Influence of Methylotrophic actinobacteria and bacteria with varying methanol carbon use efficiency on rice growth and development.

The present study utilized methylotrophic actinobacteria and bacteria isolated from rice rhizosphere soil, differentiated based on their methanol carbon use efficiency, as a sustainable strategy to reduce methane gas emissions and improve the growth and yield of Basmati rice (PB1121). Inoculating Basmati rice seeds with both inefficient methanol carbon utilizers (Streptomyces capillispiralis strain KA10, Streptomyces albogriseolus strain D4, Sphingobium sp strain MB6) and efficient utilizers (Streptomyces tritici strain KA11, Streptomyces macrosporeus strain U3 and Rhizobium pusense strain MB4) significantly enhanced the germination percentage, shoot length, root length, and seed vigour index compared to the uninoculated control. Results from pot experiments demonstrated the highest values of leaf chlorophyll a, chlorophyll b, and carotenoids (1.94, 1.35, and 3.81 mg g^-1 of FW) in treatments inoculated with methylotrophs compared to the uninoculated control (0.52, 0.17, and 2.35 mg g^-1 of FW). In addition, leaf phosphorus (P) and potassium (K) contents increased by 45% and 13% over the control, respectively. The methylotroph inoculations also enhanced root architecture and plant yield parameters, including fresh shoot weight, biological yield, number of grains per plant, and harvest index, compared to the control. The significantly highest grain yield was recorded in the Rhizobium pusense strain MB4 inoculated plants with 75% increase as compared to the uninoculated plants. Pearson correlation analysis showed a highly significant positive correlation between grain yield and the number of grains per plant (r = 0.87) as well as shoot length (r = 0.85). The path coefficient analysis at phenotypic level revealed a positive direct effect of grain yield on harvest index, proline content, total chlorophyll, and indirect positive effects on all the studied yield related traits, except for root dry weight, root to shoot ratio and total carotenoids. In conclusion, methylotrophic actinobacteria and bacteria hold great potential as bio-inoculants with a dual role in promoting sustainable rice production and reducing global warming.