8 0 C. The climate of the region is very dry. The average annual precipitation is 129 mm. In some dry years, precipitation can be 40-70 mm. The soil of the experimental field is meadow-boggy, typical for rice crop rotations in the region. It has a low humus content of 0.9% and a high value of dissolved solids -0.88%.
The climatic conditions of the piedmont zone of the Almaty region are characterized by cold winters, hot and dry summers, warm and dry autumns. Average air temperature 7.6 0 C. The average annual precipitation is 414 mm. The soil cover is represented by light chestnut (nonsaline) soils.
The topcross method is widely used to assess the combining ability of lines. The essence of the method lies in the fact that all lines being studied are crossed with a common tester. Lines, hybrids or varieties can be used as a tester, and, as a rule, there should be at least two testers.
Testers can be used as both female and male parents. The more testers are used in crossing, and the more genetically diverse they are, the more accurate the assessment of the general and specific combining ability will be. The stress factors of the environment (salinity, drought, and dryhot winds), characteristic of the soil and climatic conditions of the Kyzylorda region, greatly reduce the setting of grain during hybridization and averages 3-5%.Therefore, it is very difficult to obtain the entire set of planned hybrid populations in diallel crossings. Many hybrid combinations -fall out‖ and it is not possible to carry out a genetic analysis. In this regard, in our research we widely use the topcross method, based on which we have created not only valuable genetic material, but also salttolerant high-yielding fodder barley varieties that are in demand withagricultural commodity producers in the country. In this research, using the topcross method for F 1 hybrids, the general (GCA) and specific (SCA) combining ability of barleyvarieties were studied: WI2291*2/WI2269; WI2291/Roho/WI2269; Rihane, Harmal (ICARDA) used as female parents. Variety-testerswere used as male parents: Donetskiy8, Odessa 100 (Ukraine), andSaule (Kazakhstan). The main criteria for the selection of female parents were early maturity anddwarfness; of male parents-high grain content, grain size and tallness.
Seeds were sown on 1-meter rows with 15 cm row spacing in three repetitions. F 1 plants were harvested by hand together with roots. 50 plants were analyzed according to individual quantitative traits: productivity (grain weight) of a plant, its structural elements (productive tilling capacity, number of grains perspike, thousand grain weight), as well as plant height and spike length. The reliability of impact of factors on the variability of combining ability indicators under the influence of environmental factors was assessed by the method of Tarutina A.I. and KhotylevаL.V. [15]. The analysis of combining ability in topcrossbreeding was carried out by the method of V.K. Savchenko [10].

ResultsandDiscussion
Analysis of variance showed the presence of a significant variation in the studied traits depending on the testingsites with the exception of the generalcombining abilityof the grainweight per plant of male parentsand the productive tilling capacity of female lines (Table 1). 48 Note: i, j -lines and testers, respectively, * significant at P <0.05; ** -at P <0.01; ns -the effect is not significant Analysis of variance revealed significant differences in the GCA and SCA of the traits under study (Fact>Ftabl), which made it possible to proceed to the estimatesof the GCA and SCAeffects.
The determination of the studied traits involved additive (GCA) and non-additive effects (SCA), and the predominance of certain types of gene interactions depended on the cultivation conditions (Table 2).  in the course of further analysis of the combining ability, their negative impact on all traits of productivity have been revealed. However, as studies by Al-Imran Dianga [14] have shown, the results of one population cannot be extrapolated to another population. The effect of the gene must be assessed for each population, that is, the values of the specific combining ability must be assessed and taken into account.
One of the determining factors in the zoning of a particular variety of barley in the conditions of the rice crop rotation of the Kyzylorda region is the height of the plants, since it is mainly cultivated as a cover crop of perennial grasses. Therefore, the development of varieties with optimal stem sizes (not lower than 75 cm), combining early maturity to avoid overgrowth of grasses above, is an urgent direction in barley breeding for this region.
Considering the greatest practical value of these traits, the best seed parentsshould be recognized as the Odessa 100 and Harmal varieties, in which a very favorable combination of high GCA and SCAhas been noted, besides the additive variance in quantitative terms somewhat has predominated over the non-additive one, which indicates the possibility of positive transgressions in subsequent generations.
Spike length. Novarieties with stable highestimates of the GCAwere identified simultaneously at two sites according to the spike length. We can note Harmal, which is characterized by relatively stable positive estimates, that is, independent of the environmental differences of high and average GCA. In the conditions of the Aral Sea region, the Odessa 100 variety, which also has high variances of the SCA, can be used in heterosisand linear selection to improve this trait (Table 4).   (Table 5).  -theGCA effects, in contrast to variance of the SCA, were higher and more stable in most of the traits. The changeability of variance of the SCAdepending on the years and testing sites is associated with the determination of this parameter by genes with dominant and epistatic effects, which are characterized by high sensitivity to numerous environmental factors.
In conclusion, we would like to note that the results of this research cannot fully reveal the genetic traits of objects, but they give a general idea of the inheritance of important economic and biological traits in various environmental conditions and allow breeders to build a model for future varieties and a strategy for selection work.

Data Availability
Data used in preparing this manuscript is available from the corresponding author on reasonable request.

Conflicts of Interest
The authors declare that they have no conflicts of interest.