THE NEW-ZEALAND APPLE GENOME MAPPING PROJECT - A PROGRESS REPORT

This project was initiated three years ago to support the New Zealand apple breeding programme at HortResearch and is funded by both the New Zealand Foundation for Research, Science and Technology and the New 2ealand Apple and Pear Marketing Board. Our initial goal is to construct a linkage map comprising RFLP, RAPD and isoenzyme markers as well as characters of importance to our breeders and this will enable the breeders to use marker assisted selection to identify the most promising seedlings within progeny populations at an early age. Characters of interest in the shorter term include resistances to scab, powdery mildew, woolly apple aphid and silver leaf, and in the longer term more complex traits such as early and late fruit maturity, fruit quality characters, low temperature tolerance and rootstock influences such as dwarfing and precocity are under consideration. We are currently developing long-term plans for isolation of apple genes in association with other molecular biologists in HortResearch. We have used a cDNA library from apple flesh as a prolific source of RFLP probes and detect their hybridization to Southern blots using a chemiluminescent method. We have screened our mapping line of seedlings for more than 160 markers so far (1/3 RFLP, 2/3 RAPD). Detection of in situ hybridization of key RFLP probes to metaphase chromosome preparations for the purpose of associating marker linkage groups with physical chromosomes is by a digoxygenin or biotin linked immunoassay. The project has collaborative links to apple genome mapping projects in America and Europe.