| Maize plays an extremely important role in the economy and agricultural production.Fusarium graminearum species complex(FGSC)can cause maize cob and stalk rots and produce a variety of fungal toxins and secondary metabolites,resulting in reduced maize yield and quality and posing a serious threat to food safety.In this study,we investigated the population structure and toxin-producing types of FGSC in samples from maize production areas in 16 provinces in China,and studied the effects of environmental conditions on the toxin-producing ability and expression levels of toxin-producing genes of representative strains.The correlation between virulence production and pathogenicity of different strains infesting maize and wheat was analysed,with the aim of improving information on the distribution of FGSC populations in maize,exploring the relationship between virulence production and pathogenicity,and providing basic information for maize disease prevention and control and risk warning for safe maize production.1 Study on population structure and toxin-producing type of Fusarium graminearum species complex in maizeFrom 2019 to 2021,samples were collected from the main maize producing areas in China for three consecutive years.According to morphological and molecular biological methods,205 strains were identified,including F.graminearum,F.boothii,F.asiaticum and F.meridionale,and F.graminearum was the dominant species.In terms of geographical distribution,F.graminearum and F.boothii are mainly distributed in the north,and F.meridionale is mainly distributed in the southwest.The biological characteristics showed that the most suitable temperature for FGSC was 25℃,and the growth rate of F.boothii was the slowest.There was no significant difference in asexual reproduction ability among the four strains.Among the 14 triazole fungicides,prothioconazole 2μg/m L,difenoconazole 2μg/m L and prochloraz 0.2μg/m L had stronger inhibition rate on FGSC strain.Toxigenic genotype and chemotype analysis showed that F.graminearum and F.boothii mainly produced deoxynivalenol(DON)and its derivatives and zearalenone(ZEN).F.meridionale and F.asiaticum mainly produce Nivalenol(NIV)and its derivatives and ZEN,and F.boothii has the strongest ability to synthesize DON and ZEN.F.graminearum and F.asiaticum strains with different toxin-producing genotypes were selected for sequential inoculation of maize ears at silking stage.F.graminearum+5 d F.graminearum sequential inoculation had the most serious pathogenicity and strong virulence.2 Effects of environmental factors on toxin production and toxin-producing gene expression in Fusarium graminearum species complexTwo representative strains of each FGSC species were selected to explore the effects of different conditions(water activity,temperature and culture time)on the toxin production ability and gene expression level of the strains.From the analysis of the experimental results,it can be seen that the optimal conditions for toxin production are different.The optimum conditions for DON,3ADON and 15ADON production were0.98 a_w,30℃ or 0.99 a_w,25℃.The optimal conditions for NIV and 4ANIV production were 0.99 a_w and 30℃.With the prolongation of culture time,the concentrations of DON and NIV gradually increased,while the concentration of its derivatives decreased.The optimum conditions for ZEN production are 0.99 a_w,30℃ or 0.95 a_w,25℃.The optimal condition for the expression of toxin-producing genes is usually 0.95 a_w,and low water activity induces the expression of toxin synthesis genes.Temperature has different gene expression levels for different strains.Single factor and multi-factor analysis showed that environmental conditions had significant effects on toxin synthesis and gene expression in the tested strains.3 Study on the correlation between virulence characteristics and pathogenicity of FGSC infecting cropsDifferent strains infected maize(seedling stage,adult stage and silking stage)and wheat(flowering stage),and analyzed the correlation between pathogenicity,in vitro toxin synthesis ability and in vivo toxin synthesis ability.The infection of maize seeds by representative strains of different species caused dwarfing and root shortening of maize seedlings,but there was no significant difference in pathogenicity between species.The pathogenicity of F.boothii、F.meridionale and F.asiaticum was positively correlated with root toxin content.Fusarium inoculation at the base of maize seedling stem showed typical water-soaked lesions,and the pathogenicity was positively correlated with the content of DON and NIV in vitro.The ability of F.asiaticum to cause typical symptoms of ear rot was significantly lower than that of F.boothii.In Suqian maize grain with high toxin concentration,the pathogenicity was positively correlated with DON and NIV content in ear.F.graminearum and F.asiaticum showed significantly higher disease index than F.boothii,and toxin content was positively correlated with pathogenicity in susceptible varieties. |
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