Chen F, Liu X, Schnabel G
College of Agriculture and Biotechnology, China Agricultural University, Beijing 100193.
School of Agricultural, Forest & Environmental Sciences, Clemson University, Clemson, SC 29634.
Plant Dis. 2013 Aug;97(8):1063-1068. doi: 10.1094/PDIS-12-12-1177-RE.
In 2012, significant brown rot disease was observed on stone fruit in Pennsylvania, Maryland, and South Carolina despite preharvest application of methyl benzimidazole carbamate (MBC) and demethylase inhibitor (DMI) fungicides. In total, 140 Monilinia fructicola isolates were collected from diseased orchards and examined for fungicide sensitivity. In addition to isolates resistant to either the DMI propiconazole or the MBC thiophanate-methyl, 22 isolates were discovered that were resistant to both fungicides, including 4 isolates from peach in South Carolina, 12 isolates from peach and sweet cherry in Maryland, and 6 isolates from sweet cherry in Pennsylvania. Analysis of MBC resistance revealed that dual-resistant isolates from South Carolina carried the β-tubulin E198A mutation, whereas isolates from Maryland and Pennsylvania carried E198 mutations not previously described in the Monilinia genus, E198Q or F200Y. The genetic element Mona, associated with DMI fungicide resistance in M. fructicola, was detected in the dual-resistant isolates from South Carolina but not in the isolates from the two more northern states. An investigation into the molecular mechanism of DMI resistance in the latter isolates revealed that resistance was not based on increased expression or mutation of MfCYP51, which encodes the target of DMI fungicides. Label rates of formulated propiconazole or thiophanate-methyl were unable to control dual-resistant isolates on detached peach fruit, confirming field relevance of dual resistance. The same isolates were not affected by fitness penalties based on mycelial growth rate, ability to sporulate, and virulence on detached peach fruit. The emergence of M. fructicola strains resistant to both DMI and MBC fungicides in multiple states and multiple stone fruit crops is a significant development and needs to be considered when designing resistance management strategies in stone fruit orchards.
2012年，尽管在收获前施用了甲基苯并咪唑氨基甲酸盐（MBC）和脱甲基酶抑制剂（DMI）类杀菌剂，但在宾夕法尼亚州、马里兰州和南卡罗来纳州的核果上仍观察到严重的褐腐病。总共从患病果园收集了140株核果褐腐病菌株，并检测了它们对杀菌剂的敏感性。除了对DMI丙环唑或MBC甲基硫菌灵耐药的菌株外，还发现了22株对两种杀菌剂均耐药的菌株，其中包括来自南卡罗来纳州桃子的4株、来自马里兰州桃子和甜樱桃的12株以及来自宾夕法尼亚州甜樱桃的6株。对MBC耐药性的分析表明，来自南卡罗来纳州的双重耐药菌株携带β-微管蛋白E198A突变，而来自马里兰州和宾夕法尼亚州的菌株携带在核果褐腐病菌属中未曾描述过的E198突变，即E198Q或F200Y。与核果褐腐病菌对DMI类杀菌剂耐药性相关的遗传元件Mona，在来自南卡罗来纳州的双重耐药菌株中被检测到，但在更北部两个州的菌株中未检测到。对后一类菌株中DMI耐药分子机制的研究表明，耐药性并非基于编码DMI类杀菌剂作用靶标的MfCYP51表达增加或突变。制剂丙环唑或甲基硫菌灵的标签推荐剂量无法控制离体桃子果实上的双重耐药菌株，证实了双重耐药在田间的实际情况。相同的菌株在菌丝生长速率、产孢能力以及对离体桃子果实的致病力方面并未受到适合度惩罚的影响。在多个州和多种核果作物中出现对DMI和MBC类杀菌剂均耐药的核果褐腐病菌株是一个重大进展，在设计核果果园的抗性管理策略时需要加以考虑。
