Reynolds Katherine L, Brenneman Timothy B, Bertrand Paul F
Department of Plant Pathology, University of Georgia, Athens 30602-7274.
Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton 31793.
Plant Dis. 1997 Feb;81(2):163-166. doi: 10.1094/PDIS.1997.81.2.163.
Monoconidial isolates of the pecan scab fungus, Cladosporium caryigenum, were obtained in 1993 and 1994 from one pecan orchard each in Jeff Davis and Troup counties in Georgia, counties with no previous history of exposure to demethylation-inhibiting (DMI) fungicides. Isolates were grown on potato dextrose agar (PDA) amended with propiconazole or fenbuconazole at 0,0.0001, 0.0005, 0.001, 0.005, 0.01, 0.05, 0.1, 0.5, 1.0, or 5.0 µg ml. After 4 to 5 weeks at 25°C, the diameter of each colony was measured. Relative growth was expressed as the colony diameter for each fungicide concentration as a percentage of the diameter on unamended PDA. (ED) values for both fungicides in all years and locations were lognormally distributed. Mean (ED) values ranged from 0.19 to 0.30 µg ml for fenbuconazole and 0.12 to 0.17 µg ml for propiconazole. There were highly significant positive correlations between sensitivity to propiconazole and sensitivity to fenbuconazole at all locations and years, indicating significant potential for development of cross-resistance to these compounds. A discriminatory concentration of 0.2 µg ml propiconazole was selected for further monitoring of DMI sensitivity. With this discriminatory concentration, a sample size of 50 isolates was estimated to be sufficient to detect a difference of 8.3% in mean relative growth between two populations.
1993年和1994年，从佐治亚州杰斐逊戴维斯县和特鲁普县的一个山核桃果园中分别获取了山核桃疮痂病菌（Cladosporium caryigenum）的单孢分离物，这两个县此前没有接触过脱甲基抑制剂（DMI）类杀菌剂的历史。将分离物接种在添加了丙环唑或腈苯唑的马铃薯葡萄糖琼脂（PDA）上，浓度分别为0、0.0001、0.0005、0.001、0.005、0.01、0.05、0.1、0.5、1.0或5.0 μg/ml。在25°C下培养4至5周后，测量每个菌落的直径。相对生长率以每种杀菌剂浓度下的菌落直径占未添加杀菌剂的PDA上菌落直径的百分比表示。所有年份和地点两种杀菌剂的（ED）值均呈对数正态分布。腈苯唑的平均（ED）值范围为0.19至0.30 μg/ml，丙环唑的平均（ED）值范围为0.12至0.17 μg/ml。在所有地点和年份，对丙环唑的敏感性与对腈苯唑的敏感性之间存在高度显著的正相关，表明对这些化合物产生交叉抗性的可能性很大。选择0.2 μg/ml的丙环唑作为鉴别浓度，用于进一步监测DMI敏感性。采用该鉴别浓度时，估计50个分离物的样本量足以检测两个群体之间平均相对生长率8.3%的差异。
