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Inheritance of Increased Sensitivity to N-Phenylcarbamates in Benzimidazole-Resistant Venturia nashicola. H. Ishii, Phytopathologist, Fruit Tree Research Station, Tsukuba, Ibaraki 305, Japan; M. van Raak, Masterís degree candidate, Department of Phytopathology, Agricultural University, Binnenhaven 9, 6709 PD Wageningen, The Netherlands. Phytopathology 78:695-698. Accepted for publication 7 January 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-695.

Most of the highly resistant isolates of Venturia nashicola to the benzimidazole fungicide carbendazim showed increased sensitivity in vitro to the N-phenylcarbamate compounds MDPC and diethofencarb, but the intermediately and weakly carbendazim-resistant isolates did not. A segregation ratio of 1:1 was obtained from the cross between MDPC-sensitive and -resistant isolates. In an allelism test, no MDPC-resistant progeny appeared from the cross between two MDPC-sensitive isolates, and no MDPC-sensitive progeny resulted from the cross between two MDPC-resistant isolates. These results indicated that the increased sensitivity to MDPC is controlled by a single chromosomal gene. When a highly carbendazim-resistant isolate (MDPC-sensitive) was crossed with an intermediately carbendazim-resistant or a carbendazim-sensitive isolate (both resistant to MDPC), several progeny strains were doubly resistant, i.e., highly resistant to carbendazim and resistant to MDPC. Such strains also were detected among field isolates, and the double resistance was heritable.

Additional keywords: benomyl, negatively correlated cross-resistance, pear scab, thiophanate-methyl.