Thomas A, Langston D B, Sanders H F, Stevenson K L
Department of Plant Pathology, University of Georgia, Tifton, 31793.
Plant Dis. 2012 Dec;96(12):1780-1784. doi: 10.1094/PDIS-02-12-0129-RE.
Gummy stem blight (GSB), caused by the fungus Didymella bryoniae, is the most destructive disease of watermelon and is managed primarily with fungicides. D. bryoniae has developed resistance to many fungicides that were once very effective, including azoxystrobin, boscalid, and thiophanate-methyl. Field experiments were conducted in Tifton (TN) and Reidsville (RV), GA in 2009 and 2010 to establish a relationship between frequency of resistance to a fungicide based on in vitro assays and its efficacy in the management of GSB. Frequency of resistance to boscalid, thiophanate-methyl, and azoxystrobin was >0.80 in isolates collected from nontreated plots in both locations and years. All isolates collected after six applications of boscalid, thiophanate-methyl, or azoxystrobin were resistant to the respective fungicide. All isolates collected from treated and nontreated plots were sensitive to tebuconazole and difenoconazole. GSB severity was assessed on a weekly basis from 63 days after planting. GSB severity in plots treated with boscalid, thiophanate-methyl, or azoxystrobin was not significantly different from that in the nontreated plots (39%, TN-2009; 45%, TN-2010; and 16%, RV-2010). GSB severity in tebuconazole-treated plots (27%, TN-2009; 14%, TN-2010; and 4%, RV-2010) was significantly lower than all other treatments and the nontreated control. There was a consistent negative association between frequency of fungicide resistance and disease control in the field. Thus, knowledge of the frequency of fungicide resistance in the pathogen population will be helpful in selecting the most effective fungicides for the management of GSB in watermelon fields.
由真菌瓜亡革菌（Didymella bryoniae）引起的蔓枯病（GSB）是西瓜最具毁灭性的病害，主要通过杀菌剂进行防治。瓜亡革菌已对许多曾经非常有效的杀菌剂产生了抗性，包括嘧菌酯、啶酰菌胺和甲基硫菌灵。2009年和2010年在佐治亚州的蒂夫顿（TN）和里兹维尔（RV）进行了田间试验，以建立基于体外测定的杀菌剂抗性频率与其在蔓枯病防治中的效果之间的关系。在两个地点和年份从未处理地块采集的分离物中，对啶酰菌胺、甲基硫菌灵和嘧菌酯的抗性频率均>0.80。在使用啶酰菌胺、甲基硫菌灵或嘧菌酯进行六次施药后采集的所有分离物均对相应的杀菌剂具有抗性。从处理地块和未处理地块采集的所有分离物对戊唑醇和苯醚甲环唑敏感。从种植后63天开始每周评估蔓枯病严重程度。用啶酰菌胺、甲基硫菌灵或嘧菌酯处理的地块中的蔓枯病严重程度与未处理地块中的蔓枯病严重程度无显著差异（2009年TN为39%；2010年TN为45%；2010年RV为16%）。戊唑醇处理地块中的蔓枯病严重程度（2009年TN为27%；2010年TN为14%；2010年RV为4%）显著低于所有其他处理和未处理对照。在田间，杀菌剂抗性频率与病害防治之间存在一致的负相关关系。因此，了解病原菌群体中杀菌剂抗性频率将有助于选择最有效的杀菌剂来防治西瓜田中的蔓枯病。
