Effect of azoxystrobin on the physiology, morphology, and sclerotial formation of Rhizoctonia solani from tobacco

Tobacco, as one of the major cash crops in Guizhou province, China, is severely affected by diseases caused by Rhizoctonia solani . Azoxystrobin is a quinone outside inhibitor (QoI) fungicide extensively used to control various crop diseases in China. To evaluate the potential effect of azoxystrobin on the physiology, morphology, and sclerotial formation of Rhizoctonia solani , 104 isolates of R. solani from tobacco collected in Guizhou were evaluated for in vitro sensitivity to azoxystrobin, and scanning electron microscopy was used to observe the effects of azoxystrobin on mycelial morphology. The effects of azoxystrobin on reactive oxygen species (ROS), superoxide dismutase (SOD), catalase (CAT), and succinate dehydrogenase (SDH) in hyphae at three time points (at 5, 10 and 15 days) and on sclerotial differentiation were examined. The effective concentration that caused 50% growth inhibition (EC 50 ) ranged from 0.3 to 552 μg/mL with a geometric mean of 8.4 μg/mL, and the frequency distribution of EC 50 values was unimodal. Scanning electron microscopy revealed that azoxystrobin caused folding, collapse and crumpling of hyphae. Under azoxystrobin stress, sclerotial differentiation was inhibited, and the production of hydrogen peroxide (H 2 O 2 ) and superoxide anion (O 2− ) as well as activities of SOD, CAT and SDH in hyphae increased significantly compared to the untreated control at day 5; while at day 10 or 15, H 2 O 2 production decreased significantly, CAT activity increased significantly, and O 2− , SOD, and SDH concentrations returned to normal levels. In general, the results provide a better understanding of the physiological effects of azoxystrobin on R. solani .