Cultivation of taioba in hydroponic system ( ebb and flow ) using different substrates

Taioba is a plant species from the group of unconventional vegetables that has currently been introduced into the Brazilian diet. The objective of the present work was to study the technical feasibility of the cultivation of taioba in the hydroponic ebb and flow system and the influence of the substrate. The experimental design was in randomized blocks and the treatments consisted of 10 different substrates: (1) 60% sand + 40% coal powder; (2) 80% coconut fiber + 20% vermiculite vermiculite; (3) 80% Sand + 20% coal powder; (4) 70% sand + 30% humus; (5) coconut fiber; (6) 70% sand + 30% vermiculite; (7) 80% sand + 20% vermiculite; (8) sand; (9) commercial substrate Carolina and (10) 50% sand + 30% humus + 20% vermiculite. The best results were obtained with treatments 2 and 9 for the number of leaves, plant height, stem diameter, transverse and longitudinal leaf diameters, dry and fresh root mass, and dry and fresh plant mass. Except for the total carotenoid contents, no statistical differences were observed for the physical-chemical characteristics. It was concluded that cultivation of taioba in the hydroponic ebb and flow system has technical feasibility. The substrate has influence in the technical feasibility.


INTRODUCTION
Xanthosoma sagittifolium (L.) Schott is a hardwood crop originating from South America and its cultivation and consumption come from Central America, Asia and Africa [1]. In Brazil this species is known as taioba [2]. High temperatures, which can be found in the tropical and subtropical regions, are required for taioba development. Its leaves and rhizomes are used for human nutrition. Its rhizomes are a source of vitamins A and C and also rich in iron, potassium, calcium and manganese [1].
One of the largest obstacles preventing increased production of this crop is related to the scarcity of options as far as the system of cultivation adopted producers. The cultivation is mostly carried out directly in the soil, using its rhizomes. This methodology has limited the expansion of the cultivation area [1]. However, this method makes it difficult to expand the cultivation area since a plant originates a main rhizome and few secondary shoots after six months of cultivation. Thus, seedling production is low with a high volume of material to be transported [1]. Hydroponic cultivation could be an alternative of great potential for taioba production. However, one of the great challenges to cultivate taioba using a hydroponic method is related to the mode of reproduction (vegetative propagation) resulting in the lack of hydroponics utilized in the producing areas.
Alternatively, there are reports of a successful technique called sub-irrigation, which consists of the application of water and nutrients to the bottom of the cultivation pots filled with substrate [3,4,5]. The system can use other equipment, being the most common tables of sub-irrigation (ebb-and-flow). The ebb and flow technique was successfully used for the production of salvia (Salvia officinalis L.) [6]. It was also used for the production of arum lily (Zantedeschia aethiopica L. Spreng.) [3] whose structural part of roots and rhizomes are similar to taioba. Ensinas et al. (2011) [7] report that the development of plants confined in a pot with substrate depends on several factors, and its composition is a factor of great importance, since root initiation and rooting are directly linked to the chemical, physical and biological characteristics of the substrate. Environmental conditions, fertilization, genetic factors, degree of maturation, plant variety, among others, have a large influence on the phytochemical content of vegetables [8]. However, studies that correlate cultivation practices with the production of phytochemicals are rather scarce [9]. On the other hand, accord Vence (2008) [10] in addition to sub-irrigation, it is necessary to correctly define the ideal substrate for the best performance of the plant.
Thus, the objective of the present work was to study the technical feasibility of the cultivation of taioba in the hydroponic ebb and flow system and the influence of the substrate.

