Di Ya-Li, Cong Meng-Long, Zhang Ran, Zhu Fu-Xing
College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, 430070, China.
Plant Dis. 2016 Oct;100(10):2113-2118. doi: 10.1094/PDIS-03-16-0403-RE. Epub 2016 Aug 2.
Sclerotinia sclerotiorum is a devastating ascomycete plant pathogen with an extremely wide host range. Fungicides are still the mainstay for control of this pathogen, and stimulations to mycelial growth and aggressiveness by subtoxic doses of fungicides carbendazim and dimethachlon have been reported. The present study assessed hormetic effects of the quinone outside inhibitor (QoI) fungicide trifloxystrobin on aggressiveness of S. sclerotiorum. Trifloxystrobin at 0.0001, 0.0005, and 0.001 μg/ml exerted significant stimulatory effects on aggressiveness to potted rapeseed plants, and the highest percent stimulation were 20.5 and 24.2% for isolates HB15 and SX11, respectively. At 18 h postinoculation (HPI), initial necrotic lesions were visible to the naked eye on leaves treated with trifloxystrobin, whereas no obvious disease symptoms were discerned for the nontreated control. At 24, 36, and 48 HPI, aggressiveness stimulation was more obvious than at 18 HPI. Scanning electron microscopic observations demonstrated that no mycelia were detected on the nontreated leaves at 4 HPI; by contrast, mycelia were observed on leaves treated with trifloxystrobin at 0.0001 μg/ml. At 8 and 12 HPI, there were more mycelia and infecting hyphae on the treated leaves than on the nontreated control. These results indicated that fungal stimulation had occurred in the first 4 and 8 HPI, suggesting that direct stimulation was likely to be the underlying mechanism for hormetic actions of trifloxystrobin. Pretreatment with trifloxystrobin did not significantly affect subsequent mycelial growth on PDA or aggressiveness to detached rapeseed leaves in the absence of trifloxystrobin. However, in the presence of trifloxystrobin, mycelial growth and aggressiveness were significantly (P < 0.05) greater for the pretreatment with trifloxystrobin at 0.003 and 0.03 μg/ml compared with the nonpretreatment control, indicating that a prior exposure to the fungicide may undermine its subsequent effectiveness. These studies will raise our awareness of fungicide hormesis and have important implications for judicious application of fungicides.
核盘菌是一种极具破坏性的子囊菌植物病原菌，寄主范围极广。杀菌剂仍是防治该病原菌的主要手段，据报道，低毒剂量的多菌灵和抑霉唑能刺激菌丝生长和致病性。本研究评估了醌外抑制剂（QoI）杀菌剂肟菌酯对核盘菌致病性的兴奋效应。浓度为0.0001、0.0005和0.001μg/ml的肟菌酯对盆栽油菜植株的致病性有显著刺激作用，分离株HB15和SX11的最高刺激率分别为20.5%和24.2%。接种后18小时（hpi），用肟菌酯处理的叶片上肉眼可见初始坏死病斑，而未处理的对照则未发现明显的病害症状。在接种后24、36和48小时，致病性刺激比接种后18小时更明显。扫描电子显微镜观察表明，接种后4小时，未处理的叶片上未检测到菌丝；相比之下，在浓度为0.0001μg/ml的肟菌酯处理的叶片上观察到了菌丝。在接种后8小时和12小时，处理过的叶片上的菌丝和侵染菌丝比未处理的对照更多。这些结果表明，在接种后4小时和8小时发生了真菌刺激，这表明直接刺激可能是肟菌酯兴奋作用的潜在机制。在没有肟菌酯的情况下，用肟菌酯预处理对随后在PDA上的菌丝生长或对离体油菜叶片的致病性没有显著影响。然而，在有肟菌酯的情况下，与未预处理的对照相比，浓度为0.003和0.03μg/ml的肟菌酯预处理的菌丝生长和致病性显著更高（P<0.05），这表明预先接触杀菌剂可能会削弱其随后的效果。这些研究将提高我们对杀菌剂兴奋效应的认识，并对杀菌剂的合理应用具有重要意义。
