Please use this identifier to cite or link to this item: https://hdl.handle.net/20.500.14279/1009
Title: Determination of natural resistance frequencies in Penicillium digitatum using a new air-sampling method and characterization of fludioxonil- and pyrimethanil-resistant isolates
Authors: Forster, Helga 
Adaskaveg, James 
Kanetis, Loukas 
Major Field of Science: Agricultural Sciences
Field Category: AGRICULTURAL SCIENCES;Agricultural Biotechnology;Other Agricultural Sciences
Keywords: Fungicides;Botrytis cinerea;Cinerea isolates
Issue Date: Aug-2010
Source: Phytopathology, 2010, vol. 100, no. 8, pp. 738-746
Volume: 100
Issue: 8
Start page: 738
End page: 746
Journal: Phytopathology 
Abstract: Fungicide resistance was identified in natural populations of Penicillium digitatum, the causal agent of green mold of citrus, to two of three new postharvest fungicides before their commercial use. Using a new air-sampling method where large populations of the pathogen in citrus packinghouses were exposed to agar plates with a continuous, wide-range fungicide concentration gradient, isolates with reduced sensitivity to fludioxonil or pyrimethanil were obtained. Resistance frequencies to fludioxonil and pyrimethanil were calculated as 9.5 x 10-7 to 1.5 x 10-5 and 7.3 x 10-6 to 6.2 x 10-5, respectively. No isolates resistant to azoxystrobin were detected. Isolates with reduced sensitivity to fludioxonil or pyrimethanil were also obtained in laboratory selection studies, where high concentrations of conidial mixtures of isolates sensitive to the three fungicides were plated onto agar amended with each fungicide at 10 ug/ml. Isolates obtained from fludioxonil selection plates in laboratory and packinghouse experiments were placed into two categories based on mycelial growth: moderately resistant isolates had 50% effective concentration (EC50) values of 0.1 to 0.82 ug/ml and highly resistant isolates had EC50 values > 1.5 μg/ml. Isolates resistant to pyrimethanil all had EC50 values >8 μg/ml. Representative isolates of the two categories with reduced sensitivity to fludioxonil varied widely in their virulence and sporulation capacity as measured by the incidence of decay and degree of sporulation on inoculated fruit, respectively, whereas pyrimethanil-resistant isolates were mostly similar to the wild-type isolate. Fungicide sensitivity characteristics for isolates from fludioxonil and pyrimethanil selection plates remained stable after passages on nonamended agar, and disease could not be controlled after treatment with the respective fungicides. Types of fungicide resistance were visualized on thiabendazole- (TBZ) and imazalil-amended selection plates that were exposed in packinghouses where resistance to these fungicides was known to occur. The qualitative, single-site resistance to the benzimi- dazole TBZ was visualized by two distinct subpopulations in regard to fungicide sensitivity, whereas the quantitative, multi-site resistance to the demethylation inhibitor imazalil was apparent as a continuous density gradient of colonies along the fungicide concentration gradient. Types of resistance could not be assigned to fludioxonil or pyrimethanil because a limited number of resistant colonies was obtained on each plate. Thus, with this new method, we were able to estimate fungicide resistance frequencies as well as characterize and visualize types of resistance within populations of a fungal species. This information will be used to design resistance management strategies for previous and newly registered postharvest fungicides of citrus
URI: https://hdl.handle.net/20.500.14279/1009
ISSN: 19437684
DOI: 10.1094/PHYTO-100-8-0738
Rights: © The American Phytopathological Society
Type: Article
Affiliation: Cyprus University of Technology 
Affiliation : University of California 
Publication Type: Peer Reviewed
Appears in Collections:Άρθρα/Articles

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