Plant Growth-Promoting Bacillus sp. Cahoots Moisture Stress Alleviation in Rice Genotypes by Triggering Antioxidant Defense System.

Drought is considered one of the major obstacles for agricultural productivity worldwide such that greater efforts are required to boost crop production under this stress. One of the methods to overcome this obstacle is to harness the potential of microbe-induced systemic tolerance against moisture stress. The present work evaluated the potential role of two bacterial strains, namely Bacillus altitudinis FD48 and Bacillus methylotrophicus RABA6 and their combination as a co-inoculant for promoting plant growth and moisture stress resilience in two contrast cultivars of Oryza sativa L: CO51 (moderately drought tolerant) and IR64 (drought susceptible) under conditions of terminal moisture stress. B. altitudinis FD48- and B. methylotrophicus-primed rice seeds (CO51 and IR64) significantly influenced the source-sink relationship and reduced the relative water content (RWC). While photosynthetic pigments and proline showed a steady increase owing to the co-inoculant priming, the activity of reactive oxygen species (ROS)-quenching enzymes, such as catalase, superoxide dismutase, ascorbate peroxidase, and peroxidase constitutively increased in plants treated with co-inoculant besides,reducing the trend during the recovery phase. The productive tillers and grain weight were further augmented by the co-inoculant under induced moisture stress. Moreover, the results revealed a 14% and 19% increase in the harvest index (HI) in CO51 and IR64, respectively, attenuated with Bacillus sp. as a co-inoculant. The key mechanism in augmenting energy metabolism by B. altitudinis FD48 and B. methylotrophicus RABA6 could be attributed to the regulation of ROS-quenching enzymes that aid in moisture stress resilience. The results of the present study conclude that these strains may be used as a novel bioinoculant for enhancing the drought tolerance in rice grown under moisture stress regimes.

Antagonistic and plant-growth promoting novel Bacillus species from long-term organic farming soils from Sikkim, India.

Three bacteria namely Bacillus luciferensis K2, Bacillus amyloliquefaciens K12 and Bacillus subtilis BioCWB possessing plant growth promotion and biocontrol potential against phytopathogens and rice leaf folder were identified from organic soils of Sikkim, India. The results revealed significant higher production of phytohormones IAA (97.1 µg mL-1) and GA3 (10.6 µg mL-1) was found in K2, whereas BioCWB had higher phosphate solubilization (570.0 µg mL-1) efficacy and also possessed nitrogen fixation ability (5.34 log copy number mL-1 culture). All these bacteria had higher antagonistic activities against phytopathogens viz. Rhizoctonia solani, Fusarium proliferatum, Athelia rolfsii and Colletotrichum gloeosporioides and also had higher larvicidal activity against rice leaf folder Cnaphalocrocis medinalis (Guenne) under in vitro conditions. Molecular insights into the antagonistic mechanisms of Bacillus strains deciphered the presence of several antimicrobial peptides (ericin, subtilin, surfactin, iturin, bacilysin, subtilosin, fengycin and bacillomycin), volatiles (dimethyl disulphide, methyl-Furan, acetic acid, Z-1,3-pentadiene and 3-hexyn-2-ol) and soluble metabolites (9-octadecenamide, E-15-heptadecenal, E-3-eicosene and 5-octadecene). Furthermore, liquid microbial inoculum prepared using the bacterial strains (K2, K12 and BioCWB) were evaluated under glass house (rice) and field condition (capsicum), which significantly enhanced plant growth in rice and yield in capsicum compared to control. The present study revealed the combination of Bacillus spp. (K2, K12 and BioCWB) can be used as bio-inoculants for improving agricultural production in Sikkim. Moreover, for the first time, we demonstrated plant growth promoting (PGP) traits, antifungal and insecticidal properties of B. luciferensis.