Response of Colletotrichum coccodes to QoI Fungicide in vitro

摘要

One hundred twenty-two isolates of C, coccodes, belonging to six VCGs, were collected from North America from 1994 to 2004 and assayed for sensitivity to azoxystrobin. Sensitivity to azoxystrobin was determined using an in vitro spore germination assay to calculate the EC_50 values for each isolate by determining the effective fungicide concentration that inhibited conidial germination by 50%. The EC_50 values of the 122 isolates ranged from 0.001 to 0.1 mu g mL~(-1) of azoxystrobin a mean value of 0.011 mu g mL~(-1), indicating a high activity of azoxystrobin toward C. coccodes. NA-VCGs of C. coccodes differed significantly in their response to azoxystrobin. NA-VCGs 2 and 6 were less sensitive to azoxystrobin (EC_50 means were 0.011 and 0.017, respectively), while NA-VCGs 3 and 5 were more sensitive (EC_50 means were 0.006 and 0.007, respectively). However, the resistance factor is 2, indicating that the variation between the least sensitive and most sensitive isolates may not be biologically significant. This investigation demonstrated sensitivity of C. coccodes isolates regardless the NA-VCGs. The mean EC_50 value of baseline isolates (0.008 mu g mL~(-1)) significantly lower than the mean of EC_50 value of non-baseline isolates (0.012mu g mL~(-1)). While this difference is statistically significant, it may not necessarily be biologically significant, as the resistance factor between baseline and non-baseline.