Evaluation sites and experiment design

The evaluations were established in three environments: two in the experimental field of the College of Postgraduates, Montecillo Campus and one more in the lands of the Campo Experimental Valle de Mexico (CEVAMEX) of the Instituto Nacional de Investigaciones Forestales Agricolas y Pecuarias (INIFAP), located in Santa Lucía de Prías, Coatlinchán, Texcoco, State of Mexico.

The materials were sown in March 2018 in the three environments under a randomized complete block experimental design with three repetitions. Sowing was manual, depositing two seeds per bush every 0.5 m in plots of two furrows with separations of 0.8 m wide and 6 m long. Each plot consisted of 52 plants, equivalent to a density of 60 000 plants ha^-1. In the two environments of the Montecillo Campus, it was fertilized with the dose 140-60-00 and in the environment of CEVAMEX with the dose 140-40-00.

In the three cases, half of the N and all of the P were applied at the time of sowing and the rest of the N was applied in the second weeding. In all cases, a germination irrigation and an emergence irrigation were applied. Subsequently, supplemental irrigations were applied when necessary, since the crop developed mainly with the moisture of summer rain.

In each plot, the days to male (MF) and female flowering (FF) were measured, the first when 50% of the tassels released pollen and the second when 50% of the baby ears exposed stigmas of at least 3 cm in length. Plant height (PH) and ear height (EH), two weeks before harvest, were recorded, measuring all the plants of each plot, from the base of the stem to the insertion node of the tassel and from the base of the stem to the insertion node of the upper ear, respectively.

Variables evaluated

In five randomly selected ears of each material, the length (LEN) and ear diameter (ED), number of rows (NR), and number of grains per row (GR) were recorded. The weight of 200 grains of each material was also determined. To calculate the yield of each plot (kg plot^-1), the harvested ears were weighed, and this weight was adjusted to 12% moisture.

The grain yield per hectare (YIE) was calculated based on the yield per plot, by multiplying the grain weight of the ears harvested in the useful plot by their respective factor of area and adjusting to 15% moisture (^{Mejía and Molina 1999}). The variables were measured in triplicate in each genotype. All variables were subjected to a combined analysis of variance and the means were compared with the F test and a Tukey mean test (p≤ 0.05). The analyses were performed using the GLM procedure of the SAS^® program (^{SAS Institute, 2019}).

Results and discussion

The combined analysis of variance detected significant differences (p≤ 0.05) between genotypes (GEN), for all study variables (Table 1). Between environments (ENV), significant differences (p≤ 0.01) were detected in seven of the 10 variables evaluated. While for the interaction genotype × environment (GEN × ENV), there were significant differences (p≤ 0.05) only in two variables, which were male flowering (MF) and female flowering (FF). The analysis with Anova and the F test are global analyses, this is only an indicator of the effect between environments and genotypes.

The fact that statistical differences were observed between genotypes and between environments indicates, on the one hand, the existence of genetic diversity between the varieties evaluated and, on the other, that the environmental effects, measured by the behavior of the genotypes, were different between environments. On the other hand, the interaction between GEN × ENV indicates that the genotypic and phenotypic expression of the varieties for most agronomic characteristics was consistent across the environments, so that the yield and its components were stable despite the fact that the environments were contrasting (^{Becker and León, 1988}). Likewise, the effect of a genotype not significant by the F test in environments can be significant in an average or contrast test. So, it is important to check for minimal and non-global specific differences between genotypes.

Behavior of varieties in environments

The mean test for environments of the combined analysis shows that the environment of the Montecillo Campus CP-C8 was the most favorable in terms of grain yield with 9.2 t ha^-1 (Table 2). Likewise, in this environment it is observed that the populations had the highest values for plant height (PH) and ear height (EH), and on average they were later. On the contrary, the environments of CEVAMEX and the Montecillo Campus CP-C13 had the lowest yield (6 and 7.3 t ha^-1, respectively), lower values for PH and EH, and in flowering, they were earlier.

