Location

The present research work was carried out in module one of a ‘Baticenital’ greenhouse covered with white plastic with a thickness of 720 gauges and 25% shading. The size is 120 m² and it was installed in the Puebla Campus of the Postgraduate College, located at 19° 04’ north latitude and 98° 15’ west longitude, at 2 130 meters above sea level, in the Auxiliary Board of Momoxpan, municipality of San Pedro Cholula, Puebla.

Vegetal material

The plant material used was the saladette-type tomato seed of indeterminate growth variety Santorini from the company ^©King Seeds & Cia SA de CV.

Experimental design

The treatment design was a factorial and the experimental design a completely randomized one, with 16 repetitions. The factors under study were the four substrates, two levels of the Steiner nutrient solution and a growth regulator. For them, 200-cavity polystyrene trays were used. The factors were: red tezontle sand, vermicompost, coconut fiber and peat moss, the latter from the Sunshine brand mix 3. The levels of Steiner nutrient solution at 50 and 100% and the rooting agent (growth regulator) Radix 1500 (with and without), a total of 16 treatments. The experimental unit was a seedling in each tray cavity, using one tray per treatment.

Establishment and management of the experiment

Sowing was carried out on June 7, 2018 in 200-cavity polystyrene trays, which were immersed in 3% sodium hypochlorite for 16 h. The substrates were prepared prior to sowing: the red tezontle sand was disinfected with a solution of water and 10% sodium hypochlorite for 19 h, then it was washed and used for sowing, the vermicompost and the coconut fiber where they were moistened with water for 19 h before sowing and the peat moss was moistened with water 15 min before sowing, leaving it at field capacity. This information was obtained from experimental data. Once the trays and substrates were prepared, they proceeded to sowing, for which 20 cavities of each tray were used, which were filled manually with the corresponding substrates. One tomato seed per cavity was sown and deposited 2 mm deep.

When the seedlings emerged, a daily irrigation was applied manually with rainwater, it was until the seedlings presented the appearance of the first true leaves that the application of the nutrient solution began (Steiner, 1968) in concentrations of 50 and 100% for each of the treatments. The amount of fertilizer used to prepare the 100% concentrated nutrient solution was: 6 g of KNO₃, 11 g of Ca (NO₃)₂, 3 g of KH₂PO₄, 6.5 g of MgSO₄, 6.3 g of K₂SO₄ and 0.8 g of micronutrients Fe, Mn, B, Zn, Cu and Mo. The 50% nutrient solution was prepared equally. As for the rooting agent, Radix (0.15% Indole-3-Butyric Acid) was used as an active ingredient, it was applied when the plant was five days old.

Variables evaluated

The variables evaluated were days to emergency. Days it took at least 50% of the seedlings to emerge. Days to the appearance of the first two true leaves. Time it took for the first true leaves to appear. Seedling height (ALT) (in cm). It was recorded by measuring the base of the stem to the growth point of the last true leaf using a graduated ruler. Stem thickness (DIA) (in mm). The thickness of the stem of the seedlings was measured at the base of the tray, for this a vernier was used. Number of leaves (NH). The number of extended leaflets were counted.

The data of the three previous variables were taken once a week, and with this information, the logistic growth model of ^{Hunt (2017}) was also applied. Fresh weight of biomass and root (PFB) (in g). To measure this variable, the root was cleaned and the weight was recorded using a digital scale. Dry weight of biomass and root (PSB) (in g). For this variable, the seedlings were placed in a drying oven at a temperature of 50 °C for 24 h, then the weight was recorded on an analytical balance, these data were obtained from eight repetitions and were recorded at the end of the experiment (44 DDS). Root length and width (LOR and ANR) (in cm). They were measured using a graduated ruler.

Statistical analysis

The analysis of variance and the Tukey mean comparison test (p≤ 0.05) were performed using the statistical package Statistical Analysis System version 9 (^{SAS, 2002}).

