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Introduction
The moringa plant (Moringa oleífera) is a native species from India that grows in tropical and subtropical regions throughout the world (Jahn, 1998; Parrota, 2000; Gopalakrishnan et al., 2016). Its foliage is rich in minerals, vitamins and other photochemical essential compounds (Gopalakrishnan et al. 2016), in addition to a high content of antioxidant compounds (Tesfay et al., 2016), with possible use for human consumption, animal feed, medicine, water purification (Rashid et al., 2008), as well as for live fence, windbreaker, green fertilizer, and ethanol production (Pérez et al. 2010). Traditional uses have reported for their leaves, flowers, fruits, seeds and pods (Coppin, 2008). Currently one of the most promoted properties is its capacity to fight human malnutrition, due to its high content of vitamin A and C, calcium, protein, iron and potassium (Lakshmipriya et al., 2016). In animal feed for tropical livestock production, the use of the foliage is recommended, as an agroecological alternative to face the seasonality of the amount and quality of the fodders (Pérez et al. 2010), due to its high protein content of 21.5 to 28.7 (García et al., 2006; Teixeira et al., 2014) and a foliage biomass yield of up to 27 kg MS cut-1 tree-1 (García et al., 2009). In turn, Martin et al. (2013) report that the fruits and seeds are used to obtain other high-quality food resources such as oil. Moringa presents a high adaptation capacity to different soil and climate conditions with temperature ranges of -1 to 48 ºC, with the ideal range of 25 to 35ºC (Gopalakrishnan et al., 2016); in this sense, it has been shown that at higher temperatures the nutrient content of the foliage decreases (Asante et al., 2014). In latitudes without relevant temperature variations, it presents flowering and foliage production throughout the year (Ramachandran, 1980). It adapts to altitudes of 0 to 1800 m (García-Roa, 2003); with rain regimes of 250 to 3,000 mm in slightly acidic or basic soils, flatlands or hills (Thurber & Fahey, 2010). It tolerates dry periods of more than six months (Mendieta-Araica et al., 2013) and can reproduce sexually and asexually (Pérez et al., 2010). The young moringa seeds present a germination rate of up to 90 % under natural conditions (Ahmed, 2014); in these circumstances of the seed age, scarification is not necessary since it does not improve the germination indices (Parrota, 2000); these seeds lose viability six months after their harvest (Fotouo et al., 2016). The scarification treatment can be an option in seeds older than three months old, in which germination can increase up to 7.5 % (Sharma & Raina, 1982; Baskin & Baskin, 2014). Therefore it is necessary to test low-cost scarification methods and easy to apply, to disrupt the dormancy in moringa seeds. Based on this, the objective of this study was to determine the effect of two physical methods of scarification on germination of six-month-old Molinga oleifera seeds and on the development of seedlings in nursery stage.
Material and Methods
Localization and location of the study
The study was carried out in the nursery at Colegio de Postgraduados, Campeche Campus. Located on kilometer 17.5 of the Haltunchén-Edzná federal highway in the municipality of Champotón, Campeche. Localized in coordinates 19º 29’56.80’’N - 90º 32’ 34.65’’W; 19º 29’ 46.02’’N - 90º 32’ 21.89’’W; 19º 29’ 48.01’’N - 90º 31’ 56.64’’W; 19º 30’ 11.56’’N - 90º 32’ 13.55’’W. The sub-humid warm climate with summer rains predominates in the region (García, 2004). The annual precipitation varies between 900 and 1200 mm. The site presents mean annual temperature of 25.5 to 26.4°C and an elevation of 21 m.
Treatments and procedure
M. oleifera seeds of six months of age were used, which were collected in commercial plantations in Yucatán, Mexico. They were sown in polystyrene forest trays with 77 wells and a capacity per well of 210 mL. The substrate consisted in a mix of local black soil and peat moss (50-50). Three treatments were applied: 1) soaking in drinking water for 24 hours, 2) fissure of seed coat with scalpel (done individually in the lab, making sure the embryo was not harmed), and 3) seed without treatment as control. Each tray was considered an experimental unit and there were 10 replicas per treatment. The seeds from the three treatments were sown on the same day after preparation according to treatment.
