Submitted to: International Journal of Food, Agriculture, and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 15, 2006
Publication Date: April 12, 2006
Citation: Malik, N.S., Bradford, J.M. 2006. Regulation of flowering in 'Arbequina' olives under non-chilling conditions: the effect of high daytime temperatures on blooming. International Journal of Food, Agriculture, and the Environment. 4:283-286. Interpretive Summary: Cultivation of olives in Texas was previously discouraged because southern and coastal Texas do not experience enough chilling (nighttime temperature below 7°C ) to induce flowering. However, we recently discovered that the ‘Arbequina’ cultivar of olive can produce flowers and fruits in the absence of typical chilling temperatures. Based on this finding, several sites along coastal Texas appear suitable for cultivation of olives. However, several of these sites experience fairly high temperatures during days (e.g. several hours above 24°C) which could adversely affect flowering in ‘Arbequina’. This investigation was therefore conducted to study the effect of daytime temperatures above 24°C on the extent of flowering in ‘Arbequina’. The results of this study show that daily exposure of trees to temperatures around 24°C for 4-5 hours could significantly inhibit flowering in ‘Arbequina’ olives. Additional studies are needed to determine minimal hours at or above 24°C each day, or the number of days during winter when daytime temperatures reach at or above 24°C that would seriously damage the crop. The present results, however, clearly suggest that it would be important to consider daytime temperatures while selecting a site for a new olive grove; i.e., areas that experience fewer days when daytime temperatures reach 24°C or above should be preferred.
Technical Abstract: Recently, we have shown that flowering and fruiting in ‘Arbequina’ cultivar of olives (Olea europaea) can be achieved in the absence of chilling temperatures (less than or equal to 7°C). In our previous studies we showed that absence of flowering in certain subtropical climates (e.g. southern Texas) is not due to lack of chilling temperatures but due to high temperatures during winter days. Based on these initial results, we hypothesized that daytime temperatures less than or equal to 23°C could produce adverse effects on flowering in ‘Arbequina’ olives. In the present study trees were subjected to 24 ± 1°C for 4-5 hrs during the day in temperature-controlled chambers. We found that exposure to temperatures of 24 ± 1°C for a few hours during daytime (from November 15, 2004 until February 15, 2005) could significantly inhibit flowering in ‘Arbequina’ olives while night time temperature was maintained at 9 ± 1°C. In addition, flower formation occurred when nighttime temperatures were raised from 8 ± 1°C to 12 ± 1°C. In the growth chamber where daytime temperatures reached to 24 ± 1°C for 4-5 hrs, three trees flowered even when the night temperatures were kept at 8 ± 1°C. However, these trees flowered again when the nighttime temperatures were raised to 12 ± 1°C. This resulted in a unique phenomenon where new flowers were being formed just a node away from developing or fully developed fruits (but before color change, or maturity). Thus, fruit development seems to have little ramification on the formation of new blooms in olives.