What Is Wrong with Winter Chill Models in Warm Climates?

Bud dormancy is an evolutionary strategy that protects temperate fruit trees from low temperatures during winter. With adequate winter chilling, it a process consisting of rapid entrance phase where growth inhibition increases to maximum and then released via exit phase. This progression is, however, different in areas with insufficient chill. In such areas, the protracted, often incomplete. Several chill models have been designed describe plants’ response accumulation match cultivar site. Although known these are less accurate warm their accuracy two phases has always assumed equal. The aim this study was investigate four bud ‘Royal Gala’ buds contrasting climatic areas. One-year-old shoots were collected commercial orchards forced determine level. Before forcing, received varied amounts additional field represented as joint two- or three-line phases. For each phase, level every sample plotted against its based on (Chilling Hours, Utah, Positive Dynamic Model). Results compared ability model predict linearity progression. results indicated although all able successfully, none could linear suggests onset dormancy, respond temperature differently what measured by making unreliable when inadequate.