Can Bradyrhizobium strains inoculation reduce water deficit effects on peanuts?

Abstract

Drought is one of the environmental factors that most affects peanut cultivation in semi-arid regions, resulting in economic losses to growers. However, growth promoting bacteria are able to reduce water deficit damage in some plant species. In this context, this study aimed to evaluate the interaction of Bradyrhizobium strains reducing water stress effects on peanut genotypes by antioxidant enzymes activities, leaf gas exchanges and vegetative growth, as well as to determine the taxonomic positioning of strain ESA 123. The 16S rRNA gene of ESA 123 was amplified by PCR and sequenced by dideoxy Sanger sequencing method. An experiment was performed in greenhouse with three peanut genotypes (BRS Havana, CNPA 76 AM and 2012-4), two Bradyrhizobium strains (SEMIA 6144 and ESA 123), a mineral source of N and an absolute control (without N) under two water regimes (with and without irrigation). Seeds of peanut were sown and the plants were grown until 30 days after emergence. On the 20th day, the water deficit plants group had their irrigation suspended for 10 days. At in silico analyzes, ESA 123 presented 98.97% similarity with the type strain of B. kavangense. Leaf gas exchange was affected by water deficit; as well as alteration of antioxidant activities and reduction of vegetative growth variables. However, some plants inoculated with SEMIA 6144 and ESA 123 strains presented lower reductions and increment of some evaluated variables, mainly the ones inoculated with the ESA 123 strain, Bradyrhizobium sp. from the semi-arid region of Northeast Brazil. This data suggests beneficial effects of the peanut-Bradyrhizobium interaction in a water stress condition, specially with the ESA 123 strain.

Research Article <i>Bradyrhizobium</i> spp. as attenuators of water deficit stress in runner peanut genotypes based on physiological and gene expression responses

“…The ESA 123 strain probably mitigated the effects of water deficit, especially in the IAC Runner 886 and 2012-33 genotypes, since it provided an increase in root dry mass and lower reduction parameters in the plant height and shoot dry mass variables under stress conditions. Similar results (for shoots and roots) were observed to the inoculation of ESA 123 to upright peanut genotypes under drought (Barbosa et al, 2018), highlighting the efficiency of ESA 123 in such divergent peanut genotypes under drought.…”

“…Plant-growth-promoting rhizobacteria, such as rhizobia, can stimulate root growth, which in addition to the Biological Nitrogen Fixation (BNF) by several other mechanisms. The growth promotion of peanut roots by ESA 123 was already observed (Santos et al, 2017), even under water stress (Barbosa et al, 2018), indicating a beneficial feature of this strain, in addition to BNF.…”

“…Plant inoculation with selected rhizobia can allow plants to overcome drought conditions (Dakora, 2003;Barbosa et al, 2018), as observed for the plants inoculated with ESA 123 in our study, since water stress was not a limiting factor for the nodules maintenance in the genotypes inoculated with the ESA 123 strain, and although some treatments did not promote an increase in the number of nodules under conditions of water deficit, red nodules were observed in the roots, indicating full activity of N-fixation (Cardoso et al, 2009). Although it did not increase plant height and shoot dry mass in the inoculated genotypes, there was no significant difference between control and stress, or severe reductions under stress conditions, once again demonstrating the importance of this symbiosis.…”

“…The use of rhizobia, bacteria that induce the development of root and/or stem nodules in legumes, has been an alternative to optimize agricultural production through a reduced need for nitrogen fertilizers. In addition to nitrogen fixation, the rhizobium-legume interaction may contribute to host resistance to abiotic stresses such as drought, as has been demonstrated for tropical legumes such as cowpea (Oliveira et al, 2012) and peanut (Melo et al, 2016;Barbosa et al, 2018).…”

“…The inoculation of Bradyrhizobium sp. ESA 123 in upright peanut genotypes, in addition to inducing higher growth and yield, induces reduction of water deficit damages altering the activities of oxidative stress enzymes and increasing the proline concentration in tissues (Barbosa et al, 2018).…”