Rhizospheric Soil from Rice Paddy Presents Isolable Bacteria Able to Induce Cold Tolerance in Rice Plants

Rice is the basic food for over half the global population. Paddy cultivation is limited by environmental stressors, which tend to worsen with climate change. In addition, an increase in food demand is expected soon. Therefore, innovative agricultural technologies capable of increasing food production without increasing agricultural frontiers are needed. Some microorganisms can confer plant tolerance to environmental stresses; however, research with rhizospheric bacteria inducing cold tolerance in rice plants is scarce. In this work, we evaluated the prokaryotic community of cold-impacted rice paddies and the ability of selected rhizospheric bacteria towards increasing rice tolerance to cold temperatures without resulting in yield penalties. The most abundantly identified phyla (Proteobacteria, Acidobacteria, and Actinobacteria) are common soil bacteria, which harbor most plant growth-promoting bacteria (PGPB) and should be responsible for plant protection from abiotic stresses, such as low temperature. From these soils, nine PGPB were selected and inoculated in cold-stressed rice plants, and two (Kosakonia sp. CIR2 and Staphylococcus sp. CSR1T2) were able to confer cold tolerance to rice plants. These cold-stressed plants inoculated with CIR2 and CSR1T2 presented higher survival rates (69% and 85%, respectively) than non-inoculated plants (33%). In the greenhouse, cold-stressed inoculated plants reached the reproductive cycle approximately 25 days earlier than non-inoculated plants, besides presenting increased fertility (percentage of full seeds/full seeds per plant) and improvement in yield parameters (weight of 1,000 full seeds, grain length, seed weight per plant, and seed yield). These data can contribute to the improvement of inoculation practices in rice plants and to the maintenance of rice production in environments impacted by low-temperature stress in early developmental stages.