Variables evaluated
Germination
The germination percentage of all the trays sown for each treatment was measured; they were monitored daily from day 3 to 15 after sowing, and the percentage of germination was calculated with the accumulated value on day 15 with the formula: % G= % [np*100] /77 where: %G= percentage of germination, np= number of seedlings germinated and 77 corresponds to the number of wells in each tray.
Height, basal diameter and number of branches
Five trays from each treatment were randomly selected. From each tray, 10 seedlings were selected and identified on which three variables were recorded.
Height: the length was measured on each seedling selected, taking as starting point the substrate of the tray up to the tallest branch using a calibrated ruler.
Diameter of the basal stem: on all the seedlings selected, the diameter was measured at a height of 1 cm from the surface of the substrate using a digital Vernier.
Number of branches: the branches were counted in each plant selected.
Measurements were made of all the variables every 5 days, starting on day 16 after sowing and until day 40.
Data analysis
The data were analyzed through ANOVA with repeated measurements at the time of GLM with the software STATISTICA V 7.1 (Stat Soft, 2005). The Spearman correlation was performed for the variables evaluated and a Tukey means test p < 0.05.
Results and discussion
Germination
No differences were observed as a result of the scarification method on the germination of M. oleifera seeds; the values observed were 80, 78.4 and 73.5 % for the treatment of soaking in drinking water, control and fissure of the seed coat. The germination values observed in this study are higher than those reported by Barraza (2017) of 54, 37 and 28 % of seed germination in moringa seeds with 24, 48 and 72 hours of soaking. They are similar to those reported by Toral et al. (2013) in eight origins of moringa seeds for which a range of germination was reported of 49 to 84 % under nursery conditions without pre-germination treatment of the seeds. However, the values found in this study with the treatment of seed coat fissure are lower than those reported by González & Navarro (2001) with a similar treatment in Albizia lebbeck where they obtained a germination of 96.8 % in moringa; these differences are because in the M. oleifera seeds there is physiological dormancy, while in A. lebbeck there is physical dormancy, so it responds better to these type of scarification treatments (Baskin & Baskin, 2014). On the other hand, the effect of the treatment in water immersion is more efficient in legume seeds because the presence of suberin in the seeds allows increasing the water imbibition and the exchange of gases necessary for the renovation of embryo growth and germination (Sanabria et al., 2004).
Height
The greatest height of the M. oleifera seedlings was observed with the treatment of soaking in drinking water with an average of 19.07 cm (p < 0.05). The height was different in the five assessments carried out (p < 0.05), it was greatest after 25 days with an average of 26.04 cm (Figure 1). The interaction scarification treatment with age of the seedling presented an effect (p < 0.05) and the highest values were found with the treatment of seed coat fissure after 25 days, soaking in water at 25 and 20 days, and control at 20 days with values of 26.2, 26.2, 24.2 and 22.7 cm respectively (Table 1). The values of seedling height found in this study are higher than those observed by Valdez-Rodríguez et al. (2014), who report values at 25 days post-germination of 7.5 to 18 cm with different substrates. The trend of higher values with the treatment of water imbibition was reported before by Ramírez et al. (2012) in Leucaena leucocephala seedlings. This behavior can be because the availability of water determines the imbibition, which leads to the activation of metabolic processes, increases the metabolism of nutrients, accelerating the rehydration and activating the mechanisms of membrane and biomolecule repair that allow cellular elongation, germination and the development of structural tissue (Doria, 2010: Dubreucq et al. 2000). Similar to the effect described by Jones and Sharitz (1989), who suggest that the seeds that germinate first have an advantage from environmental factors that are temporarily present at the time of germination, such as luminosity, and availability of water and nutrients.
Table 1 Effect of two scarification methods of M. oleifera seeds on the height, basal diameter and generation of branches in the nursery stage.
