Identification Of Pathogenic Fusarium Spp. Of Corn Sheath Rot In Sichuan Province

Corn sheath rot caused by Fusarium spp.is a common corn disease in China.The disease occurs in the middle and later growth period of corn,which is mainly harmful to corn sheath.The disease usually lead to the ability reduction of resisting lodging,the increase of corn bald tip and the decline of kenerls per row,which sigenificantly influences production and quality of corn.In view of the serious threat to the corn industry from corn sheath rot in Sichuan Province,and the ambiguity of pathological populations,we studied the population of pathogenic Fusarium and pathogenicity of corn sheath rot on basis of the extensive collection of samples,which may lay a foundation for further study on occurrence regularity and control strategy.From 2015 to 2016,a total of 250 corn sheath rot samples were collected in 7regions.To know the degree of disease occurrence,a random sample survey was conducted covering 80 sampling areas in 5 regions at the same time.The results showed that the disease occurred in all sampling areas with 54% to 76% diseased plants,and the disease index ranged from 8.89 to 31.95.A total of 138 strains of Fusarium were obtained by tissue block and single spore separation,and 8 species were identified by morphological and molecular biological methods: F.verticillioides(45 strains,33%),F.proliferatum(35 strains,26%),F.fujikuroi(23 strains,16%),F.asiaticum(11 strains,8%),F.incarnatum-equiseti species complex(9 strains,7%),F.asiaticum(8 strains,6%),F.graminearum(5 strains,3%),F.oxysporum(2 strains,1%).To complete Koch’s postulates,3 representative strains from all identified Fusarium species(only 2 strains of F.oxysporum)were tested for pathogenicity from2016 to 2017.During the flowering stage,4 varieties of corn were inoculated by injecting spore suspension.Results showed that all the tested strains could cause typical symptoms of corn sheath rot.It was proved that the 8 species of Fusarium were pathogens of corn sheath rot,but their pathogenicity had significant differences.The average disease index of F.proliferatum and F.fujikuroi was 29.70 and 27.56 respectively,which is significantly higher than the others.F.incarnatum-equiseti species complex and F.verticillioides were took second place in pathogenicity,with21.56 and 15.78 respectively.F.meridionale,F.asiaticum,F.graminearum and F.oxysporum had relatively weaker pathogenicity,with 13.63,12.82,11.11 and 10.11,respectively.In summary,a total of 8 species of pathogenic Fusarium which causes corn sheath rot in Sichuan.F.verticillioides was the dominant species and F.proliferatum was the subdominant species.The F.proliferatum and F.fujikuroi had the highest pathogenicity.Among them,F.fujikuroi,F.meridionale and F.asiaticum as pathogens of corn sheath rot had not been reported in China.