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.