Rhizobacteria improve sugarcane growth and photosynthesis under well-watered conditions

Morpho-physiological changes caused by particular plant growth-promoting rhizobacteria were evaluated in sugarcane plants under varying water availability. Under well-watered conditions, we have found one rhizobacteria isolate (IAC-RBcr5) able to enhance root dry matter and photosynthesis of sugarcane plants. The IAC-RBcr5 genome was sequenced and high similarity was found with Pseudomonas putida GB-1. Based on increased root system size of inoculated plants, we hypothesised that sugarcane plants inoculated with IAC-RBcr5 would have improved performance under water deficit. Although IAC-RBcr5 had improved plant leaf CO2 assimilation under water shortage, inoculation caused reduction of biomass accumulation in sugarcane. The negative influence of water deficit on shoot growth rate and root traits such as volume, area, diameter, length and specific root area was higher in plants treated with IAC-RBcr5 as compared to non-inoculated ones. However, rhizobacteria-induced improvements in leaf and root proline contents would represent a strategy for storing carbon and nitrogen during low water availability and helping both organisms to resume their metabolism after rehydration. In conclusion, we found and identified a rhizobacterium able to improve growth and photosynthesis of sugarcane plants. Such benefit for plant growth was lost under low water availability as a likely consequence of increased carbon-energy demand by rhizobacteria and their sensitivity to drought.