Effects of diurnal temperature alternations and light quality on growth,morphogenesis and carbohydrate content of Cucumis sativus L.

The effects of the difference (DIF) between day/night temperature (DT/NT) and end-of-day (EOD) light quality on growth, morphology, dry matter (DM) content and carbohydrate status in cucumber (Cucumis sativus L.) were examined. Plants were grown under a 12 h high light intensity period and DT/NT of 25/19 °C (positive DIF) or 19/25 °C (negative DIF) in combination with an exposure of 30 min EOD-red (EOD-R) or far-red (EOD-FR) light. A significant interaction between DIF and EOD light quality was found on morphology, DM and carbohydrate content in axial plant organs like stems and petioles, but not in leaf blades and roots. Positive DIF induced taller stems, and higher DM and carbohydrate content than negative DIF when the plants were grown under EOD-R. The stems developed under EOD-FR were tall and accumulated the highest content of DM and carbohydrates and only small differences were found between positive DIF and negative DIF. Under EOD-R a higher content of glucose and fructose was found under positive than negative DIF, while EOD-FR light resulted in a high glucose and fructose content under both positive and negative DIF and thereby equalized the effect of the two temperature treatments. The results show that positive DIF can induce similar responses in elongation growth, DM and carbohydrate accumulation as EOD-FR, and further that phytochrome status interact with the responses to alternating DT and NT.     

Effects of greenhouse cooling method on growth,fruit yield and quality of tomato (Solanum lycopersicum L.) in a tropical climate

A tomato (Solanum lycopersicum L.) crop was grown in four greenhouses during the dry season 2005/06 in Central Thailand. Sidewalls and roof vents of two greenhouses were covered with nets and these greenhouses were mechanically ventilated when air temperature exceeded 30 °C (NET). The other two greenhouses were covered with polyethylene film and equipped with a fan and pad cooling system (EVAP). Overall mean air temperature was significantly reduced by 2.6 and 3.2 °C (day) and 1.2 and 2.3 °C (night) in EVAP as compared to NET and outside air, respectively. Temperature maxima in EVAP averaged about 4 °C lower than in NET and outside. The relative humidity was around 20 and 30% (day) and 10 and 15% (night) higher in EVAP than in NET or outside, respectively. Vapour pressure deficit averaged 0.25 kPa in EVAP, 1.03 kPa in NET and 1.48 kPa outside. The crop water-consumption was significantly lower in EVAP (1.2) than in NET (1.8 L plant⁻¹ day⁻¹), which is ascribed to reduced transpiration in EVAP. Total fruit yield was similar in NET (6.4 kg plant⁻¹) and EVAP (6.3 kg plant⁻¹). The quantity of undersized (mostly parthenocarpic) and blossom-end rot (BER)-affected fruits was reduced in EVAP. However, the proportion of marketable yield was significantly higher in NET (4.5 kg plant⁻¹) than in EVAP (3.8 kg plant⁻¹), owing largely to an increased incidence of fruit cracking (FC) in EVAP. Higher FC but lower BER incidence coincided with higher fresh weight and Ca concentration in the fruits in EVAP. It is concluded that in regions with high atmospheric relative humidity evaporative cooling without technical modifications allowing dehumidification will not improve protected tomato production.     

Cucumber fruit quality at harvest affected by soilless system,crop age and preharvest climatic conditions during two consecutive seasons

Cucumber fruits (Cucumis sativus L., cv. Trópico F1) grown on perlite substrate and NFT (Nutrient Film Technique) were harvested during two seasons (winter and spring) to monitor the effects of climatic conditions and hydroponic growth systems on fruit quality at harvest. The best fruit quality at harvest, as measured by lightness and hue angle parameters, was obtained during the 3 weeks following the first winter picking. When values of a parameter of preharvest climate value called G^* were lower than 0.4 MJ m⁻² °C day⁻¹ interval⁻¹, the cucumber achieved its optimum quality at harvest, as measured by the dark green color of the skin. NFT-grown fruits showed darker and greener skin color (higher hue angle and lower lightness) compared with perlite-grown fruit, irrespective of the season considered. During the winter season, the plant transpiration rate was 30% higher in perlite than in NFT culture, which correlates with higher differences in G^* and 40% additional yield in perlite. However, in spring G^* was not sensitive enough to discriminate between the two hydroponic systems. In general, fruit quality at harvest in spring was lower than during the winter, due to flesh whitening, higher longitudinal and equatorial calibers, and slightly higher pH, as well as worse epidermal color coordinates (ranging from the dark and dull green color typical of winter fruit to light and a vivid green-yellow color). During the spring season, NFT-grown fruit were less acid than perlite-grown fruit with no apparent correlation with the climatic conditions or fruit nutrition.