Resistance mechanism of Phytophthora nicotianae to dimethomorph
Tobacco black shank is an important oomycete disease that can cause serious tobacco yield loss in China. As a new fungicide, dimethomorph, has been used more and more widely to replace metalaxyl to control tobacco black shank. As the emergence of fungicide resistance will reduce the control effect and duration of the fungicide, it is of great importance to study the resistance mechanism of Phytophthora nicotianae to dimethomorph. In this study, four stable high resistant mutants with a resistance level 250 times greater, were obtained in the laboratory using a dimethomorph-amended media method. No significant difference was observed between the resistant mutants and the sensitive isolates, which indicates that the resistance risk of P. nicotianae to dimethomorph is moderate. The comparison of cellulose synthase gene sequences between resistant mutants and sensitive strains suggested that two different base mutations in the CesA3 gene resulted in Type I high resistant mutant G3325C (V1109L) and Type II high resistant mutant G3231T (Q1077H), respectively. Thus, we speculated that the point mutants of V1109L and Q1077H on CesA3 were responsible for the molecular resistance of P. nicotianae to dimethomorph. Two AS-PCR methods corresponding to the above point mutations were also established to detect the high resistant mutants. This study will guide the scientific use of dimethomorph and provide a reference for dimethomorph-resistance management strategies.