Evidence for a second type of resistance against Cydia pomonella granulovirus in field populations of codling moths

Abstract

ABSTRACT Cydia pomonella granulovirus (CpGV) is an important biocontrol agent for the codling moth (CM) in organic and integrated apple production worldwide. Previously, Z chromosome-linked dominant resistance in at least 38 CM field populations in Europe was reported, threatening organic apple production. Growers responded by switching to a different resistance-breaking isolate of CpGV that could control these populations. Here, we report a nonuniform response of different CM field populations to CpGV isolates from CpGV genome groups A to E. Even more strikingly, one field population, NRW-WE, was resistant to all known CpGV genome groups except group B. Single-pair crossing experiments with a susceptible strain, followed by resistance testing of the F1 offspring, clearly indicated cross-resistance to CpGV isolates that had been considered to be resistance breaking. This finding provides clear evidence of a second, broader type of CpGV resistance with a novel mode of inheritance that cannot be fully explained by Z-linkage of resistance.