Conditioning factors in the distribution of palomero toluqueño maize and alternatives for its conservation

Edgardo Bautista-Ramírez1; Jesús A. Cuevas-Sánchez2; Amalio Santacruz-Varela1; Enrique Hernández-Leal3; César del Ángel Hernández-Galeno4; Aurelio Hernández-Bautista1; Rosalí Gómez-Maldonado2

1. Colegio de Postgraduados-Campus Montecillo. Carretera México-Texcoco, km 36.5. Montecillo, C. P. 56230, Texcoco, Estado de México, México., Colegio de Postgraduados, Colegio de Postgraduados,

<state>Estado de México</state>
, Mexico , 2. Universidad Autónoma Chapingo, km 38.5 carretera México-Texcoco, CP 56230, Chapingo, Estado de México, México. , Universidad Autónoma Chapingo, Universidad Autónoma Chapingo,
<state>Estado de México</state>
, Mexico ,
3. Instituto Tecnológico Superior de la Sierra Norte de Puebla. Av. José Luis Martínez Vázquez No. 2000, C.P. 73310, Jicolapa, Zacatlán, Puebla, México. , Instituto Tecnológico Superior de la Sierra Norte de Puebla, Instituto Tecnológico Superior de la Sierra Norte de Puebla,
, Mexico ,
4. INIFAP, Campo Experimental Iguala. Iguala de la Independencia, Guerrero. Carretera Iguala-Tuxpan km 2.5, C. P. 40000, Iguala, Guerrero, México., Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias, INIFAP,
, Mexico

Correspondence: *. Corresponding Author: César del Ángel Hernández-Galeno, INIFAP, Carretera Iguala-Tuxpan km. 2.5, Iguala de la Independencia, Guerrero. México. C. P. 40000, E-mail: , Celular 5951149368 Oficina: 5538718700 ext. 86518, enlace electrónico de la institución:


Palomero Toluqueño is considered as an endangered maize race. The objective of this study was to analyze the conditioning factors of the presence of this race in the State of Mexico, to suggest alternatives for its conservation and exploitation, using distribution areas modeling and ethnobotanical exploration as a tool. Potential areas were estimated with MaxEnt, and could be superimposed with those proposed by CONABIO. In January and February 2017 an ethnobotanical exploration was carried out in the areas where MaxEnt estimated probabilities higher than 0.61 for the presence of maize Palomero Toluqueño race, with the respondent-driven sampling method. Fifteen accessions were obtained from Mazahua and Otomí groups that preserve this race by a combination of favorable social and environmental factors. The threat of disappearance of the race will remain unless new strategies are found to promote its conservation and exploitation. Distribution models were determined to be useful in the assessment of potential areas of cultivation, but not in the planning of harvests since the decision of sowing involves, besides favorable ecological conditions, the combination of social and cultural aspects that promote their cultivation and exploitation; therefore, participatory improvement and promotion of the race in seed fairs would be useful tools for in situ conservation.

Received: 2018 March 23; Accepted: 2018 July 4

revbio. 2018 Nov 26; 5(spe2): e476
doi: 10.1574/revbio.05.nesp.e476

Keywords: Key words: Zea mays L., native maize, potential areas, ethnobotany, conservation.


In order to conserve biodiversity, understanding how species are distributed and which environmental aspects are decisive is necessary (Newbold, 2010). Therefore, distribution models have been used, which are based on the hypothesis that sample data covers the whole ecological range of the species or race (Sánchez-Fernández et al., 2011), as well as specific features of the area of cultivation (van Proosdij et al., 2016); however, despite the many applications they have, distribution models simply remain as incomplete representations of reality (Seoane & Bustamante, 2001).

To be able to consider databases of harvests and modeling as useful tools in decision making, they have to involve data from geo-referencing and be based on wellestablished methods (Scheldeman & Zonneveld, 2010); for instance, planning harvests and in situ conservation of 32 species of wild relatives of potato were performed from online databases associated to worldwide research community (Castañeda-Álvarez et al., 2015). Determining priority areas for harvesting and conservation of sorghum in Eastern Africa was performed with the information from ICRISAT gene bank (Upadhyaya et al., 2017). In the case of maize in Mexico, Ruíz et al. (2013) used passport data of accessions available on the CONABIO webpage and they correlated them with temperature, precipitations and elevation to determine potential area for each race, allowing setting out in situ conservation works for each one.

