IS CHILLING A PREREQUISITE FOR FLOWERING AND FRUITING IN OLIVES?

Authors: Malik, Nasir; Bradford, Joe

Submitted to: International Journal of Fruit Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2005
Publication Date: 7/16/2006
Citation: Malik, N.S., Bradford, J.M. 2006. Is chilling a prerequisite for flowering and fruiting in olives? International Journal of Fruit Science. 5(3):29-39.

Interpretive Summary: It is generally believed that induction of flowering in olives requires winter chilling (i.e., average night temperatures of 7.2ºC or below), and that for optimal flower and fruit production chilling temperatures of 2-4ºC are required for several nights. Such temperatures rarely occur in southern and coastal Texas; therefore, cultivation of olives in these areas has been discouraged. While experimenting with the 'Arbequina' tree, a common cultivar of olives, we discovered that trees of this cultivar flower and fruit quite extensively while kept at nighttime temperatures higher than 10ºC. Since the nighttime temperatures in our controlled environment experiments were comparable to or higher than the ambient temperatures in southern Texas, we hypothesized that the lack of flowering in southern Texas is not due to insufficient nighttime chilling as was thought previously, but is due to the presence of too many days with high daytime temperature (above 20ºC). This information could be used to exploit olive cultivation in coastal areas that do not experience high daytime temperatures during winter even though optimal nighttime chilling temperatures do not occur frequently in these areas.

Technical Abstract: It is generally known that olives (Olea europaea) require several days (over 80 days) of chilling temperatures ('7.2ºC) for flower induction; minimum nighttime temperatures between 2-4ºC, and maximum daytime temperatures of 15.5-19ºC are considered optimum for flower and fruit production. Environmental chamber studies were conducted on potted olive trees for the purpose of defining flowering conditions for 'Arbequina'. We observed, and then confirmed, the second year, that good flower and fruit production in 'Arbequina' can be achieved even when the plants are subjected to zero days (even zero hours) of 'chilling' temperature or any chilling criteria that had previously been described necessary for flower and fruit production in olives. This phenomenon could be of great practical value because the results obtained can be exploited to cultivate olives in subtropical climates (e.g., southern and coastal Texas) where typical 'chilling' temperatures are not commonly observed for prolonged periods of time.