Table_1_Fluopyram Sensitivity and Functional Characterization of SdhB in the Fusarium solani Species Complex Causing Soybean Sudden Death Syndrome.pdf

The succinate dehydrogenase inhibitor (SDHI) fungicide, fluopyram, is used as a soybean seed treatment to manage Fusarium virguliforme, the casual agent of sudden death syndrome (SDS). More recently, other species within clade 2 of the Fusarium solani species, F. tucumaniae in South America and F. brasiliense in America and Africa, have been recognized as additional agents capable of causing SDS. To determine if fluopyram could be used for management of SDS caused by these species, in vitro sensitivity tests of the three Fusarium species to fluopyram were conducted. The mean EC50 values of F. brasiliense and F. virguliforme strains to fluopyram were 1.96 and 2.21 μg ml-1, respectively, but interestingly F. tucumaniae strains were highly sensitive (mean EC50 = 0.25 μg ml-1) to fluopyram compared to strains of the other two species. A sequence analysis of Sdh genes of Fusarium strains revealed that the F. tucumaniae strains contain an arginine at codon 277 in the SdhB gene instead of a glycine as in other Fusarium species. Replacement of glycine to arginine in SdhB-277 in a F. virguliforme wild-type strain Mont-1 through genetic transformation resulted in increased sensitivity to two SDHI fungicides, fluopyram and boscalid. Similar to a F. tucumaniae strain, the Mont-1 (SdhBG277R) mutant caused less SDS and root rot disease than Mont-1 on soybean seedlings with the fluopyram seed treatment. Our study suggests the amino acid difference in the SdhB in F. tucumaniae results in fluopyram being efficacious if used as a seed treatment for management of F. tucumaniae, which is the most abundant SDS causing species in South America. The establishment of baseline sensitivity of Fusarium species to fluopyram will contribute to effective strategies for managing Fusarium diseases in soybean and other pathosystems such as dry bean.

琥珀酸脱氢酶抑制剂（succinate dehydrogenase inhibitor, SDHI）类杀菌剂氟吡菌酰胺（fluopyram）常被用作大豆种子处理剂，用于防控弗氏镰孢（Fusarium virguliforme）——大豆猝死综合症（sudden death syndrome, SDS）的病原菌。
近期研究发现，茄镰孢复合种（Fusarium solani species complex, FSSC）进化枝2中的其他菌种亦可引发大豆猝死综合症，其中南美洲分布的为图科曼尼镰孢（F. tucumaniae），美洲与非洲分布的为巴西镰孢（F. brasiliense）。
为明确氟吡菌酰胺是否可用于防控上述菌种引发的大豆猝死综合症，本研究针对这3种镰孢开展了氟吡菌酰胺的体外敏感性试验。结果显示，巴西镰孢与弗氏镰孢菌株对氟吡菌酰胺的平均半最大效应浓度（EC50）分别为1.96与2.21 微克/毫升；有趣的是，与另外两种镰孢菌株相比，图科曼尼镰孢菌株对氟吡菌酰胺的敏感性显著更高，其平均EC50仅为0.25 微克/毫升。
对镰孢菌株的琥珀酸脱氢酶基因（Sdh gene）进行序列分析后发现，图科曼尼镰孢菌株的琥珀酸脱氢酶亚基B（SdhB）基因第277位密码子编码的氨基酸为精氨酸，而其余镰孢物种该位点均为甘氨酸。通过遗传转化技术，将弗氏镰孢野生型菌株Mont-1的SdhB基因第277位的甘氨酸替换为精氨酸后，该突变菌株对两种SDHI类杀菌剂——氟吡菌酰胺与啶酰菌胺（boscalid）的敏感性均显著提升。
与图科曼尼镰孢野生菌株类似，经改造的Mont-1（SdhBG277R）突变体在经氟吡菌酰胺种子处理的大豆幼苗上引发的大豆猝死综合症与根腐病症状均轻于原始Mont-1菌株。
本研究结果表明，图科曼尼镰孢SdhB基因的氨基酸差异，使得氟吡菌酰胺作为种子处理剂时可有效防控该菌种引发的病害——而图科曼尼镰孢是南美洲最主要的大豆猝死综合症病原菌。明确镰孢属物种对氟吡菌酰胺的基线敏感性，将有助于制定针对大豆及其他寄主病害系统（如菜豆镰孢病害）的高效防控策略。