American Journal of Plant Sciences, 2013, 4, 19-25 doi:10.4236/ajps.2013.47A1003 Published Online July 2013 (http://www.scirp.org/journal/ajps) 19 The Effect of High Day and Low Night Temperature on Pollen Production, Pollen Germination and Postharvest Quality of Tomatoes B. Khanal, A. Suthaparan, A. B. Hückstädt, A. B. Wold, Leiv Mortensen, H. R. Gislerød Department of Plant and Environmental Sciences, The Norwegian University of Life Sciences, Ås, Norway. Email: lei-mo@online.no Received April 25 th , 2013; revised May 26 th , 2013; accepted June 15 th , 2013 Copyright © 2013 B. Khanal et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT Temperature integration where high day temperatures are compensated by lower night temperatures is one strategy that can be used to reduce energy consumption in greenhouses. Crop tolerance to temperature variation is a prerequisite for using such a strategy. Greenhouse experiments were conducted on tomatoes cvs, Capricia, Mecano and Cederico in order to investigate the effect of different day/night temperature regimes (24/17, 27/14 and 30/11˚C) where the same mean temperature was maintained for the production and germination of pollen. In addition, fruit quality as determined by fruit firmness, dry matter content, soluble solids, titratable acids, and pH was examined at harvest and after seven and 14 days of storage. The 30/11˚C treatment significantly increased pollen production and germination compared to the 24/17˚C treatment, while the 27/14˚C treatment was generally in between the other two treatments. Fruits grown at the 27/14˚C treatment were significantly firmer, while fruits grown at 24/17˚C had higher dry matter content, soluble solids, and titratable acids compared to the other treatments. There were significant differences between cultivars with respect to firmness, dry matter, titratable acidity, and pH. The quality of the fruits changed during storage, but the stor- ability of the tomatoes was not affected by preharvest temperature treatments. The overall conclusion was that the 27/14˚C treatment was superior to the other two temperature treatments with respect to the studied parameters. Keywords: Daily Mean Temperature; Day Temperature (DT); Night Temperature (NT); Pollen; Temperature Integration; Dry Matter; pH; Titratable Acids; Soluble Solids; Postharvest; Tomato 1. Introduction Temperature integration where high day temperatures are compensated by lower night temperatures is an important means of reducing energy consumption in greenhouses [1]. Temperature increases with increasing irradiance to a maximum accepted level at which ventilation takes place, and the night temperature is reduced sufficiently to se- cure an optimal mean temperature level. Depending on the season and weather conditions, energy savings of more than 20% can be achieved by means of such temperature control [2,3]. However, the effectiveness of temperature integration depends on the plant’s ability to tolerate tem- perature variation. Results of studies conducted on a wide range of vegetables including tomato and ornamentals, have shown that within a certain temperature range, grow- th and development respond to the mean daily tempera- ture rather than to the day/night temperature variation [4- 6]. Tomato is an important vegetable worldwide, in which temperature is known to affect various physiological as- pects, including pollen viability and fruit quality [7]. It has been reported that pollen germination was signifi- cantly reduced when tomatoes were grown at tempera- tures of up to 32/26˚C day/night temperature [8]. To- mato quality includes visual characteristics such as color and firmness, nutritional constituents, and organoleptic cha- racteristics such as aroma compounds and the content of sugar and acids. Dorais et al. (2001) reviewed the quality of greenhouse tomatoes [9], and the fruit quality might be affected by high and low temperatures as well as the differences between day and night temperatures [10]. The effect of preharvest and postharvest factors, including temperature, on soluble solids in tomatoes has been re- viewed [11]. For cherry tomatoes, the percentage dry weight, glucose, and fructose were found to be higher in fruits developed under high temperature variation (30/ Copyright © 2013 SciRes. AJPS