Rhizobacteria and silicon mitigate multiple stresses in upland rice

This study selected plant growth-promoting rhizobacteria (PGPR) combined with silicon (Si) able to alleviate biotic and abiotic stresses. The PGPRs were Serratia sp. (BRM 32113, BRM 32114, BRM 63521, BRM 63523, and BRM 63522), Bacillus sp. (BRM 32110 and BRM 32109), Pseudomonas nitroreducens (BRM 32112) and Burkholderia cepacia (BRM 32111). E1 and E2 assays detected indoleacetic acid (IAA) production and ACC deaminase activity. In E3 and E4 assays, PGPRs isolates combined with monosilicic acid (0.5 g L−1) were tested for resistance to osmotic potential induced by PEG-6000 in the concentrations of 79.8 g L−1 (-0.1 MPa); 121.1 g L−1 (-0.2 MPa); 180.2 g L−1 (-0.4 MPa); 264.2 g L−1 (-0.8 MPa); 298.1 g L−1 (-1.0 MPa) and 328.9 g L−1 (-1.2 MPa). In E5, rice seed, treated with BRM 32110, BRM 32111 and BRM 63523 were cultivated in culture medium containing different concentrations of PEG-6000 and Si (0.5 g L−1) in a completely randomized design, with six replications. In E6, BRM 32110, BRM 32111 and BRM 63523 was tested for antagonist efficiency to Magnaporthe oryzae, under osmotic pressure. In E7, rice seeds were sown in plastic trays containing 3 kg of soil fertilized with calcium and magnesium silicate (2 ton ha−1), in a greenhouse. Treatments T1 (control), T2 (Si fertilized soil), T3 (BRM 32111), and T4 (T2 + T3) were submitted to water deficit, followed by challenge spray inoculation with M. oryzae (3 × 105con.mL−1), at 25 days after sowing. The treatments were evaluated for photosynthetic rate (A, μmol CO2 m‒2 s‒1), transpiration rate (E, mmol H2O m‒2 s‒1), stomatal conductance (gs, mol H2O m‒2 s‒1), internal carbon (Ci, μmol mol‒1), and leaf blast severity. BRM 32110, BRM 32111 and BRM 63523 were resistant to osmotic stress (E3 and E4) and were identified as IAA and ACC deaminase producers (E1 and E2). Rice plants treated with BRM 32110, BRM 32111 and BRM 63523 and in the presence of monosilicic acid, showed an increase of 71.34, 110.27 and 126.56% in the total root length and 60.75, 127.60 and 180.82% in the total root surface area, respectively (E5). The rhizobacteria BRM 32110, BRM 32111 and BRM 63523 reduced 78.36, 60.89 and 39.37% of M. oryzae mycelial growth (E6), respectively. In (E7), rice plants treated with BRM 32111 and Si showed higher rates of A, E, gs and Ci with an increase of up to 56.25%, 58.63%, 71.33% and 37.4% under water deficit conditions, in addition to 62.8% of leaf blast suppression. Therefore, we prove that rhizobacteria and silicon, in combination, are efficient to mitigate the water deficit and suppress the severity of leaf blast in the tropical region, thus constituting an alternative to compose sustainable rice management.