Seleção de populações segregantes e linhagens de feijão-comum preto desenvolvidas em sistema exclusivo de fixação biológica de nitrogênio

Abstract

Common bean is a legume protein source in the diet of populations in many countries, such as Brazil. The crop can benefit from the biological nitrogen fixation (BNF) process; however, its symbiotic capacity is characterized as low compared to other legumes. The formation and testing of segregating populations and the selection of lines in soils where the main nitrogen source is BNF can assist in the development of specific genotypes for these environments. The objectives of this study were: i) to select parents and segregating populations of black-seeded common bean, developed exclusively under BNF, promising for grain yield and 100-grain weight; (ii) to evaluate if the cultivation of genotypes in environments where the main nitrogen source is BNF was efficient in selecting lines with good symbiotic performance, using grain yield as a selection criterion; (iii) to verify the relationship that traits related to BNF establish among themselves and with agronomic traits. In the first study, 28 segregating populations were obtained from crosses in a complete diallel scheme among eight parents with black seeded grains, high yield, and potential for BNF. The segregating populations were evaluated in soils where the main nitrogen source was BNF, in four environments. One hundred-grain weight and grain yield were evaluated. The diallel analysis showed the existence of additive and non-additive effects in the genetic control of the traits, with a predominance of additive effects for 100-grain weight and non-additive effects for grain yield. The highest estimates of general combining ability (gi), in the joint analysis, for the 100-grain weight, were observed for the parents BRS FP403, CNFP 15188, and BRS Esteio, while the parents BRS Esplendor and CNFP 15310 were the most indicated for forming populations with higher grain yield in BNF cultivation systems. The populations BRS FP403 / BRS Esplendor and BRS FP403 / CNFP 15310 combined good mean estimates and specific combining ability (sij) for the two characters, being promising for extracting superior lines in environments focused on BNF. In the second study, 76 lines from a population resulting from the cross between parents with favorable alleles for grain yield and BNF were evaluated. This population was grown in soils where the main nitrogen source was inoculation with rhizobia until generation F5, when the lines were collected. The 76 lines and 5 checks were evaluated in the winter seasons of 2021 and 2022, in Santo Antônio de Goiás-GO, under rhizobia inoculation conditions. Grain yield, 100-grain weight, and visual grain aspect were evaluated. Direct selection of the ten best and ten worst lines for grain yield was performed. The twenty selected lines were evaluated in two greenhouse trials, along with five checks. The evaluated traits were chlorophyll content, shoot and root dry weights, nodule number, and dry and specific nodule weights. A Wilcoxon test was conducted to compare the means of the two groups of lines, as well as genetic and phenotypic correlation analyses and principal component analyses to verify the existence of associations between the traits. There was a significant difference between the groups of lines only for specific nodule weight, indicating that there was no statistical difference in the symbiotic performance of the lines for most traits. The result indicates that the cultivation of the segregating population in environments where the main nitrogen source was BNF was efficient in maintaining in the populationonly genotypes with better symbiotic capacity and promoting high gains for grain yield. There were important significant correlations between the evaluated traits. Chlorophyll content, shoot dry weight and specific nodule weight were indicated for indirect selection of genotypes with better symbiotic performance. Eight lines were selected for advanced trials, with the ultimate goal of releasing recommended black common bean cultivars for BNF environments.