Introduction

Cereals are still the most important food source in the world, both for direct human consumption and, indirectly, for the inputs of livestock production. The production task facing world agriculture is impressive, by the year 2030, one more billion tons of cereals will be needed each year (^{FAO, 2016}). After corn and beans, wheat is one of the three most important sources of low-cost nutrients in the Mexican diet, both the crop and its processing and consumption, generate a significant economic income and a large number of jobs (^{Peña et al., 2008}).

The first wheat plantations in Mexico were established in 1865 in the Valleys of Atlixco and San Martin, Toluca and the Valley of Mexico, the Bajío of Guanajuato and Morelia-^{Fernández et al., (1934)}, which currently cover a total area of 1 598 ha (SIAP, 2015). The geographical expansion of the production areas has not considered the requirements of the plant in terms of climate and soil to ensure the success of the crop, in High Valleys these are located in altitudinal strata that range between 2 200 and 2 600 meters above sea level which includes diverse types of climate, which is reflected in a heterogeneity in the phenological behavior, in the production and in the risk condition to which the crop is subjected. According to the ^{SIAP (2014)}, Mexico produced more than 3 669 000 tons under irrigated and seasonal conditions; the largest proportion of seasonal wheat grown in the summer cycle is concentrated in five out of twenty states. In the 2014 cycle, the states of Tlaxcala, Zacatecas, Nuevo Leon, Guanajuato and the State of Mexico produced approximately 191 thousand tons, equivalent to 80% of the volume harvested in this cycle (^{SIAP, 2014}).

The potential yield of wheat is conditioned mainly by climatic variations, specifically by the incident radiation and the average temperature during the period before flowering (^{Magrin and Travasso, 1997}). Due to the partial coal of wheat (Tilletia indica) (^{Brennan et al., 1990}), seed production has had serious restrictions; however, there is another important disease in the temperate and semitropical zones (^{Ireta et al., 1989}), as is the case with spike blight due to Fusarium sp. (TEF), causing weight reduction in grains and consequently decreasing yield (Gosw ^{Goswami and Kisler, 2004}; ^{Nicholson et al., 2007}) and causing contamination in grains due to the presence of mycotoxins, among which is the deoxinivalenol (DON) (^{Miller et al., 2001}; ^{Sip et al., 2007}).

The development of TEF depends mainly on the interaction of climatic conditions and factors such as genotype, fertilization, date of sowing, among others (^{Velázquez et al., 2012}). According to ^{Flores et al. (2007)} the variables of minimum temperature, average temperature, thermal oscillation and rainfall showed a high correlation with the relative index of the disease (IRE), in the period of emergence of the spike to flowering at the base of the spike, or stages of phenological development from 59 to 83 according to the scale of Zadoks (^{Zadoks, 1974}). The critical values of the elements of the climate to intensify the IRE were: minimum temperature higher than 11 ºC, average temperature higher than 16.5 ºC, thermal oscillation lower than 13.4 ºC and pluvial precipitation greater than 30 mm.

The agro-ecological zoning (ZAE) defines zones based on combinations of soil, physiography and similar climatic characteristics related to land aptitude, potential production and environmental impact. The sum of other layers of information, such as land tenure and availability, the nutritional requirements of human and livestock populations, infrastructures, costs and prices, has made possible the development of more advanced applications in the analysis of resources natural resources and land use planning (^{FAO, 1994}).

A study conducted by ^{CIMMYT (2008)} delimited potential areas for wheat production in Mexico; however, it does not consider the climatic characteristics that favor TEF, nor the use of land. The objective of the present work was to delimit geographically and quantitatively potential areas taking into account the criteria that define places and surfaces climatically apt for the cultivation of the wheat of temporary (may-October) and not apt for the TEF, doing a discrimination of the zones urban and other uses other than agriculture; therefore, the generated map can be used as a planning tool for the establishment of wheat cultivation, extension of areas and renewal of plantations for the production and increase of seed in the High Valleys of Mexico.

