RESUMO: No presente estudo objetivou-se avaliar a reação de genótipos de soja a Meloidogyne javanica (Est J3), Meloidogyne sp.0 (Est R0) e M. graminicola (Est VS1). No primeiro experimento, todos os genótipos (BMX Potência RR, BMX Valente RR, BMX Icone IPRO, PELBR10-6049 RR, and TECIRGA 6070 RR) testados mostraram-se suscetíveis a M. javanica, com fator de reprodução (FR) >1.0, e resistentes a Meloidogyne sp.0 (0.01 > FR < 0.15), enquanto no segundo experimento, todos os genótipos (BRS 246 RR, PELBR11-6038 RR, PELBR11-6001 RR, PELBR10-6005 RR, BMX Apolo RR, PELBR11-6028 RR, PF11651, PF103251, PELBR11-6035 RR, PELBR10-6050 RR, PELBR11-6042 RR, PELBR10-6017 RR, PELBR11-6007 RR, PELBR10-6016 RR, and PELBR10-6049 RR) testados comportaram-se como resistentes a M. graminicola (0.06 > FR < 0.43).

ABSTRACT: This study aimed to evaluate the host status of soybean genotypes to Meloidogyne javanica (Est J3), Meloidogyne sp.0 (Est R0), and M. graminicola (Est VS1). In the first experiment, all tested genotypes (BMX Potência RR, BMX Valente RR, BMX Icone IPRO, PELBR10-6049 RR, and TECIRGA 6070 RR) were susceptible to M. javanica, with reproduction factor (RF) >1.0, and resistant to Meloidogyne sp.0 (0.01 > RF < 0.15), whereas in the second experiment, all genotypes (BRS 246 RR, PELBR11-6038 RR, PELBR11-6001 RR, PELBR10-6005 RR, BMX Apolo RR, PELBR11-6028 RR, PF11651, PF103251, PELBR11-6035 RR, PELBR10-6050 RR, PELBR11-6042 RR, PELBR10-6017 RR, PELBR11-6007 RR, PELBR10-6016 RR, and PELBR10-6049 RR) were resistant to M. graminicola (0.06 > RF < 0.43).

ABSTRACT: In this work, we compared nitrate-supplied plants (non-nodulated) with non-nitrate-supplied plants (nodulated) under oxygen privation of root system (hypoxia) and re-oxygenation (post-hypoxia; recovery) in order to verify whether N sources affect the antioxidant system during oxidative stress caused by hypoxia and post-hypoxia conditions. Antioxidant enzymatic activities, ascorbate redox state, and reactive oxygen species (ROS) levels were analyzed in roots and leaves of two soybean genotypes, Fundacep 53 RR and BRS Macota at reproductive stage R2, during hypoxia and post-hypoxia in an experiment carried out in a hydroponic system. The antioxidant system was strongly induced in roots of nitrate-supplied plants of both genotypes, with high activity of superoxide dismutase, ascorbate peroxidase, catalase, glutathione reductase and guayacol peroxidase. It also increased reduced ascorbate and ascorbate redox state and decreased ROS production under hypoxia and recovery, while in leaves of nodulated and non-nodulated plants, a slight increase on antioxidant system was observed. Nitrate may benefit soybean plants under hypoxic conditions and subsequent re-oxygenation by inducing the antioxidant system mainly in roots to cope with ROS production and reduce oxidative damage.

Waterlogging blocks the oxygen supply to the root system which inhibits respiration, and greatly reduces the energy status of cells that affect important metabolic processes. This study evaluated fermentative metabolism and carbohydrate contents in the root system of two soybean (Glycine max L. Merril) genotypes under hypoxic and post-hypoxic conditions. Nodulated plants (genotypes Fundacep 53 RR and BRS Macota) were grown in vermiculite and transferred to a hydroponic system at the reproductive stage. The root system was submitted to hypoxia by flowing N2 (nitrogen) gas in a solution for 24 and 72 h. For recovery, plants returned to normoxia condition by transfer to vermiculite for 24 and 72 h. Fermentative enzyme activity, levels of anaerobic metabolites and carbohydrate content were all quantified in roots and nodules. The activity of alcohol dehydrogenase, pyruvate decarboxylase and lactate dehydrogenase enzymes, as well as the content of ethanol and lactate, increased with hypoxia in roots and nodules, and subsequently returned to pre-hypoxic levels in the recovery phase in both genotypes. Pyruvate content increased in nodules and decreased in roots. Sugar and sucrose levels increased in roots and decreased in nodules under hypoxia in both genotypes. Fundacep RR 53 was more responsive to the metabolic effects caused by hypoxia and post-hypoxia than BRS Macota, and it is likely that these characteristics contribute positively to improving adaptation to oxygen deficiency.