Genetic material

San Luis variety ancho pepper seeds, packed on February 16, 2017.

Treatments

Three products were used: KNO₃≥ 99.6% (2, 4 and 6% w/v), promoter I (0.5, 1 and 1% v/v), promoter II (1, 2 and 3% v/v) and as control distilled water for imbibition of the seeds. All the products were diluted in distilled water.

Location

The tests were carried out in the Seed Physiology Laboratory of the Center for Training and Development in Seed Technology (CCDTS), of the Autonomous Agrarian University Antonio Narro (UAAAN), which is located between the geographic coordinates of 25° 22’ of latitude north and 101° 02’ west longitude and at an altitude of 1 742 m.

The experiment was carried out in two stages

Stage I. Imbibition curves

To determine the imbibition curve, the weight of 120 seeds was taken on an Ohaus analytical balance with a precision of 310 g x 0.001 g, then submerged in 20 ml of distilled water for the controls and 20 mL in solution of each treatment, for this, 40 mL beakers were used. During the first 12 h, every 2 h, the seeds were drained in plastic strainers, dried with absorbent paper towels and weighed again; this activity was repeated every 12 h until the end of the process at 48 h (0, 2, 4, 6, 8, 10, 12, 24, 36, 48 h). The volume imbibed (mL) of the treatments by the seeds, was determined with the difference of weight between the initial weight and the final weight, the imbibition of the units of weight was calculated, transforming them to units of volume (on the basis of which 1 g of increased weight= 1 mL imbibed).

Stage II. Germination tests between paper

After 48 hours, the seeds were sown between anchor paper moistened with distilled water, 4 repetitions per treatment of 25 seeds each, rolled into a cue and placed vertically in plastic bags inside a Thermo Cientific bioclimatic chamber (Precision) at a controlled temperature of 25 ±2 °C and photoperiod of 16 h light/8 h of darkness (^{ISTA, 2016}). Germination was evaluated at 21 days by quantifying percentage of: normal seedlings (PN), abnormal seedlings (PA) and ungerminated seeds (SSG), in addition to the plumule (LP) and radicle (LR) lengths, which were measured with a millimeter paper template and the mean per repetition of each treatment was determined.

The percentage of normal seedlings (PN) was considered as the total of those whose essential structures were well developed under favorable conditions of water, light and temperature (^{Moreno, 1996}), were counted and divided between the total of seeds planted between paper, in the same way the percentage of abnormal seedlings (PA) and ungerminated seeds (SSG) was obtained.

For the study of the variables the statistical package Statistical Analysis System (SAS) version 9.0 (^{SAS Institute, 2002}) was used, with the data an analysis of variance was carried out (Andeva). The mean values were submitted to the Tukey test p≤ 0.05.

Stage I. Imbibition curves

For the first phase of the germination process, it was observed among the seeds, that the highest imbibition rate occurred during the first 2 h (Figure 1a and 1b), raising its initial dry weight to 46%; after 2 h, the increase in weight was slower as time passed.

Figure 1 a) imbibed volume (mL) of 120 ancho pepper seeds during 48 h, in nine treatments; b) imbibed weight (g) of 120 ancho pepper seeds during 48 h, in nine treatments.  

After 24 hours, the second phase of the germination process was reached, registering an increase of 78% with respect to its dry weight (Figure 1b). In this second stage of germination, a constant behavior was observed in the hydration of the seeds, there was no emergence of radicle in any of the evaluated treatments, that is to say, no phase III was reached.

This is attributed to the fact that the water capacities of the seed and of the solution come into equilibrium, so that the metabolic processes stop when liquid is not introduced into the seed (^{Akers and Holley, 1986}), which prevents the radicle emergency occurs. ^{Sousa et al., (2006)} reported that during the process of imbibition of Swietenia macrophylla seeds, the increase in the weight of the seed was greater, with respect to the volume, which was discrete. In this experiment the same behavior was observed in the imbibition curves for the first two phases of the germination process; that is, the first of rapid absorption of moisture and the second stationary phase that was characterized at the end, by the absence of solution absorption of the treatments (Figures 1a and 1b), without reaching stage III.