Materials and methods

With the climatic requirements of the wheat crop (Tritucum durum) the optimum zones were mapped for its establishment, zones to increase and produce quality seeds considering the climatic conditions required for the development of the pathogen (Fusarium) in the region of Central High Valleys included in the states of Hidalgo, Mexico, Puebla and Tlaxcala; It has elevations between 90 and 4 200 meters above sea level, with a precipitation from May to October of 260-2 500 mm and an average temperature of 5 to 28 °C, with an area of 81 612.95 km². The variables evaluated are: average temperature and accumulated precipitation from May to October and altitude of the region.

According to ^{FAO (1997)}, agricultural production is determined by similar combinations of climate and soil characteristics. Table 1 shows the appropriate climatic conditions for the establishment and obtaining of optimal wheat yield. There are biotic or abiotic factors that reduce the yield and quality of the grain, as it is the case of the disease of late blight caused by Fusarium graminearum that occurs during the flowering period in humid temperate conditions (^{Flores et al., 2007}). The requirements for the occurrence of the disease are shown in Table 2.

For the cartography, the database obtained from ERIC III (rapid extractor of climatic information, ^{IMTA 2009}) was used from 531 stations located within the study area and 66 stations around the study area. The variables analyzed were: precipitation and average temperature during the period from May to October; besides considering the altitude of the region. Table 3 shows the ranges of altitude, precipitation and average temperature by state.

For the elaboration of the cartography, the ArcMap GIS 10.2 program (system that allows to compile, organize, analyze and distribute geographic information) was used with the IDW interpolation method (Inverse Distance Weighting: reverse distance method) which is used in the representation of variables with spatial continuity since it does not change the range of values ​​in the sample points (^{Siabato and Yudego, 2004}; ^{Pineda and Suárez, 2014}).

In the determination of the interval and number of classes of each of the maps, the method proposed by ^{Law et al. (2009)}, which consists of taking into account the mean and standard deviation of the map values to determine the classes.

Results and discussion

From the elaborated map, it was obtained that in the study area the conditions that are found for the establishment of the crop are: marginally apt (mA), apt (A) and very apt (MA) (Figure 1). With regard to the classification of the relative index of the disease (IRE) in cartographic presentation, it was obtained that the climatic conditions of the study area divide it into: Not suitable (NA), mA, A and MA (Figure 2).

Figure 1 Classification of areas by climatic requirements for the establishment of wheat. 

Figure 2 Classification of the relative index of the disease (IRE). 

The combination of the wheat classification maps and the IRE made it possible to identify the potential zones for the increase of quality seed production (genetic, physical, physiological and sanitary) of the crop (Figure 3).

Figure 3 Zoning of Central High Valleys according to the climatic requirement of wheat and the IRE. 

It is necessary to consider that varieties for rainfed crops are an important technological component for the producer, since they must have certain agronomic and phytopathological characteristics that allow them to achieve a good harvest, in the face of biotic and abiotic problems (^{Villaseñor and Moreno, 1998}).

The best areas are those that are very suitable for cultivation and that do not have a high IRE, as is the case of Tepetitla, Nativitas, Santa Isabel and Tepeyanco. The final map was generated for storm conditions, with the mean average temperature and accumulated precipitation during the months of May to October obtained from climatological normals. The area was estimated for each type of land use in the region of the Central High Valleys (Table 4).

Table 5 shows the municipalities and the assigned classification according to the optimal or unsuitable environmental conditions for the crop and the pathogen.

According to Figure 3, the state with the best characteristics for crop production and seed production is Tlaxcala in the municipalities of Nativitas, Tepetitla and Acuamanala. The less appropriate municipalities are: Huejutla, Francisco Z. Mena and Hueytamalco. It is important to mention that some municipalities may have more than one classification due to their physiographic and climatic characteristics.

Conclusions

The geographic information systems (GIS), allowed to determine the optimal production zones for wheat and seed increase, with the least potential damage from spike blight, considering the land uses.

According to the zoning, the northern part of the Central High Valleys region is a favorable area for the development of Fusarium sp. and marginally suitable for the establishment of wheat; in contrast, the central part is marginally suitable for the development of Fusarium sp. but suitable for the establishment of the crop, resulting in the best area to achieve greater production and obtain good quality seed.