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Introduction
Jatropha curcas L., native to Mexico and Central America, belongs to the family Euforbiaceae and has wide adaptation to different edaphic and environmental conditions (Kumar & Sharma, 2008). The species is known in Mexico as piñón or piñoncillo and its fruit is an oval drupe. The seeds are used for the preparation of Mexican foods such as tamales, atole (traditional hot beverage) and mole (Martínez, Siddhuraju, Francis, Dávila, & Becker, 2006).
In Mexico, edible plants of this species are found mainly in the states of Puebla and Veracruz (Martínez, Martínez, Makkar, Francis, & Becker, 2010); they are distinguished by lack of esters of phorbol, which is an alkaloid present in the seeds of J. curcas not suitable for human consumption (Pabón & Hernández-Rodríguez, 2012).
The plant material of J. curcas for cultivation is demanded. The species is used as live fence and its leaves as cattle feed (Toral et al., 2008), while seeds (54 %), due to their high oil content, are used to generate biodiesel (Shah, Sharma, & Gupta, 2004).
Jatropha curcas, not suitable for human consumption, has been propagated in vitro (Jha, Mukherjee, & Datta, 2007), by cuttings (Noor-Camellia, Thohirah, Abdullah, & Mohd-Khidir, 2009) and seeds (Díaz-Chuquizuta, Valdés-Rodríguez, & Tello-Salas, 2017); however, there is little information on the vegetative propagation of the species for human consumption. In this regard, Enciso and Castillo (2010) recommend using cuttings of young material. Kochhar, Singh, and Kochhar (2008) indicate that the age of the tissue, time of collection, biochemical composition, position of the cutting in the mother plant and presence of leaves and buds influence the response to rooting. Previous studies have shown the capacity of rooting of cuttings obtained in different positions of the same branch, and the importance of carbohydrates (Swamy, Puri, & Singh, 2002) and plant hormones (Kochhar et al., 2008), for dedifferentiation of cells in the formation of roots.
The vegetative propagation of J. curcas suitable for human consumption produces uniform individuals, which would facilitate their agronomic management. An easy method of propagating for producers would be advantageous in regions where J. curcas seeds are commercialized or consumed in regional dishes.
The objective of this study was to test a method of vegetative propagation of J. curcas, planted in the field, whose seeds are consumed by humans.
Materials and methods
Experimental conditions
The study was carried out at the Experimental Field Emiliano Zapata (18° 49´ 44.27'' N, 99° 05´ 34.29'' W; 1 059 m) of the Centro de Desarrollo de Productos Bióticos (CEPROBI) del Instituto Politécnico Nacional in Yautepec, Morelos, Mexico. The experiment was installed outdoors in a sandy loam soil with pH 7.21 and 1.11 % organic matter. The average environmental temperature was 27 °C (maximum 38 °C and minimum 7 °C). The vegetative material was collected when the plant was completely defoliated in March (spring) of 2010. The month was chosen based on the study of Evangelista, Serrano, Martínez, Martínez, and Quintero (2010), who evaluated the time of collection of J. curcas cuttings and concluded that the material obtained in March had a better response of rooting and sprouting of buds.
Plant material
A total of ten J. curcas plants (2 m height), for human consumption, were selected at random from an orchard of 900 plants, which was established with seed for 28 years in the CEPROBI. The seeds came from Tionoxtla, Guerrero, Mexico.
The branches of the trees selected were classified as primary (basal), secondary (from the primary branches) and tertiary (branches from the secondary branches) (Figure 1). The cuttings were obtained from secondary and tertiary branches, at a height between 130 and 160 cm from the ground, being the most abundant in the field. Both groups of cuttings had smooth or exfoliating bark that naturally occurs in J. curcas plants (Tavecchio, Reinoso, Ruffini-Castiglione, Spanò, & Pedranzani, 2016). After cutting, a basal portion of the cuttings (10 cm) was immersed in water for 5 min and placed horizontally on a blanket under shade for 24 h. Subsequently, the cuttings were tied and placed vertically on the blanket, where they remained for 15 days while preparing the ground for the establishment.
The size of the cuttings propagated was 55 ± 5 cm in length and they were divided according to the diameter of their base, frequencies, into five groups; the least thick (1.6 to 2.0 cm) came from tertiary branches, and the thickest (3.6 to 4.0 cm), from secondary branches.
