Occurrence of Penicillium digitatum and P. italicum Resistant to Benomyl, Thiabendazole, and Imazalil on Citrus Fruit from Different Geographic Origins. Vincent G. Bus, Agricultural Research Service, U.S. Department of Agriculture, European Marketing Research Center, Marconistraat 38, 3029 AK Rotterdam, The Netherlands. Anton J. Bongers, and Lawrence A. Risse. Agricultural Research Service, U.S. Department of Agriculture, European Marketing Research Center, Marconistraat 38, 3029 AK Rotterdam, The Netherlands. Plant Dis. 75:1098-1100. Accepted for publication 8 April 1991. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1991. DOI: 10.1094/PD-75-1098.

In 1 yr, 1,287 isolates of Penicillium digitatum and P. italicum were collected from decayed mandarins (Citrus reticulata), oranges (C. sinensis), lemons (C. limon), and grapefruit (C. paradisi) at the wholesale markets in Rotterdam and Paris. The isolates were cultured on media with various fungicides and concentrations. Thirty-seven percent of the P. digitatum isolates grew at 4 and 10 mg/L of thiabendazole (TBZ), 35 and 34% grew at 4 and 10 mg/L of benomyl (BEN), respectively, and 17 and 12% grew at 0.2 and 0.5 mg/L of imazalil (IM), respectively. Ninety percent of the P. digitatum strains resistant to TBZ were also resistant to BEN, and 13% of the strains tolerant to either one or both benzimidazoles showed double resistance to IM. Forty percent of the P. italicum isolates showed resistance to 4 mg/L of TBZ and 38% to 10 mg/L of TBZ, but only 29 and 13% were resistant to BEN at 4 and 10 mg/L, respectively, and 1% to 0.2 mg/L of IM. The level of cross-resistance between the benzimidazoles was 73%. Resistance of Penicillium to the benzimidazoles was highest in isolates taken from grapefruit, less in those from oranges and mandarins, and least in isolates recovered from lemons. However, the level of resistance to IM was higher in isolates from lemons.

Keyword(s): blue mold, green mold, postharvest fungicides.