Control Effect Of Metconazole On Rice Spikelet Rot Disease And Mycotoxins Contamination And Its Mechanism

Rice spikelet rot disease（RSRD）,caused by the mycotoxigenic fungus Fusarium spp.This is a newly emerging fungal disease that affects rice yield and quality,and its incidence has been increasing in rice production areas in recent years.Currently,there is a lack of research on the pathogenesis and field control techniques of RSRD.In this study,we isolated and identified 14 Fusarium species from rice spikelets,belonging to the Fusarium graminearum species complex（FGSC）,the Fusarium fujikuroi species complex（FFSC）,and the Fusarium incarnatum-equiseti species complex（FIESC）.Among them,58 highly pathogenic strains were selected for testing the inhibitory effects of the triazole fungicide,metconazole,on their growth and mycotoxin production,and the underlying mechanism of action was also investigated.This study found that the seven selected species of Fusarium fungi associated with rice were capable of causing ear rot disease in rice.Mass spectrometry analysis revealed that these Fusarium species primarily produce B-type fumonisins（FBs）,and some emerging Fusarium toxins.Results from sensitivity determination of fungicides showed that metconazole exhibited strong inhibitory activity against mycelial growth of 58 strains of Fusarium fungi associated with rice,with an EC₅₀ range of 0.002～0.048μg/m L.metconazole treatment also significantly inhibited the production,germination,and germ tube elongation of conidia from the seven Fusarium species.At a concentration of five times the EC₅₀,metconazole treatment suppressed conidial production,germination,and germ tube elongation by 17.60%～80.50%,33.00%～90.00%,and 24.31%～80.73%,respectively.The mass spectrometry results showed that the fungicide metconazole significantly inhibited the biosynthesis of several mycotoxins,including FBs,beauvericin（BEA）,15-acetyldeoxynivalenol（15-ADON）,and nivalenol（NIV）,as well as the expression levels of related toxin biosynthesis genes in Fusarium species.Further research revealed that metconazole treatment significantly altered the physiological functions of the cell membranes of seven toxin-producing Fusarium species.The biosynthesis of ergosterol,a major component of the cell membrane,was significantly decreased（with inhibition rates ranging from 35.77%to 92.95%）,while relative conductivity,glycerol content,and peroxidase activity were significantly increased.Greenhouse experiments showed that spraying 20%metconazole suspension during the heading stage had a significant effect on the control of RSRD.The best control effect was achieved in the metconazole preventive and therapeutic treatment group,with a disease control efficacy of 53.61%,followed by the metconazole preventive group,with a disease control efficacy of46.77%,with a toxins control efficacy of 63.68%～77.91%.In summary,this study found that the triazole fungicide metconazole exhibited significant inhibitory effects on the main toxin-producing Fusarium species in Chinese rice,mainly by inhibiting germ tube elongation and mycelial growth,suppressing toxin gene expression,and damaging cell membrane function by disrupting ergosterol synthesis.These results provide a theoretical basis for the efficient prevention and control of RSRD and toxin contamination.