连作压砂地生防哈茨木霉对西瓜根分泌物的响应机制

Watermelon Fusarium wilt, which is an important soil-borne disease, aggravating the harm to the watermelon in gravel-sand mulched fields. The biocontrol effect of Trichoderma species is not stable on controlling watermelon Fusarium wilt. It is mainly related to accumulation of watermelon root exudates in the soil that caused by continuous cropping. The research object, Trichoderma harzianum M3 is used as biocontrol agent for watermelon Fusarium wilt, the agent comes from the local soil. Based on control experiments and soil experiments, we will research the biological characters, colonization dynamics of rhizosphere, antifungal activity and biocontrol efficacy of strain M3. The high-throughput sequencing and transcriptome analysis would be applied in this study, in order to analyze the differential expression of cell wall degrading enzymes represented by chitinase and glucanase. Variation characteristics, which invole the antibacterial mechanism and the antifungal efficacy of strain M3, will be studied at the molecular level. The function and the action mechanism of watermelon root exudates will be revealed in the antagonism of Trichoderma harzianum to watermelon Fusarium wilt pathogen. The study will further clarify the response mechanism of biocontrol fungi Trichoderma harzianum to watermelon root exudates in continuous cropping soil from gravel-sand mulched field. The result of the research will serve as a theoretical basis of using biocontrol fungi effectively and alleviating the continuous cropping obstacles of gravel-sand mulched field.

西瓜枯萎病作为重要的土传病害对西北地区压砂地西瓜生产的危害逐年加重，生防木霉的生物防控效果却不稳定，主要与西瓜连作导致根分泌物在土壤中累积有关。本项目在前期研究基础上，以西瓜枯萎病病原菌的土著生防真菌——哈茨木霉（Trichoderma harzianum）M3菌株为研究对象，采用控制试验和土培试验，开展西瓜根分泌物影响下哈茨木霉M3菌株的生物学性状、根际定殖动态、抑菌活性和生防效果研究，同时利用高通量测序技术和转录组分析，解析以几丁质酶和葡聚糖酶为代表的细胞壁降解酶的差异表达，从分子水平探明哈茨木霉M3菌株的抑菌机制和抑菌作用的变化特征，以期揭示西瓜根分泌物在生防哈茨木霉拮抗西瓜枯萎病病原菌机制中的功能与作用机理，进而阐明连作压砂地中生防哈茨木霉对根分泌物的响应机制，为有效利用生防菌，缓解压砂地连作障碍提供理论依据。

西瓜枯萎病对压砂西瓜的危害逐年加重，生防木霉的防效却不稳定，主要与西瓜连作导致根分泌物的土壤累积有关。以尖镰孢菌西瓜专化型（Fusarium oxysporum f. sp. niveum, FON）的土著生防真菌——哈茨木霉（Trichoderma harzianum）M3为研究对象，采用控制试验和土培试验，利用LC-MS、GFP、qPCR和CLSM技术，进行西瓜根分泌物和连作压砂田土壤中的酚酸鉴定，开展根分泌物影响下M3的生物学性状、根际定殖动态、抑菌活性和生防效果研究，利用高通量测序和转录组分析，解析2种细胞壁降解酶几丁质酶和葡聚糖酶的差异表达，探究M3的抑菌机制和抑菌作用的变化特征。.研究结果表明，根分泌物中的10种主要酚酸随耕作年限增加形成土壤积累。M3对FON的生防机制涉及竞争、寄生、分泌抑菌物质。根分泌物能抑制M3菌落生长，促进FON生长，对2菌株的生物量积累、产孢量及孢子萌发为低浓度促进，高浓度抑制。M3的生物量积累较FON更易受根分泌物负面影响。2菌株都能快速定殖于瓜苗根内。初期，FON较M3定殖速度更快，定殖量更大。M3定殖量随时间增加而增加，FON相反。10种酚酸和FON对M3定殖均有抑制作用，且二者有协同作用。.M3分泌的抑菌蛋白较其他抑菌物质发挥更强的抑菌作用。营养充足时，根分泌物抑制M3分泌抑菌蛋白，包括几丁质酶和葡聚糖酶。土培试验中，酚酸和酚酸+FON均显著降低M3的防效。酚酸影响下的M3转录组分析结果表明，哈茨木霉主要依靠甘氨酸、丝氨酸和苏氨酸代谢途径降解酚酸；不同酚酸对不同代谢途径有抑制作用；对羟基苯甲酸和对香豆酸能降低M3菌株的能量代谢水平，可能是导致M3菌株根际定殖量下降的主要原因。.总之，根分泌物积累主要影响哈茨木霉的菌丝生长、生物量积累、根际定殖和抑菌蛋白分泌，同时促进FON生长；根分泌物中的对羟基苯甲酸和对香豆酸通过降低哈茨木霉的能量代谢水平抑制其根际定殖，从而导致其防效下降。以上研究揭示了连作压砂瓜田土壤中哈茨木霉生防效果降低的主要原因，为有效制定生防哈茨木霉施用策略提供参考依据。

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