Shabi, E., Department of Plant Pathology, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan, 50 250, Israel
Koenraadt, H., Department of Phytopathology, Agricultural University, Binnenhaven 9, Wageningen, 6709 PD, Netherlands
Dekker, J., Department of Phytopathology, Agricultural University, Binnenhaven 9, Wageningen, 6709 PD, Netherlands

Isolates of Venturia inaequalis and of V. pirina sensitive (S) or resistant (R) to benomyl were examined in vitro on media amended with two phenylcarbamate fungicides. There was a negatively correlated cross-resistance (NCCR) to both methyl N-(3,5-dichlorophenyl) carbamate (MDPC) and isopropyl N-(3,4-diethoxyphenyl) carbamate (NPC) in some benomylresistant isolates. In V. inaequalis, isolates with low benomyl resistance (LR) did not show NCCR to MDPC, whereas isolates with medium (MR), high (HR) and very high (VHR) resistance to benomyl were more sensitive to MDPC than were the benomyl-sensitive isolates. To NPC, MR and VHR isolates showed NCCR whereas LR and HR isolates reacted similarly as sensitive isolates. In V. pirina only HR and VHR isolates showed NCCR to MDPC. The VHR isolates were sensitive to NPC, whereas the reactions of S, LR, MR and HR to NPC were similar. Crosses between benomyl-sensitive and benomyl-resistant V. pirina as well as between different resistant isolates showed that NCCR is inheritable and controlled by a single Mendelian gene. © 1987 Koninklijke Nederlandse Planteziektenkundige Vereniging.