Research Advances on Mechanisms and Preventions of Soil-borne Diseases Exacerbated by Root Exudates in Continuous Cropping Systems
The rhizosphere microbial communities play a crucial role in assisting plants in dealing with soil-borne pathogens.When plants encounter specific soil pathogen invasions,they adapt the composition and quantity of root exudates to recruit beneficial microorganisms that can utilize these substances to resist soil pathogen infections.However,recent studies have revealed that certain root exudates can promote the occurrence of soil-borne diseases.This paper aims to provide a comprehensive review and summary of existing evidence regarding the role of root exudates in continuous cropping systems,which contribute to the occurrence and outbreaks of soil-borne diseases.The paper begins by presenting observations of soil-borne diseases exacerbated by continuous cropping and the accumulation of key root exudates.Subsequently,it summarizes the potential mechanisms through which some root exudates in continuous cropping promote the invasion of soil-borne pathogens.Considering the process of soil-borne pathogens causing plant diseases in continuous cropping involves introduction(soil to the rhizosphere),colonization(rhizosphere to root surface),and infection(root surface to root interior),the substances exacerbating soil-borne pathogen invasion in each stage are categorized into the following three groups based on their functions:1)substances that facilitate the migration,proliferation,and pathogenicity of soil-borne pathogens from soil to the rhizosphere("enriching pathogens");2)substances that disrupt the defense line of beneficial microbial communities in the rhizosphere("suppressing beneficial microbes");and 3)substances that hinder the root immune system("self-toxic").Subsequently,the paper explores the mechanisms of diversified cropping systems such as rotation,grafting,row intercropping,relay intercropping,and companion planting in alleviating soil-borne diseases from the perspective of root exudates.These mechanisms include:1)enhancing the diversity of root exudates;2)reducing the secretion of self-toxic substances by main crops;3)secreting root exudates that suppress pathogens;4)promoting the formation of a protective rhizosphere microbial community to enhance plant disease resistance and 5)regulating the synthesis pathways of metabolites to reduce the production of self-toxic substances.Finally,the paper outlines several green,efficient,safe,and comprehensive control strategies for soil-borne diseases.These strategies include:1)identification of"enriching pathogens","suppressing beneficial microbes"and"self-toxic"root exudates;2)application of diversified planting,rootstock grafting,biochar,and organic fertilizer to regulate root exudates,improve soil microbial community structure,enhance plant growth,and reduce diseases;and 3)establishment of biodegradation technologies for identifying,isolating,and culturing bacterial and fungal strains capable of decomposing the"enriching pathogens","suppressing beneficial microbes"and"self-toxic"plant root exudates.
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