Introduction

Currently, corn is the cereal with the highest production worldwide, in which, curiously, Mexico occupies the fifth place (^{FAOSTAT, 2020a}), despite the great importance of its consumption (76 %) (^{Martínez & Villezca, 2005}; ^{Jaramillo et al., 2018}) and energy contribution in the Mexican diet (59 %) (^{Sierra et al., 2004}), besides being considered one of the centers of origin and domestication (^{Carrillo, 2009}). Corn production in Mexico since the opening of trade and especially since the North American Free Trade Agreement (NAFTA) has been insufficient to meet domestic demand (^{Moreno-Sáenz et al., 2016}), such that the volume of imports is currently estimated at 36 % (^{SIAP, 2018}; ^{FAOSTAT, 2020b}), despite the efforts that have been made to counteract this deficit (^{Cadet-Díaz & Guerrero-Escobar, 2018}), so it is advisable to develop new technologies that contribute to increasing supply.

Salicylic acid (SA), is a secondary metabolite synthesized, naturally, by plants as a defense mechanism against the attack of pathogens and environmental stress (^{Muthulakshmi & Lingakumar, 2017}; ^{Ding & Ding, 2020}). However, when supplied exogenously and in low concentrations, it potentiates several physiological and biochemical processes that affect crop yields, suggesting its potential use in agricultural production (^{Tucuch-Haas et al., 2017}a). This is in the same way that its analogue acetylsalicylic acid (ASA), commonly known as aspirin (^{Shinwari et al., 2018}), which, although it has not been identified as a natural plant product, has been used in some research as a substitute for SA, without any risk of phytotoxicity and with similar effects (^{Raskin, 1992}).

Answers such as the control in the opening and closing of the stomatal that regulate the rate of perspiration (^{Larqué-Saavedra, 1978}; ¹⁹⁷⁹), have been documented before the supply of ASA. Likewise, it has been reported its participation in the protection against damages caused by pathogens (^White,1979; ^{Mills & Wood,1983}) due to its capacity to produce pathogenesis-related (PR) proteins (^{Jung et al., 1993}), induce a programmed cell death (^{Garcia-Heredia et al., 2008}) and act as a biotic inducer in the production of secondary metabolites (^{Godoy-Hernández & Loyola-Vargas, 1996}); the latter linked to the activation of the expression of genes that regulate biosynthetic pathways (^{Qin et al., 2014}). It has also been suggested to intervene in reducing the impact of environmental stress (^{Cai et al., 2006}; ^{Shinwari et al., 2018}) by relieving damage to photosynthetic pigment content, increasing proline content and stimulating the antioxidant system (^{Daneshmand et al., 2009}; ^{Mahmoud, 2019}) that inhibits the accumulation of superoxide free radicals and reduces the activity of phenylalanine ammonia-lyase, cinnamylalcohol dehydrogenase, and guaiacol peroxidase (^{Soliman et al., 2018}).

In the corn crop (Zea mays L.), it has been documented that the supply of SA acts as an effective regulator of several physiological processes that favor plant development (^{Tucuch-Haas et al., 2016}), yield (^{Tucuch-Haas et al., 2017b}) and grain quality (^{Tucuch-Haas et al., 2017c}). It is not known if commercial ASA (Aspirin) tablets express the same response. For this reason, based on the benefits reported for ASA and given the availability, easy acquisition of aspirin tablets and the search for easy application techniques, without having negative repercussions on the environment, this research was developed.

Material and Methods

The experiment was carried out in the town of La Rosita Angostura, Sinaloa, during the agricultural cycle autumn-winter 2017- 2018, in a plot of agricultural use (clay texture, EC 1.70 dS m-1 and pH 7.6), whose maximum average relative humidity was 92.80 ± 14.99 and minimum 33.89 ± 12.44, the maximum average temperature was 37.82 ± 8.45 °C and minimum 11.22 ± 6.34 °C. Hybrid corn seed was used, commercially known as Armadillo (Asgrow®). Soil preparation consisted of double subsoiling, cross-harrowing, soil leveling and marking. Planting was carried out on December 8th, 2017 with a precision seed drill at a furrow spacing of 0.80 m and a density of eight seeds per linear meter in incoming soil. Two fertilizations were made with ammonia as a nitrogen source (200 kg ha-1 in pre-sowing and 200 kg ha-1 in the phenological stage (v6).

