Fire Blight Resistant Pre-Breeding Apple Genotypes Developed Using the Early Flowering Approach

Wild apple accessions often carry traits (e.g. resistances) which are of high interest to apple breeders. The selection of new cultivars carrying these traits can take 25 years and sometimes longer due to the long juvenile phase of the apple (minimum of 4 to 5 years) and to the four to five pseudo-backcrosses that are necessary to progressively reduce the undesired traits of the wild apple introduced together with the trait of interest. The early flowering approach based on the BpMADS4 gene from Betula pendulawas developed in order to reduce the introduction time of such traits in pre-breeding genotypes purified from the “wild” genome (BC’4 generation). These pre-breeding selections (without the early flowering cassette) will then be used as parent in large crosses in which it should be possible to identify a new cultivar carrying the trait of interest.

The ornamental cultivar ‘Evereste’ carries a major QTL for fire blight resistance (Fb_E) on the linkage group 12. The resistance locus induces a high level of resistance. Tightly linked molecular markers developed in the frame of a positional cloning of the QTL are available.

In this poster we will show that seeds of the BC’4 generation can be obtained in less than six years and that the fire blight resistance level of individuals of the BC’3 generation carrying both the early flowing cassette and the FB_E locus is in general comparable to that of ‘Evereste’. Consequences for apple breeding will be discussed.