Molecular Soil Biology 2024, Vol.15, No.1, 8-16 http://bioscipublisher.com/index.php/msb 12 In summary, genomic and proteomic studies have provided valuable insights into the molecular mechanisms underlying PGPR-plant interactions. The identification of key genes and proteins involved in these interactions paves the way for the development of more effective PGPR-based biofertilizers and biocontrol agents, contributing to sustainable agricultural practices. 4 Applications and Future Directions 4.1 Agricultural practices The integration of Plant Growth-Promoting Rhizobacteria (PGPR) into crop management practices has shown significant promise in enhancing crop productivity and sustainability. PGPR can be applied through various methods such as seed inoculation, soil application, and fertigation. These methods have been demonstrated to improve nutrient availability, enhance root growth, and increase crop yields (Lopes et al., 2021; Mohanty et al., 2021; Stoll et al., 2021). For instance, the use of Bacillus velezensis strain BBC047 in nurseries and post-transplantation stages has significantly improved the growth and productivity of horticultural crops like basil, cabbage, tomato, and bell pepper (Stoll et al., 2021). Additionally, the combination of biochar with PGPR inoculants has been shown to enhance soil fertility and crop yield, particularly in acidic sandy soils (Kari et al., 2021). The formulation and application methods for PGPR inoculants are critical for their effectiveness. Successful PGPR formulations should possess high rhizosphere competence, extensive competitive saprophytic ability, and ease of mass production (Mohanty et al., 2021). Seed coating, soil application, and root inoculation are common methods used to apply PGPR. However, challenges such as inconsistent results due to varying soil conditions and environmental factors need to be addressed (Lopes et al., 2021). Innovative approaches like immobilizing PGPR on biochar surfaces have shown promise in enhancing the effectiveness of PGPR inoculants (Kari et al., 2021). Moreover, the timing of PGPR application is crucial, with early-stage applications in nurseries being more effective than late-stage applications (Stoll et al., 2021). 4.2 Biotechnological advances Genetic engineering of PGPR offers the potential to enhance their efficacy in promoting plant growth and stress tolerance. Advances in molecular biology and genetic engineering have enabled the development of PGPR strains with improved traits such as enhanced nutrient solubilization, hormone production, and stress tolerance (Oleńska et al., 2020; Mellidou and Karamanoli, 2022). For example, genetically engineered PGPR strains can produce higher levels of phytohormones like indole acetic acid (IAA) and ethylene, which are crucial for plant growth and stress response (Oleńska et al., 2020; Mohanty et al., 2021). Additionally, the identification and manipulation of genes associated with induced systemic resistance (ISR) can further enhance the biocontrol capabilities of PGPR (Meena et al., 2020). The development of synthetic microbial consortia involves combining multiple PGPR strains to create a synergistic effect that enhances plant growth and health. These consortia can be tailored to specific crops and environmental conditions, providing a more robust and effective solution compared to single-strain inoculants (Li et al., 2020). For instance, a consortium of Providencia rettgeri, Advenella incenata, Acinetobacter calcoaceticus, and Serratia plymuthica has been shown to improve the growth and soil properties of various crops (Li et al., 2020). The use of synthetic microbial consortia can also help in overcoming the limitations of individual PGPR strains by providing a broader spectrum of beneficial traits (Li et al., 2020; Kong and Liu, 2022). 4.3 Challenges and future research Despite the promising potential of PGPR, several challenges hinder their widespread application. Inconsistent results due to varying soil conditions, environmental factors, and the complex interactions within the rhizosphere are major obstacles (Lopes et al., 2021). Additionally, the survival and persistence of PGPR in the soil environment are critical factors that influence their effectiveness (Kong and Liu, 2022). Technical issues related to the formulation and application methods, such as seed coating, also need to be addressed to ensure the successful integration of PGPR into conventional agricultural practices (Stoll et al., 2021).
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