| Maize(Zea mays.L.)is an important food and fodder crop,maize ear rot casued by Aspergillus flavus seriously influenced yield of pre-harvest and quality of post-harvest in China.Isolates of A.flavus can produce aflatoxins,with strong carcinogenicity,which seriously threaten health of human and animals.Sichuan Province is one of the important maize producing areas where Aspergillus ear rots occur more and more serious,because of vast territory and climate variability.In this study,we investigated the occurrence of Aspergillus ear rots,the difference of pathogen population structure of A.flavus and mainly influence factors of this disease.Results are shown below:To know the incidence of maize Aspergillus ear rots,a random sample survey was conducted covering 13 regions of 11 cities in Sichuan from 2017 to 2019,and disease incidence ranged from 0.3 % to 5 %.No maize Aspergillus ear rot was observed in high altitude areas over 1000 m obove sea level as Miyi and Xichang.109 samples of maize Aspergillus ear rots were collected and 146 strains were identified as A.flavus with phylogenetic analysis based on RPB2 and Ca M genes,where contained 42 stored strains and104 field strains.To ensure the difference of pathogenicity by infected maize kernels with 146 strains to verified pathogenicity.The results showed that all strains could infect maize kernels with disease index ranged 7.33 to 58.67.The high,middle and slight pathogenicity strains were 1,118 and 27,accounted for 0.69 %,80.82 % and 18.49 %,respectively.In addition,122(83.56 %)strains could produce sclerotia,and 109(72.6%)strains were L-type,13(8.9 %)strains were S-type.83(56.85 %)strains could produce aflatoxin B1(AFB1)which were scattered among 9 survey sites,and all toxigenic A.flavus contained three key genes as afl R,ver-1 and omt-1 at the same time.Correlations showed that pathogenicity of stored strains was significant correlation of AFB1 and low correlation of sclerotia siaze.Field inoculation test showed that A.flavus began to infect maize ear between enlongation stage and flowering stage.The disease incidence and disease index were 25 %,6.94 at flowering stage,respectively.Filling stage was easily infected maize ear with 100% of disease incidence and diseae index reached to 47.47.On the other hand,occurrence rate by insects was was significant correlation of disease incidence of maize Aspergillus ear rots.Field inoculation showed that A.flavus had different infective ability in different maize varieties,and varieties were the major factors of occurrence of maize Aspergillus ear rot.Results showed that Zhongyu 3 was high resistant variety;meanwhile Quanyu 9 and Jinrong1 were middle resistant varieties,with disease index of 8.22,11.66 and 11.11,respectively.In addition,Zhongyu 3 and Quanyu 9 accumulated less AFB1 in filed with 0.35 mg/kg and 0.65mg/kg,respectively.In summary,maize Aspergillus ear rot was occurred lightly in the field,but toxigenic A.flavus isolated had a wide distribution in all sampling sites.Moreover,we find three scleroria types and L-type strains were predominant.And 59.02 % strains could produce AFB1 which could also produce sclerotia.And pathogenicity of stored strains was significant correlation of AFB1.Another,A.flavus began to infect maize ear between enlongation stage and flowering stage,and occurrence rate by insects was was significant correlation of disease incidence of maize Aspergillus ear rots.And varieties were the major factors of occurrence of maize Aspergillus ear rot,diasease-resistant variety showed good resistance to A.flavus and AFB1 accumulation. |
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