| Orobanche cumana Wallr.is a holoparasitic parasitic weed that relies on nutrients,waters and minerals from its host to satisfy its own growth and development.Inner Mongolia is the main area for sunflower cultivation in China.Affected by the serious parasitism of O.cumana,the yield and quality of sunflower have reduced,the farmers’ income have shrunk,which inhibited the agricultural development.The germination and parasitism of O.cumana seeds occur underground,and existing measures are difficult to solve the problem of O.cumana parasitism during this period.The mechanism of rhizosphere bacteria regulated of O.cumana parasitism on sunflower is not clearly understood.Therefore,in this study,sunflower rhizosphere microorganisms were used as the research object.Differences in the composition of sunflower rhizosphere microbial communities with different levels parasitism of O.cumana in farmlands with serious O.cumana disease incidence in Inner Mongolia.In combination with metagenomic sequencing and metabolomic analysis,we studied the mechanism of metabolite regulation of O.cumana germination by relying on molecular docking technology.Streptomyces rochei D74 was added to the co-culture experiment to clarify the response of sunflower to the biocontrol bacteria S.rochei D74 and its mechanism of resistance to O.cumana parasitism.The role of S.rochei D74 in reducing O.cumana parasitism and promoting sunflower yield and quality was verified by planting experments.The results were as follows:(1)The composition of sunflower rhizosphere microbial community is closely related to that of O.cumana parasitism.The analysis of healthy and parasitized microbial communities in different agricultural fields revealed that observed OTUs index were reduced in the parasitism soils.The abundance of Verrucomicrobia,Actinobacteriah and Gemmatimonadetes was significantly higher in the parasitism soils than in the healthy soil.The abundance of Xanthomonadaceae was positively correlated with the number of O.cumana,and Microscillaceae was negatively correlated the number of O.cumana.Co-occurrence network analysis showed that healthy soils have higher density and modularity of microbial networks and have more complex and stable microbial communities.By metagenomic sequencing,microorganisms affecting the KO pathway and EC differential expression were distributed in Lysobacter,Pseudomonas and Variovorax.Meanwhile,the number of culturable bacteria,actinobacteria and fungi were significantly increased in the soils of O.cumana parasitism.(2)Metabolites of sunflower rhizosphere bacteria HX79 can promote "suicidal" germination of O.cumana.282 strains of bacteria were isolated from sunflower rhizosphere soil by cultivable method.Combined with the results of high-throughput sequencing,five potential bacterial strains associated with O.cumana parasitism were obtained,and germination experiments showed that Lysobacter antibioticus HX79 promoted O.cumana germination and parasitism.Whole-genome sequencing analysis showed that L.antibioticus HX79 contains a large number of NRPS gene clusters for the synthesis of secondary metabolites.The secondary metabolites of L.antibioticus HX79 were analyzed using the metabolomics and tested for nucleophilic reactions with the KAI2d2 protein of O.cumana in combination with molecular docking models.Three compounds,Cyclo(Pro-Val),2’-deoxyinosine and 2-hydroxyadenosine,were identified to promote O.cumana germination,among which Cyclo(Pro-Val)had the highest O.cumana germination rate(40.26%)at 10 μM.Pot experiments have shown that L.antibioticus HX79 can be used as a suicide germination inducing substance for O.cumana,reducing the number of O.cumana seed banks in the soil and reducing parasitism on sunflower.(3)Streptomyces rochei D74 suppresses O.cumana parasitism through multiple methods.Sunflower – O.cumana – S.rochei D74 co-culture trials demonstrated that S.rochei D74 significantly inhibited O.cumana parasitism in sunflower roots.In pot experiments,it is shown that S.rochei D74 significantly reduced the number of emergence(13.04%–29.86%)and parasitism(24.58%–30.81%)of O.cumana,and increased sunflower plant height and dry matter accumulation.Thereby,inhibiting O.cumana parasitism.For example,S.rochei D74 colonized sunflower root surface,increased host jasmonic and salicylic acid hormone synthesis(31.29%–243.86%),inhibited the synthesis of 5-deoxymonoginol compounds(37.56%),enhanced plant stress-related enzyme activities(11.78%–40.00%),and increasing the expression of SAR-and ISR-related genes and Ha Or7 gene(1.66 times–7.91 times).S.rochei D74 enhanced sunflower systemic resistance through multiple aspects.(4)The S.rochei D74 agent has a good application effect in the field.Farmland experiments showed that S.rochei D74 significantly reduced the number of O.cumana parasitism(27.76%–45.66%),increased sunflower root,stem(36.99%–40.44%),and disk biomass(21.26%–36.59%),increased the percentage of large grains(64.64%–66.80%),100-grain weight(7.48%–17.75%)and protein content(4.91%–9.28%)in the seeds,and improved sunflower yield(28.94%–38.26%),confirming the effect of S.rochei D74 on suppressing O.cumana parasitism and improving sunflower yield and quality.In summary,this study elucidated the differences in the microbial communities of sunflower roots at different levels of O.cumana parasitism,and obtained L.antibioticus HX79 strain that promotes O.cumana parasitism.We confirmed the effect of S.rochei D74 on suppressing O.cumana parasitism and improving sunflower yield and quality.The mechanism by which S.rochei D74 suppresses O.cumana parasitism and promotes sunflower growth by enhancing the synthesis of resistance genes and phytohormones in the sunflower system was elucidated.This study demonstrates that microorganisms can regulate O.cumana parasitism,and provides a strain resource for O.cumana biocontrol. |
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