1. Introduction
New trends in global consumption are geared towards fresh, healthy, and safe foods that are sources of vitamins, proteins, and fiber, increasing the global demand for these foods [
1]. The yellow pitahaya is listed by the International Colombia Corporation (CCI) as a promising fruit for export because of its sensory and organoleptic attributes and its prevention of some disorders related to oxidative stress [
2,
3], as well as some respiratory, gastrointestinal, and urinary disorders [
4,
5]. It has attracted attention not only because of its flavor, color, and attractive appearance but also because of its enormous health benefits [
6,
7]. Currently, pitahaya is the most important cactus in the country and one of the most important native genetic resources from ethno-botanical and economic points of view [
2].
At the global level, the main importing countries are the United States, Japan, the European Union, and Canada, while the main exporters are Israel, Mexico, and Nicaragua. Colombia provides 38% of the international exports, reaching 17,773 t in 2018, where the main producing departments were Huila, Santander, and Boyacá [
8], The latter has edaphoclimatic conditions and an advantageous geographical position that focus economic activities on traditional agriculture, with 12 yellow-pitahaya-producing municipalities that yield 6.59 t ha
−1 [
8]. Despite its productive potential, limiting factors in the development of this crop in Colombia include the high incidence of pests and diseases, the low fruit quality, the technological level, the associativity, and the lack of certified planting material, which generate significant crop losses [
3,
9,
10].
The pitahaya is a native fruit that has not been domesticated; however, genetic variants related to improving fruit size, increased sugars, ease of vegetative propagation, parthenocarpy, loss of thorns and self-incompatibility, and resistance to pests, as well as increased productivity, quality, storage, and shelf-life, have been selected [
2]. Worldwide, morphological characterization studies on yellow pitahaya have found great morphological and genetic heterogeneity in many of this fruit’s characteristics, such as sweetness, size, shape, color, and number of bracts, resulting from intra- or interspecific hybridizations between different cultivated and wild materials, which make it difficult to raise quality standards for the export market, posing serious problems when it comes to improving yield and post-harvest shelf-life [
6]. Studies carried out by [
6] through morphological, biochemical, and molecular characterizations allowed the correct identification of four
Hylocereus species. The authors of [
11] determined in Pangadaran that differences in the morphological, physiological, and anatomical structures of the plants allowed them to adapt to different agroclimatic conditions. A previous study showed that morphoagronomic characterizations could be used to determine the variation in natural pitahaya populations [
6].
In Colombia, morphological, molecular, and biochemical characterization studies are scarce [
3]; most studies have been focused on the physiological component of seeds for in vitro propagation and on the identification of limiting pathogens in production, among others [
12,
13,
14,
15]. Morphological and molecular characterization studies carried out on the germplasm at the Department of Boyacá have shown that there is genetic diversity in the province of Lengupá, which is the basis for the establishment of any selection process that would identify elite materials that respond to the needs of the farmer, producers, and consumers.
Selenicereus megalanthus, or yellow pitahaya, a native fruit tree, constitutes a key product for the fruit and vegetable sector, with significant demand for its flavor, appearance, quality, and nutraceutical properties. In addition, it has market potential, both domestically and internationally. However, the prospects for the international market require research to raise the fruit quality and to supply elite genotypes for planting and managing the production chain with added value.
The municipality of Miraflores has the productive potential to make pitahaya an economically profitable crop, but first, it must generate strategies to promote cultivation in a technical way to position itself with the highest quality and develop research and technology for the yellow pitahaya production chain. Therefore, this research seeks to morphoagronomically evaluate yellow pitahaya genotypes in the municipality of Miraflores to identify elite genotypes adapted to the edaphoclimatic conditions that respond to current market needs.
4. Discussion
The yellow pitahaya (
Selenicereus megalanthus Haw.) is native to the southern and central regions of Mexico and the Americas. It is an exotic and nutritious fruit tree that is cultivated in the tropical and subtropical regions of the world. Pitahaya production has attracted interest from the United States, Australia, southeast Asia, Israel, and other regions [
1]. This fruit has attracted considerable attention from consumers because of the particular shape of the fruit and its richness in polyphenols, vitamins, sugar, amino acids, and betalains [
20]. In addition, it presents great adaptation to extreme environmental conditions [
12], mainly because of its broad phenotypic and genetic variations in its fruits and cladodes [
3,
6,
21].
