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Introduction
Corn (Zea mays L.) is one of the most important crops in several regions of the world. Depending on the production region, the type of corn and the purpose production varies greatly. In 2018, approximately 193 million ha were sown with corn, with a grain yield of 5923 kg ha-1; about 80% is cultivated under rainfed conditions and the rest with irrigation (FAOSTAT, 2020). In Mexico, around 15 million tons of corn are imported (SIAP, 2018), making it urgent to increase production and to have varieties with greater productivity. In 2018, around 7567 million ha were sown with a mean yield of 3759 kg ha-1, and a production volume of 26 582 million tons. The mean yield obtained is generally low, compared with other countries; this is because of among other factors, biotic and abiotic stresses that commonly limit production (Virgen-Vargas et al., 2016; Tadeo-Robledo et al., 2017).
In the High Valleys of the Central Mesa of Mexico, which include the states of: Puebla, Hidalgo, Tlaxcala, Querétaro, Michoacán, Morelos, State of Mexico, and Mexico City, at an altitude above 2200 meters above sea level (masl), about 1.5 million ha are cultivated with corn. In these areas, the prevailing production systems are with residual humidity, point irrigation, and good rainfall (Ávila et al., 2009; SIAP, 2020). In this region, the State of Mexico stands out for its importance, since around 500 000 ha are cultivated with corn annually, with a mean state yield of 4289 kg ha-1, and a production volume of two million tons (SIAP, 2020). Regardless, with the application technological recommendations and a wider use of improved varieties among producers, the corn yield could be increased from 4.2 to 6.0 Mg ha-1 (Tadeo-Robledo et al., 2014, 2016, 2017; Virgen-Vargas et al., 2016).
One of the most important supplies in agricultural production is the use of improved seeds. In this sense, one alternative to facilitate seed production and to raise the degree of adoption of hybrids corn seeds in the High Valleys is the use of types and sources of male sterility (genetic-cytoplasmic); this eliminates the hand detasseling or emasculation labor (Martínez-Lázaro et al., 2005; Tadeo-Robledo et al., 2016). These genetic methods offer advantages in corn production and constitute an alternative for easy management in seed production (Sierra et al., 2016).
The National Institute of Forest, Agriculture, and Livestock Research (INIFAP) and the National Autonomous University of Mexico (UNAM) have developed the corn hybrids: H-51 AE, H-47 AE, H-49 AE, and H-53 AE (Espinosa et al. 2008, 2012, 2018), in which the male sterility scheme was used in the parents to facilitate seed production and promote the upkeep of the genetic quality (Tadeo-Robledo et al., 2014, 2016). Corn hybrids have been well documented to respond differently to high plant densities with standard fertilization doses (Njoka et al., 2004; De la Cruz-Lázaro et al., 2009; Xu et al., 2017; Soleymani, 2018; Wang et al., 2019). In the United States of America, the country with the highest corn production in the world, plant density varies from 82 230 to 92 100 plants ha-1 (Xu et al., 2017). Contrastingly, plant density is complicated in corn producing regions in Mexico, where density varies from 20 000 to 42 000 plants ha-1, for native varieties and from 65 500 to 83 333 plants ha-1 for other varieties improved and hybrids (Tinoco et al., 2008; van der Wal et al., 2006).
Population density is one of the factors that producers frequently modify to increase grain yield, although they do not always establish the correct density (De la Cruz-Lázaro et al., 2009). As the number of plants increases, the crops increase competition for light, water, and nutrients, which causes a decrease in root volume, number of ears, grain quantity and quality per plant, and reduces stalk diameter, favoring corn flopping (Vega et al., 2000; Maya and Ramírez, 2002; Sharifi et al., 2014). Ziegler et al. (1994) reported that grain yield increased when increasing plant density from 54 000 to 94 000 plants ha‑1, but decreased when reaching 97 000 plants ha-1. Because of this, the objectives of the present study were: (1) to define the yield of six commercial corn hybrids released for the High Valleys of Mexico by the INIFAP and UNAM, established under three population densities in two environments of the State of Mexico, and (2) to determine the hybrid with the highest grain yield in two study areas and then define the adequate population density to recommend farmers.