The analysis of variance did not show significant differences (p≤ 0.01), for the increase in grams of weight in the seeds and the volume imbibed (mL) of solution between the treatments (Table 1); this is due to the fact that the rates of absorption of solution in the seeds exposed to the different treatments were uniform, which indicates that the type of conditioning solution of the treatments did not influence the water disposition by the seed.

Stage II. Germination tests between paper germination

According to the analysis of variance, in all the variables: percentages of normal seedlings (%PN), abnormal seedlings (%PA), ungerminated seeds (%SSG), plumule length (LP) and length of radicle (LR) significant differences were obtained (p≤ 0.01) between treatments (Table 2).

It is important to mention that due to the possible deterioration that the seeds presented, the percentage of normal seedlings had variable responses that is confirmed by observing the result of the control (34%), with respect to the KNO₃ treatments at 2 and 6% and the promoter II at 1%. The treatment with promoter I at 1.5% showed a better percentage of normal seedlings (Figure 2), with 90%, which showed an increase of 56% with respect to the control. This result is attributed to the concentrations of phytohormones and microelements, whose positive effect is expressed with the increase in the percentage of germination, which agrees with the gibberellic acid that could have stimulated in the seeds, the synthesis of the starch for its cleavage in sugars more simple ones such as glucose, which were available as an energy source for the cells of the embryo during the germination process; likewise possibly the concentration of auxins and cytokinins (zeatin) had stimulating effects on the growth of stems and roots and in general in the formation of seedlings, since they promote cell elongation.

Figure 2 Comparison of means in percentage of normal seedlings (%PN).  

With the 4% KNO₃ (47% of PN) a greater number of normal plants was obtained with respect to the concentrations of 2% (6% of PN) and 6% (19% of PN), which coincides with the reported with ^{Garruña et al. (2014)} who evaluated the effect of a concentration close to 3% on the conditioning of seeds of habanero pepper and obtained a positive effect in the emergence of seedlings (91% of PN) surpassing the control (72% of PN).

The seeds imbibed with KNO₃ at 2% obtained the highest percentage in abnormal seedlings with 60% (Figure 3), this result could be due to the concentration of the treatment, in addition to the effects of potassium nitrate on the process of germination in pepper seeds (^{Andrade and Laurentin, 2015}). The treatment with the highest percentage in ungerminated seeds was obtained with the promoter II at 1% with 82% (Figure 3), this result can be attributed to the concentration, since in normal seedlings at 2 and 3% numerically exceeded the control, this increase agrees with the results obtained by ^{Gonzalez et al. (2015)} who with the same promoter at 1.6% and during 24 h of immersion of amashito pepper seed (Capsicum annuum L. var. Glabriusculum), significantly increased the germination up to 86%.

Figure 3 Comparison of means in percentage of abnormal seedlings (% PA) and non-germinated seeds (% SSG).  

In relation to plumule length (LP), according to Tukey, significant differences were obtained (p≤ 0.05), in Figure 4 it is observed that the KNO₃ treatment at 4% was statistically better with 3.69 cm, the previous coincides with the exposed by ^{Shim et al. (2008)}, mention that this product favors the metabolic repair of tissues and the increase of respiration, which improves the rate of growth and germination. The treatments were followed: KNO₃ at 2% with 3.50 cm, KNO₃ at 6% with 3.28 cm, promoter II at 1% with 3 cm, compared to the control which was 2.74 cm. For the variable length of radicle (LR) in Figure 4 it can be seen that the promoter II at 1% was statistically better at 14 cm.

Figure 4 Comparison of means in length of plumule (LP) and length of radicle (LR).  

Although they were statistically equal to the control, numerically exceeded, the treatments: Promoter II 3% with 12.03 cm, Promoter I with 1% with 11.77 cm, 0.5% with 11.53 cm, 1.5% with 11.48 cm and promoter II with 2% with 11.29 cm. It is important to note that although the latter at 1%, it was statistically similar to the control, this treatment obtained the lowest percentage of normal seedlings (2%) (Figure 4).