Clinal variation of dormancy progression in apricot

The aim of this study was to determine the bud dormancy progression in apricot at different latitudes and altitudes. Six locations in regions with a Mediterranean climate in South Africa (SA) and Spain were chosen. The study was carried out during two consecutive years, 2007 and 2008, in SA and results were compared to those obtained in Spain in 2008. Locations ranged from low-chill areas, such as Ladismith and Villiersdorp in SA and Campotéjar in Spain, to high-chill areas, such as Ceres in SA and Barranda in Spain. A number of apricot cultivars comprising the range of chilling requirements in both countries were selected. In addition, a second, parallel study was performed to evaluate the paradormancy progression in ‘Palsteyn’ (SA) and ‘Rojo Pasión’ (Spain). Deeper dormancy was not observed in high-chill cultivars located in cold areas than in low-chill cultivars in warm areas. However, low-chill cultivars located in warm areas entered and released from dormancy earlier than high chill cultivars in warm areas. Thus, a clinal variation in dormancy progression under warm temperatures in apricot cultivars is suggested. The role of photoperiod and minimum temperatures is proposed to have a key role in dormancy onset. Paradoxically, an earlier maximum depth of dormancy was found in those areas with higher minimum temperatures at the end of summer. Before the beginning of winter, all cultivars showed an important increase of budburst rate, which indicated the end of endodormancy. Afterwards an ecodormancy period followed during winter, while chilling continued to accumulate. These results contrast with the assumed concept of the breaking of dormancy through chilling accumulation during winter and suggest a possible mediation by photoperiod in overcoming of dormancy. On the other hand, paradormancy exerted a reduction in budburst rate during dormancy entry, whereas decapitation increased the budburst rate throughout the dormant season, indicating interaction between different plant parts during this period.

Research Highlights►Dormancy onset took place in late summer, prior to the advent of chilling temperatures ►The deepest dormancy was reached earlier in warmer areas ►Endodormancy release in low chill apricot can begin before chill accumulation ►A clinal variation in dormancy progression is suggested