The treatments were concentrations of 100, 1, 0.01 and 0.0001 μM ASA and well water as control. These concentrations, as well as the control, were sprayed with a backpack fumigator (Swissmex®) directed to the aerial part up to dew point in corn plants established in the field, during one week, in 24 hours intervals, starting seven days after germination. Bayer branded effervescent soluble Aspirin® tablets containing 500 mg of ASA were used as a source of ASA. To obtain the different ASA concentrations, the molecular weight of the ASA (180,158 g M-1) as well as the concentration and weight of the tablets were taken into account. These were diluted in well water until reaching the desired concentration, and the pH was adjusted to 5.5 with 1N HCL or 1N NaOH to lower or raise the pH of the solution, respectively, and surfactant (TWEEN® 20) was added at 0.1 %.

After 180 days after sowing (end of the experiment) six plants were evaluated at random from each experimental plot. The experimental plot was made up of four eight-meter-long furrows, and the plants evaluated came from the central furrows to avoid errors in the results, due to the contamination of the different treatments. There was collected data on plant height, measured from the base of the stem to the terminal apex; stem diameter, taken at 10 cm from the ground; dry weight of total biomass; length, diameter, weight of the cob and grain yield per plant. An analytical balance (Sartorius®), flexometer and digital vernier (Truper®, Mexico) were used to make the measurements. To determine the nutrient contents of nitrogen (N), phosphorus (P) and potassium (K) in plant tissue and grain, a sample was taken from the aerial part of the plants and 100 g of grain from each treatment; these were placed in a forced circulation oven at 70 °C until they reached a constant weight and were ground for laboratory analysis.

The evaluation of the nitrogen (N), phosphorus (P) and potassium (K) content was carried out under the following methodologies: N was determined by the semi-micro Kjeldahl procedure (^{Etchevers, 1987}). The P was determined by colorimetry of molybdophosphoric complexes reduced with ascorbic acid (^{AOAC, 1980}). The K by flame photometry according to ^{Rodriguez & Rodriguez (2015)}. For K and P extracts from dry digestion were used. For the estimation of total contents, it was considered the concentrations of each element in the plant tissue and grains, as well as the weights of dry biomass of the aerial part and the grain.

The experimental design used was a randomized block with five repetitions, each repetition was made up of six plants. The results were analyzed by an analysis of variance (ANOVA) and a Tukey mean comparison test (p ≤ 0.05) using SAS software.

Results and Discussion

For plant height variable (Figure 1a) a significant increase of 8 to 12 % was observed with respect to the control, where the maximum value was registered with 1μM, however, between treatments they were not significant, although it can be seen that there is a slight variation between treatments. The lowest values correspond to the treatments with lower (0.0001 μM) and higher concentration (100 μM), which suggests that the highest expression of sensitivity to height increase, is subject to the concentration applied. These values allow reaffirming the capacity of ASA to regulate plant growth, as it has been pointed out for Solanum bulbocastanum cultivation (^{Daneshmand et al., 2009}), Pisum sativum (^{El-Shraiy & Hegazi, 2009}) and Lycopersicon esculentum (^{Shinwari et al., 2018}), in which they found the induction of significant effects on plant height.

Figure 1 Effect of different concentrations of acetylsalicylic acid sprayed on corn seedlings on plant height (a) and total dry biomass (b). Means ± standard error are shown; n = 5. Identical letters on the bars indicate absence of significant difference (Tukey, α ≤ 0.05). 

With respect to the dry biomass of the aerial part of the plant (Figure 1b), the concentration of 1μM of ASA presented a statistically significant value with respect to the control with a 21.1 % difference, not so for the rest of the treatments, which, although not significant, the values exceeded the control from 6 to 15 %, which is consistent with the work of ^{Daneshmand et al. (2009)} and ^{Soliman et al. (2018)}, who reported the same trend of behavior in Solanum bulbocastanum and Phaseolus vulgaris when this same concentration was supplied.

Regarding the accumulation of macroelements, in the aerial dry biomass (Table 1) 1 μM of ASA showed the best results with increases of 48.6, 42.5 and 19 %, respectively, for N, P and K, however, for K concentrations no statistical difference was observed. In the grain (Table 1), it can be seen that, for all the elements evaluated, the values of the treatments were above the control. However, greater significant impact was observed with the concentrations 0.01 and 1 μM with increases of 42.3 and 40.7 % for N, 33.3 and 53.3 % for P and 17.5 and 32.5 % for K respectively. The demonstration of the ability of ASA to intervene in the accumulation of nutrients supports the results of ^{Daneshmand et al. (2009)} who reported a significant increase (9.2 % under normal conditions and 44.2 % under salinity stress) of K in the dry biomass of Solanum bulbocastanum with 1.0 μM AAS.

