Marker-assisted selective breeding for resistance against American foulbrood (Paenibacillus larvae)

American foulbrood (AFB) is a devastating brood disease of honey bees (Apis mellifera L.). Colonies with visible symptoms typically die if not treated, resulting in considerable economic loss to beekeepers. Relying on antibiotic treatment is problematic, due to the development of resistance and the potential to contaminate honey. A more sustainable approach is to select and breed bees with increased ability to limit or eliminate brood
diseases. Bees bred for hygienic behaviour (HB) have the ability to detect and remove infected or dead brood from the colony, thus eliminating the spread of disease. We have previously reported the identification of protein markers that correlate with HB and their use in selective breeding. In this study, we demonstrated the utility of this proteomic tool to enhance disease-resistance over three generations. In the first year, we evaluated 635 colonies from four provinces in western Canada, for hygienic behaviour using the freeze-killed brood assay. The F0 population was established from hygienic colonies and a benchmark population was randomly selected. In the two subsequent years, we evaluated, selected, and propagated three successive generations based on either hygienic behaviour (Field-Assisted Selection, FAS), or protein marker selection (Marker Assisted Selection, MAS). The performance of the two selectively bred lines, FAS and MAS, in F1 and F3, was compared with the unselected benchmark and a commercially imported stock. In each generation, colonies from all four stocks were challenged with Paenibacillus larvae, by introducing a 15 x 15 cm section of comb containing 30-50% cells with visible AFB symptoms.

Our results showed that by the F3, MAS was as efficient as FAS for selective breeding for HB as tested using a freeze-kill brood assay. Selectivelybred FAS and MAS stocks had fewer clinical symptoms of AFB as well as fewer colonies infected by the end of the season. Colony survival was also higher in selected colonies, compared with the benchmark and imported stocks. No difference was observed in honey production among
stocks, indicating that selective breeding for HB using MAS improves resistance to disease without compromising colony productivity.