Activity of the dinitroaniline fungicide fluazinam against Bipolaris maydis

Fluazinam is a dinitroaniline fungicide with broad-spectrum activities. However, the activity of fluazinam against Bipolaris maydis which is the causal agent of southern corn leaf blight is unknown yet. In this study, baseline sensitivity of B. maydis to fluazinam was determined using 92 isolates collected during 2015 and 2016 from different geographical regions in Jiangsu Province of China, and the EC50 values ranged from 0.0396 to 0.9808 mu g/ml with average value of 0.3853 +/- 0.2297 mu g/ml, and 0.079 to 0.7832 mu g/ml with average value of 0.3065 +/- 0.1384 mu g/ml for mycelial growth and conidium germination respectively. Fluazinam did not affect the distribution of cell nucleus and the formation of septum of B. maydis. However, fluazinam could make mycelium of B. maydis contorted and the mycelia] branches increased and inhibit the development of conidia. The result of transmission electron microscope showed that fluazinam damaged cell wall and cell membrane of mycelium, and make organelles in mycelial cell dissolved and vacuolated, and the cell almost broke up, which caused the intracellular plasma leakage increase. The protective activity test of fluazinam suggested that fluazinam had great control efficiency against B. maydis on detached corn leaves. Application of fluazinam at 10 mu g/ml and 20 mu g/ml, the control efficacy reached to 87.70% and 98.25% respectively. However, fluazinam had no curative activity against B. maydis on detached corn leaves. These results will contribute to us on evaluating the potential of the dinitroaniline fungicide fluazinam for management of diseases caused by B. maydis and understanding the mode of action of fluazinam against B. maydis.

氟啶胺是一种具有广谱活性的二硝基苯胺类杀菌剂。然而，氟啶胺对玉米小斑病菌（南方玉米叶枯病的病原菌）的活性尚不明确。本研究利用2015年至2016年从中国江苏省不同地理区域采集的92个菌株，测定了玉米小斑病菌对氟啶胺的基线敏感性。菌丝生长的EC50值范围为0.0396 - 0.9808微克/毫升，平均值为0.3853 ± 0.2297微克/毫升；分生孢子萌发的EC50值范围为0.079 - 0.7832微克/毫升，平均值为0.3065 ± 0.1384微克/毫升。氟啶胺不影响玉米小斑病菌细胞核的分布以及隔膜的形成。然而，氟啶胺会使玉米小斑病菌的菌丝扭曲，菌丝分支增多，并抑制分生孢子的发育。透射电子显微镜结果显示，氟啶胺破坏菌丝的细胞壁和细胞膜，使菌丝细胞内的细胞器溶解和空泡化，细胞几乎破裂，导致细胞内细胞质渗漏增加。氟啶胺的保护活性试验表明，氟啶胺对离体玉米叶片上的玉米小斑病菌具有良好的防治效果。施用10微克/毫升和20微克/毫升的氟啶胺时，防治效果分别达到87.70%和98.25%。然而，氟啶胺对离体玉米叶片上的玉米小斑病菌没有治疗活性。这些结果将有助于我们评估二硝基苯胺类杀菌剂氟啶胺对玉米小斑病菌所致病害的防治潜力以及了解氟啶胺对玉米小斑病菌的作用方式。