Resistance monitoring and mechanism of Stagonosporppsis citrulli to thiophanate methyl and boscalid in Zhejiang Province

A total of 112 isolates of Stagonosporppsis citrulli were collected from 5 locations in Zhejiang Province. The resistance to thiophanate-methyl (Ben) and boscalid (Bos) was detected by the method of differentiated doses. The results showed that the respective resistance frequencies were 100% and 28.6% to Ben and Bos, respectively. The high-level resistance (Ben^HR) of thiophanate-methyl reached 100%, and the low-level resistance (Bos^LR) and high-level resistance (Bos^HR) of boscalid were 18.8% and 9.8%, respectively. Further studies on the molecular mechanism of resistance showed that the Ben^HR of S. citrulli was caused by the E198A point mutation in β-tubulin, which was the mutation of 198^th amino acid of from Glu (E) to Ala (A). The mechanism of Bos^HR was the point mutation in 277^th amino acid of Sdh B from His (H) to Tyr (Y), but the mechanism of low-level resistance (Bos^LR) still needs to be studied. To sum up, the resistance of S. citrulli population to benzimidazole fungicides in Zhejiang Province was very serious. Most isolates were sensitive to boscalid, but the high-level resistance has occurred in some regions. Therefore, attention should be paid to the scientific use of SDHIs and resistance monitoring should be strengthened.