Abstract
Simple SummaryWith the application of fungicide in agriculture, resistance to fungicide has become a serious problem. It is important to assess the evolution of resistance for development of disease prevention and control. We confirmed, by site-directed mutagenesis, that single mutations conferring moderate or low resistance are more likely to evolve into double mutations conferring higher resistance under the selective pressure of SDHI. However, the double mutations suffer large of fitness penalty than single mutation. We recommend that the use of SDHI in agriculture should be appropriately reduced or that other types of fungicides should be used to control plant diseases, such as dicarboximide fungicides (DCFs), to avoid the emergence of very resistant plant pathogens.With the further application of succinate dehydrogenase inhibitors (SDHI), the resistance caused by double mutations in target gene is gradually becoming a serious problem, leading to a decrease of control efficacy. It is important to assess the sensitivity and fitness of double mutations to SDHI in Corynespora cassiicola and analysis the evolution of double mutations. We confirmed, by site-directed mutagenesis, that all double mutations (B-I280V+D-D95E/D-G109V/D-H105R, B-H278R+D-D95E/D-G109V, B-H278Y+D-D95E/D-G109V) conferred resistance to all SDHI and exhibited the increased resistance to at least one fungicide than single point mutation. Analyses of fitness showed that all double mutations had lower fitness than the wild type; most of double mutations suffered more fitness penalties than the corresponding single mutants. We also further found that double mutations (B-I280V+D-D95E/D-G109V/D-H105R) containing low SDHI-resistant single point mutation (B-I280V) exhibited higher resistance to SDHI and low fitness penalty than double mutations (B-H278Y+D-D95E/D-G109V) containing high SDHI-resistant single mutations (B-H278Y). Therefore, we may infer that a single mutation conferring low resistance is more likely to evolve into a double mutation conferring higher resistance under the selective pressure of SDHI. Taken together, our results provide some important reference for resistance management.
Highlights
Several studies have shown that double mutation in succinate dehydrogenase (SDH) gene further reduces susceptibility to succinate dehydrogenase inhibitors (SDHI) than single point mutation, leading to a reduction of control efficacy of SDHI fungicides [6,20,21]
Site-directed mutagenesis was performed to create double mutations in the SDH gene, and these double mutations were analyzed for their resistance to SDHI and fitness, and to further understand the evolution of resistance
Previous studies have shown that multiplex amino acid substitution in target genes of pathogens such as SDH, CYP51, and β-tubulin genes significantly decreased the sensitivity to corresponding fungicides compared with the single mutation [6,21,22,28]
Summary
Corynespora leaf spot (CLS), caused by Corynespora cassiicola, has become one of the most important plant diseases. The plant pathogenic fungus C. cassiicola can infect more than 530 species of plants, including Hevea brasiliensis, cucumber, tomato, cowpea, and other vegetables, causing substantial economic losses [1,2,3]. Due to the lack of resistant cultivars, chemical fungicides are the main method to control Corynespora leaf spot. The control of Corynespora leaf spot was mainly dependent on benzimidazole fungicides, dicarboximide fungicides, and quinone outside inhibitors [4]. Due to the decline in the efficacy of these fungicides and the emergence of resistance [5,6], these fungicides are gradually being replaced
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