Feasibility to breed for biological nitrogen fixation in soybean

Abstract

Soybean [Glycine max (L.) Merril] is one of the most important legumes grown worldwide. It is the main source of protein and edible oil because of the high oil content (20-25%) and protein (42-45%) in the seeds. Due to the high protein content in the grains, plants need a large amount of N, about 80 kg to produce a ton of grains. In Brazil, due to the selection of Bradyrhizobium strains highly efficient in biological nitrogen fixation (BNF), this demand can be fully supplied from BNF, not requiring nitrogen fertilization. The substitution of nitrogen fertilizers by BNF in soybeans crops results in savings of around 20 billion dollars annually for Brazilian agriculture. As agriculture is increasingly competitiveness and seeking to be more efficient by reducing production costs while respecting the environment. In this context, BNF is a viable alternative serving to meet these objectives. Therefore, the development of soybean genotypes efficient in BNF is important. Thus, the purpose of this work was to study the BNF ability of soybean progenies and their ability for symbioses using different Bradyrhizobium strains as well as to select more efficient progenies and strains for BNF, aiming to guide strategies in soybean breeding to BNF. In a greenhouse experiment, were evaluated 24 soybean progenies and five Bradyrhizobium strains (SEMIA 5079, SEMIA 587, SEMIA 5019, UFLA 06-24 and INPA 03-11B). For the trial progenies and strains, analysis of variance was conduct and means were compared by Scott-Knot test. Partial diallel analysis was performed to estimate the general and specific combination ability for the progenies and Bradyrhizobium strains. The best progenies and strains were selected considering their means and general combining ability for the following traits: nitrogen content, chlorophyll content, number of nodules, fresh and dry weight of nodules and Z index. Ten progenies and two strains (SEMIA 587 and INPA 03-11B) were selected to carry out a field trial experiment. The BNF was influenced by genotype, strain, and genotype-strain interactions. There was a predominance of additive effects on the traits related to BNF, indicating that recurrent selection could be a strategy for improvement of these traits. Late maturity progenies showed higher values for the traits related to field nodulation but did not show gains in grain yield. The EA-8 progeny stood out as having a high yield, with good results in traits related to BNF and early maturity. INPA 03-11B strain showed the best result for grain yield, indicating high potential for its use as an inoculant in soybean crops.