Human activity is an important aspect that has altered distribution patterns of some species and determines their presence or absence in viable or inviable sites for their survival and persistence (López-Sandoval et al., 2015); however, that species must necessarily present plasticity among its natural traits, as well as a wide diversity of usages, such as maize (Vargas, 2014). Only in Mexico, maize richness is clustered into 59 races (Sánchez et al., 2000), which are due to heterogeneous groups of farmers that cultivated different populations of this species in multiple agro-ecological conditions (Mera, 2009); however, in the landlots of many farmers this diversity is decreasing in an accelerated and worrying way (Arias et al., 2007; Dyer et al., 2014), therefore, it is necessary to understand the relationship that the diverse cultural groups hang on to with maize races, using ethnobotanical exploration as a tool (Hernández, 1972); allowing to generate conservation strategies.

Palomero Toluqueño maize race has 45 accessions sampled mainly in the states of: Mexico, Puebla and Tlaxcala (CONABIO, 2011). Potential distribution areas of this race, estimated with average annual cumulative precipitation (mm), annual average temperature (°C), annual average minimum temperature (°C), annual maximum temperature (°C), maximum temperature of the warmest month (°C), minimum temperature of the coldest month (°C), annual humidity and elevation index (msnm), were located in mid-north of the state of Mexico, the whole state of Tlaxcala, the center of Puebla and Southern Hidalgo (Ruíz et al., 2013; CONABIO, 2015); however, these modellings did not consider human activity, which can be an important factor of variation. Therefore, performing an ethnobotanical exploration is necessary to confirm the presence of maize Palomero Toluqueño race in potential assessed areas. The objective of this study was to analyze conditioning factors of the presence of maize Palomero Toluqueño race in its distribution areas within the state of Mexico, in order to generate conservation schemes, favor its genetic improvement and exploitation.

Material and methods

Potential areas assessment

To demarcate the study area and to be able to identify climatic groups associated with Palomero Toluqueño race, a delimitation of potential areas was performed, by means of the following methods:

  1. The first group of polygons was obtained from National Commission for the Knowledge and Use of Biodiversity (CONABIO) webpage in SHP format (CONABIO, 2015) in ArcGis 10.3, picture was cut to obtain only the part corresponding to the state of Mexico.
  2. The second group of polygons was generated by means of the MaxEnt system (maximum entropy) that models areas from real distribution data with bioclimatic variables (Phillips et al., 2006). Information of accessions of Palomero Toluqueño race was obtained from CONABIO (2011), accessions were refined to avoid duplicity, keeping accessions originating from Mexico City, State of Mexico, Hidalgo, Tlaxcala and Puebla as useful information. Environmental variables that were considered were 19 bioclimatic variables and elevation, with a resolution of 2.5 minutes available on WorldClim-Global Climate Data website version 1.4. The model that generates MaxEnt was according the probability of finding Palomero Toluqueño race, ranging from 0 to 0.99. In Arc Gis 10.3 groups of polygons were generated with probabilities from 0.3 to 0.4, from 0.41 to 0.5, from 0.51 to 0.6 and from 0.61 to 0.74. The value of 0.74 was the highest probability of incidence of Palomero Toluqueño race in the state of Mexico.

Exploration was initiated in locations of municipalities where the probability of finding Palomero Toluqueño was higher than 0.61 with MaxEnt and that corresponded with estimations made by CONABIO (CONABIO, 2015). Climatic groups associated with potential areas and sampling points were identified in Arc Gis 10.0, superimposing the layers of climate of the state of Mexico (Casa, 1997) with harvest projections and potential areas.

Population sampling

In 2017, germplasm was sampled, trying to obtain at least 5.0 kg of sample in ears of maize, the five most representative ears being used for its racial identification, based on attributes indicated by Wellhausen et al. (1951). The rest of the sample was threshed and set up for its preservation in the National Bank of Vegetal Germplasm of the Autonomous University of Chapingo. Each accession went with its passport data for its correct identification and geographical location.

Ethnobotanical exploration

Ethnobotanical exploration was based on what Hernández (1972) proposed. This activity was performed in January and February 2017, since in this period producers already harvested and have stored ears of maize, making field identification and material sampling easier.

In locations where it was possible, a local representative was initially visited; with his orientation and occasional accompaniment, producers that sowed similar maize to those sampled (Palomero Toluqueño race) were visited. Interviews were realized only to producers having ears of maize presenting any similarity with Palomero Toluqueño race and giving their consent to use the provided information for research purposes.