Logistics models

These models allow to express the growth or development of plant parameters, in such a way that for the variables of this study: plant height (ALT), stem thickness (DIA) and number of leaves (NH), the models were used plant growth logistic presented by ^{Hunt (2017}). With the following expression: Y= A/(1+B*EXP^(-C*X)). Where: Y, is the dependent variable (ALT, DAY or NH); X is the independent variable (DDS, days after sowing); EXP, is the natural or natural logarithm (e) = 2.718281828; A, is a parameter that is related to the maximum value of the logistic model curve; B, is a parameter that is related to the ordinate at the origin y; C, is a parameter that is related to the slope of the model at its point of greatest increase. These parameters were calculated with the PROC NLIN program of the Statistical Analysis System of the SAS Institute (^{SAS, 2002}).

Days to the appearance of the first two true leaves

In Figure 1, the days that elapsed from emergence, until the appearance of the first two true leaves in the tomato seedlings, produced in the different substrates evaluated, are shown. Again, the peat moss substrate presented the shortest time in the appearance of the first two true leaves, compared to the rest of the substrates. In general, the coconut fiber and vermicompost substrate took the longest with more than 20 and 30 days to generate the first two true leaves.

In relation, ^{Berrospe-Ochoa et al. (2015}), report that the first two true leaves in tomato take between 13 and 14 days after sowing, data that coincide with the results obtained in the seedlings that were produced in the peat moss and tezontle substrates (11 and 14 days respectively). The appearance of vegetative organs in seedlings is favored by the use of peat-based substrates (peat moss), since their porosity provides greater aeration, with adequate biological characteristics that facilitate the emission of the number of true leaves (^{Sarduy and Castellanos, 2011}).

Figure 1 Days of organ appearance in tomato seedlings produced on different substrates. 

Analysis of variance and test of means of the study variables

The analysis of variance for the rest of the variables evaluated indicates that there were statistically significant differences (Table 1), the means comparison tests are also presented to identify the outstanding treatments (Table 2 and 3).

Seedling height

This variable was adjusted to the logistic growth model (Table 4) and according to the results obtained from the analysis of variance presented in Table 2, there was a significant effect when any of the concentrations of the Steiner nutrient solution was applied to the evaluated substrates. When analyzing this variable, according to the means comparison test (Table 3), it was obtained that the highest seedling height was presented with treatment 8 (P + S100), with a height of 16.3 cm, followed by treatments 12 (P + S50 + E), 4 (P + S50) and 16 (P + S100 + E), which can be observed in Figure 2. For its part, treatment 13 (T + S100 + E) also presented values favorable for seedling height, since a height of 13.4 cm was recorded. ^{Ortega-Martínez et al. (2010}) obtained values of 12-17 cm for the height variable in tomato seedlings grown on different substrates, including peat moss (15 cm).

Figure 2 Height of tomato seedlings produced in different treatments of nutrient solution, substrates and rooting. T= tezontle; V= vermicompost; F= coconut fiber; P= peat moss; S50= 50% nutrient solution; S100= 100% nutrient solution; E= rooter. 

Regarding the application of rooting agent, there were no significant differences (Table 3); however, regarding the application of the nutritive solution, the seedlings with the best values were those produced in treatment 8 (P + S100). ^{Arebalo-Madrigal et al. (2019}) report that the use of rooters in the production of tomato seedlings favors the development of important parameters at the time of transplantation, including the height of the seedling. In addition, the development of the seedlings, in their initial stage, is directly related to the uniformity in germination and this, in turn, can be attributed exclusively to the characteristics of the substrate (^{Fernández-Bravo et al., 2006}).

Stem thickness

In relation to the thickness of the stem, the test of comparison of means shown in Table 2, indicates that the best values were obtained with the substrate and tezontle. For its part, regarding the application of the nutritive solution and rooting agent (Table 3), there were no significant differences, however, in the last sampling carried out the treatments that showed the highest values were treatment 5 (T+S100) and 13 (T+S100+E), as can be seen in Figure 3, which was adjusted to the logistic growth model presented in Table 5.

