Genetic Characterization of Apple Accessions with Very Low Chilling Requirements in Israel

The life cycle of deciduous trees includes a dormant stage (endo-dormancy) induced by daylight shortening and decreasing temperatures during autumn and winter. The release from the endo-dormant state can occur after a sufficient exposure to low temperatures. The required exposure is termed chilling requirements (CR) and it can be measured by several methods. Inadequate exposure to the required CR results in irregular bud break and may lead to symptoms such as poor fruit set, extended harvest period and reduced branching. Most commercial apple varieties have medium to high CR and therefore cannot be grown in regions with warm winter. In addition, global climate changes raise concerns that some areas where commercial apples are currently grown might become unsuitable for these varieties due to weather warming.  Yet, there are some apple accessions that have very low CR and can thrive under warm climate; most of them are not commercial. Those might serve as a genetic source to breed new commercial cultivars better adapted to warm climate. In the apple germplasm collection at the Newe-Ya'ar Research Center there are 19 accessions exhibiting very low CR. These include ten local accessions that were collected around Israel as well as eight cultivars that were bred in Israel (including 'Anna') and one foreign cultivar. The germplasm collection includes approximately sixty additional accessions, local and 'Western', with medium-to-high CR. Results of bud-break phenology surveys and genetic characterization will be presented and discussed.