The Role of Chilling in Releasing Olive Floral Buds from Dormancy

Abstract

<jats:p>Experiments with olive (<jats:italic>Olea europaea</jats:italic> L.) shoot explants were carried out to determine the influence of winter chilling on the release of axillary buds from dormancy. This investigation was designed to explore an alternative explanation for the confusing concept surrounding the role of chilling in olive floral induction. Leafy explants collected from 10 Nov. to 6 Mar. were grown in a greenhouse under mist at 13/24C (night/day) and in a growth chamber at 10/21C (night/day) to determine the end of dormancy. Growth of floral buds from leafy explants was first recorded from 5 Jan. samples. After that date the percentage of developing floral buds and rate of their development increased. Floral bud abscission, increase in bud fresh weight, and simultaneous decrease of relative bud dry weight were associated with growth initiation of floral buds. Manual defoliation of adult trees during the period of shoot explant collection indicated that leaves play a critical role in development once the floral buds had completed dormancy. Supplementary chilling of isolated shoots collected 20 Jan. demonstrated that 7.2C was sufficient to complete chilling requirements, while 12.5C allowed both the completion of chilling requirements and the proper temperature for subsequent floral bud growth. Winter chilling is required to release previously initiated floral buds from dormancy, and we question the previous concept that the role of chilling is to induce olive floral initiation.</jats:p>

Model for forecasting Olea europaea L. airborne pollen in South-West Andalusia, Spain

“…It was therefore the best variable for predicting both the total annual pollen (pollen index) and the maximum daily value, and should therefore be borne in mind by both allergists and pollen-allergy sufferers. Although winter chilling is required to release previously initiated floral buds from dormancy, Rallo and Martín (1991) and Fornaciari et al (1997) reported a correlation between this variable and the pollen index. In this experiment, neither this variable nor evapotranspiration was included in models.…”

“…In Cordoba, the chilling requirement for arboreal species usually occurs from mid-December to late January; a previous paper reported a mean of 348 chilling hours on the basis of the model proposed by Aron (1983). Since it has been shown that winter chilling is required to release previously initiated floral buds from dormancy (Rallo and Martín 1991), the chilling hours of the preceding year were also taken into account. Evapotranspiration was computed according to the Food and Agriculture Organization rules (FAO 1998).…”

The role of temperature in the onset of the Olea europaea L. pollen season in southwestern Spain

“…With regard to bud break, a certain temperature requirement needs to be met, and this may vary with varieties and climate adaptation. In the area studied (Andalusia, southern Spain), a stress period during the winter is necessary (induced by low temperatures) to break the state of bud dormancy of the summer months (Rallo and Martin 1991;Maracchi et al 1994). This is the case for Olea europaea L., which flowers from April to June in our area, depending on topography (Fornaciari et al 2000).…”

The use of phenological data to calculate chilling units in Olea europaea L. in relation to the onset of reproduction

“…Hartmann and Whisler (1975), who were among the first to carry out morphological studies at different temperatures, showed that olives, if not exposed to cold during the winter ( , ), do not develop flower buds and consequently do not flower. More recently, Spanish researchers Rallo and Martin (1991) studied flower bud development at various temperatures, and reported that 7.2°C is the best temperature for chilling in the olive, while temperatures of 10/21°C favour bud development. At the end of the 1980s, numerous studies reported that flowering is a direct effect of chilling (T ≤ 7.2°C) and that every cultivar requires specific amounts of chilling in order to set fruit. This is evidence of a direct relationship between chilling and the biological development that leads to fruit setting.…”

“…Studies conducted by Badr and Hartmann (1972) and by Rallo and Martin (1991), on the biochemical changes in the olive bud, showed that winter chilling can induce flowering by changing the ratio between endogenous gibberellins and some growth inhibitors (e.g. abscissic acid).…”