Juan Antonio Reyes-Aguero* a, b , Juan Rogelio Aguirre Rivera a
a Instituto de Investigación de Zonas Desérticas, Universidad Autónoma de San Luis Potosí. Mexico.
b Center of Natural Resources and Development, Cologne University of Applied Sciences. Betzdorfer Straße 2. 50679 Cologne, Germany.
*Corresponding author: email@example.com
Mexico is characterized by a remarkable richness of Opuntia, mostly at the Meridional Highlands Plateau; it is also here where the greatest richness of Opuntia variants occurs. Most of these variants have been maintained in homegardens; however, the gathering process which originated these homegardens has been disrupted over the past decades, as a result of social change and the destruction of large wild nopaleras. If the variants still surviving in homegardens are lost, these will be hard to recover, that is, the millenary cultural heritage from the human groups that populated the Mexican Meridional Highland Plateau will be lost forever. This situation motivated the preparation of a catalogue that records the diversity of wild and cultivated Opuntia variants living in the meridional Highlands Plateau. To this end, 379 samples were obtained in 29 localities, between 1998 and 2003. The information was processed through Twinspan. All specimens were identified and preserved in herbaria. Botanical keys and descriptions were elaborated. The catalogue includes information on 126 variants comprising 18 species. There were species with only one variant (Opuntia atropes, O. cochinera, O. jaliscana, O. leucotricha, O. rzedowskii and O. velutina), two (O. durangensis, O. lindheimeri, O. phaeacantha and O. robusta), five (O. joconostle and O. lasiacantha), seven (O. chavena), 12 (O. hyptiacantha and O. streptacantha), 15 (O. ficus-indica), 22 (O. albicarpa), and up to 34 (O. megacantha). Additionally, 267 common cactus pear names were related to those variants.
In Mexico there are 78 wild species of the genus Opuntia (sensu stricto) (Guzmán et al., 2003), several of them prosper in Meridional Highland Plateau of Mexico (Reyes-Agüero and Aguirre, 2006) (Figure 1); relicts of the cactus shrubland, also known as nopaleras for the prevalence of Opuntia populations, still exist in this region (Rzedowski, 1978); furthermore, it is here where the greatest richness of Opuntia variants is found (Barbera, 1995). Many of these variants have become cultivars and have been preserved in homegardens (Figueroa et al., 1980), and in Mexico only less than ten of them have been grown in over 51,112 ha for the production of cactus pear, and in over 10,200 ha to produce nopalito (Gallegos et al., 2009).
Cactus pear cultivars have evolved from a long relationship between Homo sapiens and Opuntia, and most of them are concentrated in homegarden nopaleras (Reyes-Agüero et al., 2005a); however, the process that gave rise to peasant homegardens over the centuries is being lost steadily over the past decades as a result of either the destruction of the large nopaleras and abandonment after emigration of homegardens owners. Therefore, if the Opuntia cultivar richness of the homegardens is lost, it will be hard to recover, that is, this millenary cultural heritage of the human groups that inhabited Meridional Highland of Mexico will be lost forever. The above motivated the preparation of a catalogue to record the richness of wild and cultivated Opuntia variants.
Material and Methods
Field collections were carried out in 29 localities (Table 1) across the Meridional Highland (Figure 1). Opuntia specimens were collected: (1) if variant was valued and grown for the cladode, nopalito or fruit; (2) if the variant was given a clear and unmistakable common name; and (3) if the variant grew preferentially in a homegarden or commercial plantation, although specimens were also collected from wild populations and experimental plantations. A total of 379 variants were sampled, obtaining six replicates from each. Morphological features were recorded using a descriptor (Reyes-Agüero and Aguirre, 2000). One two-year cladode, one nopalito and one fruit were assessed from each replica, and information on 118 traits was recorded. Specimens were processed for preservation (Reyes-Agüero et al., 2007) and deposited in the SLPM, MEXU and CHAP herbaria.
For the statistical analyses, a basic matrix was elaborated followed by a multivariable analysis of classification, using Twinspan program (McCune & Mefford, 1999). All the specimens collected were previously identified based mostly on the keys by Britton & Rose (1919) and Bravo (1978). Afterwards, these identifications were matched to the Twinspan output. Both dichotomous keys and poly-keys were elaborated, based primarily on indicator traits revealed by the Twinspan In most cases, the botanical descriptions comprised the 118 morphological traits. Each description was elaborated according to a standard sequence: starting with the life form and ending with seed characteristics; was described based on mean and modal values from the six replicates; in turn, the description of each species was prepared based on their variants, and the description of the genus was prepared based on its species.
Results and Discussion
The information derived from the 379 samples was used to prepare a catalogue in a book format (Reyes-Agüero et al. 2009); into the catalog the arrangement of species and its cultivars (Table 2) reflect the Twinspan analysis; a complementary multivariate ordination analysis was made in order to review the relationship of morphological variation and process of domestication (Reyes-Agüero et al., 2005a); the core of catalog consists of identification keys and botanical descriptions, including photographs for 126 resulted variants, most of them as cultivars. Almost fifty percent, 197 samples, were carried out from in situ and 182 from ex situ localities (Table 3). About in situ, is important to note that there are cultivars in wild environments and other few are in cropland as fences and/or on agricultural terraces, to give them firmness. The most high percent of samples were from home gardens; this environment is a crucial space for the in situ conservation in order to protect and use the genetic diversity, but also for to develop new variants (Engels 2002; Galluzi et al. 2010), and in this process is important to maintain the link between home gardens and wild environment, from one side and the same time home gardens with commercial croplands, from the other side (Engels 2002).There are 18 Opuntia species with 126 cultivars appreciated for their cladodes, nopalitos or fruits. There were species with only one cultivar (Opuntia atropes, O. cochinera, O. jaliscana, O. leucotricha, O. rzedowskii and O. velutina), two (O. durangensis, O. lindheimeri, O. phaeacantha and O. robusta), five (O. joconostle and O. lasiacantha), seven (O. chavena), 12 (O. hyptiacantha and O. streptacantha), 15 (O. ficus-indica), 22 (O. albicarpa), and up to 34 (O. megacantha) (Table 2). This richness of cultivars is high if is comparable with Zea mays, with 59 landraces in Mexico (Bellón et al. 2008) and 52 in Peru (Tapia 2000) or Persea americana and its three landraces in Mexico (Bellón et al. 2008); but in comparation with Solanum tuberosum with its 1000 landraces also in Peru (Tapia 2000), the richness of Opuntia is very low.