MATERIAL AND METHODS
The experiment was conducted in Quintas da Fazendinha (19°30'37.9"S; 44°05'31.9"W) in the region of Matozinhos, central region of Minas Gerais, Brazil. The average altitude is 808 m in relation to sea level. The ebb and flow system was characterized by wooden boxes leveled and waterproofed with black plastic with the following dimensions: 2.70 m x 1.30 m x 0.10 m. At a height of 0.05 m at the edge of the box was placed an exit to return the nutrient solution to a reservoir restricting the capacity of the box to a volume of 175.5 L.
It was used average sand used in civil construction. Is was determinate the aparent density and volume retained by this material after pre-drying in sun obtaining the following results 1.55 kg dm -3 e 0.115 L dm -3 . The Carolina ® commercial substrate had the following constitution: sphagno turf, expanded vermiculite, dolomitic limestone, agricultural plaster and NPK Fertilizer (traces), density: 145 kg m -3 , water retention capacity (CRA), 55%, maximum humidity: 50%, without granulometric specification.
Seedlings of the cultivar Common taioba were produced by shoots treated against Fusarium spp., which were packed in plastic pots drilled with dimensions of 18 cm in diameter at the top, 12.2 cm in depth and 15 cm in height, making up volume of 2719.3 cm 3 which were filled with the substrates tested. After bud bursting, they were transferred to the ebb and flow irrigation system.
The plots were composed of five pots for each treatment. The pots were spaced 10 cm apart, arranged in a randomized block design with four repetitions. A nutrient solution adapted from The circulation of the nutrient solution in the system was adjusted after preliminary trials. From 6 am, the nutrient solution circulates for 30 minutes every 4 hours until 9 pm and circulated again at 6 am the other day, with the same regime. In this way, the plants were sub irrigated by capillarity action with immersion of 30 to 33% of the volume of the pots [14]. This was possible, since in addition to the delimitation output of the nutrient solution volume, a drainage orifice of the nutrient solution was drilled into the bottom of the irrigation system to allow it to return to the reservoir. The drainage orifice has been dimensioned to provide an inlet flow of the nutrient solution greater than the outlet flow allowing flooding up to the 0.05 m box height limit. The nutrient solution was conducted with an electrical conductivity (EC) of 3.5 mS/cm in order to maintain the original nutrient content of the nutrient solution.
Immediately after harvest, which occurred 80 days after planting, the taioba plants were stored in thermal boxes and transported under refrigeration to the Food Conservation Laboratory of Federal University of São João del-Rei (UFSJ), Sete Lagoas, MG, where they were prepared and evaluated for their physico-chemical characteristics and bioactive compounds. Physical characteristics such as number of leaves, plant height, stem diameter and transverse and longitudinal leaf diameters were obtained through counts and direct measurements in the plant using a graduated ruler and digital caliper.
The total soluble solids content (TSSC) were determined by extracting the untreated and filtered leaves of the taioba in natura on the prism of the digital refractometer Reichert R2MINI [15]. To determine the total solids content, five grams of the in natura leaves were placed in crucibles submitted to 105ºC in a sterilization oven and dried to a constant weight. The total solids content was calculated based on the difference between the initial and final masses [15].
The pH was determined using a Tekna T-1000 digital pHmeter by direct electrode immersion in the extract of the macerated and filtered in natura leaves [15]. In determining the titratable acidity (TA), about five grams of the leaves of the in natura sample were macerated, filtered and the extract obtained was diluted in 50 mL of distilled water and titrated with 0.01 N NaOH solution, where the indicator used was phenolphthalein, according to the methodology described in AOAC (2012) [15].
For the determination of the total carotenoid content, the methodology proposed by Rodriguez-Amaya (2001) [16] was followed using in natura samples. After extraction, the total carotenoids were quantified in a Femto 700 spectrophotometer without 450 nm and the results were expressed in μg of total carotenoids per 100 grams of fresh sample. The spectrophotometric method of Folin-Ciocalteau, modified by Neves et al. (2009) [17], was used for the quantification of total phenolic compounds which were expressed in g EAG per 100 g dry sample.
The quantification of the total chlorophyll content was performed according to the methodology proposed by Silva et al. (2009) [18] where in natura samples were used. After extraction with acetone, the quantification was done in spectrophotometer (Femto 700S) at 652 nm. The results were expressed in mg per 100 g fresh sample [19] After the verification of the assumptions by analysis of normality of the residues (Kolmogorov's test), homogeneity of variances (Lilliefors's test) and additivity of the blocks, analysis of variance (test F, p <0.05) was performed and, in case of significant effect, the mean test (Tukey p <0.05) was performed. The analysis were performed with the software GENES [20]. For this work only the data of the first harvest were considered not being evaluated, therefore, data of subsequent harvests as it is common in the commercial production of taioba.

