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Better understanding of the effects of irrigation frequency and dose on flower production of gerbera plants (Gerbera jamesonii) can lead to optimal water management and crop yield. Measurements of greenhouse microclimate and production and quality characteristics of a gerbera crop were carried out under two irrigation frequency regimens in soilless cultivation in a greenhouse located in Arta, Greece. Irrigation scheduling was based on solar radiation and performed whenever accumulated solar radiation energy outside the greenhouse reached 1650 kJ·m⁻² [high irrigation frequency (HIF)] or 3300 kJ·m⁻² [low irrigation frequency (LIF)]. The amount of water applied was 0.125 mm and 0.250 mm for HIF and LIF, respectively. Stem fresh weight, length and thickness, and number of harvested gerbera flowers were measured along with crop evapotranspiration, crop leaf area, and greenhouse microclimate variables. Measurements started 8 months after transplanting and lasted 90 days (May to July). Leaf area, fresh weight, harvested cut flowers, and the main quality characteristics of gerbera flowers (stem length and flower diameter) were unaffected by the irrigation frequency. In the framework of the experiment, simple formulas for calculation of leaf area index were developed. Finally, a first approach study of an alternative remote sensing irrigation control method using a reflectance index was made and the results are presented.

The use of chemical growth retardants is a standard practice for compact gardenia plant production. The aim of this study was to investigate the possibility of using a photoselective polyethylene greenhouse covering film as an alternative to chemical treatment for production of compact potted gardenia (Gardenia jasminoides Ellis) plants. Two types of experiments were carried out: 1) on gardenia cuttings rooted in rooting benches; and 2) on young potted plants grown under low tunnels. In both experiments, two types of cover materials were used: 1) a photoselective polyethylene (P-PE), filtering light within the wavelength range 600 to 750 nm; and 2) a common polyethylene film (C-PE) routinely used in greenhouse practice. Values of photosynthetically active radiation (in a wavelength of 400 to 700 nm), cover materials' spectral properties (in a wavelength range of 400 to 1100 nm), air temperature, and relative humidity were recorded inside the rooting benches and under the low tunnels. Plant growth parameters (main shoot length and leaf area and lateral shoot number, leaf area, and fresh and dry weight) were determined along the growth cycle. Cuttings rooted under the P-PE film received light with high ζ_n values (ratio of R_n: 655 to 665 nm to far red FR_n: 725 to 735 nm) and high blue (B: 400 to 500 nm) to red (R: 600 to 700 nm) ratio (B:R) and were 68.7% shorter and had 21% lower leaf area compared with cuttings rooted under the C-PE film. Similarly, plants that were rooted and then grown under the low tunnels covered with the P-PE film, compared with plants rooted and grown under C-PE film, were 59% shorter, had 85% lower leaf area, 89% lower fresh weight, and 86% lower dry weight, whereas they did not produce lateral shoots. However, plants rooted under the C-PE film and then grown under the P-PE-covered low tunnels were 26% shorter and developed fewer laterals than plants rooted and grown under tunnels covered with C-PE film. Finally, plants rooted under the P-PE film and then grown under tunnels covered with C-PE film developed into compact, well-shaped plants, because they had a drastic reduction of height (56%) without an effect on leaf area, shoot and leaf fresh and dry weight, and the number of lateral shoots.

Leaf gas exchange and photosynthetic light acclimation of sweet pepper leaves were investigated in a Mediterranean area (central Greece) in the open field and in three screenhouse nets differing in color, shading intensity (SI), and porosity from May to Oct. 2011. The screenhouse nets were two insect-proof white nets (W13 and W34, SI = 13% and 34%, respectively) and a green shading net (G36, SI = 36%). Leaf net CO₂ assimilation (A _n), transpiration rate (E), and stomatal conductance (g _S) were measured by means of a portable gas exchange device on leaves located in three canopy layers. The differences in light regime within the canopy induced by the three shading nets had only a slight effect on A _n, thereby resulting in substantially higher light-use efficiency under shading than in the open field. The observed tendency toward higher g _S in shaded plants was counterweighted by a lower intercellular-to-ambient CO₂ concentration gradient, leading to similar A _n in leaves of shaded and non-shaded plants. Ontogenic effects (leaf aging) appeared to be the main factor determining the decreasing seasonal trend of leaf photosynthetic attributes. Overall, shaded sweet pepper plants display a physiological light acclimation allowing them to maintain the photosynthetic activity to a level similar to that observed in non-shaded plants across a wide range of growth light regimes, irrespective of the type of net and its shading intensity.