These results coincided with that reported by ^{Pérez-de la Luz et al. (2011)}, who point out that native populations evaluated in different environments present different yields, mainly due to the effect of environmental factors on genotype expression. On the other hand, based on the yield, it was observed that the germplasms of Elotes Occidentales evaluated in the Valles Altos of Mexico adapt well to this region, since their average yield, for the three environments, was three times higher than the regional average yield, which is 2.8 t ha^-1 in Valles Altos (^{SIAP, 2018}).

Behavior of genotypes

The genotypes evaluated equaled and, in some cases, exceeded the grain yield of the control varieties (Table 3), but the genotypes EOM-1 and EOM-6 presented average yields of 8.4 and 8.6 t ha^-1, respectively, significantly higher than that of the controls. The ancho control (TMA) had a yield of 7.9 t ha^-1 and the Cacahuazintle corn (TMC) yielded 3.1 t ha^-1. The rest of the genotypes yielded between 6.5 to 8.2 t ha^-1.

The competitive yields obtained by the Elotes Occidentales genotypes in Valles Altos are attributed to the good characteristics in terms of agronomic behavior and adaptation that the native genotypes have for diverse environments. These results show that the initial sowings of exotic corn in a new region where it generally presents maladaptation, susceptibility to diseases, modification of the vegetative cycle and low yield (Gordon-^{Navas and Cervantes, 1991}; Mendoza et al., 2006) is not strictly acceptable for evaluations of agronomic behavior of exotic material in a new study region.

This is a product of its wide intrapopulation genetic variation and good yield, aspects achieved over many years of cultivation, as pointed out by ^{Muñoz (2005}); ^{Pérez-de la Luz et al. (2011)}. These advantages of Elotes Occidentales corns can be used for genetic improvement purposes for rainfed or irrigation tip areas in Valles Altos.

In Table 3, morphological and physiological variables of the genotypes were analyzed, because it was considered that they have a direct or indirect contribution in the expression of yield, it is observed that the diameter of ear and number of rows of all genotypes were equal to the controls. Only in grains per row and ear length, the values of the genotypes EOM-1, EOM-2, EOM-6, EOM-7 and EOM-12 were higher. On the other hand, the average values of the days to female flowering (FF) showed that the populations were of early cycle for the three environments of evaluation, except for the populations EOM-2 and EOM-12 which presented 92 and 93 days to flowering on average, according to the classification of ^{Ángeles-Gaspar (2010}).

These results indicate that the genetic materials of Elotes Occidentales in the Valles Altos of Mexico present physiological characteristics of short cycle since they showed potential for development in cold environments, coupled with the presence of high grain yields (Table 2), which gives an advantage over the germplasms of the region since there are few materials with these characteristics in the market and less in the process of improvement programs.

The materials of pozolero corn Elotes Occidentales, according to the results obtained, had grain yields of up to 8.6 t ha^-1, presenting competitiveness compared to the two commercial local controls and in some cases higher than the local average yield of the commercial corns ancho and Cacahuacintle of Valles Altos, which presented average yields of 2.8 t ha^-1.

Likewise, it was identified that two of the germplasms, EOM-1 and EOM-6, of Elotes Occidentales presented the best characteristics in terms of agronomic behavior and adaptation to the environment (YIE, LEN, GR, FF and MF) compared to the commercial pozolero controls Maíz Ancho and Cacahuazintle.

Regarding plant height (PH) and ear height (EH), the genotypes evaluated showed homogeneous heights and lower than those of the commercial control, mainly for the populations EOM-5 and EOM-8 H-48 with 2.3 m in plant height and 1.4 m for ear height, which is desirable for corn improvement germplasms for the Valles Altos, which prefer low size materials since they are more tolerant to lodging, in addition to being able to be harvested mechanically.

The above is due to the fact that, because they are native populations, Elotes Occidentales corns can have wide intrapopulation genetic variation and good behavior per se (^{López et al., 2008}), advantages that can be exploited for genetic improvement purposes for poor rainfed or irrigation areas in High Valleys (^{Gil et al., 2004}).

With the results obtained, it can be established that the proposed hypothesis that, of the populations evaluated, at least one will exceed control local materials in grain yield is verified. This shows the importance of introducing and taking advantage of native germplasms from other regions in High Valleys and also indicates the importance of evaluating these materials under different environments, to generate strategies to improve the germplasm of pozolero corn in Valles Altos de México.