Can "Caricia" and "Princesa" apples be considered low-chilling cultivars?

ABSTRACT. The purpose of this work was to study the response of two apple cultivars bred for low chilling environments to artificial chilling accumulation. Two trials were carried out; in experiment one, excised shoots were randomly taken from "Caricia" and "Princesa", and in experiment two, intact and excised shoots of "Caricia", "Princesa" and "Gala" (control) were collected. After collection, both shoot types were exposed to artificial chilling accumulation (4.0 ± 0.5°C) from 0 to 1200 chill units (CU). Bud break of mixed buds of "Caricia" and "Princesa" was higher than 50% between 0 CU to 1200 CU, irrespective of shoot type. Bud break of "Gala" mixed buds exceeded 50% only in intact shoots after accumulating 900 CU. The mean time to bud break of "Caricia" and "Princesa" diminished with increasing chilling accumulation and stabilized after ~600 CU, depending on the type of shoot and the year of experimentation. The low-chill apple cultivars tested in this work showed shallow dormancy, but they required moderate cold accumulation (800 - 1150 CU) to fully satisfy their chilling requirements. Thus, although their shallow dormancy makes them suitable for cultivation in chill-deficient environments, they cannot be considered low-chill cultivars.摘要 本研究旨在探究两个专为低需冷量环境选育的苹果品种对人工需冷量累积的响应。本研究共开展两组试验：试验一随机采集“Caricia”与“Princesa”的离体枝条；试验二则采集“Caricia”“Princesa”及作为对照的“Gala”的完整枝条与离体枝条。采集完成后，两类枝条均置于（4.0±0.5）℃的环境中进行人工需冷量累积处理，处理时长对应0至1200冷量单位（chill units, CU）。在0至1200 CU的处理范围内，“Caricia”与“Princesa”的混合芽萌发率均高于50%，且不受枝条类型影响。而“Gala”的混合芽萌发率仅在完整枝条经900 CU累积处理后才超过50%。“Caricia”与“Princesa”的平均芽萌发时间随需冷量累积增加而缩短，在约600 CU后趋于稳定，具体表现受枝条类型与试验年份影响。本试验中测试的低需冷量苹果品种虽表现出浅休眠特性，但需达到800~1150 CU的中等冷量累积才能完全满足其需冷量需求。因此，尽管其浅休眠特性使其适配需冷量不足的种植环境，但这类品种并不能被归类为低需冷量品种。