Green Elizabeth A, Gustafson Gary D
Dow AgroSciences, European Development Centre, 2nd Floor, 3 Milton Park, Abingdon, UK.
Pest Manag Sci. 2006 Jun;62(6):492-7. doi: 10.1002/ps.1189.
Quinoxyfen is a protectant fungicide that provides excellent control of many powdery mildew diseases. Prior to the launch of quinoxyfen in vines in 1998, a leaf disc sporulation assay was developed to assess the sensitivity of Uncinula necator (Schw) Burr to quinoxyfen. The distribution of EC(50) values from 56 monoconidial U. necator isolates collected from six countries between 1993 and 1996 was found to range from less than 0.03 to 2.6 mg litre(-1). Although this range of EC(50) values was quite broad, the inability to establish a minimum inhibitory concentration (MIC) for the majority of these isolates, including some of the most sensitive isolates, was unexpected and suggested that the leaf disc sporulation assay may not reflect the true activity of quinoxyfen in the field. In 2002, following the detection of isolates resistant to quinoxyfen in Blumeria graminis Speer f. sp. tritici Marchal, a discriminatory dose screen was developed to test large populations of U. necator for rare individuals with significantly decreased sensitivity to quinoxyfen. The individual isolates selected by this method were tested with the leaf disc sporulation assay. Although a significant proportion were found to have EC(50) values within the original distribution, a number of isolates with apparent reduced sensitivity to quinoxyfen were also detected. However, further examination of a subset of these isolates in a more quantitative germination/germ tube elongation inhibition assay suggested that the magnitude of the reduction in sensitivity for some of these isolates was much less than predicted by the sporulation assay. Thus, for an exclusively protectant fungicide such as quinoxyfen, a leaf disc sporulation assay may overestimate the frequency of isolates with significantly reduced sensitivity and the threat of decreased performance due to resistance.
喹氧灵是一种保护性杀菌剂，对多种白粉病具有出色的防治效果。在1998年喹氧灵于葡萄上推出之前，开发了一种叶盘产孢测定法来评估葡萄钩丝壳菌（Uncinula necator (Schw) Burr）对喹氧灵的敏感性。1993年至1996年间从六个国家收集的56个单孢葡萄钩丝壳菌分离株的半数有效浓度（EC(50)）值分布范围为小于0.03至2.6毫克/升。尽管这个EC(50)值范围相当宽，但无法为大多数这些分离株（包括一些最敏感的分离株）确定最低抑菌浓度（MIC），这是出乎意料的，表明叶盘产孢测定法可能无法反映喹氧灵在田间的真实活性。2002年，在禾本科布氏白粉菌（Blumeria graminis Speer f. sp. tritici Marchal）中检测到对喹氧灵耐药的分离株后，开发了一种鉴别剂量筛选法来检测大量葡萄钩丝壳菌群体中对喹氧灵敏感性显著降低的罕见个体。用这种方法挑选出的单个分离株用叶盘产孢测定法进行检测。尽管发现很大一部分分离株的EC(50)值在原始分布范围内，但也检测到一些对喹氧灵敏感性明显降低的分离株。然而，在更定量的萌发/芽管伸长抑制测定法中对这些分离株的一个子集进行进一步检测表明，其中一些分离株敏感性降低的程度远小于产孢测定法所预测的。因此，对于像喹氧灵这样的纯保护性杀菌剂，叶盘产孢测定法可能高估了敏感性显著降低的分离株的频率以及因耐药性导致性能下降的威胁。
