Molecular Microbiology Research 2024, Vol.14, No.6, 298-306 http://microbescipublisher.com/index.php/mmr 300 better root development and higher nutrient uptake, contributing to improved plant health and yield. Potassium is a vital nutrient for plant growth, and its availability can be enhanced by potassium-solubilizing bacteria such as Bacillus circulans. These bacteria help in mobilizing potassium from soil minerals, making it accessible to plants. Research indicates that the application of potassium-solubilizing bacteria significantly improves the potassium content in the soil, thereby supporting the growth and development of kiwifruit (Shen et al., 2016; Li et al., 2017). 3.2 Hormone production Beneficial microorganisms also contribute to plant growth by producing phytohormones such as auxins, gibberellins, and cytokinins. These hormones play a pivotal role in regulating various physiological processes, including cell division, elongation, and differentiation. Studies have shown that the presence of plant growth-promoting bacteria in the rhizosphere can lead to increased production of these hormones, thereby enhancing the growth and development of kiwifruit plants (Liu et al., 2020; Wang et al., 2021). For instance, the application of arbuscular mycorrhizal fungi has been found to increase the production of growth hormones, which in turn improves root biomass and overall plant health (Xia et al., 2022; Sharma et al., 2022). 3.3 Soil structure improvement The improvement of soil structure is another critical mechanism through which beneficial microorganisms enhance plant growth. Microbial activity leads to the formation of soil aggregates, which improve soil aeration, water retention, and root penetration. Long-term organic fertilization has been shown to increase microbial diversity and network complexity in the rhizosphere, leading to better soil structure and enhanced plant growth (Ku et al., 2018; Liu et al., 2020). Additionally, the use of microbial fertilizers has been found to improve soil enzyme activities and physicochemical properties, further contributing to the growth and yield of kiwifruit (Fan et al., 2016; Sui et al., 2021). In summary, the application of beneficial microorganisms in kiwifruit cultivation can significantly enhance growth and disease resistance through various mechanisms, including nutrient uptake facilitation, hormone production, and soil structure improvement. These findings underscore the potential of using microbial inoculants as a sustainable practice to improve kiwifruit production (Yang et al., 2022). 4 Enhancing Disease Resistance 4.1 Antagonism against pathogens Beneficial microorganisms can produce a variety of antimicrobial compounds that inhibit the growth of pathogens. For instance, endophytic bacteria from the medicinal plant Leptospermum scopariumhave been shown to produce phenazine, 2,4-DAPG, and hydrogen cyanide, which are effective against Pseudomonas syringae pv. actinidiae (Psa), the causal agent of bacterial canker in kiwifruit (Wicaksono et al., 2018). These compounds disrupt the cellular processes of the pathogens, thereby reducing disease incidence. Hyperparasitism involves beneficial microorganisms directly attacking and parasitizing pathogenic organisms. This mechanism is less commonly reported in kiwifruit cultivation but is a potential area for further research. The presence of beneficial fungi and bacteria that can parasitize harmful pathogens could significantly enhance disease resistance in kiwifruit. Beneficial microorganisms can secrete lytic enzymes such as chitinases and glucanases that degrade the cell walls of pathogenic fungi and bacteria. For example, methyl jasmonate (MeJA) treatment in kiwifruit has been shown to enhance the activities of chitinase and β-1,3-glucanase, which are crucial for breaking down the cell walls of pathogens like Botryosphaeria dothidea (Pan et al., 2020). This enzymatic activity helps in reducing the pathogen load and preventing disease spread. 4.2 Induced systemic resistance Induced systemic resistance (ISR) is a plant defense mechanism activated by beneficial microorganisms. Sulfur application in kiwifruit has been shown to trigger the salicylic acid signaling pathway, leading to the activation of defense genes such as AcPR-1 and AcICS1. This results in increased lignin content and enhanced resistance to
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