Decrease of yield components and morphological traits of soybean full-sibs under drought conditions

Soybean, as a plant species, is native to regions with conditions favourable of humidity and temperatures for its growth and development. The expansion of the soybean growing area resulted in requirements of varieties with higher tolerance and more stable grain yield under drought conditions. In order to develop high yielding varieties, the method of full-sib (FS) selection was applied in this study, as one of many methods of recurrent selection. The basic principle of recurrent selection is a cyclic selection, with the aim to accumulate favourable alleles. Three most yielding F2:3 sister lines obtained from the crossing combination of varieties Kunitz and Kador, were used for two combinations. Progenies of two FS crossing combinations were tested in two locations during two years (2011 with more favourable and 2012 with less favourable precipitation distribution). The values of grain yield per plant, the most important components of yield and morphological traits decreased under less favourable conditions. The highest decrease was recorded in the number of pods and the number of grains per plant, whereas the lowest decrease was found for the 1000-grain weight. Regardless of the relatedness of the tested material, significant differences in response to drought were observed not only between two FS progenies, but also within progenies of each combination. Soybean grain yield is a complex trait strongly affected by environmental conditions. Under unfavourable conditions, the reductions in the following traits were observed in progenies of two sister combinations: grain yield per plant (26.5-36.0% and 25.6-42.7%), number of pods per plant (18.6-33.0% and 12.6-38.2%) and the number of grains per plant (18.1-30.2% and 14.3-37.6%). Three progenies of FS crossings with the lowest yield reduction were identified as suitable initial material for the development of varieties with higher tolerance to drought conditions.