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Sensitivity of Penicillium digitatum and P. italicum to Imazalil and Thiabendazole in Morocco

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Author(s): H. Boubaker | B. Saadi | E.H. Boudyach | A.A. Benaoumar

Journal: Plant Pathology Journal
ISSN 1812-5387

Volume: 8;
Issue: 4;
Start page: 152;
Date: 2009;
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Keywords: thiabendazole | imazalil | P. italicum | Penicillium digitatum | fungicide resistance | citrus fruit

ABSTRACT
Green and blue molds (caused by Penicillium digitatum and P. italicum, respectively) are the main postharvest diseases of citrus fruits in Morocco. Following packing houses reports of reduced efficacy of fungicides used to control theses diseases, a survey was conducted during 2005-2006 packing season to characterize, both qualitatively and quantitatively, the resistance of P. digitatum and P. italicum to imazalil (IMZ) and thiabendazole (TBZ). Isolates of P. digitatum and P. italicum were obtained from decayed citrus fruits collected from commercial citrus packing houses located in the Souss-Massa-Draa (SMD), South of Morocco and were evaluated in-vitro for their sensitivity to IMZ and TBZ. Of the 290 P. digitatum isolates, 19% (55/290) were resistant to IMZ and 37% (107/290) were resistant to TBZ tested at discriminatory concentrations of 0.1 or 20 μg mL-1, respectively. In contrast, only 2.5 (5/204) and 21% (44/204) of P. italicum isolates collected from packing houses were resistant to IMZ and TBZ, respectively. No resistance to TBZ and IMZ were detected in Penicillium sp., isolates collected from a citrus orchard which has no known history of fungicide use. The proportion of collected isolates that were resistant to both fungicides was 1.5% for P. italicum and 10% for P. digitatum. The mean EC50 values for in vitro inhibition of mycelial growth of the P. digitatum resistant-isolates were between 0.81 and 0.98 μg mL-1 for IMZ, whereas those of TBZ were between 39.23 and 50.84 μg mL-1. The mean EC50 values for P. italicum resistant-isolates ranged from 0.53 to 0.61 μg mL-1 for IMZ and from 52.97 to 59.92 μg mL-1 for TBZ, whereas the mean EC50 values for orchard collected isolates were 0.04 μg mL-1 for IMZ and 0.16 μg mL-1 for TBZ. The data will provide a baseline for monitoring resistance to IMZ and TBZ in populations of P. digitatum and P. italicum in the SMD commercial citrus packing houses in the future.
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