Survey was performed using a semi-structured questionnaire as a guide, with the following points: a) general identification (producer’s name, age, academic level, sex, indigenous group, property type and years sowing maize Palomero Toluqueño race), b) characteristics related to seeds (cultivated surface, utilities, cultural aspects related to the maize of interest, main virtues, date of sowing and harvesting, problems in production and production costs) and, c) selection criteria of the seed for sowing.

Sampling method

The “respondent-driven sampling” (RDS) method was used, which is a variant of chain or “snowball” sampling. This method is focused on the study of populations which are not registered in sampling frames and do not offer special difficulties to make contact with (Mantecón et al., 2008). Its application required initial informers that in this study were representatives of the localities or contacts of researchers that worked in the region of interest. The first localities of exploration were those with the highest probability of incidence of maize Palomero Toluqueño race (from 0.61 to 0.74). This sampling method led to the exploration of areas where the probability of incidence was low (less than 0.3) and that key informers suggested to visit.

Data analysis

Racial identification was performed at Postgraduates College and according to this, accessions which did not correspond to Palonero Toluqueño race were discarded, allowing to project in ArcGis 10.0 only those that presented distinctive characteristics of the race.

A synoptic table was made where the information pointed out by producers about seed utility, main attributes and selection criteria were included. For the variables of elevation, producer‘s age, years of sowing of the Palomero Toluqueño race, cultivated surface and production costs, descriptive variables were estimated (minimum and maximum values, mean and standard deviation). In addition, dates of sowing and harvesting that were used for production cycle assessment of the race were added.

Results and discussion

Potential distribution areas of maize Palomero Toluqueño race

Potential distribution areas proposed by CONABIO (CONABIO, 2015) included more than half of 125 municipalities of the state of Mexico. With MaxEnt, the probability of finding Palomero Toluqueño was detected to be higher than 0.61 in only 18 municipalities of the studied region (Figure 1). Ethnobotanical exploration studies were initiated in those municipalities, since it was where areas of estimation of both prediction methods overlapped.

[Figure ID: f1] Figure 1.

Estimation of potential distribution areas of maize Palomero Toluqueño race in the State of Mexico.

The marked difference among the areas considered as potential and estimated by the two indicated technics must be attributed to the statistical method that substantiates both of them. Areas proposed by CONABIO (CONABIO, 2015) were based on works of Perales & Golicher (2011), who used Generalized Additive Models (GAM), estimating the most approximate areas to the distribution of the effective ecological niche, while MaxEnt is a model based on presence, generating a spatial distribution of the basic ecological niche of the race (Zaniewski et al., 2002).

The estimation of potential areas with MaxEnt was performed considering the whole national territory where the maximum probability was 0.99, located in the state of Tlaxcala (data not shown), while the maximum value in the state of Mexico was 0.74. The value of the cumulative threshold (CT) was 0.99, therefore model reliability generated with MaxEnt is excellent according to Araújo et al. (2005) classification, while areas considered as potential by CONABIO (CONABIO, 2015) are suitable for sowing maize Polomero Toluqueño race, its use as a tool for harvest planning has to be taken with precaution, since those areas are very vast to cover, significantly increasing requested time and investment.

Harvest data that were used for estimating potential areas with MaxEnt are the same used by CONABIO (CONABIO, 2015); that data presented limitation, such as: 1) After 1969, only two accessions of Palomero Toluqueño race were registered in the state of Mexico, in San Felipe del Progreso and San Marcos Tlazalpan, municipality of San Bartolo Morelos (sampled in 2009) and 2) the region with the highest number of harvests in the state of Mexico (8 accessions) were made up by Otzolotepec, San Mateo Atenco, Toluca and Villa del Carbón municipalities with harvests from 1943 to 1954.

The 37 accessions, used while estimating potential areas, covered the complete ecological range of the race to use them for modelling their distribution (Sánchez-Fernández et al., 2011); however, their unbalanced distribution made MaxEnt consider the municipalities close to Toluca as those with the highest probability to find the race, not necessarily indicating that Palomero Toluqueño race is present in these areas, since no accession was found in those municipalities between January and February 2017. The human factor favors the presence or absence of the race, in agreement with what mentioned by Hernández (2007) and López-Sandoval et al. (2015), who observed a determining influence of human activity in the distribution of cultivated species (races in the present case).

Potential distribution areas of Palomero Toluqueño were in a semi-cold sub-humid climate, with a percentage of winter precipitations lesser than 5 mm, long summer, isothermal, and the highest temperature before the summer solstice (C(E)(w2)(w)b(i)g), while harvests of 2017 were found in temperate, sub-humid climate with long summer, winter rain lesser than 5.0 %, iso-thermal and the highest temperature before the summer solstice C(w2)(w)b(i)g. The previously said does not imply any change in the adaptability of the race, since Mazahua and Otomí producers, who gave seeds in 2017, mentioned they have been sowing them for more than 50 years. Therefore, if those communities had been visited during the forties and fifties, samples of this race would have been found as a part of the diversity of the cultivated maize by both cultural groups.

