Introduction

Corn smut is the name given to the gills or tumors that form in corn plants (Zea mays ssp. mays) and teozintle (Zea mays ssp. parviglumis) by the action of the fungus Ustilago maydis. The production of this fungus is not planned for cultivation, it is produced by natural infections and random, as it is considered a pathogen and can be a devastating disease for growing sweet corn. Natural infection is sometimes not very reliable, since the appearance of fungus in corn depends on environmental conditions that lead to infection coal and association between stage in the development of the host during the period of infection and plant tissue in which the guts (^{Pataky, 1991}) are formed. Corn smut appears in almost all maize growing regions; favorable weather conditions for their development are varied: the natural production of this fungus can increase in a humid environment (relative humidity of 72-80%) and mild (17 to 20 °C) (^{Villanueva et al., 1999}; ^{Martínez-Martínez et al., 2005}), and is more common in warm areas (26-34 °C) and moderately dry (^{Agrios, 2006}).

There are several factors that favor the development of fungus U. maydis, such as temperature, relative humidity and genetic material. The vast majority of maize varieties have some degree of resistance to fungal attack, being sweet corn varieties are the most susceptible to this disease ^{Pataky (1995)}. Corn smut is a food with nutritional characteristics essential for humans. It has been found that high levels of dietary fiber and oligosaccharides suggest that corn smut could bring significant benefit to health, as these compounds have been shown to be directly involved in reducing the risk of colon cancer. Also, high concentrations of phenolic compounds of this fungus provide high antioxidant activity; said bioactive components are related to the decreased incidence of chronic degenerative diseases (^{Pataky, 1991}; ^{Méndez-Morán and Ruíz-Herrera, 2008}; ^{Beas et al., 2011}).

The evaluating maize genotypes for production of corn smut can know their level of genetic susceptibility ^{Pan et al. (2008)}. The state of Aguascalientes, Mexico, is producer of corn and corn during the spring-summerautumn (March-November). However, no data on genetic materials susceptible corn or on the incidence of infection by Ustilago maydis in the region. Therefore, the objective of this research was to determine the natural production of corn smut in the state of Aguascalientes in different maize varieties, locations, type of irrigation and planting seasons.

Materials and methods

The study area is located in the State of Aguascalientes, located in the central part of the Mexican Republic (101° 53’ and 102° 52’ O and 22° 27’ and 21° 28’ N), with an area of 5 680.33 km² (568 033 ha) representing 0.3% of the country. The political division consists of eleven municipalities: Aguascalientes, Asientos, Calvillo, Cosio, Jesús María, Pabellón de Arteaga, Rincón de Romos, San José de Gracía, Tepezala, San Francisco de los Romo and El Llano; National Institute of Statistics and Geography (^{INEGI, 2008}).

Sampling was carried out in seven municipalities in the state of Aguascalientes: Aguascalientes, Seats, Jesús María, Rincón de Romos, San José de Gracía, Tepezala and El Llano, 13 treatments each consisting of a municipality, locality, sowing period were obtained, type of crop, use of seed and seed type (Table 1).

Sampling was conducted in in five golds, with a total of 500 m² for each treatment. Fungus samples were cut and placed in ice chests to be transferred to the Laboratory of Parasitology Agricultural Center Agricultural Sciences at the Autonomous University of Aguascalientes; the temperature at which they were kept during transportation and handling was 25 °C ± 2 °C. Environmental variables of temperature, precipitation and relative humidity were taken into account from planting to harvest for each of the locations with the weather station nearest the sampling site INIFAP. The samples were photographed, measured and weighed for each repetition per treatment. The following four variables were evaluated.

Severity index (IS). It corresponded to the proportion of the corn covered by galls formed by the fungus, with the following scale of severity (Table 2) (^{Madrigal et al., 2010}, as amended by Aguayo- González, 2014).

Percentage of incidence (PI). It was determined as the number of infected corn with some degree of severity divided by the number of corn tested multiplied by 100 (^{Madrigal et al., 2010}).

Grams per infected ear (GMI). The total weight was evaluated in grams of shelled corn smut of all infected corn and divided by the number of infected corn fungus (^{Madrigal et al., 2010}).

Yield per hectare (RH). It was obtained by multiplying the population density of corn by GMI, the PI and the number of corn per plant (^{Madrigal et al., 2010}).

The results were analyzed in a completely randomized design. The data analysis of variance (ANOVA) with SAS statistical software version 9.1 were subjected to determine whether there were significant differences (p≤ 0.05) between variables IS, PI, GMI and yield per hectare of 13 treatments. When statistical differences were detected, we proceeded to compare means with Tukey test (p= 0.05).

