Breeding for fire blight resistance in an interspecific pear breeding programme

The Plant & Food Research (PFR) pear breeding programme in New Zealand is developing interspecific pear (ISP) hybrids for pear industries globally. Its major aim is to produce a new type of pear that is attractive, crisp, juicy, and flavoursome with long storage life. Historically from 1983 to 2002, the programme used European, Japanese and Chinese pear progenitors, which are mostly regarded as susceptible to fire blight disease caused by the bacterium Erwinia amylovora. Since 2003, breeding lines were initiated to actively introgress multiple fire blight resistances from nine original progenitors. Seedlings produced from these breeding lines and inoculated with E. amylovora in the glasshouse in each of eight years tended to show either complete or no infection after inoculation. A generalised linear mixed modelling approach with a logit-link function was therefore used on these binary data to estimate genetic parameters of the populations, and breeding values for parents and ancestors for the probability that seedlings will not show necrosis after inoculation. Only additive (and not non-additive) genetic variances contributed to the total phenotypic variation, with narrow-sense heritabilites for individual seedlings also being low (h²=0.20 across years). Original PFR progenitors with resistances derived from ‘Roi Charles de Würtemberg’, ‘Duchesse d’Angoulème’, or ‘Old Home’/‘Early Sweet’ were more efficient in transmitting fire blight resistance to their progenies than those progenitors derived from ‘Seckel’. This knowledge is being used to further improve the fire blight screening process and guide parental selection in the breeding of new high quality and fire blight resistant ISP cultivars.