RESULTS AND DISCUSSION
It was observed ( Table 1) that the diameter of the stem (ST) was significantly higher in plants grown with treatments 2 and 9 respectively coconut fiber with 20% vermiculite and commercial substrate Carolina ® . Regarding the number of leaves (NL), only the treatment 3 (sand 80%; coal powder 20%) differed statistically from the other treatments presenting a significantly lower result. According to Santos et al. (2010) [21] the number of leaves is a factor that can be influenced by the environment, so the environment, together with the genetic component of the plant, provides physiological changes. For lettuce, the number of leaves is very important, since it indicates adaptation of the genetic material to the environment and because it is related to commercialization [22], which may be valid for taioba. Longitudinal length of the leaf (LLL) and transverse length of the leaf (TLL) are characteristics that define the size and shape of the leaves. For vegetables whose leaves are the edible parts and therefore marketable, size they are important because define the classification and the commercial standard. It was observed that treatment 2 and treatment 9 were the ones that provided the optimization of these characteristics indicating marketable leaves ( Table 2). The commercial substrate (treatment 9), has its constituent components that probably to potentially absorb nutrients from the nutrient solution, resulting in a better development of rhizomes of the taioba with consequent advanced results currently.
Specifically, sphagno peat, second, increases oxygenation and nutrient availability, has greater water retention, due to low temperature and promotes excellent root development [23], the same with treatment 2 (80% coconut fiber + 20% vermiculite). Coconut fiber is a substrate of excellent use for seedling production because it has good physical properties, long durability without changing physical characteristics [24]. The productivity gains are related to the plants with larger diameter and mass of leaves and stem, which is valid for hardwoods [25].
This feature combined with the larger ST, NL, LLL and TLL shows a robust and well-adapted plant with potential for growth and production. In summary, treatments 2 and 9 were those that optimized all these characteristics indicating the adaptation of taioba to the culture system. As was observed for the characteristics (LLL) and (TLL) ( Table 2), the composition of the substrates referring to these treatments (Sphagno peat, expanded vermiculite, dolomitic limestone, agricultural gypsum, traces of NPK fertilizer and coconut fiber, favored the best development of the plant.  Table 3) that for plant height (PH) treatment 9 (commercial substrate) provided a significantly lower height than the other treatments. For the results of fresh root mass (FRM), dry root mass (DRM), fresh plant mass (FPM) and mass dry plant (MDP), it was also observed that the best results were obtained with treatment 9 These results indicate good response of the plants to the ebb and flow production system and specifically to the substrate. (Tables 3, 4   For Titratable Acidity (TA), Total Soluble Solids (TSS), pH, Carotenoids Total (CT), Phenolic Compounds Total (FCT) and Chlorophyll (C) no significant differences were observed (Tables 5, 6 and 7). In the case of lettuce, chicory and arugula, Arbos et al. (2010) [9] found significant differences in the content of phenolic compounds of these vegetables between organic and conventional cultivation (0.108, 0.092, 0.128 and 0.091, 0.081, 0.090 g EAG), respectively. These values of phenolic compounds were higher than those found for taioba. In terms of total carotenoids (CT), although significant differences were found, this was only due to the substrate 6 (sand 70% + vermiculite 30%), which produced lower total carotenoid content (Table 7). For the different treatments, taioba presented pH values lower than 7 ( Table 6). The pH of this vegetable is similar to that of Caruru (Amaranthus viridis), 6.72 and peixinho (Stachislanata), 6.11 according to a study carried out by Viana (2014) [26] on fresh samples. There are still few studies showing values of titratable acidity, total soluble solids and pH of this herbaceous in the literature and with different substrates studied in this situation.

and 5).
According to Fagundes et al. (2007) [27] the decrease of chlorophyll due to nitrogen deficiency results in the yellowing of leaves and indicates foliar senescence which was not observed in the present study.
The significant differences observed in the agronomic characteristics of taioba, show superiority of the treatments 2 and 9 respectively coconut fiber with 20% vermiculite and commercial substrate Carolina ® . Probably the characteristics of these substrates have provided better root development. In order to evaluate the production of strawberry varieties in different production systems and environment technology, including coconut fiber and charcoal rice husk as pure substrates [28] observed that the best hydroponic production system in all environments was which contained the coconut fiber. On the other hand, the use of the pure commercial substrate Carolina ® probably showed results significantly superior to the others due to the characteristics of its components. Although the coal powder has adequate characteristics, the high value of its pH (9.4) may have had a negative influence on the evaluated characteristics.

CONCLUSION
It that cultivation of taioba in the hydroponic ebb and flow system has technical feasibility. The substrate has influence in the technical feasibility.