Monitoring and characterization of prochloraz resistance in Fusarium fujikuroi in China

Rice bakanae disease, caused by Fusarium fujikuroi, is a destructive seed-borne disease throughout the world. Prochloraz, a DMI (C-14 alpha-demethylase inhibitor) fungicide, has been registered in China for >20 years. Prochloraz resistance in F. fujikuroi was severe in China with resistance frequencies of 34.56%, 45.33%, and 48.45% from 2019 to 2021. The fitness of prochloraz-resistant population was lower than that of sensitive population, with an average CFI of 2.86 x 10(6) and 4.56 x 10(6), respectively. No cross-resistance was detected between prochloraz and tebuconazole or hexaconazole, and the prochloraz-resistant isolates were still sensitive to fludioxonil, phenamacril, and pydiflumetofen. S312T mutation in Ffcyp51b or overexpression of Ffcyp51a and Ffcyp51b was detected in the highly resistant isolates. AS-PCR primers were designed to detect the prochloraz-resistant isolates with S312T mutation in the field. Resistant isolates carrying S312T mutation were the dominant group in prochloraz-resistant population with frequencies of 43.26%, 23.59%, and 71.20% from 2019 to 2021, which indicated that more attention should be paid to this genotype when monitoring and managing the prochloraz resistance in F. fujikuroi.

Automated summary

Rice bakanae disease caused by Fusarium fujikuroi is a destructive seed-borne disease worldwide. Prochloraz resistance in China is severe, with reduced fitness in resistant populations. There is no cross-resistance between prochloraz and tebuconazole or hexaconazole, and resistant isolates remain sensitive to fludioxonil, phenamacril, and pydiflumetofen. Highly resistant isolates show S312T mutation in Ffcyp51b or overexpression of Ffcyp51a and Ffcyp51b. Attention should be paid to the genotype carrying S312T mutation when monitoring and managing prochloraz resistance in F. fujikuroi.