Molecular Pathogens, 2025, Vol.16, No.3, 100-110 http://microbescipublisher.com/index.php/mp 103 the pH value and carbon source structure of the rhizosphere, thereby affecting the construction of microbial communities. Studies have shown that rotating sorghum for one year can change the abundance of pathogenic Ralstonia solanacearum in the rhizosphere after continuous cropping of legumes or potatoes, and significantly promote the recovery of beneficial actinomycete communities in the soil. 3.2 Enhancement and antagonistic mechanism of beneficial bacteria 3.2.1 Antagonistic relationship between actinomycetes and rhizosphere Actinomycetes, especially Streptomyces, are important microorganisms with broad-spectrum antagonism in the soil, and their metabolites can inhibit a variety of pathogenic fungi and bacteria. The rotation system helps to increase the abundance and diversity of actinomycetes in the soil and break the pathogen dominance pattern (Torres-Rodríguez et al., 2022). In a sorghum-leguminous rotation system, researchers observed that Streptomyces griseus and S. lydicus were enriched in the rhizosphere of sorghum and showed strong antibacterial effects on Fusarium oxysporum and Rhizoctonia solani (Carrión et al., 2019). Actinomycetes are a systemic process by which they produce antagonistic effects on plant pathogenic fungi through five main mechanisms. First, actinomycetes can inhibit the colonization of pathogens by competing for rhizosphere space and nutrients. Second, they can synthesize a variety of secondary metabolites with antibacterial activity (such as Streptomycin, Actinomycin D, etc.), directly interfering with the metabolism and cell structure of pathogens. Third, actinomycetes can release volatile organic compounds (VOCs), exert long-range antibacterial effects and induce plant defense mechanisms. Fourth, by secreting lytic enzymes such as chitinase and β-1,3-glucanase, actinomycetes can directly destroy pathogen cell walls. Fifth, they can also induce plants to produce systemic acquired resistance (ISR), stimulate the expression of defense-related enzymes, and thus improve the overall disease resistance of crops (Figure 2) (Carrión et al., 2019 ;Torres-Rodríguez et al., 2022). Figure 2 Main actinomycete antagonistic mechanisms to phytopathogenic fungi (Adopted from Torres-Rodríguez et al., 2022) In addition, the community dynamics of actinomycetes are highly sensitive to soil physical and chemical properties. The rotation system provides a suitable ecological niche for actinomycetes by regulating pH, organic matter content and redox conditions. It is reported that the actinomycete population in the soil of continuous peanut cropping degraded, but after a season of sorghum rotation, its number and activity recovered significantly, and formed a relatively stable "pathogen resistance barrier" (Zhou et al., 2023).
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