| Treatment | Age (days) | ||||
|---|---|---|---|---|---|
| 5 | 10 | 15 | 20 | 25 | |
| Basal diameter of the stem (mm) | |||||
| Control | N.R. | 1.2b±0.09 | 1.8ª±0.07 | 1.9ª±0.07 | 1.9ª±0.07 |
| Soaking in water | N.R. | 1.6a±0.08 | 1.9ª±0.04 | 1.9ª±0.06 | 1.9ª±0.05 |
| Seed coat fissure | N.R. | 1.3ab±0.11 | 1.8ª±0.08 | 1.8ª±0.06 | 1.9ª±0.03 |
| Average | N.R. | 0.14b | 0.18a | 0.19a | 0.19a |
| Number of branches | |||||
| Control | N.R. | 3.1ª±0.15 | 4.7ª±0.15 | 5.5ª±0.13 | 5.9ª±0.17 |
| Soaking in water | N.R. | 3.1ª±0.11 | 5.0ª±0.09 | 5.6ª±0.11 | 6.1ª±0.10 |
| Seed coat fissure | N.R. | 3.0ª±0.11 | 4.8ª±0.16 | 5.6ª±0.15 | 6.2ª±0.18 |
| Average | N.R. | 3.1d | 4.8c | 5.6b | 6.1a |
N.R. Not recorded. Different letters in the same line and column indicate significant statistical difference, Tukey p < 0.05.
Basal diameter
The scarification method of the M. oleifera seeds did not influence the development of the basal diameter, and averages of 1.7, 1.7 and 1.8 mm were observed for control, seed coat fissure and soaking in drinking water. The age of the seedling had an effect on the basal diameter of the seedlings (p < 0.05), with the lowest value found after 10 days with a value of 1.4 mm, and similar values recorded at 15, 20 and 25 days (Table 1). A difference (p < 0.05) was found as a result of the interaction of treatment with age of the seedling, with the lowest values observed with control and seed coat fissure after 10 days with 1.2 and 1.3 mm, while the treatment of soaking in drinking water and all the treatments starting at 15 days of seedling age were similar. The values of stem diameter of moringa seedlings at 25 days of age observed in this study are lower than the ones reported by Valdez-Rodríguez et al. (2014), who found values of 2.7 to 4.5 mm. This study did not find that the scarification method had an effect on the development of the basal diameter, which differs from what was reported by Ramírez et al. (2012) who found an effect from soaking in drinking water on the stem diameter in Ziziphus mauritiana seedlings.
Number of branches
No differences were observed between treatments with regards to the number of branches with values of 4.84, 4.9 and 5.0 for control, seed coat fissure and soaking in drinking water. The age of the seedling showed effect (p < 0.05) on the number of branches, which was the highest after 25 days with 6.06 branches (Table 1). As a result of the effect of the interaction scarification treatment and seedling age, the highest values were observed in the three treatments with 20 and 25 days of age. There was also no record of an effect from the type of scarification on the number of branches in the first days of the seedlings. The values observed in this study are lower than those reported by Valdez-Rodríguez et al. (2014) who found 5.2 to 7.3 branches in moringa seedlings at 25 days of age in different organic substrates. Likewise, the trend observed in this study differs from what was reported by Ramírez et al. (2012), who reported an effect from the pre-germinative treatment with soaking in drinking water, sanding down of the seed and gibberellic acid on the variables number of knots and number of branches in seedlings of the legumes Leucaena leucoephala and Pithecellobium dulce, as well as the fruit tree Ziziphus mauritiana.
Correlations between variables
A correlation was observed between the height of the seedling and the number of branches (rs = 0.50, p = 0.0006). The basal diameter was not correlated with the number of branches or with the height of the seedling. This suggests there is a need for fertilization programs in the nursery stage to replace the nutritional requirements of the species and obtain young vigorous seedlings that are apt to be transplanted, given that it has been argued that this process tends to produce physiological stress and that it is higher in older seedlings (Flores et al. 2009). In this sense, Gómez et al. (1986) suggest that the variations in stem diameter of tree and shrub species justifies between 60 and 80 % of the variations in the weight of the branches, which defines the photosynthetic rate and the survival of seedlings in the field.
Conclusions
The physical methods of scarification used in this study did not improve significantly the germination rate of six-month-old M. oleifera seeds. They also didn’t improve the stem diameter or the number of branches of the seedlings emerged from the scarified seeds. Therefore, it is possible to assume that at this age the seeds show a high potential of natural germination, and that they can be used under nursery conditions. However, it is necessary to evaluate the potential of this type of seeds to be used in sowing systems directly in the field. Finally, for seedlings from seeds with long periods of storage, it is advisable to establish fertilization programs to obtain young seedlings with an adequate development of the stem and buds to transplant in the field.
