Ma Hui-Xia, Feng Xi-Jie, Chen Yu, Chen Chang-Jun, Zhou Ming-Guo
College of Plant Protection, Nanjing Agricultural University, Nanjing, 210095, China.
Plant Dis. 2009 Jan;93(1):36-42. doi: 10.1094/PDIS-93-1-0036.
Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is the main fungal disease of oilseed rape (Brassica napus) in China. Numerous fungicide applications are required for control. Dimethachlon, one of the dicarboximide fungicides, has been the major fungicide for disease control after benzimidazole resistance became widespread. Fungal populations were collected throughout Jiangsu Province between 2006 and 2007 in order to determine their sensitivity to dimethachlon. A total of 1,066 single-sclerotium isolates of S. sclerotiorum were collected, and most of the isolates were considered sensitive to dimethachlon. Five isolates collected in Yancheng and Changzhou showed normal growth at 5 μg/ml dimethachlon with the resistance factor ≈10 (resistance factor was estimated as ratios between the EC values of resistant isolates and the average EC values of sensitive ones) compared to the sensitive isolates (EC is the concentration of fungicide causing 50% reduction in growth). Through in vitro selection for resistance to the fungicide, 25 dimethachlon-resistant mutants were derived from 10 wild-type isolates of S. sclerotiorum. The resistance factors for the isolates ranged from 198 to 484, and the isolates were considered highly resistant to dimethachlon. Therefore, at least two different mechanisms of resistance seem to be involved: one that may provide a moderate resistance (insensitivity) and a second that may give a high resistance level under laboratory conditions. There was positive cross-resistance between dimethachlon and other dicarboximide fungicides, such as iprodione and procymidone, in these S. sclerotiorum isolates. The field dimethachlon-insensitive and the laboratory-induced dimethachlon-resistant isolates appeared to have mycelial growth, sclerotial production, and pathogenicity comparable to their wild-type parental isolates. Also, results of osmotic tests showed that there were no significant difference in mycelial radial growth between the field dimethachlon-sensitive and field dimethachlon-insensitive isolates on potato dextrose agar plates amended with 2, 4, 6, or 8% (wt/vol) NaCl, but the laboratory-induced dimethachlon-resistant isolates grew significantly more slowly than their wild-type sensitive parents under all concentrations of NaCl. Because these studies yielded a high frequency of laboratory resistance in S. sclerotiorum, together with the occurrence of field insensitivity, appropriate precautions against resistance development in natural populations should be taken.
由核盘菌（Sclerotinia sclerotiorum）引起的菌核病是中国油菜（Brassica napus）的主要真菌病害。需要多次施用杀菌剂来进行防治。二甲菌核利是二羧酰亚胺类杀菌剂之一，自苯并咪唑类药剂广泛产生抗性后，它一直是防治该病的主要杀菌剂。为了测定江苏省核盘菌对二甲菌核利的敏感性，于2006年至2007年在全省范围内采集了菌核菌样本。共采集了1066个核盘菌单菌核分离株，大多数分离株对二甲菌核利敏感。在盐城和常州采集的5个分离株在5μg/ml二甲菌核利浓度下生长正常，与敏感分离株相比，其抗性因子约为10（抗性因子以抗性分离株的EC值与敏感分离株平均EC值之比估算；EC是导致生长降低50%的杀菌剂浓度）。通过对该杀菌剂的体外抗性筛选，从10个核盘菌野生型分离株中获得了25个二甲菌核利抗性突变体。这些分离株的抗性因子在198至484之间，被认为对二甲菌核利具有高抗性。因此，似乎至少涉及两种不同的抗性机制：一种可能提供中等抗性（不敏感性），另一种在实验室条件下可能产生高抗性水平。在这些核盘菌分离株中，二甲菌核利与其他二羧酰亚胺类杀菌剂如异菌脲和腐霉利之间存在正向交互抗性。田间对二甲菌核利不敏感的分离株以及实验室诱导产生的二甲菌核利抗性分离株，其菌丝生长、菌核形成和致病性与野生型亲本分离株相当。此外，渗透压试验结果表明，在添加2%、4%、6%或8%（重量/体积）NaCl的马铃薯葡萄糖琼脂平板上，田间对二甲菌核利敏感的分离株与田间对二甲菌核利不敏感的分离株之间，菌丝径向生长没有显著差异，但在所有NaCl浓度下，实验室诱导产生的二甲菌核利抗性分离株的生长速度明显慢于其野生型敏感亲本。由于这些研究表明核盘菌在实验室中产生抗性的频率较高，再加上田间出现了不敏感性，因此应采取适当措施防止自然种群中抗性的发展。
