Physical and sanitary quality of the grain

The evaluations were made in the Systemic-Transdisciplinary Laboratory of the Systems Engineering Program at ESIME-IPN, Mexico City, Mexico. A random sample of 1 kg of grain per repetition was used. To determine the physical quality of the grain, we measured: 1) hectoliter weight, was determined on an Ohaus^® scale and expressed in kg hL^-1; and 2) commercial grain size, the grain was classified with round perforation screens of 8 and 7 mm in diameter, the weight of the grain retained in both screens was added and reported as a percentage.

To determine the sanitary quality of the grain, the drying and freezing paper sanitation test was used (^{Warham et al., 1996}), 50 grains per repetition were used. The grains were disinfested with 10% sodium hypochlorite (NaCl) for 3 min and rinsed with distilled water for 1 min, then the grains were placed on moist filter paper in a clear plastic box and sealed with parafilm. For incubation, the boxes were placed at 25 °C for two days (12 h with cold white light and 12 h dark every day).

After the time, they were subjected to freezing at -1 °C for 24 h. Finally, the boxes were placed at 25 °C for 11 days. After 14 days, the number of grains infected with Fusarium spp., and Penicillium spp. and expressed as a percentage. To detect the presence of mycelial development, each grain was observed with Olympus SZ51⁽ stereoscopic microscope. In the grains, mycelial growth was observed with a variation in white-yellow, salmon pink and gray. For the morphological identification of Fusarium species, it was elaborated with the specific keys and descriptions reported by ^{Nelson et al. (1983)} and for Penicillium (^{Pitt, 1979}).

A variance analysis combined with the PROC GLM procedure of the Statistical Analysis System (^{SAS, 2014}) was carried out for the main factors and for the variables whose mean squares showed significant differences, the Tukey (α= 0.05) multiple comparison test was used. The percentage variables were transformed with the arcsine function to have them in a normal distribution and to be able to carry out the aforementioned analysis.

Establishment of corn seedlings in field conditions

In the field of production, the establishment of seedlings is a basic indicator for the productivity of the crop. The exposure of the seed to electromagnetic field, intensity of 3.6 mT (Figure 1), as pre-sowing treatment caused significant differences (p≤ 0.05), in the establishment of corn seedlings under field conditions (Table 1).

This is due to the biostimulation of the seed by the transfer of energy on the matter that contains free radicals that are attracted or repelled according to their charge, which increase their load and are activated (^{Galland and Pazur, 2005}) causing changes in enzymes, chlorophyll and photosynthesis reflected in the growth of the seedling (Javed et al., 2011; ^{Shine and Guruprasad, 2012}). The improvement in the germination and growth of corn seedlings under controlled conditions was reported by Domínguez et al. (2010) and Shabrangi et al. (2015) and in field conditions by ^{Shine and Guruprasad (2012)}.

The corn seed exposed to 24 min to electromagnetic field (EMF) increased 10.54% (p≤ 0.05), the establishment of seedlings in field conditions compared to the control not exposed to EMF (Table 1). With 12 min, 6.66% was increased compared to the control, both statistically equal (p≤ 0.05). With 24 and 12 min of exposure of the seed to EMF allowed to register values (85% of seedlings established in the field; however, only with 24 min, 91% of established seedlings were registered in the corn varieties, value ˃90% of germination, quantified with the standard germination test, minimum required in the rule for the qualification of corn seed in Mexico (^{SAGARPA-SNICS, 2016}).

The non-irradiated control and 6 min of EMF exposure had a seedling establishment <85%. Under controlled conditions, Domínguez et al. (2010) and Zepeda-Bautista et al. (2010) reported 90 and 2% increase in the establishment of corn hybrid seedlings with 30 and 15 minutes of EMF exposure at an intensity of 560 and 480 mT compared to the control not exposed to electromagnetic field. Between corn varieties and years of production there were no significant differences (p≤ 0.05), for establishment of seedlings in field conditions (Table 2) because the size of the seed was homogeneous (large, round perforation screen of 8 mm in diameter), indirect measurement of the quantity of reserve, used during the germination and establishment of the seedling.

Likewise, in each sowing soil conditions, drip irrigation (per week 167 m³ ha^-1 at 100% of corn evaporation), average temperature (18.6 °C) and without precipitation were similar (^{SMN, 2018}). In field conditions, similar results have not been reported. Among varieties, 85.81% of seedling establishment (EP) was registered under field conditions. The V-60 variety had the highest establishment of seedlings, 2.44 and 1.05% more than the hybrids H-61R and H-70. In 2015, 3.67% more seedlings were established in the field compared to 2016, statistically equal (α= 0.05).