Materials and Methods
Study site
The experiments were carried out in two different ecological niches during the spring-summer season of 2015 in the State of Mexico: School of Higher Studies Cuautitlán, UNAM (Experimental Field no. 7, 19° 41' NL, 99° 11' WL, 2274 masl) and Santa Lucía de Prias, Texcoco (Experimental Field of the Valley of Mexico, 19° 27' NL, 98° 51' WL, 2240 masl). In the latter environment, two experiments were established at different sowing dates.
Genetic material
Six commercial white-grain corn hybrids adapted to the Haigh Valleys of Mexico were used: H-51 AE, H-53 AE, H-47 AE, H-49 AE, H-48, and Tsíri PUMA, developed by the INIFAP in collaboration with the UNAM.
Experimental design
Each of the six hybrids was combined with three population densities: 50 000, 65 000, and 80 000 plants ha‑1. The experiment was established under a completely randomized block design with four replicates, with a total of 72 experimental units. Each experimental unit consisted of a row, five meters long × 0.8 m wide.
Experiment development
Sowing was done on June 5th and 26th, 2015 in rows of 5 m long by 0.8 m wide. Two or three seeds were sown in each hole to ensure good plant density. The population density adjustment was done 45 days after sowing (das) as follows: (32 plants: 80 000 plants ha-1), (26 plants; 65 000 plants ha-1), and (20 plants; 50 000 plants ha-1).
Harvest was done manually on December 10th and 14th of 2015, when the crops reached physiological maturity. All the ears were harvested and weighed for each experimental unit. Subsequently, 10 ears were selected to register the yield components. The evaluated variables were: plant height (cm), ear height (cm), male flowering (days), female flowering (days), ear cover (%), volumetric weight (kg hl-1), weight of 200 grains (g), ear length (cm), ear diameter (cm), number of rows per ear, number of grains per ear, total number of grains per ear, grain percentage, and grain yield (kg ha-1), calculated with the following formula: Yield = (TFW*DM*PG*CF)/8,600. Where: TFW= total field weight harvested in the experimental unit, DM = percentage of dry matter of a grain sample from five ears, PG= grain percentage estimated from five ears, CF= conversion factor to obtain grain yield per hectare, the quotient of dividing 10 000 m2 by the useful plot in m2, and 8600 = is a constant to estimate grain yield at a commercial humidity of 14% (Tadeo-Robledo et al., 2014).
Statistical analysis
Analyses of variance and multiple means comparisons (Tukey HSD, P ≤ 0.05), were done for all variables. The mean values were considered significantly different when P ≤ 0.05. The statistical analyses were done with the SAT/STAT( ver. 9.0 software (SAS, 2002).
Results and Discussion
Climatic parameters in the evaluation sites
The climatic variables were registered during the development of the experiment. The total accumulated rainfall in the FESC-UNAM was 669.6 mm, while minimum and maximum temperatures fluctuated from 9.2 to 22.8 °C, respectively. For CEVAMEX, the total accumulated rainfall was 465.8 and the minimum and maximum temperatures varied from 9.9 to 25.1 °C, respectively (Figure 1). According to Kiniry and Bonhomme (1991), temperatures above 40 °C during the flowering period can affect pollen grain emission, which directly affects crop productivity. Furthermore, temperatures below 8 °C affect crop growth and development (Martínez, 2015).
Combined analysis
The combined analyses of variance indicated significant (P ≤ 0.05) effects in the genotype (G) and environmental (E) variation sources for all the evaluated variables, with the exception of ear length. These results indicate that the hybrids presented differential responses in the environments and the evaluated variables were influenced by effect of the environment. The population density (D) factor produced no differential response (P ≥ 0.05) in any variable. In the interactions, no differences (P ≥ 0.05) were registered with the exception of the ExG interaction on the grain yield variable (Table 1). The variation coefficients for the evaluated variables were in the order from 2.1 to 25.1%.
Table 1: Mean squares and statistical significance for different traits evaluated in six corn hybrids released by INIFAP and UNAM, considering three different population densities and three evaluation environments, FESC-UNAM and CEVAMEX. Spring-summer season, 2015.