Results and discussions

The IS ranged from 0.17 to 18.67%, the PI ranged from 0.05 to 6.7%, the GMI was 3.38 to 49.81 g and the yield ranged from 0.728 to 90.554 kg ha^-1 in the 13 treatments evaluated (Table 3). Significance tests indicated that at least one of the treatments was significantly different for each of the evaluated variables (p≤ 0.05). The comparison of Tukey showed that treatment 3 that corresponded to the municipality of Aguascalientes, Ejido Peñuelas, with sowing period from June to September, in culture temporary and native seed, differed significantly in IS with 18.67% in the PI with 6.47% and RH of 90.554 kg ha^-1 with respect to the other treatments (p= 0.05).

The IS was obtained for treatments 3 and 13 differed significantly from those of more treatments with IS 18.67 and 8. 10%, respectively, for the IP, treatment 3 and 13 also had the highest percentages with 6.47 and 2% respectively in relation to other treatments in GMI treatments 8 and 10 were differentiated from other treatments to obtain 36.67 and 49.81 g, respectively; and they stressed the RH treatments 3 and 10 with a natural production of 90.554 and 46.5 kg ha^-1, respectively, being significantly different to other treatments.

The treatments 3 (Aguascalientes, Ejido Peñuelas), 8 (Rincón de Romos, Ejido el Bajío) and 13 (El Llano, Localidad de la Luz) sown in June-September and seeds used were of native origin and treatment 10 (San José of Gracia, City Walls) sown in mayaugust and native seed in temporary crop for the four treatments. These treatments were the best and significantly different from other treatments in each of the characters evaluated (Table 3).

The appearance of corn smut in maize depends on several factors such as environmental conditions, stage of development of the corn plant, genetic susceptibility seed and pathogenicity of the fungus (^{Pataky, 1991}; ^{Pataky et al., 1995}; ^{Pan et al., 2008}). This was reflected in the variability of the results for the yield per hectare due to environmental conditions, type of seed and crop type that were used in each of the treatments, in addition to agronomic practices and types of pathogenicity fungus prevalent in the evaluated regions could significantly affect yield components, as there is a wide genetic diversity in Ustilago maydis, as reported ^{Jiménez (2010)}; ^{Calderón (2010)}.

Treatments under irrigation condition (Figure 1) is not reflected in higher yields of corn smut precipitation conditions, although this food is mainly composed of water (~90%; ^{Beas et al., 2011}); however, the temperature condition there is a close relation to the yield per hectare (Table 4). In treatments 3 and 10 obtained the best natural production of the fungus, environmental conditions that occurred in the two treatments are completely different (Figure 2), these are not related to the performance of the fungus it was obtained (Table 4).

Figure 1 Comparison of the environmental conditions in irrigation treatments. 

Figure 2 Comparison of the environmental conditions in temporary treatments. 

Some authors ^{Valdez et al., (2009)}; ^{Salazar et al., (201)3} mention that with the method of artificial inoculation and under controlled conditions in production, reached yields of up to 15 t ha^-1 with landraces. The natural production for temporary native seeds the best yield was 90.554 kg ha^-1.

The production under artificial inoculation method for hybrid maize is 7 to 8 t ha^-1 (^{Martínez et al., 2000}; ^{Madrigal et al., 2010}). In this work it was found that, for hybrid maize under irrigation, treatment 6 was the best performance with about 14.027 kg ha^-1, as compared to treatment 4 where the same seed used with 0.728 kg ha^-1 but in a different location. The average temperature may have given the best performance in treating 6, since there is a close relationship between these two variables (Table 4).

Conclusions

The treatment 3 based yellow native seed temporary sown in June-September, in the village of Ejido Peñuelas, Aguascalientes, showed the severity and incidence rate of coal maize (corn smut) higher with 18.67 and 6.47% respectively, and therefore he obtained the highest yield of corn smut with 90.554 kg ha^-1.

The treatment 10 of the town of Paredes, San José of Gracia with white pozolera temporary native seed sown in mayaugust, obtained in grams per cob infected corn smut the highest average with 49.81 g; however, by its low incidence rate (0.74%) showed a yield of 46.5 kg ha^-1.

The hybrid and native seeds differ in natural production results since the susceptibility of seeds and pathogenicity of the fungus Ustilago maydis are closely related for a massive infection in maize cultivation.

The environmental conditions are not closely related to the yield per hectare for temporary native seeds.