Establishment of total carbohydrates
Total carbohydrates were determided by a colorimetric method (Ting, 1956) two months before the establishment of J. curcas in the field and at the end of the experiment, eight months later. At each date of establishment (January, March, May, July, September, and November) five secondary cuttings with exfoliating bark were used, which at the time of propagation, had proximal and distal diameters of 3.6 ± 0.5 cm and 2.9 ± 0.3 cm (high rooting capacity), respectively. These were contrasted with five other tertiary cuttings with smooth bark with proximal and distal diameters of 1.9 ± 0.1 cm and 0.8 ± 0.0 cm (low rooting capacity), respectively. The distal and basal parts were ground and analyzed. Means and the standard error (Di Rienzo et al., 2016) of the total carbohydrates in the basal and distal parts of the cuttings were obtained during the six months of measurement (January, March, May, July, September and November 2010)
Establishment of cuttings in the field
A total of 120 cuttings arranged in a completely random design were planted; 24 for each of the five diameter groups. Previously holes (30 cm deep and 20 cm wide) were drilled, at a distance of 3 m, which were open for five days. After establishment, the plants were irrigated with 2 L of water, using a watering can; each week, 1 L of water was applied per cutting until the end of the experiment and weeded in the drip zone every two weeks.
Variables evaluated and statistical analysis
The variables evaluated in the rooted cuttings were: total height of the plant, number of developed branches, branches with flowering or fruiting, branches with or without leaves and branches with smooth stem or exfoliating bark. The plants were evaluated with a qualitative scale, based on general phenology (Rawson & Gómez, 2001); 1 for individuals without fruit, without leaves or smooth stem, and 2 for individuals with flower or fruit, leaves and exfoliating bark. These evaluations were made 120 days after the experiment was established (Evangelista et al., 2010).
The data of the five groups with different basal diameter and the five variables studied were evaluated by canonical discriminant analysis (CDA) with InfoStat through the discriminant analysis procedure (Di Rienzo et al., 2016). The data of the standardized values in the two canonical functions were subjected to an analysis of variance; subsequently, significant differences between groups were determined by the Tukey test (P ≤ 0.05) (Cruz-Castillo, Ganeshanandam, Mackay, Lawes, & Woolley, 1994).
Results and Discussion
The CDA was used in order to differentiate the five groups of cuttings, generated according to their basal diameters, with respect to the linear relationships of the five variables studied (Cruz-Castillo et al., 1994). Four canonical discriminant functions (CDFs) were obtained from the data of the five study variables in the five groups of cuttings. The first function, shown in Table 1, was used to interpret the results, due to its statistical significance (P ≤ 0.05) and because it explained 89 % of the variation among the five groups of cuttings.
In the standardized canonical coefficients of CDF1 (Table 1), the presence of exfoliating bark, number of branches and height reached the highest absolute values. The values of these coefficients indicated that the discrimination between the five groups of cuttings was influenced, mainly, by these three variables. Likewise, individually, the correlation coefficients of these variables showed greater association with the CDF1 compared to the rest of these (Table 1).
Table 1 Standardized canonical coefficients (SCC) and correlation coefficients (CC) between the first canonical discriminant function (CDF) and the variables measured in Jatropha curcas cuttings.
| Variables | CDF 1 | |
|---|---|---|
| SCC | CC | |
| Height (cm) | 0.72 | 0.61 |
| Number of branches | 0.90 | 0.69 |
| Branches with fruits | -0.25 | -0.12 |
| Branches with leaves | 0.51 | 0.24 |
| Branches with exfoliating bark | 1.44 | 0.54 |
According to Table 2, the group of cuttings with the largest diameter (3.6 to 4.0 cm) had the highest vegetative growth in the field and differed significantly (P ≤ 0.05) from the other groups. The cuttings had height of 104.2 cm, on average, and three branches per plant with presence of exfoliating bark.
Table 2 Standardized canonical mean values of the first canonical discriminant function (CDF) in five groups of Jatropha curcas cuttings.
| Basal diameter of the cutting (cm) | CDF 1 |
|---|---|
| 1.6-2.0 | -1.64 e |
| 2.1-2.5 | -0.72 d |
| 2.6-3.0 | -0.07 c |
| 3.1-3.5 | 0.79 b |
| 3.6-4.0 | 1.57 a |
Separation of means according to the Tukey test (P ≤ 0.05)
On the other hand, Table 3 shows that, in general, the secondary branches had a higher carbohydrate concentration than the tertiary ones. The content was higher in the secondary growth cuttings collected in March.
