Field Crop 2024, Vol.7, No.3, 171-181 http://cropscipublisher.com/index.php/fc 174 to the nitrogen requirements of sugarcane, with some varieties obtaining up to 70% of their nitrogen from this process (Oliveira et al., 2006). Studies have shown that inoculation with diazotrophic bacteria can lead to increased nitrogen content in sugarcane plants, especially under nitrogen-deficient conditions (Sevilla et al., 2001; Renan et al., 2016). The efficiency of nitrogen fixation can vary depending on the bacterial strain, plant genotype, and environmental conditions (Oliveira et al., 2006; Antunes et al., 2019). For instance, G. diazotrophicus has been shown to actively fix nitrogen within sugarcane plants, enhancing their growth and nitrogen content (Sevilla et al., 2001; Bertalan et al., 2009). 3.3 Other plant growth-promoting activities In addition to nitrogen fixation, diazotrophic bacteria promote sugarcane growth through various other mechanisms. These include the production of phytohormones such as indole-3-acetic acid (IAA), which stimulates root growth and development, and the solubilization of phosphate and zinc, making these nutrients more available to the plant (Saravanan et al., 2007; Bertalan et al., 2009; Kruasuwan and Thamchaipenet, 2016). Furthermore, these bacteria can enhance the plant's resistance to pathogens and abiotic stresses, such as drought. For example, G. diazotrophicus has been shown to confer drought tolerance to sugarcane by modulating hormone pathways and activating stress-responsive genes (Vargas et al., 2014). Co-inoculation with diazotrophs and actinomycetes has also been found to significantly enhance sugarcane growth compared to individual inoculations, indicating the potential for synergistic effects among different plant growth-promoting bacteria (Kruasuwan and Thamchaipenet, 2016). In summary, diazotrophic bacteria play a crucial role in promoting sugarcane growth and yield through their ability to fix atmospheric nitrogen, produce growth-promoting substances, and enhance the plant's resistance to various stresses. The interaction between these bacteria and sugarcane is complex and influenced by multiple factors, including bacterial strain, plant genotype, and environmental conditions. 4 Impact on Sugarcane Growth Diazotrophic bacteria, known for their ability to fix atmospheric nitrogen, play a significant role in enhancing the growth and yield of sugarcane. These bacteria not only provide essential nutrients but also improve various physiological and morphological aspects of the plant. 4.1 Enhanced nutrient uptake Inoculation with diazotrophic bacteria has been shown to significantly enhance the uptake of essential nutrients such as nitrogen (N), phosphorus (P), and potassium (K) in sugarcane. For instance, a study demonstrated that the accumulation rates of N, P, and K were highest around 180 days after planting (DAP) for N and P, and around 160 DAP for K, in treatments involving bacterial inoculation, compared to the control (Renan et al., 2016). This enhanced nutrient uptake is crucial for the overall growth and development of the plant, leading to improved biomass and crop growth rates. 4.2 Improved root development The application of diazotrophic bacteria also positively impacts root development in sugarcane. Research has shown that inoculation with a mixture of diazotrophic strains can lead to a significant increase in root dry mass, root initiation, volume, and area, especially of the fine roots (Santos et al., 2019). This improved root architecture enhances the plant's ability to absorb water and nutrients from the soil, thereby supporting better growth and resilience against environmental stresses. 4.3 Increased biomass and plant vigor The overall biomass and vigor of sugarcane plants are markedly improved with the inoculation of diazotrophic bacteria. Studies have reported that inoculated plants exhibit higher total dry matter accumulation and stem yield compared to non-inoculated controls. For example, inoculation with a consortium of five diazotrophic bacterial strains resulted in significant increases in stem yield and total dry matter in different sugarcane varieties (Schultz et al., 2017). Additionally, the presence of these beneficial bacteria can enhance the plant's tolerance to abiotic stresses, such as drought, further contributing to increased biomass and plant vigor (Figure 2) (Vargas et al., 2014). In conclusion, the role of diazotrophic bacteria in promoting sugarcane growth and yield is multifaceted,
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