Identification of Pathogenic Fusarium spp. Causing Maize Ear Rot and Susceptibility of Some Strains to Fungicides in Jilin Province

The objective of this study is to clarify the population distribution of Fusarium spp. of maize ear rot in Jilin Province and the inhibitory effect of fungicides on the growth of Fusarium mycelium, and to provide a basis for the targeted control of maize ear rot.

149 samples of maize ear rot collected from 36 cities and counties in Jilin Province in 2020 were isolated and identified by tissue isolation and molecular biology methods. The specific toxin synthesis primers of related genes were synthesized using Fusarium graminearum species complex (FGSC) toxin. The toxigenic chemotypes were detected, and the pathogenicity of some FGSC was determined. The inhibitory effect of 7 fungicides on FGSC was determined by the mycelial growth rate method.

A total of 233 Fusarium strains were isolated, belonging to 4 Fusarium complex species, including 9 Fusarium species, which were F. verticillioides, F. boothii, F. graminearum, F. proliferatum, F. asiaticum, F. chlamydosporum, F. fujikuroi, F. equiseti and F. subglutinans. The isolation frequencies were 33.05%, 26.18%, 25.32%, 12.45%, 0.86%, 0.86%, 0.43%, 0.43% and 0.43%, respectively. The isolate frequency of FGSC was the highest, which was 52.36%, and it was the dominant pathogen of maize ear rot in Jilin Province. The proportions of F. boothii, F. graminearum and F. asiaticum in FGSC were 50.00%, 48.36% and 1.46%, respectively. The phylogenetic tree showed that the interspecific and intraspecific genetic diversity of FGSC was rich. The results of pathogenicity assay showed that 52.73% of FGSC were medium pathogenic strains. F. graminearum isolated from the main maize producing areas in the east had the strongest pathogenicity. Toxigenic chemotype detection showed that F. asiaticum produced nivalenol (NIV) chemotype, F. graminearum and F. boothii produced 15-acetyl-deoxynivalenol (15-AcDON) chemotype. The EC₅₀ of the 7 fungicides for inhibiting the growth of FGSC ranged from 0.02 to 19.45 μg·mL^-1. Fludioxonil (FS), imazalil (FS), flusilazole (EC), tebuconazole (TC) and myclobutanil (EW) had good inhibitory effects on FGSC and the difference was not significant. The EC₅₀ of FGSC was less than 1.20 μg·mL^-1 and EC₉₀ was less than 100 μg·mL^-1. The difference of EC₅₀ between F. graminearum and F. boothii was significant under 30% pyraclostrobin treatment. The EC₅₀ of F. graminearum was 10.24 times higher than that of F. boothii.

The dominant pathogenic Fusarium of maize ear rot in different maize producing areas of Jilin Province is different. F. graminearum and F. boothii are dominant species in the east and west, and F. verticillioides is dominant species in the middle. The interspecific and intraspecific genetic diversity of FGSC is rich. Fludioxonil, imazalil, flusilazole, tebuconazole and myclobutanil have better antifungal effect on FGSC. There is no significant difference in the fungicides susceptibility among FGSC.