Physiological and N2-fixation-related traits for tolerance to drought in soybean progenies

The objective of this work was to evaluate six soybean (Glycine max) genotypes for physiological traits and biological nitrogen fixation in drought conditions, and their capacity for recovery after rewetting, based on yield components. The genotypes evaluated in a greenhouse were the following: 'BRS 317', susceptible to drought; R01-581F and R02-1325, which show biological nitrogen fixation tolerant to drought; and the BRB14-207525, BRB14-207526, BRB14-207527 breed lines resulting from crossings between commercial genotypes and PI 471938, which shows a slow-wilting phenotype under drought. Drought conditions were applied to the genotypes at the full-flowering stage (R2) for ten days, whereas control plants were kept well-watered. Photosynthetic rate and gas exchanges under drought were more stable in the BRB14-207526 genotype. Root biomass increased 3.5 times in R02-1325 as an adaptive response to drought. In addition, leaf ureides - a trait related to biological nitrogen fixation in plants tolerant to drought - remained stable in genotypes R02-1325 and R01-581F exposed to drought, but decreased in BRB14-207527. Genotypes BRB14-207526, BRB14-207527, and R02-1325 show more favorable physiological performances and a lower accumulation of ureides under drought, besides a higher grain yield after rehydration. The BRB14-207526 and BRB14-207527 progenies show drought-tolerance traits from PI 471938, whereas R02-1325 is a promising source of tolerance to drought for soybean breeding. Resumo: O objetivo deste trabalho foi avaliar seis genótipos de soja (Glycine max) quanto aos parâmetros fisiológicos e à fixação biológica de nitrogênio, em condições de restrição hídrica, e sua capacidade de recuperação após reidratação, com base em componentes de produção. Os genótipos avaliados em casa de vegetação foram os seguintes: 'BRS 317', suscetível à seca; R01-581F e R02-1325, que apresentam fixação biológica de nitrogênio tolerante à seca; e os recombinantes BRB14-207525, BRB14-207526, BRB14-207527 resultantes de cruzamentos entre genótipos comerciais e PI 471938, que apresenta o fenótipo “slow wilting” em condições de seca. A restrição hídrica foi aplicada por dez dias aos genótipos em fase de florescimento pleno (R2), enquanto as plantas-controle foram mantidas bem irrigadas. A taxa fotossintética e as trocas gasosas sob restrição hídrica foram mais estáveis no genótipo BRB14-207526. A biomassa das raízes aumentou 3,5 vezes em R02-1325 como resposta adaptativa à seca.