Combining plant growth-promoting bacteria as a tool to improve the metabolism and productivity of sugarcane

Sugarcane (Saccharum spp.) is a globally important crop, and strategies to minimize the negative impacts of its cultivation and enhance its development are highly relevant. Plant growth-promoting bacteria (PGPB) can sustainably foster plant growth in agricultural systems and mitigate adverse effects of stress on plants. This is the first study to investigate the combined use of Azospirillum brasilense (Ab) and Nitrospirillum amazonense (Na), two microorganisms widely applied in agricultural systems, aiming to elucidate their effects on the nutritional status, biochemical responses, and productive parameters of sugarcane. Greenhouse experiments were conducted under controlled water and temperature conditions with four treatments: application of Ab, Na, or Ab + Na (Mix) or no PGPB application (control). Sugarcane was cultivated until the middle of the rapid growth stage. To validate the results, the greenhouse trials were replicated under field conditions at two sites (Maracaí-SP and Pradópolis-SP). The results showed that the inoculation of sugarcane with plant growth-promoting bacteria (PGPB), particularly Ab and Mix, enhanced nutritional aspects, especially N content. These increases were significant under greenhouse (p ≤ 0.05) and field conditions (p ≤ 0.10). Additionally, inoculation reduced oxidative stress and improved photosynthetic parameters, such as net photosynthetic rate, water use efficiency, and carboxylation efficiency. These cascading effects contributed to significant gains in crop productivity, with an average increase in stalk yield of 10.9 % for Ab and 12.2 % for Mix across both environments. Similarly, there was an increase in sugar yield per hectare, with gains of 13.3 % for Ab and 13.7 % for Mix compared to the control. These findings highlight the potential of PGPB as a sustainable strategy to enhance crop productivity and resilience, contributing to environmentally balanced agricultural systems. Although the benefits of PGPB were evident, differences between Ab and Mix were not pronounced. Therefore, additional studies are needed to explore the potential of these combinations under adverse conditions, when their effects could be more pronounced.