Effects of a novel SDHI fungicide pyraziflumid on the biology of the plant pathogenic fungi Bipolaris maydis

Pyraziflumid is a novel member of succinate dehydrogenase inhibitor (SDHI) fungicide Southern corn leaf blight (SCLB) caused by Bipolaris maydis is an important foliar disease of maize crop. In this study, baseline sensitivity of B. maydis to pyraziflumid was determined using 100 strains of B. maydis collected from different geographical regions in Jiangsu Province of China during 2015 and 2016, and EC50 values ranged from 0.0309 to 0.8856 mu g/ml with the average value of 0.2780 +/- 0.2012 mu g/ml for mycelial growth, and 0.032 to 0.9592 mu g/ml with the average value of 0.3492 +/- 0.2450 mu g/ml for conidium germination. After treatment with pyraziflumid, the distribution of cell nucleus and septum of mycelium was not changed, but hyphae of offshoot and conidia production decreased, cell secretion decreased, the cell membrane was damaged, mycelium electrolyte leakage increased, and organelles in mycelial cell dissolved and vacuolated. The protective and curative activity test of pyraziflumid suggested that pyraziflumid had great control efficiency against B. maydis on detached corn leaves. In protective activity assay with application of pyraziflumid at 5 mu g/ml and 10 mu g/ml, the control efficacy reached to 87.32% and 100% respectively. In curative activity assay with application of pyraziflumid at 20 mu g/ml and 50 mu g/ml, the control efficacy reached to 82.10% and 100% respectively.