Source of variation |
Grain yield |
Plant height |
Plant ear |
Male flowering |
Female flowering |
Volumetric weight |
Weight 200 grains |
Ear length |
Grain percentage |
kg ha-1 |
- - - - - - cm - - - - - |
- - - - - days - - - - |
g hL-1 |
cm |
% |
||||
Environments (E) |
21172913.6 ** |
130291.8** |
23375.0** |
2373.4** |
3408.2** |
20311.6** |
2198.2** |
24.2** |
2290.4** |
Genotype (G) |
27688183.9 ** |
1981.0** |
1564.7** |
101.5** |
91.0** |
24962.7** |
442.6** |
3.9 |
8040.9** |
Density (D) |
NS |
NS |
NS |
NS |
NS |
NS |
NS |
NS |
NS |
E G |
4659638.3 ** |
NS |
NS |
NS |
NS |
NS |
NS |
NS |
NS |
|
E D |
NS |
NS |
NS |
NS |
NS |
NS |
NS |
NS |
NS |
|
G D |
NS |
NS |
NS |
NS |
NS |
NS |
NS |
NS |
NS |
E G D |
NS |
NS |
NS |
NS |
NS |
NS |
NS |
NS |
NS |
CV (%) |
NS |
NS |
NS |
NS |
NS |
NS |
NS |
NS |
NS |
Mean |
4893 |
222.7 |
98.7 |
81.4 |
83.2 |
743.1 |
54.9 |
14.3 |
468.9 |
* Significant 0.05; ** significant 0.01; CV = coefficient of variation.
Table 2, shows the significant groups that define the contrasting responses of the hybrids in the evaluation environments. The higher mean yield corresponded to the first sowing date in CEVAMEX with 5497 kg ha-1 grain, and a difference of 765 kg ha-1 in relation to FESC-UNAM which had a lower yield (4732 kg ha-1), both experiments were established on June 5th, 2015. The second sowing date (June 26th, 2015) affected the productivity of the evaluated hybrids in CEVAMEX, this was mainly due to the distribution of the rainfall which was concentrated in the first three months after sowing (Figure 1). To this regard Aguilar et al. (2015), mention that the water requirements of the crop are approximately 550 to 575 mm. It is important to point out that even though the environment in CEVAMEX was below the water requirements, it was the better environment for the performance of the hybrids in the first sowing date, compared with FESC-UNAM (Table 2).
Table 2: Comparison of means of three test environments for the different traits evaluated considering the average of six corn hybrids and three environments of the High Valleys. FESC-UNAM and CEVAMEX. Spring-summer season, 2015.
|
Traits |
HSD (0.05) |
||||
|
First sowing date |
Second sowing date |
||||
|
- - - - June 5th, 2015 - - - - |
June 26th, 2015 |
||||
|
Grain yield |
5497 a |
4732 b |
4449 b |
485.1 |
|
|
Plant height (cm) |
247 a |
174 b |
247 a |
5.1 |
|
|
Plant ear (cm) |
109 a |
78 b |
109 a |
3.8 |
|
|
Male flowering (days) |
78 b |
88 a |
78 b |
0.7 |
|
|
Female flowering (days) |
79 b |
91 a |
79 b |
0.8 |
|
|
Volumetric Weight ((g hL-1) |
752 a |
754 a |
724 b |
8.2 |
|
|
Ear coverage |
8.7 a |
8.2 b |
7.4 c |
0.3 |
|
|
Weight 200 grains |
55.6 b |
60.1 a |
49.1 c |
2.7 |
|
|
Ear length (cm) |
15.0 a |
14.1 b |
13.9 b |
0.5 |
|
|
Ear row grains |
15.1 a |
15.6 a |
15.5 a |
0.5 |
|
|
Row grains |
31.3 a |
30.3 a |
39.1 a |
18 |
|
|
Ear diameter (cm) |
4.5 a |
4.5 a |
4.3 b |
0.1 |
|
|
Ear grains |
472 a |
472 a |
462 a |
24 |
|
|
Grain percentage (%) |
85.7 b |
86.5 a |
84.5 c |
0.6 |
|
† Different letters in the same row indicated different differences, according to the Tukey test (P ≤ 0.05); HSD = honest significant difference; CEVAMEX = Valley of México Experimental Station; FESC-UNAM = Faculty of Superior Studies-Cuautitlán.
In the evaluation of corn genotypes, it is important to consider, besides grain yield, the precocity of the materials. Through the three environments, male and female flowering days oscillated from 78 to 88 and from 79 to 91 days, respectively. The greatest precocity was in the CEVAMEX environment for both sowing dates (Table 2). Similar results are reported by Arellano et al. (2013), in a group of synthetic varieties and corn hybrids for Tlaxcala state. Moreover, CEVAMEX (in two sowing date) showed greater plant and ear height. Reynoso et al. (2014) reported similar values in plant and ear height in a group of 17 hybrids evaluated in different environments in the High Valleys.
