Field Crop 2024, Vol.7, No.3, 171-181 http://cropscipublisher.com/index.php/fc 172 a key focus. Assessing the impact of environmental factors, such as soil type and nitrogen fertilization, on the effectiveness of bacterial inoculation, is also crucial. This study seeks to identify potential benefits and limitations of using diazotrophic bacteria as biofertilizers in sustainable sugarcane cultivation. 2 Overview of Diazotrophic Bacteria Diazotrophic bacteria are a group of microorganisms capable of converting atmospheric nitrogen (N2) into a form that is bioavailable to plants, a process known as biological nitrogen fixation (BNF). This ability is crucial for enhancing plant growth and yield, particularly in crops like sugarcane, which have high nitrogen demands. These bacteria can be found in various environments, including the rhizosphere, root tissues, and even within plant tissues as endophytes. Their role extends beyond nitrogen fixation to include promoting plant growth through the production of phytohormones, enhancing nutrient uptake, and providing resistance against pathogens. 2.1 Types of diazotrophic bacteria Several types of diazotrophic bacteria have been identified as beneficial for sugarcane growth. Notable examples include Pseudomonas spp., Pantoea spp., Enterobacter spp., GluconAcetobacter diazotrophicus, Acetobacter diazotrophicus, Herbaspirillum spp., and Burkholderia spp. Strains such as Pseudomonas koreensis CY4 and Pseudomonas entomophila CN11 have been shown to significantly enhance nitrogen fixation and promote plant growth by increasing the activity of defense-related enzymes and phytohormones in sugarcane varieties GT11 and GXB9 (Singh et al., 2023). Similarly, strains like Pantoea dispersa-AA7 and Enterobacter asburiae-BY4 have demonstrated high nitrogenase activity and the ability to promote plant growth by inducing nitrogen uptake and defense-related gene expression (Figure 1) (Singh et al., 2021). GluconAcetobacter diazotrophicus is an endophytic bacterium well-known for its nitrogen-fixing capabilities and plant growth-promoting traits, including the synthesis of auxins and organic acids (Bertalan et al., 2009). Acetobacter diazotrophicus has been shown to enhance sugarcane growth under nitrogen-deficient conditions by transferring fixed nitrogen to the plant (Sevilla et al., 2001). Herbaspirillumspp. and Burkholderia spp. are also recognized for their role in promoting sugarcane growth and nutrient accumulation (Renan et al., 2016). These bacteria contribute to the overall health and productivity of sugarcane by facilitating nutrient uptake and enhancing plant vigor. 2.2 Nitrogen fixation mechanism The nitrogen fixation mechanism in diazotrophic bacteria involves the enzyme nitrogenase, which catalyzes the conversion of atmospheric nitrogen (N2) into ammonia (NH3). This process is energy-intensive and requires a low-oxygen environment to function effectively. The key steps include nitrogenase activity and gene regulation. The nitrogenase enzyme complex, which includes the nifH gene, is responsible for the reduction of N2 to NH3. This enzyme is highly sensitive to oxygen and requires ATP and reducing power to function (Singh et al., 2021; Singh et al., 2022). The expression of nitrogenase and other related genes is tightly regulated by environmental factors such as oxygen levels and the availability of fixed nitrogen. For instance, the nifH gene is a common marker used to study nitrogen-fixing microbiomes (Singh et al., 2022). Diazotrophic bacteria can form symbiotic relationships with sugarcane, either in the rhizosphere or as endophytes within plant tissues. These symbiotic and endophytic associations facilitate the direct transfer of fixed nitrogen to the plant, enhancing its growth and reducing the need for chemical fertilizers (Kruasuwan and Thamchaipenet, 2016; Antunes et al., 2019). In addition to nitrogen fixation, diazotrophic bacteria produce phytohormones such as indole-3-acetic acid (IAA), gibberellic acid, and abscisic acid, which further promote plant growth and stress tolerance (Bertalan et al., 2009; Singh et al., 2021). In summary, diazotrophic bacteria play a multifaceted role in promoting sugarcane growth and yield through nitrogen fixation, phytohormone production, and enhancing plant defense mechanisms. Their application as biofertilizers offers a sustainable alternative to chemical fertilizers, contributing to improved crop productivity and environmental health. 3 Interaction Between Diazotrophic Bacteria and Sugarcane 3.1 Colonization and symbiosis Diazotrophic bacteria, such as GluconAcetobacter diazotrophicus and Acetobacter diazotrophicus, establish a symbiotic relationship with sugarcane by colonizing its roots and stems. These bacteria are known to persist in
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