engleski

Onset of flowering in olive cultivars in relation to temperature

The flowering process is adjusted to seasons through environmental signals, particularly photoperiod and temperature. Breaking dormancy, in trees, requires the completion of a period of chilling, which can be measured in hours below a certain temperature threshold. Budburst occurs once a heat requirement of accumulated degree days has been met. The studies of interactions between olive phenology and weather variables in a particular region can help us to predict the onset and length of flowering. The impact of air temperature on flowering phenology in five olive cultivars (‘Lastovka’, ‘Leccino’, ‘Levantinka’, ‘Oblica’ and ‘Pendolino’) was examined over a 5-year period (2005-2010) in an experimental orchard near Split (Croatia ; central part of the Adriatic coast). The flowering periods were assessed by visual examination of trees. The flowering date (FD) was calculated as the number of days from January 1 until the start of the flowering period. The method proposed by Aron and Gat (1991) was used to estimate the number of chilling units (CU) using the daily maximal and minimal air temperatures. Number of CUs ranged from 282 to 1441. The heat accumulation dates started in the first days after the calculation of hours of chilling had been finished and continued until the start of flowering season. Heat units were expressed in growing degree days (GDD), and one GDD unit denoted 1°C above base temperature in 24 h. Three base temperatures were considered (9, 11, and 12.5°C). The flowering periods of most of the studied cultivars overlapped to some degree in each experimental year. The earliest start of flowering was recorded in 2007, while the latest start date was delayed for nine days in 2005. Duration of flowering period differed between cultivars and ranged from six to nine days. The temperatures during the months prior to anthesis influenced the onset of the flowering. A positive correlation was found between FD, CU and GDD, respectively. The highest correlation (R2=0.655) between FD and GDD was found when the threshold temperature was set to 9°C.

anthesis, chilling units, growing degree days, Olea europaea L., threshold temperature

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