With regard to the yield components, differences were identified in the following variables: volumetric weight, weight of 200 grains, ear length, ear diameter, and grain percentage, but not in number of rows per ear, number of grains per row, and total number of grains per ear (Table 2). Of these variables, hectoliter weight stands out with a mean of 754 g hL-1 for the FESC-UNAM environment. It is worth mentioning that this parameter is a value that reflects grain health and the starch ratio in the kernel. These values are ideal for the Nixtamalized Flour Industry and the Corn Dough and Tortilla Industry (Salinas et al., 2010; Vázquez et al., 2015).
Agronomic performance among genotypes
Table 3, shows the means comparison of the hybrids considering the three test sites. The high-yield hybrids were Tsíri-PUMA, H-49 AE, and H-53, with 5856, 5572 and 5569 kg ha-1, respectively. Hybrid H-47 had the lowest grain yield with 3773 kg ha-1. Similar results were reported by Martínez-Gutiérrez et al. (2018), in this same group of corn hybrids established in five sites in the High Valleys of the State of Mexico. Although the mean grain yield in this group was 11.2 Mg ha-1, this is justified because in the evaluated sites, good agroclimatic conditions predominated, as well as deep soil types, optimum sowing dates, and mainly due to the characteristics of the materials, which are genetically different. Moreover, these hybrids were generated by the INIFAP and UNAM under a scheme of male sterility (AE), where there is coincidence in one or two lines that make up its genetic structure as hybrids (Espinosa et al., 2009; Tadeo-Robledo et al., 2014, 2016).
Table 3: Comparison of means between six different corn hybrids, considering the average of three environments and three different population densities for the different traits evaluated. FESC-UNAM and CEVAMEX. Spring-summer season, 2015.
|
Traits |
TSÍRI PUMA |
H-49 |
H-53 |
H-51 |
H-48 |
H-47 |
|
| AE | AE | AE | AE | -0.05 |
|||
|
Grain yield (kg ha-1) |
5856 a† |
5572 a |
5569 a |
4406 b |
4179 b |
3773 b |
836.6 |
|
Male flowering (days) |
78 c |
83 a |
82.7 a |
82.3 a |
80.7 b |
81.8 ab |
1.2 |
|
Female flowering (days) |
80 c |
84 a |
84.5 a |
83.9 a |
82.4 b |
83.9 a |
1.4 |
|
Plant height (cm) |
230 ab |
218 cd |
212.8 d |
232.2 a |
220.3 cd |
222.8 bc |
8.8 |
|
Ear height (cm) |
96 bc |
92 c |
93.4 bc |
110.6 a |
99.4 b |
99.9 b |
6.6 |
|
Volumetric Weight (g hL-1) |
775 a |
765 ab |
759.4 b |
713.3 c |
723.9 c |
721.9 c |
14.1 |
|
Ear coverage |
8 a |
8 a |
8.7 a |
7.7 bc |
8.2 ab |
7.4 c |
0.6 |
|
Weight 200 grains (g) |
60 a |
55 ab |
58.3 a |
51.9 b |
51.8 b |
52.5 b |
4.7 |
|
Ear length (cm) |
14 a |
15 a |
14.6 a |
14.6 a |
13.8 a |
14.1 a |
0.9 |
|
Ear row grains |
15 b |
15 b |
15.3 ab |
15.9 a |
15.9 a |
15.4 ab |
0.9 |
|
Row grains |
31 a |
31 a |
30.9 a |
30.6 a |
30.1 a |
47.9 a |
31.1 |
|
Ear diameter (cm) |
5 a |
4 b |
4.5 a |
4.5 a |
4.4 |
4.5 a |
0.1 |
|
Ear grains |
455 a |
464 a |
472.7 a |
488.8 a |
481.7 a |
450.8 a |
41.6 |
|
Grain percentage (%) |
86 ab |
86 ab |
85.7 ab |
84.9 b |
86.1 a |
84.8 b |
1.1 |
† Different letters present significant differences between treatments in the different variables according to the Tukey test (P ≤ 0.05); HSD = honest significant difference.
