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Response of Colletotrichum coccodes to QoI Fungicide in vitro

Author(s): Abdullah M. Aqeel

Journal: Plant Pathology Journal
ISSN 1812-5387

Volume: 6;
Issue: 4;
Start page: 283;
Date: 2007;
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Keywords: Black dot | vegetative compatibility group | azoxystrobin

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 EC50 values for each isolate by determining the effective fungicide concentration that inhibited conidial germination by 50%. The EC50 values of the 122 isolates ranged from 0.001 to 0.1 μg mL-1 of azoxystrobin a mean value of 0.011 μg 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 (EC50 means were 0.011 and 0.017, respectively), while NA-VCGs 3 and 5 were more sensitive (EC50 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 EC50 value of baseline isolates (0.008 μg mL-1) significantly lower than the mean of EC50 value of non-baseline isolates (0.012 μg mL-1). While this difference is statistically significant, it may not necessarily be biologically significant, as the resistance factor between baseline and non-baseline.

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