Agronomic characteristics, yield and physical grain quality

Between time of exposure of the seed to the electromagnetic field as pre-sowing treatment, there were significant differences (p≤ 0.05), for male mean flowering (Table 1) because the biostimulation of the seed had an effect on the plant’s growth. The positive effect of the magnetic field in several cultivated plants has been reported by several authors (^{Pietruszewski and Martínez, 2015}).

With 24 min of EMF exposure, two days were increased for male mean flowering compared to the non-irradiated control, which can be useful in a batch of corn seed production, registered and certified categories, to achieve floral synchrony between male and female parents (^{Virgen-Vargas et al., 2016}). ^{Zepeda-Bautista et al. (2014)} reported a one-day increase in male mean flowering with 15 min of seed exposure to EMF at an intensity of 480 mT.

The application of electromagnetic field to the seed did not have a significant effect (p≤ 0.05), for plant height and grain yield (Table 1); however, an increase in them was observed in comparison with the control (p= 0.08 and p= 0.06, respectively). Based on these results and the positive effect of the electromagnetic field on the growth and yield of the cultivated plants reported by several authors (^{Pietruszewski and Martínez, 2015}; ^{Carbonell et al., 2017}), it is recommended to perform electromagnetic field applications during the phenological cycle of the plant, in the stages of greater nutrimental absorption: floral differentiation (V10), flowering (V18) and grain filling (R2).

The positive effect of magnetic field on wheat yield was reported by ^{Pietruszewski and Kania (2010)} and in pea by ^{Iqbal et al. (2013)}. In corn, ^{Zepeda-Bautista et al. (2014)} reported that with 12 min of seed exposure to EMF (480 mT) in pre-sowing, grain yield was increased by 6%. With 12 min of exposure of the seed to EMF, at an intensity of 3.6 mT, an increase in plant height and grain hectoliter weight of 3 and 0.71% was observed, both statistically equal (α= 0.05). With 24 and 12 min to EMF increased 12.94 and 11.04% the grain yield ha^-1, equivalent to 1020 and 870 kg ha^-1, compared to the control not exposed to EMF.

However, for commercial grain percentage there were no significant differences (p≤ 0.05) compared to the control (Table 1). In contrast, corn hybrids showed a 5% decrease in hectoliter weight when the grain was exposed to the electromagnetic field for 15 min at 480 mT ^{Zepeda et al. (2011)}. Between corn varieties and between years of production, significant differences were observed (p≤ 0.05), for agronomic characteristics, yield and grain quality (Table 2). In the H-61R hybrid and the V-60 variety four more days were observed for the average male flowering and 2.59 and 7.17% less plant height compared to the hybrid H-70.

The average grain yield was >8.5 t ha^-1, higher than the average productivity in Mexico (3.71 t ha^-1) (^{FAO, 2018}) and similar to the yields (7.42 and 10.64 t ha^-1) reported by ^{Haegele et al. (2013)} and ^{Kovacs et al. (2014)} with the application of chemical fertilizers, which sometimes cause severe problems to the environment (^{Nazir et al., 2016}). Therefore, the application of electromagnetic field to the seed as pre-sowing treatment is an alternative to improve the yield of corn, without damaging the environment.

The hybrid H-70 yielded 22.44 and 23.21% more and 4% more commercial grain compared to H-61R and V-60. On average, 94% of commercial grain and 76.04 kg hL^-1 of hectoliter weight were observed, higher values than those required by the dough and tortilla industry (^{NMX-FF-034/1-SCFI-2002, 2002}). ^{Benítez-Rodríguez et al. (2014)} reported that the hybrid H-70 yielded 48.33% less and similar hectoliter weight of the grain, in rainy season conditions in the High Valleys of Mexico with an annual average precipitation between 583 and 816 mm, compared to the yield and hectoliter weight obtained in fertigation in Chapingo, State of Mexico with an average annual rainfall of 618.5 mm.

In the year of production 2015 four more days were observed for the average male flowering and 22.54% higher plant height, 2.66 and 2.97% more commercial grain and hectoliter weight compared to 2016. This is because the quantity and distribution of the precipitation during the phenological cycle of corn was different, which affected the growth and development of the plant, as reported by ^{Virgen-Vargas et al. (2016)} in simple corn crosses. Between the months of June to September 2015, the average temperature and precipitation were 10.24 and 5.28% higher than in 2016 (16.6 °C and 408.4 mm). Grain yield was statistically equal (α= 0.05) between years; in 2015, 320 kg ha^-1 more were produced than in 2016.

Interaction of corn varieties x time of exposure to electromagnetic field

For the established seedling variables and grain yield, the corn varieties showed a statistically equal response (α= 0.05) to the exposure time of the seed to the electromagnetic field (EMF) at an intensity of 3.6 mT. In the hybrid H-70 and the variety V-60 an increase in the established seedlings was observed in the field by increasing the time of exposure of the seed to EMF. In H-70 with exposure of 6, 12 and 24 min increased 3.75, 8.75 and 17.5% and in V-60 0, 1.17 and 8.23% more than the control (not exposed to EMF).