Table 3 Total carbohydrates in Jatropha curcas cuttings, propagated in March, with different diameter and position in the tree. The secondary stems were exfoliating and the tertiary were smooth.
| Cuttings | Diameter (cm) | Total carbohydrates (g·100 mL-1) | |||||
|---|---|---|---|---|---|---|---|
| January | March | Mei | July | Septiember | Noviember | ||
| Base secundaria | 3.6 ± 0.5 | 13.2 ± 0.1 | 17.1 ± 0.6 | 14.3 ± 0.3 | 9.7 ± 0.4 | 8.8 ± 0.1 | 9.2 ± 0.1 |
| Distal secundaria | 2.9 ± 0.3 | 10.1 ± 0.4 | 15.3 ± 0.6 | 11.8 ± 0.2 | 6.8 ± 0.1 | 7.5 ± 0.2 | 8.9 ± 0.1 |
| Base terciaria | 1.9 ± 0.1 | 8.2 ± 0.1 | 14.2 ± 0.2 | 12.5 ± 0.2 | 6.6 ± 0.0 | 6.9 ± 0.0 | 6.5 ± 0.03 |
| Distal terciaria | 0.8 ± 0.0 | 5.4 ± 0.2 | 10.5 ± 0.4 | 9.2 ± 0.1 | 5.8 ± 0.2 | 5.7 ± 0.2 | 6.3 ± 0.1 |
The determinations were made in the year 2010. ± standard error of the mean.
Higher initial growth is associated with a high concentration of carbohydrates in other species (Swamy et al., 2002). The effects of the exfoliating bark on the initial growth rate of J. curcas plants have not been studied. According to Tavecchio et al. (2016), the exfoliation of the J. curcas bark is related to its ability to grow in environments with low humidity; in this way, individuals of J. curcas exfoliated and vegetatively propagated would have less dehydration. In future studies, individuals with similar diameters with or without exfoliating bark should be compared to assess their rooting capacity.
Cuttings with basal diameters between 1.6 and 3.0 cm showed less vigorous initial growth in the field. These only reached 59.9 cm in height, developed two branches and had no exfoliating bark. The cuttings with 1.6 to 1.9 cm had a mortality of 17 %, reduced capacity to emit branches and lower concentration of carbohydrates. The rest of the cuttings did not die and did not reach the growth of the individuals with diameters of 3.6 to 4.0 cm.
The vegetative development of J. curcas is essential for rooting, since the stems are formed first and then the roots (Kochhar, Kochhar, Singh, Katiyar, & Pushpangadan, 2005). Therefore, an early and adequate vegetative growth will improve initial root production (Jimu, Nyakudya, & Katsvanga, 2009). The basal lateral buds of the group of cuttings with a diameter of 3.6 to 4.0 cm showed tissue thickening in April (20 days after being established in the field), later differentiating into branches with leaves. In that month, the leaves turned up green, with slow growth unlike the buds that developed from the middle part upwards. Individuals with diameters of 3.6 to 4.0 cm showed rapid growth; the leaf primordia showed a reddish coloration and developed long branches and abundant foliage. The propagation of J. curcas per cutting could be related to the time of collection and, due to the differences recorded in the concentrations of carbohydrates (Table 3), by the position of these in the mother plant. The application of auxins in cuttings with smaller diameters could help to improve the growth of the roots as has happened with individuals of J. curcas to produce biodiesel (Kochhar et al., 2005, 2008).
The J. curcas vegetative propagation for human consumption has been carried out in vitro (Sujatha, Makkar, & Becker, 2005), in the greenhouse (Enciso & Castillo, 2010) and in plastic bags prior to establishment in the field (Teniente et al., 2011). In the present study, J. curcas cuttings, vegetatively propageted, were established directly in the field, which is advantageous for the producer who does not have acces to in vitro propagation or use of a greenhouse for cloning. Additionally, plastic bags were not needed for their propagation, which, in some agricultural production systems, contaminate the environment, neither an application of bioregulators was used.
Conclusions
In the selection of cuttings to propagate J. curcas for human consumption, the secondary cuttings with diameters between 3 and 4 cm, with exfoliating bark, coming from trees in full production and with a higher concentration of total carbohydrates will have higher vegetative growth rate, which will ensure the initial establishment in the field. With this method of propagation it is not necessary to apply auxins to promote rooting or use greenhouse; neither is it necessary to plant in polyethylene bags, before establishment.