Material sampling and ethnobotanical exploration

Sampling and material racial identification

Among the 15 collected accessions of maize Palomero Toluqueño race, seven were with the Otomíes group, in San Marcos Tlazalpan community, San Bartolo Morelos municipality and eight with the Mazahuas group, in San Felipe del Progreso and San José del Rincón municipalities (Figure 1), this wealth represents 30 % of all existing harvests done since the forties until 2009 (CONABIO, 2011). During the harvest, three Otomíes communities were visited, but in none of them maize Palomero Toluqueño race were found. Therefore, the variation in the number of future harvests with Otomíes communities will probably be in San Marcos community, Tlazalpan, San Bartolo Morelos municipality, while with Mazahuas communities, this variation may happen in the region where they live, although there will always be the possibility to find this race in other localities of the state of Mexico. Regarding this, Bellon et al. (2009) mentioned that there is a dynamic process in maize sowing by farmers, depending more on cultural and social aspects than environmental ones (Perales & Golicher, 2014).

Uses, virtues and selection of maize Palomero Toluqueño race

Diverse studies highlight the relationship between maize wealth and indigenous groups (Ureta et al., 2013; Perales & Golicher, 2014; Orozco-Ramírez & Astier, 2016). In the state of Mexico, maize Palomero Toluqueño race was sampled between Mazahuas and Otomíes communities, who used it for elaborating diverse foods (Table 1). From those two groups, only Mazahuas pointed out that the popcorn they used as ornament in religious celebration more than 30 years ago were made from this maize race. This tradition persists, however, popcorn is now made from commercial Palomero maize and only the popping method is conserved (mud with white sand pot). The previously said may be one of the various situations contributing to the diminution in the sowing frequency of the race, since Mazahua producers pointed out that in the past, the sowing of this maize race was higher, for the necessity they had for ornamental popcorn, in addition to its performance, which is why its sowing allowed fulfilling necessities and were progressively substituted by other maize races over time (Bellon et al., 2009).

Table 1.

Uses, virtues and selection criteria of maize Palomero Toluqueño race as described by two cultural groups in the State of Mexico.

Cultural Group Uses Main virtues Seed selection criteria
Mazahua Elaboration of tortillas, tamales, atoles and gorditas; in addition, husks for tamal and animal feed for livestock are obtained. Heavy seed, easy shelling, adaptation to local climatic conditions, specialty uses and yield. Representative ear of the variety, large ears, with the maximum number of kernel rows and without rotten kernels. Large, elongated and heavy seeds.
Otomí Elaboration of tortillas, tamales and atoles, use of husks for making tamales, feed for livestock as both grain and fodder. Heavy seed, easy shelling, adaptation to local climatic conditions, specialty uses and fodder production. Large ears, with the maximum number of kernel rows and creamy color. Large, elongated and heavy seeds.

Wellhausen et al. (1951) report the use of maize Palomero Toluqueño race in tortilla and popcorn elaboration. The main consumption of this maize is currently in tortillas, which has caused that in San Marcos Tlazalpan, material of more floury grains is associated to the race to improve this food texture (Gámez et al., 2014). The previously said might be the cause of why a high number of materials with more floury grains are observed in harvests done in this locality. In the case of Mazahua localities, the sowing of different types of maize is done to obtain distinct type of grains, allowing other uses, in addition to improve the quality of tortillas made with maize Palomero Toluqueño race, as Castillo-Nonato & Chávez-Mejía (2013) reported in San Felipe del Progreso communities, close to the sampled localities.

The fact that, in seed selection for sowing, producers consider the distinct characteristics of their materials as part of them (Table 1). Therefore, this must be the cause of the race maintaining for various generations, as they are those maintaining this diversity (Perales et al., 2005). The loss of identity of Palomero Toluqueño race will not occur at seed selection; the disappearance of this race could occur if producers decide to replace it for materials with characteristics satisfying their necessities (Bellon et al., 2009).