The Tsíri PUMA hybrid had the greatest precocity with 78 and 80 days to flowering. However, all the evaluated genotypes had a precocity under 90 days to flowering, which is desirable in production systems with water deficiencies or erratic distributions (Figure 1). According to some authors, precocious varieties are generally able to avoid the water deficient periods that appear with little rainfall (De la Cruz-Lázaro et al., 2009; Ángeles-Gaspar et al., 2010); this probably allowed this group of outstanding hybrids to have better rain water use in the first months (Figure 1). Plant height in the evaluated hybrids varied from 212.8 to 232.2 cm, and ear height ranged from 92 to 110.6 cm, respectively; these values, are within those reported by Tadeo-Robledo et al. (2014, 2015). There were no high percentages of bad covering in the evaluated hybrids, which avoided damage from birds and passage of humidity, considerably decreasing damages from ear rot.
We proved that the Tsíri PUMA hybrid showed the best results in grain variables like volumetric weight, weight of 200 grains, ear length, ear width, number of rows per ear, number of grains per row, total number of grains per ear, and grain percentage, respectively (Table 3). These results outperform data reported by Espinosa et al. (2010) for hybrid H-49 in their male-sterile and fertile versions in the High Valleys of Mexico.
Population density
Given that the plant density factor had no significant effect on the evaluated variables in any of the three test sites, the optimum population density was not determined in the present study (Table 4). Thus, we can infer that the evaluated hybrids can endure high plant densities (Xu et al., 2017). These results agree with some works reported by Cervantes et al. (2014). We suggest carrying out a wider exploration of population densities in future works with the three best performing hybrids.
Table 4: Comparison of means between population densities for the different traits evaluated in the mean of six corn hybrids of INIFAP and the UNAM of High Valleys evaluated in the FESC-UNAM and CEVAMEX. Spring-summer season, 2015.
|
Traits |
Plant densities (plants ha-1) |
||||
|
65 000 |
50 000 |
80 000 |
HSD (0.05) |
||
|
Grain yield (kg ha-1) |
4964 a† |
4871 a |
4843 a |
485 |
|
|
Male flowering (days) |
81 a |
81 a |
81 a |
0.7 |
|
|
Female flowering (days) |
83 a |
83 a |
83 a |
0.8 |
|
|
Plant height (cm) |
223 a |
221 a |
224 a |
5.1 |
|
|
Ear height (cm) |
98 a |
99 a |
99 a |
3.8 |
|
|
Volumetric weight (g hL-1) |
740 a |
744 a |
745 a |
8.2 |
|
|
Ear coverage |
8.0 a |
8.1 a |
8.2 a |
0.3 |
|
|
Weight 200 grains (g) |
54.0 a |
54.1 a |
56.7 a |
2.7 |
|
|
Ear length (cm) |
14.2 a |
14.3 a |
14.5 a |
0.5 |
|
|
Ear row grains |
15.3 a |
15.5 a |
15.4 a |
0.5 |
|
|
Grains row |
30.1 a |
39.7 a |
30.8 a |
18 |
|
|
Ear diameter (cm) |
4.4 a |
4.5 a |
4.4 a |
0.1 |
|
|
Ear grains |
459 a |
473.5 a |
473.3 a |
24.1 |
|
|
Grain percentage (%) |
85.6 a |
85.4 a |
85.6 a |
0.6 |
|
† Different letters present significant differences between treatments in the different variables according to the Tukey test (P ≤ 0.05); HSD = honest significant difference.
Population density is one of the factors that producers frequently modify to increase grain yield, although they do not always establish the adequate density, since with a greater number of plants, competition for light, water, and nutrients increases.
Conclusions
The best evaluation sites were those established at the beginning of the rainy season, as is the case of CEVAMEX (June 5th, 2015). In this environment, the Tsíri PUMA, H-49 AE, and H-53 AE hybrids showed the best agronomic performance and grain characteristics. Furthermore, no differences were observed from changes in plant densities, concluding that plant density is not a factor that influences grain yield in the hybrids in this study. Therefore, we recommend using the second population density, 65 000 plants ha-1 so farmers can avoid spending in greater amounts of seeds to obtain the same yields. If a density of 50 000 plants ha-1 is used, too much space is wasted and there could be problems with regard to population. Contrastingly, a higher population density increases costs as more seeds are needed to establish greater population densities.