On average, seedlings with a stem thickness of 2.7 mm were obtained in peat moss and tezontle substrates, while using vermicompost and coconut fiber an average stem thickness of 1.5 and 1.2 mm was obtained, respectively (Figure 3). As can be seen, with these last two substrates a lower quality of the stem is obtained and with it, a lower possibility of success after transplantation.

Stem thickness is an indicator of the vigorous state of a seedling since it directly reflects the accumulation of photosynthates, which can be transferred to demand sites (^{Parra-Terraza et al., 2010}). ^{Fernández-Bravo et al. (2006}), evaluated the emergence of tomato seeds in different substrates (peat moss, compost, coconut sawdust) and obtained values for the variable stem thickness from 0.9 to 1.3 mm.

Figure 3 Variation of stem thickness in tomato seedlings produced in different treatments of nutrient solution, substrates and rooting agent. T= tezontle; V= vermicompost; F= coconut fiber; P= peat moss; S50= 50% nutrient solution; S100= 100% nutrient solution; E= rooter. 

Number of leaves

This variable was also adjusted to a logistic growth model proposed by ^{Hunt (2017}) (Table 6) and, according to the results, there were significant differences between the different substrates evaluated; as can be seen, the seedlings that presented more leaves were those that were sown in peat moss and tezontle, highlighting treatments 5 (T + 100) and 8 (P + S100) in which an average of 5 leaves per seedling were counted, on the other hand, the substrates based on vermicompost and coconut fiber showed the lowest values, 3 and 2 leaves respectively, this also due to the fact that in these substrates the seedlings took longer to emerge (Figure 4).

Figure 4 Number of leaves in tomato seedlings produced in different treatments of nutrient solution, substrates and rooting agent. T= tezontle; V= vermicompost; F= coconut fiber; P= peat moss; S50= 50% nutrient solution; S100= 100% nutrient solution; E= rooter. 

^{Parra-Terraza et al. (2010}) mention that the number of leaves is a valuable indicator in terms of the quality of the seedlings, and that in the case of tomato, the seedlings must present 6 to 7 leaves at the time of transplantation. Regarding the nutrient solution applied, there were no significant differences (Table 3); however, the number of leaves was favored when applying the 100% nutrient solution (Figure 4). Nitrogen is a structural part of the chlorophyll molecule and is the main component of essential proteins for the formation of protoplasm, a higher plant height leads to an increase in the number of leaves, influencing an increase in photosynthesis (^{Espinosa-Palomeque et al., 2019}).

Root length and width

The response in growth of the main root length did not have a significant effect for the evaluated treatments (Table 7); however, the longest root length was obtained in the plants in the treatments that applied rooting and the concentration of the nutrient solution to 100%. ^{Arebalo-Madrigal et al. (2019}) evaluated the use of rooters in tomato seedlings and indicate that these favor the number of roots, root exploration area and root length.

The root width showed the opposite since the highest values were obtained in the treatments where no rooting agent was used and with the 50% concentrated nutrient solution (Table 7). ^{Nava-Pérez et al. (2019}) mention that the longest root length in tomato seedlings was observed when irrigation included higher concentrations of phosphorus; however, roots with smaller size were presented with a concentrated nitrogen solution, a similar trend may have occurred when evaluating this variable (Table 7). Although there were no significant differences due to the use of substrates, the tezontle and peat moss showed the best results and as mentioned by ^{Fraile-Robayo et al. (2012}), this can be attributed to the fact that the germination stage time is very short and the treatments fail to show a significant effect on these variables.

Dry weight of biomass and root

For the variable of dry weight of biomass and dry weight of root, there were no significant differences due to the concentration of the nutritive solution (Table 7). On the other hand, when evaluating substrates, there were significant differences. The substrates that produced the highest values were peat moss and tezontle, with values of 0.49 g and 0.37 g respectively. In relation to the dry weight of the root, with the same substrates, a weight of 0.09 g was obtained. The seedlings that were produced in presented the lowest values for this variable of 0.03 and 0.01 g. The vermicompost and coconut fiber substrates show some type of physical or chemical deficiency that affects the development of the seedlings (^{Cruz-Crespo et al., 2013}).