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*Corresponding author: Georgios Salachas, Department of Agricultural Technology, Laboratory of Plant Physiology and Nutrition, Technological Educational Institute of Western Greece, Campus Amaliada, 27200, Patras, Greece. E-mail: gsal@teimes.gr Received: 30 May 2015; Revised: 04 November 2015; Accepted: 08 December 2015; Published Online: 08 December 2015 Salachas, et al.: Aeroponic basil. Yield and nutritional quality 912 Emir. J. Food Agric ● Vol 27 ● Issue 12 ● 2015 air oxygen, promoting thus root metabolism and plant growth (Chiipanthenga et al., 2012), in comparison with hydroponic and soil cultivations. This study investigated the impact of the available root-zone volume on the yield and nutritional quality of sweet basil plants grown aeroponically. MATERIALS AND METHODS The experiment was carried out at a fully automated aeroponic greenhouse farm (500m2), located at Mesolonghi (lat. 38°59′N, long. 22°36′E), near the coastal area of Western Greece. The detached greenhouse was situated in the north-south direction. The closed recirculated aeroponic system consisted of three growing canals (x three replications). The growing canals are made of polystyrene insulated material of rectangular section, with constant length 10 m, width 0.67 m and depths of 0.15, 0.30 and 0.70 m. The canals were covered with polystyrene panels with three parallel holes for holding the plants. Totally, 450 sweet basil seed plants of about 10cm height each transplanted (after washing the roots in order to remove the soil) in the aeroponic growing canals. A high pressure irrigation system with two parallel pipes containing aeroponic sprayers was installed inside the structures in the bottom of the canals. The roots of the plants were sprayed by the nutrient solution for 25 sec every 5 min. The whole system was controlled electronically. Plants were grown under conditions. The root zone was automatically set to 20oC. The dry biomass content, the root length, the shoot high and the number of leaves per plant were measured every 10 days during the growing period. The rate of net photosynthesis, the rate of transpiration, the stomatal conductance, the chlorophyll content and the total phenolics content of roots and leaves were also determined at the end of the growing period. Nutrient solution The nutrient solution used for irrigation had the following macronutrient composition, (mM): K+, 6.5; Ca2+, 3; Mg2+, 0.9; NO3 -, 6.75; NH4 +, 0.36; H2PO4 -, 1.6 and micronutrient (μM): Fe2+, 30; Mn2+, 5; Zn2+, 4; Cu2+, 0.75; B+3, 30; Mo+6, 0.53 pH was adjusted to 5.6 by the use of HNO3 and the electrical conductivity was kept at 1.70 dS m-1. The temperature of the nutrient solution was kept at 20o C automatically. Preparation of the nutrient solution, adjustment of pH and electrical conductivity were controlled electronically. Gas exchange measurements Gas exchange measurements were conducted for seven fully expanded, mature leaves per experimental set of conditions using the LCI Portable Photosynthesis System (ADC, BioScientific Ltd., England). In this system, CO2 is determined by an infrared gas analyzer and H2O is recorded with two laser trimmed humidity sensors. Experimental measurements included net photosynthesis rate (μmol CO2 m -2 s-1), transpiration rate (mmol m-2 s-1) and stomatal conductance for CO2 diffusion (mol H2O m -2 s-1). All measurements were performed in fully expanded leaves of the same physiological age, at the same daytime and under identical natural light (incident photon flux density on the leaf surface ≈ 1000 μmol m-2 s-1) and temperature conditions (leaf surface temperature was between 25oC and 32oC). Chlorophyll content Three discs (0.9 cm in diameter) from each leaf (first fully expanded leaf) were incubated with 3 ml of dimethylsulphoxide (DMSO 99.5% or 14.8 M; Sigma Chemical Co.) in a glass tube at 65oC for 60 min until the tissue became colorless (Shinano et al., 1996). The absorbances at 665 nm for chlorophyll a and 648 nm for chlorophyll b were determined. The chlorophyll content was evaluated according to Lichtenthaler and Wellburn (1983), using the equations: Chlorophyll a, Chla = 14,85xA665 − 5,14xA648 (mg Chla/ml) Chlorophyll b, Chla = 25,4xA648 − 7,36xA665 (mg Chlb/ml) Total chlorophyll concentration (a+b), Chl(a+b) = Chla + Chlb (mg Chl/ml). Total phenolics Fresh leafs of basil (1 g) were homogenized in an UltraTurrax in 10 ml solution of methanol: deionized water: formic acid in proportion 50 ml: 48.5 ml: 