Taking into account the results obtained in the diagnostic census of the production systems for yellow pitahaya in open fields and under cover, it was observed that, despite the fact that it is an export crop in growing demand both nationally and internationally, there is no technological package for this crop that is applied by all producers (
Figure 1). Rather, they use empirical practices for the agronomic management of the crop, which has led to many farms not being highly productive and yellow pitahaya not generating the expected profitability. Hence, characterizations of the germplasm and sustainable management alternatives that result in better crop productivity in the municipality of Miraflores are needed.
In this study, the evaluation of 12 yellow pitahaya genotypes in the municipality of Miraflores showed a significant phenotypic segregation for both the qualitative and quantitative characteristics associated with fruits and cladodes in the two productive systems (open field and under cover) (
Figure 7). This has been reported previously in characterization studies of
Hylocereus germplasm at the international level, where the wide variation in fruit characteristics was confirmed, along with the usefulness of morphological descriptors in the discrimination and identification of species in the genus
Hylocereus and
Selenicereus [
6], as well as the adaptability to different environments [
11].
Results similar to those obtained in this study for the characteristics associated with cladodes have been found in studies of morphological characterizations for
Hylocereus species, as reported by [
9,
22], who concluded that the more discriminating characteristics for cladodes included texture, the presence of wax, the distance between areolas, the height of undulations between successive areolas, the number of spines per areola, the color of the spines, and the pigmentation of the buds. The authors of [
23] stated that the main differences between
Hylocereus species were the size and color of the fruits and the shape and number of the spines. This affirmation corresponded with the analysis carried out on 12
Selenicereus materials, in which differences were observed in the shapes of the stems and the spines (
Figure 5). The authors of [
24] stated that the number of spines per areola was just as important as the height of the undulations because it differentiated genotypes. However, [
25] observed statistical differences in the stem variables, one of the most important being the presence of wax. The authors of [
26] carried out a study on the effect of pollination methods on fruit set and fruit characteristics in several pitahaya clones to improve fruit quality and yield by making pollination processes more efficient. Pitahaya plants grown in Pasuruan, Sukaharjo, and Bantul showed significant differences in cladode morphology between the different species and varieties [
27]. Variations in stem morphology, such as stem curvature, margin hardness (presence of sclerenchyma), distance between the areolas, number of spines, rib height, rib thickness, length, and stem color are important for species differentiation [
22].
In this study, it was observed that most of the genotypes (more than 70%) exhibited phenotypic variability for the pigmentation characteristics of the vegetative shoots (PVS), the shape of the margins between the areolas (MSA), and the coloration of the areolas (CAR) (
Table 7 and
Table 8). The qualitative characteristics that presented less variability were the texture of the phylloclade surface (STP), spine color (CES), presence of wax (PW) and fruit shape in both green and ripe states (GFS and MFS, respectively) (
Figure 5). This may be due to the way in which the species propagates (asexual) and the exchange of seeds between producers in the same region or between producing regions, which has led to the homogenization of some phenotypic characteristics [
3].
The evaluation of the yellow pitahaya genotypes in this study showed that the characteristics associated with the fruit were the most variable, which agrees with those that have been found in other pitahaya species by [
2,
3,
28], who have found that the most important characteristics for fruits were length, width, length/width ratio, pulp color, weight of the pulp, number of bracts, length and width of the bracts, fruit weight, pulp color, and Brix degrees, which contribute significantly to the separation of groups. The total soluble solids, being the most desirable characteristic for consumer preference, is measured in °Brix and can be affected by a set of factors, such as genetic, climatic, soil, and management factors, among others [
13]. In the present study, the SS values for the yellow pitahaya materials evaluated under cover and in open fields were 14.7 and 15 °Brix, respectively (
Table 7 and
Table 8).
