Genotypic differences of soybean (Glycine max (L.) Merrill) as a factor of biological intensification of agroecosystems

Photosynthesis of agrophytocenoses is a basis of agroecosystems primary bioproductivity. An average radiation-use efficiency (RUE, dry matter produced per unit of intercepted solar radiation) of soybean plants is 1.02 g MJ−1 [1]. It should be noted, that starting from the moment of assimilates production by photosynthesis and till the accumulation of dry matter in the seeds there are many complex interconnected processes on the molecular, cellular, organismal and population levels which all taken together have a decisive influence on the yield [2, 3, 4, et al.]. 1.1 The importance of soybean genotypic differences in agrophytocenoses Genotypic differences among soybean plants exist inability to capture solar radiation by the leaf surface and, as a result, the yield of cultivars may significantly change [5]. Soybean genotypes with reduced chlorophyll content and relatively high photosynthetic activity are promising for the crop sown with an increased plant density [6]. In addition, the ability of agrophytocenosis to intercept and use solar radiation rises in intercropping, compared with monocropping [7]. Therefore, it is possible to increase the use efficiency of soybean agrophytocenoses by selecting genotypes with higher photosynthetic capacity.

Soybean as a legume plant spends up to 20% of photosynthesis products to provide symbiotic nitrogen fixation. In its turn, high nitrogen-fixing activity of root nodules leads to an increase in the photosynthesis intensity and raise in the yield [8]. Genotypic variability in the symbiotic ability of soybean [9] and differences in the nitrogen-fixing activity of rhizobia [10] contribute to the effective combination of high values of the biological nitrogen fixation, photosynthetic capacity and yield of commercial soybean cultivars. For instance, in Brazil, where the average annual soybean yields level is relatively high (over 3 t ha−1), soybean plants receive about 80% of their required nitrogen by symbiosis with nitrogen-fixing bacteria [11, 12]. In this way, the existing genotypic variability of soybean makes it possible to improve naturally nitrogen balance of soil-biotic complex and hence the ecological safety of intensive agroecosystems [13, 11, 14]. 1.2 Unfavorable environmental factors and soybean yield Soybean plants are highly sensitive to unfavorable environmental factors, including temperature regime, conditions of moisture supply and diseases. These factors have a negative influence on the yield formation and ultimately lead to significant reduction in its quantitative and qualitative characteristics [15, 16]. In Ukraine, the soybean is represented in agroecosystems by the commercial cultivars with high yield potential and valuable morphological and biological traits. On this basis, they are listed in the State Register of cultivars suitable for introduction and dissemination. However, under conditions of the separate field, farm or group of farms (at the level of the specific agroecosystem) the environmental stress factors can cause yield instability of soybean cultivars. Due to the differences in the level of yield components stability of soybean genotypes [16] it is important to select cultivars that would be able to realize the yield potential under changing environmental conditions.

It’sneeded to highlight that the breeding programs in the world leading countries at present are increasingly oriented towards creating cultivars and hybrids of agricultural plants characterized not by the maximal yield but the optimally high and stable yield level [17, 18]. Along with the state breeding programs there are private breeding programs in Ukraine. However, it is important to keep the state breeding priorities with new content, since they may not have commercial attractiveness today but are potentially significant in the future. 1.3 Research aim Our long-term main tasks were to search for new approaches, develop and improve the methods of adaptive breeding for optimal combination of the yield, resistance, adaptability and quality in the soybean cultivars. In the breeding process were used the wild-type genotypes (Glycine soja Sieb. and Zucc.) which can adequately respond to changing environmental conditions.