Height distribution of harvests and social aspects of producers

Temperature decreases in an average of 0.65 °C every 100m of elevation increase (García, 1983), therefore there will be a difference of 1.2°C between maximum and minimum elevations of harvested localities (Table 2), while the thermic difference in origin points of accessions reported by CONABIO (CONABIO, 2011) for the state of Mexico would be of 3.4°C, due to a minimum elevation of 2400 m and a maximum of 2926 m. The difference between the two groups is just 2 °C, therefore adaptability of the race in the state of Mexico was not modified, although sample localities and potential areas were in a different climatic group, as described in previous paragraph.

Table 2.

General description of the studied variables.

Variable Minimum Maximum Average Standard deviation
Elevation (masl) 2703 2902 2746.60 53.88
Farmers age (years) 28 73 52.73 12.18
Schooling None Middle School - -
Years planting Palomero Toluqueño maize 5 50 17.5 11.91
Cultivated area (ha) 0.25 2 0.95 0.91
Planting date Early March Late April - -
Harvest date Mid October Late December - -
Production cost ($) 9,000 12,000 10,400 800

TFN1†: Mexican pesos

The presence of maize Palomero Toluqueño race in the state of Mexico until 2017 is mainly due to the tradition of Mazahua and Otomí groups, since none of the social variables presented in Table 2 showed any trend. The combination of social and environmental factors allowed to decide the type of material that will be sowed in the next crop season (Perales & Golicher, 2014).

In the group that provide the seeds, only one Otomí producer mentioned his intention of replacing his maize Palomero Toluqueño race for other material in the next crop season, while the rest (14 producers) mentioned they maintain the same seed since it ensures food for their families and animals, in addition to their preference for its quality, although they do not discard the possibility of sowing other maize with higher performance, therefore the threat of disappearance of the race will be kept permanent until strategies promoting conservation, improvement and exploitation of the race are found.

The work with farmers protecting maize Palomero Toluqueño race in San Marcos Tlazalpan community functioned until public politics changed (Gámez et al., 2014). Due to the lack of founding, it was not possible to perform a continuous study guiding in the operation and avoiding its loss, as suggested by Hernández (2007). Therefore, it is necessary to explore other alternatives of in situ conservation, considering satisfying producers’ needs as a fundamental axis.

The participative improvement and promotion of the race in seed fairs are alternatives that must be encouraged, since maize diversity can be reinforced through selection done by farmers, according to Dzib-Aguilar et al. (2016), contributing to maintaining in situ diversity. Moreover, with interested farmers, attributes favoring the burst of the race may be enhanced, giving a commercial value to this material and promoting its sowing by other famers.


Harvest data of more than 60 years of maize Palomero Toluqueño race did not allow the current distribution of this material, since they did not cover the totality of the ecological range of the race, therefore it is necessary to explore and search this material in the rest of the states where it was once sampled. Analyzed social variables were not determining for sowing maize Palomero race, Mazahua people as well as Otomíes people take the decision of the material to sow, and of the extension allocated to its cultivation by the combination of social and cultural aspects, therefore participative improvement and promotion of the race in seed fairs could be useful tools for in situ conservation.

fn1Cite this paper: Edgardo Bautista-Ramírez, Jesús A. Cuevas-Sánchez, Amalio Santacruz-Varela, Enrique Hernández-Leal, César del Ángel Hernández-Galeno, Aurelio Hernández-Bautista, Rosalí Gómez-Maldonado. (2018). Conditioning factors in the distribution of palomero toluqueño maize and alternatives for its conservation. Revista Bio Ciencias 5(nesp), e47 6 doi:


To “Tortilla de Maíz Mexicana A. C.” Foundation for the financial support given for ethnobotanical exploration and material sampling.


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Revista Bio Ciencias, Año 13, vol. 9,  Enero 2022. Sistema de Publicación Continua editada por la Universidad Autónoma de Nayarit. Ciudad de la Cultura “Amado Nervo”,  Col. Centro,  C.P.: 63000, Tepic, Nayarit, México. Teléfono: (01) 311 211 8800, ext. 8922. E-mail:,, Editor responsable: Dra. Karina J. G. Díaz Resendiz. No. de Reserva de derechos al uso exclusivo 04-2010-101509412600-203, ISSN 2007-3380, ambos otorgados por el Instituto Nacional de Derechos de Autor. Responsable de la última actualización de este número Dra. Karina J. G. Díaz Resendiz Secretaria de Investigación y Posgrado, edificio Centro Multidisciplinario de Investigación Científica (CEMIC) 03 de la Universidad Autónoma de Nayarit. La opinión expresada en los artículos firmados es responsabilidad del autor. Se autoriza la reproducción total o parcial de los contenidos e imágenes, siempre y cuando se cite la fuente y no sea con fines de lucro.

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