Figure 2 shows the yield behavior with respect to ASA concentrations, in which it is observed that all treatments exceeded the control with 35.7 % (with 0.0001 and 1.0 μM ASA) and 32.4 % (with 0.01 and 100 μM ASA). For the weight of the cob, only 0.01 μM ASA concentration was not significant regarding the control, with 19 g equivalent to 12.9 %; while for the rest of the treatments, the differences were 14.5, 16.1 and 15.3 % respectively for 0.0001, 1.0 and 100 μM. On the other hand, for the yield per hectare, only the treatment with 1 μM presented statistically significant differences with a difference of 957 kg ha-1; the rest of the treatments, although they were not significant, their values were above the control with a difference of 821.0, 73.4 and 439.9 kg ha-1, for 0.0001, 0.01, and 100 μM, respectively. This behavior allows corroborating the action of ASA, in the yield and quality of grains and fruits reported for Pisum sativum (^{El-Shraiy & Hegazi, 2009}), Prunus cerasu (^{Giménez et al., 2014}) and Hordeum vulgare (^{Kabiry & Naghisadeh, 2015}).

Figure 2 Effect of the spraying of different concentrations of acetylsalicylic acid on the grain yield in the corn crop (a. Weight of 100 grains, b. Grams per ear and c. Kilograms per ha), sprayed in the seedling stage. Means ± standard error are shown; n = 5. Identical letters on the bars indicate absence of significant difference (Tukey, α ≤ 0.05). 

The data reported in this study allow pointing out the sensitivity of corn culture tissues to both ASA and SA at low concentrations, which can be corroborated with the results reported by ^{Tucuch-Haas et al. (2017b)} who indicated a similar behavior in height, diameter and dry biomass of the plants; in accumulation of N, P, K, both in the biomass and in the grain; and in cob weight, number of grains per ear and grain yield of two harvest periods, with a foliar spray of 1.0 μM, in seedling stage (^{Tucuch-Haas et al., 2016}). This is attributed to the rapid transformation of ASA, by the plant cell, into SA (^{Raskin, 1992}), triggering a series of physiological responses such as the regulation of the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) enzymatic activity (^{Wang et al., 2010}) and control of electron transport of photosystem II, which favor photosynthesis (^{Janda et al., 2012}; ^{Wang et al., 2010}); intervention on the control of osmotic and water potentials (^{Khan et al., 2013}), regulating transpiration and stomatal conductance (^{Fahad & Bano, 2012}); and increasing root mass, allowing a greater area of exploration in the soil (^{Tucuch et al., 2015}; ^{Tucuch-Haas et al., 2016}), favoring the absorption of ions such as: NO₃, H₂PO₄, Ca, Mg, K, mostly (^{Fahad & Bano, 2012}; ^{Tucuch-Haas et al., 2019}).

Likewise, it is observed that biochemical responses controlling the activity of oxidative enzymes such as catalase (CAT), guaiac peroxidase (POD), superoxide reductase (SOD) and proline oxidase (PO) (^{Wang et al., 2010}; ^{Fahad & Bano, 2012}; ^{Ghasemzade & Jaafar, 2013}) intervening in oxidation-reduction processes (^{Mateo et al, 2006}); and participating in the accumulation of sugars, proteins, abscisic (ABA) and indoleacetic (IAA) acids and proline (^{Shakirova et al., 2003}; ^{Fahad & Bano, 2012}); it also promotes the production of secondary metabolites such as flavonoids (^{Pacheco et al., 2013}) and total phenols (^{Tucuch-Haas et al., 2017a}) that participate in the protection of crops against pathogens.

Conclusion

Corn plants show a positive response to the application of 1 μM of acetylsalicylic acid from tablets commercially known as Aspirin® (effervescent), when sprayed to the canopy in seedling stage, promoting a higher vegetative development (12 %), grain yield (35.7), and N, P and K content, both in the grain (40.7, 53.3 and 32.5 %, respectively) and in the rest of its tissues (48.6, 42.5 and 19.9 %, respectively).