The automated classification enabled to confirm the great Opuntia variant richness previously documented by Figueroa et al. (1980) and Rodríguez and Nava (1998) for Meridional Highlands Plateau of Mexico, but at the same time confirmed the need to use multivariate methods to demonstrate this agrobiorichness in a formal way. This variant richness of wild and cultivated Opuntia valued by the Meridional Highlands inhabitants reveals that the cactus pear has been an important plant for both ancient and current populations. The continued and systematic gather of cactus pear favored that some plants with outstanding traits (fruit shape and size; flavor and texture of pulp or peel; seed hardness and amount; peel thickness and glochid density; and nopalitos shape, color, abundance, precocity, flavor, tenderness and fiber content) were subjected to different degrees of tolerance, favored or planting, and they began to be taken to the homegardens (Colunga et al. 1986, Figueroa et al. 1980). In homegardens, the cactus pear selected found the conditions needed to prosper. In this way, homegarden cactus pear plantations summarize the efforts by generations of collectors to gather the most useful traits out of the genetic diversity of Opuntia in their respective gathering territories, coupled with hundredths of years of care to preserve these cultivars (Reyes-Agüero et al., 2005a).
Seventy six percent of cultivars most of them are related to eight species of the series or section Streptacanthae, with rise to 88% if the O. ficus-indica cultivars are added. This richness of the section Streptacanthae makes of it the likely source of numerous “…horticultural varieties and forms” (Bravo 1978). O. megacantha stands out as the species with the largest amount of variants. There are only 15 O. ficus-indica cultivars which, along with another 22 for O. albicarpa, are the most extensively cultivated in commercial plantations and home gardens; from this two species only O. ficus-indica is absent in wild populations (Bravo 1978; Reyes-Agüero et al. 2004, 2005a, b) and only one sample of O. albicarpa was located in wild environment.
From the cultivars, 31 were obtained only in one in situ locality, without representatives samples in ex situ localities; on the contrary, 32 were only in ex situ localities without representatives samples in in situ localities and 63 were in both kinds of spaces. About this 63, 71.4 % are in one or two in situ localities, 25.4 % are from three to five localities and only 3.17 % are in six or seven localities. During the development of this work, live samples of several cultivars were sent to the three ex situ localities and also to one fourth scientific collection in the Centro Regional Universitario Centro Norte, from the Universidad Autónoma Chapingo in El Orito, Zacatecas, where is the national official depository of the Opuntia cultivars.
As regards the cladode, the Twinspan revealed indicator traits included: shape, length, width, thickness and texture; for areoles: width and length, amount in each cladode side, and the number of areoles with spines, distance between areoles, distribution of spiny areoles in the cladode, and amount of areole rows in each cladode side; for spines: color, texture and form, length of the largest and smallest spine in each areole, average number of erect, radial or diffuse spines per areole, mean number of spines < 1.0 cm, between 1.0 and 3.0 cm and > 3.0 cm per areole. For the fruit, the indicator traits were weight, shape, width and length, depth and diameter of the floral scar; as regards peel: color, weight, diameter and amount of areoles; for the pulp: dimensions (length and diameter), weight, color and sweetness in Brix degrees; for the seed: number of normal and sterile seeds, weight of sterile seeds, width, thickness and hardness of normal seeds. The supplementary indicator traits were tepal apex shape, perianth color at flowering and pericarpel length; and, last nopalito leaf length and its number of spines per areole.
Most of the indicator traits are related to the Opuntia general domestication process (Colunga et al. 1986; Reyes et al. 2005a); these include fruit color and length, and pulp weight, followed by areole and spine traits (Reyes et al. 2005a). However, in cultivars characterized by large fruits, spine abundance displays three modalities: total absence, reduced or minimal presence, and persistence of the normal number per areole, that is, the amount of spines normally present in wild species, in dependence of domestication environment.
The variants described in the catalog (Reyes-Agüero et al. 2009) represent only a fraction of the Opuntia richness in Mexico. This effort is only a first approximation. Further in depth botanical exploration is required, both in the Meridional Plateau Highland and in the rest of the country.
A total of 126 variants were identified in association with 18 species of cactus pear; most of them preserved in homegardens, but several are also present in wild populations and commercial plantations. Seventy six percent of variants are associated with eight species of the series Streptacanthae, rising to 88% if the O. ficus-indica cultivars are also considered. O. megacantha stands out as the species with the largest number of cultivars and for being the most broadly distributed species in the study area (wild populations, homegardens and plantations). Most of the morphological characteristics that turn out to be indicator traits are related to the Opuntia domestication process.
The authors wish to thank SAGARPA, CONACYT and INIFAP for financing most of the field work. SNICS and SINAREFI funded the final stages of field work. The universities UNAM and UASLP also provided resources. Thanks also to all informers, technicians, people in charge and owners of nopaleras, homegardens and plantations, who uninterestedly shared their knowledge, time, stories and cactus pear variants.
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