Results contrary to those reported by Zepeda-Bautista et al. (2010), that when evaluating the establishment of corn seedlings under controlled conditions they observed an increase, followed by a decrease with increasing the time of exposure of the seed to EMF (3, 6, 9, 12 and 15 min). In the hybrid H-61R with 12 min of exposure had higher establishment of seedlings under field conditions (9.75%) compared to 6 min of exposure to EMF, which showed a decrease of 2.43% (Figure 2).

Figure 2 Establishment of seedlings and grain yield of corn varieties with time of exposure of the seed to the electromagnetic field as pre-sowing treatment.  

For grain yield, the hybrid H-61R and the variety V-60 yielded more (10.85 and 8%) with 12 min of exposure to EMF, while, the hybrid H-70 increased its yield 27.14% with 6 min of exposure in comparison with the control not exposed to EMF (Figure 2). This represented an increase of 800, 600 and 2 300 kg ha^-1 of grain for the producer with the application of a biophysical method friendly to the environment.

Each variety of corn had a different response to the time of exposure to the EMF, behavior similar to that observed by ^{Zepeda-Bautista et al. (2014)} when evaluating the performance of corn hybrids with EMF exposure of the seed as pre-sowing treatment. However, there is little information on the effect of the electromagnetic field in the establishment of seedlings, growth and production of corn in field conditions (^{Pietruszewski and Martínez, 2015}).

In other crops such as wheat, 12 and 14% more yield was observed with exposure to magnetic field at a dose of 12.9 and 17.9 kJ m^-3 s^-1 compared to the control (^{Pietruszewski and Kania, 2010}) and in pea, was observed the highest production of green pods per plant and per hectare with the exposure of 5 min at an intensity of 180 mT (^{Iqbal et al., 2013}).

Corn grain health

Between years of production there were no significant differences (p≤ 0.05) in the percentage of grains infected by Fusarium spp. and by F. oxysporum probably because the physical and chemical characteristics of the soil and the agronomic management were similar; in addition, between June and September the temperature and precipitation in 2015 were slightly higher (18.3 °C and 430 mm) compared to 2016 (16.6 °C and 408.4 mm), which did not affect the percentage of grains infected by Fusarium; however, there was a higher percentage of grains infected by F. graminearum (Table 3).

In 2016, the percentage of grains infected by F. graminearum was higher (2.44%) compared to 2015 (0.55%). Similar values (between 1.88 and 2.33%) were recorded by ^{Zepeda-Bautista et al. (2014)} in corn hybrids in the State of Mexico.

In the grain of corn varieties, 9.22% of grains infected by Fusarium spp., 7.72% by Fusarium oxysporum and 1.5% by Fusarium graminearum were quantified (Table 3). ^{Cendoya et al. (2018)} reported between 13 and 16% severity of ear rot of corn hybrids in Texcoco and Huamantla, Mexico associated with the presence of Fusarium verticilloides, F. subglutinans, F. proliferatum and F. oxysporum. This indicates that the grain of corn was colonized by Fusarium species that affects the grain health as reported by ^{Cendoya et al. (2018)}.

Among corn varieties there were no significant differences (p≤ 0.05) for the percentage of grains infected by Fusarium spp.; that is, the Fusarium-infected grains were similar among genotypes. Contrary results were observed by ^{Pereira et al. (2017)} when evaluating hybrids and corn lines. The hybrids H-61R and H-70 had on average 10% of grains infected by Fusarium spp. and between 8 and 9.5% by F. oxysporum; while, the variety V-60 had the lowest values (6.66 and 5.66%).

The percentage of grains infected by Fusarium spp. was lower than reported by ^{Zepeda-Bautista et al. (2014)} in corn hybrids (28.49%). Between years of production and varieties of corn there were no significant differences (p≤ 0.05) for percentage of grains infected by Penicillium spp., on average it was 3.16% (Table 3), it was always observed in grain separated from Fusarium spp. In 2015 and in the hybrid H-61R, the percentage of grains infected by Penicillium spp. They were 47.84 and 50.21% higher compared to 2016 and the H-70 hybrid.

On the other hand, the exposure of the seed during 6 and 24 min to EMF increased the presence of Fusarium spp. in 21.65 and 37.83% and F. oxysporium 31.05 and 58.69% in comparison with the non-irradiated control. For Penicillium spp. in grain of corn, an increase of 54.51 and 81.96% was observed with the exposure of 6 and 12 min of the seed to EMF as pre-sowing treatment (Table 3). In general, a lower presence of Fusarium spp. with the application of the electromagnetic field to the seed in pre-sowing, so it could be an alternative method for controlling the fungus in corn grains to produce food for human consumption.