The effects of two steady chilling temperatures on bud dormancy of two apple cultivars
The objectives of this study were to: 1) determine the effects of chilling temperatures (0 and 5°C) on dormancy completion of floral buds of one-year-old shoots and spurs in two apple cultivars (Gala and Rubinola), and 2) compare the results of dormancy completion under control temperature and orchard conditions to determine possible climatic factors affecting treatment differences. During the fall season for four years, 30 one-year-old twigs and 30 shoots with spurs were taken from trees of two temperate fruit apple cultivars (Gala and Rubinola) in October and November. The samples were held in refrigerator at 0 and +5°C. After 21 days of treatment the shoots were put in a growth chamber at 21°C. The number of opened buds (apical and lateral) was counted and expressed both as percentage of the total and as bud develop stage index. Data were compared with shoots on trees growing in the orchard under the winter outdoors temperatures from October up to the end of dormancy. Hourly temperatures were recorded and elaborated using Richardsons and Erezs formulae. The buds treated at 0 and +5°C, overcame the dormancy after 30 days. Results indicated that 0°C promoted the break of endo-dormancy in the cultivars examined similarly to +5°C, but the responses were related to phenological stage and the kind of buds when the cold treatments were applied. The formulae utilized to estimate the chilling requirement of cultivars should consider the effect of cold temperature during dormancy. Finally, the days required to overcome endo-dormancy (D50) decreased steadily according to the chilling accumulation of buds and likely overlapped the heating requirement.
Finetto, G.A. (2020). The effects of two steady chilling temperatures on bud dormancy of two apple cultivars. Acta Hortic. 1280, 161-170
bud development stage, chill unit, chilling requirement, rain, shoots