The chemical analysis of the present study also corroborated the results obtained by [
29] for the concentration of soluble solids (SS) in mature fruits, who recorded values between 10.23 and 18.84 °Brix with an average of 14.27 °Brix. In [
30], a study carried out in Ecuador on fully mature
S. megalanthus fruits, the authors found that the content of soluble solids reached 20.74 °Brix, significantly different from the present results where the genotype that showed the highest content of sugars only accumulated 17.6 °Brix. In general, the values obtained in this study in terms of SS showed that the materials had good fruit quality since previous studies have reported SS values between 11 and 15%, with a good preference in the market [
2].
For fruit weight, most genotypes had values above 100 g, which is a desirable characteristic for the market (
Table 5 and
Table 6). The materials with the highest weights were genotype 15 (223.20 g), genotype 3 (265.60 g), and genotype 5 (278.50 g). The results are comparable to those obtained by [
29] in the physicochemical and proximal characterization of yellow pitahaya cultivated in Colombia, where the average fruit weight was 222.81 g, 16% higher than that found in the genotypes of the covered system and only 1.7% greater than those of the open-field system. In addition, the percentage of pulp in relation to the total weight of the fruit was 62.64%, 15% higher than the average in both systems. The study in question covered other localities, including municipalities in the Department of Valle del Cauca, where variables such as fruit weight and pulp weight were predominant over the other materials, reporting values of 348.95 g and 225.40 g, respectively, 15.81% higher than the most outstanding genotype in the open-field system (
Table 5) and 20.18% higher than the best genotype in the covered system (
Table 6,
Figure 5).
According to Colombian Technical Standard NTC-3554,1996 for the classification of yellow pitahaya fruits, the fruits evaluated in this study, according to their unit weight (g), belonged to the following sizes: size 9 (261 to 360 g) for genotypes 3 and 5 (UC, under cover) and genotypes 5 and 7 (OF, open field); size 12 (201 to 260 g) for genotypes 15 (UC) and 1 (OF); size 14 (151 to 200 g) for genotypes 2, 4, 7, 8, 9, 14, and 16 (UB) and genotypes 6, 15, and 17 (OF); and size 16 (111 to 150 g) for genotypes 1 and 6 (UC) (
Table 5 and 6). The fruits from genotype 5 in both production systems belonged to size 9, the second-highest category for the classification of fruits according to their weight (ICONTEC).
The titratable acidity (TA) reached an average value of 0.20 for both systems, registering maximum values of 0.28 in genotype 3 of the covered system and 0.24 in genotype 17 of the open-field system (OF), as well as minimum values of 0.13 in genotype 8 (UC) and 0.18 in genotypes 5, 7, and 15 (OF) (
Table 5 and 6). Studies carried out on
Hylocereus undatus Haw in three stages of maturity showed that the percentage of titratable acidity (TA) in the state of complete maturity decreased from 0.63 (harvest time) to 0.10 (at the end of storage) [
31]. Studies in other countries have found great variation in characteristics of agronomic importance, even within the same species of
Hylocereus spp. and
Megalanthus [
6,
13,
22], which is favorable for future breeding studies. Several studies on diversity in dragon fruits have been reported. For example, a study by [
32] found variations in dragon fruits based on morphology, isoenzymes, and vitamin C content in the Pasuruan (East Java), Sukoharjo, Klaten (Central Java), and Bantul sub-districts (Yogyakarta).
Apart from differences in species or accessions, differences in fruit morphology may be related to changes at the physiological level in various stages of fruit development [
32]. The main differences between various
Hylocereus species were reported in terms of the size and color of fruits and the number and shape of spines [
23]. In addition, the variety and flowering time have large influences on the physiomorphological characteristics of pitahayas [
24,
33].
In Colombia, morphoagronomic characterization studies of pitahaya species have obtained results similar to those reported in this study, highlighting the existence of genetic variability that can be used in conservation and genetic improvement programs that can lead to the identification of elite materials, where genotypes 7 and 6 could be good production alternatives. However, it is necessary to complement these morphological characterization studies with biochemical and molecular data that better discriminate the germplasm given the limitations of this type of descriptor. Research on yellow pitahaya plants should be intensified by emphasizing value chain and production aspects for a long-term perspective.