1.5ml respectively for 100 ml solution (Mazza et al., 1999). The homogenate was centrifuged in a cooled centrifuge Centra MP4R (IEC, USA) at 10.000 g for 10 min at 4oC and the supernatant was used for the determination of phenolics. The absorbance of the supernatant was measured at 280 nm. The content of total phenolics was determined using a gallic acid standard curve and was expressed as μgr GAE/gr F.W. Isolation and analysis of the essential oils When basil plants reached full bloom, harvested samples of fresh leaves, stems and flowers, were cut in small pieces and submitted to hydro distillation with a Clevenger-type apparatus for 4 h (1.500 g with 6 lit of water). The essential oils were collected, dried under anhydrous sodium sulfate and stored in dark glass bottles at 4o C until further analysis. Essential oils yield (%) was calculated as per 100 g of dry material. The qualitative and quantitative analysis of the essential oils was performed using a Hewlett Packard 5890 II GC, equipped with a HP-5MS (crosslinked 5% PH ME siloxane) capillary column (30 m, 0.25 mm i.d., 0.25 mm Salachas, et al.: Aeroponic basil. Yield and nutritional quality Emir. J. Food Agric ● Vol 27 ● Issue 12 ● 2015 913 film thickness) and a mass spectrometer 5972 as detector. The carrier gas was helium, (rate 1 ml/min). The initial column temperature was 60oC and gradually increased to 250o C at a rate of 3 oC/min. The total time of the method was 63.33 min. For GC-MS detection, an electron ionization system was used with ionization energy of 70 Ev. Injector and detector (MS transfer line) temperatures were set at 220oC and 290oC, respectively. Diluted samples of 0.1 ml (the solvent was acetone of 99.8% purity) were injected manually and split less. Chromatographic peaks were identified by retention times and mass spectra of authentic compounds when available. Statistical data analysis Mean values of all treatments were compared by one-way ANOVA test and significant differences were determined using Duncan’s test (p < 0.05). All data were analyzed using the SPSS 17.0 program for Windows. RESULTS AND DISCUSSION Growth measurements From the beginning of the growing season and up to the first month, there were small but not statistically important differences in the mean shoot and root dry biomass content (Fig. 1, 2). After the first month, the shoot dry weight of the plants cultivated into canals with depth 15 and 30 cm significantly increased in comparison to plants cultivated into canals of 70 cm depth (Fig. 1). At the end of the growing period, the shoot dry weight of the plants in canals with depth of 15 and 30 cm was doubled compared to that plants grown in 70 cm depth. In contrast, the root dry biomass content of plants grown in 70 cm depth canals increased significantly, in comparison with plants grown in canals with depth 15 and 30cm (Fig. 2). Plants from the third week and from lower depth (15 and 30 cm) growing canals became higher than in 70 cm depth canals (Fig. 3). In contrast, after the first month of growing season, roots from lower depth were significantly shorter in comparison to roots from 70 cm depth canals (Fig. 4). The number of leaves per basil plant significantly increased for lower depth (15 and 30 cm) growing canals than in 70 cm depth canals (data not shown). The above results showed that the available root zone volume was essential for the aeroponic growth of plants. Basil plants cultivated aeroponically in the lower depth (15 and 30 cm) canals had better growth characteristics as shown by increased shoot height, higher number of leaves per plant and increased shoot dry biomass content. In comparison, plants cultivated in deeper, (70 cm) canals, had. lower shoot height, lower number of leaves per plant and lower shoot biomass content, possibly due to inadequate nutrition availability and absorption. By misting or injecting the nutrient solution under high pressure directly and closer onto the surface of the roots (15 to 30 cm), the plants were enforced profoundly with adequate nutritional substances and increased extra-oxygen concentrations (diluted into water droplets), giving to the plants optimum growth and maturation conditions. For the long-term growing periods in the deeper canals (70 cm), the mist system could not Fig 1. Mean shoot dry biomass content of aeroponically cultivated basil plants during cultivation season, in relation to the available

Yield and nutritional quality of aeroponically cultivated basil as affected by the available root-zone volume