Introduction

To face the great forces that are moving society such as malnutrition, public health problems and especially climate change, it is necessary to use plant species with characteristics that contribute to the solution of these issues. Likewise, genetic improvement programs should look for intelligent varieties that respond to the environmental conditions that occur in the growing season. Generally, this type of varieties can be created using species that by nature can grow in adverse agroclimatic conditions, such is the case of the Cariophyllales, known to contain several extremophile species.

Within this group, there is the family Amaranthaceae, which includes, among others, the genera Amaranthus and Chenopodium, characterized by having species that grow in adverse conditions, in addition to presenting high contents of proteins, unsaturated fatty acids and vitamins, as well as functional properties, therefore, they could be an excellent option to face these great health, food and environment problems the world is going through. Amaranth is an annual herbaceous plant that belongs to the genus Amaranthus, predominantly tropical, includes about 70 species native to the tropics and temperate regions around the world; of which 40 are from America and the rest belong to Australia, Africa, Asia and Europe.

Within the genus are the species A. cruentus, A. hypochondriacus and A. caudatus, which are the most important to produce amaranth grain (^{Espitia, 1992}). Quinoa is a plant of the genus Chenopodium, has wide worldwide distribution, with about 250 species (^{Zurita-Silva et al., 2014}).

The cultivation of amaranth in Mexico is poorly developed, as 3 000 to 7 000 ha are sowed annually, fluctuating according to supply and demand. There are many limitations that this crop faces, such as the low technological level with which it is carried out. Most of the sowings are carried out with low-yielding Creole varieties and disadvantageous agronomic characteristics, such as late ripening and tall plants, variation in plant and seed color, among others. There is no well-founded production technology for fertilization doses, sowing dates, densities, pest and disease control. Recently, amaranth was included in the basic basket, therefore, in order to increase the area of sowing and harvesting, it is necessary to improve the technology used so far.

Amaranth and quinoa, in addition to their agronomic potential to grow in adverse conditions, are super grains recognized among the most promising crops to help achieve food security and combat malnutrition (^{Präger et al., 2018}). In recent years, interest in these grains, rich in protein and as a source of nutraceutical compounds, has increased (^{Venskutonis and Kraujalis, 2013}; ^{Rastogi and Shuklam, 2013}). This interest is due to the great current problems associated with chronic degenerative diseases, ischemic heart diseases, cerebrovascular diseases and chronic liver diseases, which are closely linked to factors such as malnutrition, overweight and obesity.

On the other hand, quinoa is a crop of recent introduction in Mexico; however, in recent years, it has gained great boost due to the growth of its consumption globally. This interest is due to its agronomic, nutritional and nutraceutical characteristics (^{Präger et al., 2018}). This species has been cultivated in the Andes for 5 000 to 7 000 years, adapting to altitudes close to 4 000 masl. Quinoa and amaranth have high water-use efficiency and can even produce acceptable yields with rainfall of 200 mm per year. Also, some varieties of quinoa tolerate salinity conditions like those of seawater (40 dS m^-1), exceeding in many cases the tolerance of known cultivated species (^{Espitia 1994}; ^{Zurita-Silva et al., 2014}).

Quinoa is native to the Andes and is more adapted to regions between 2 500 to 4 000 masl (^{Mujica et al., 1997}), amaranth, on the other hand, is native to Mesoamerica and is more adapted to regions between 0 to 2 600 masl. Although, in recent times, these crops have been taken to environments outside their original range of adaptation. In relation to its yield potential, ^{Bazile et al. (2014}) reported yields from 200 to 2 050 kg ha^-1 in a test of 21 quinoa genotypes in different countries where quinoa was not sown in Europe and Asia. ^{Chura et al. (2019}) mention 2 836.55 to 5 099.18 kg ha^-1 for a group of six quinoa lines, whereas ^{Zurita-Silva et al. (2014}) report yield from 400 to 4 500 kg ha^-1.

For amaranth in a similar test (^{Mujica et al., 1997}), yield from 203 to 7 208 kg ha^-1 is reported for 12 genotypes in nine countries of America, in this case, it was in countries where amaranth is sown. The yields reported for Mexico are highly variable and depend on the variety and production conditions, for example, they are mentioned from 2 062 to 5 274 kg ha^-1 (^{Espitia, 1992}), from 3 875 to 4 583 kg ha^-1 (^{Mujica et al., 1997}), from 950.7 to 2 922.2 kg ha^-1 and from 1 382 to 1 668.7 kg ha^-1 (^{Ramírez, 2011}) and from 1 382 to 3 439 kg ha^-1 (^{Ortiz et al., 2018}).

In other characteristics of agronomic importance, very variable values are also reported, for example, for the maturity variable, 132.5 to 161.38 days are reported in 60 genotypes of the species A. cruentus and A. hypochondriacus (^{Espitia et al., 1992}), from 63.2 to 97.4 for 54 genotypes of A. hypochondriacus. For plant height, values from 141.88 to 228.94 cm (^{Espitia et al., 1992}) and 81.3 to 148 cm (^{Tiwari et al., 2018}) are reported. Other important characteristics are those that express the size and density of the seed, in this regard, one thousand seed weight from 0.684 to 1.32 g (^{Tiwari et al., 2018}) and hectoliter weight from 82.51 to 83.51 kg L^-1 (^{Espitia et al., 1992}) are reported.

In quinoa, the size of the seed is very relevant because the commercialization and use depend on that, so the variables that express size and weight of the seed are relevant, in this regard, seed diameter from 1.2 to 2.5 mm are reported (^{Zurita-Silva et al., 2014}), while ^{Chura et al. (2019}) report diameters from 1.64 to 2.2 mm. The same authors refer for the weight value of one thousand seeds, from 2.09 to 3.8 g, ^{Delgado et al. (2009}) explained 2.52 to 3.45g, while ^{Curti et al. (2014}) establish values from 2.2 to 3.5 g. For maturity, Zurita-Silva et al. (2014) presented values ranging from 135 to 210 days, while ^{Bhargava et al. (2007}) report values from 109.3 to 163.33 days to maturity. For the plant height variable, ^{Delgado et al. (2009)} showed values from 111.23 to 176.65 cm and the same authors report for panicle length, values from 24.03 to 37.25 cm.

Recently, quinoa has become a worldwide phenomenon, it is cultivated in many countries and with prospects of continuing to grow (^{Bazile et al., 2016}). Amaranth and quinoa are two crops with many morphological, nutritional, use and even historical development similarities; the question arises as to why quinoa has grown so much in production and consumption and amaranth, far from growing, suddenly the cultivated area has been reduced and consequently its consumption. Therefore, the objective of this work was to make an agronomic comparison of amaranth and quinoa to determine the potential of each species in the High Valleys of central Mexico.

Materials and methods

Results and discussion

Highly significant differences were found in most variables for environments, except for seed diameter and yield per day (Table 1). For species, significant differences were found in all variables, except plant height. For genotypes, within species, significant differences were also obtained, except in inflorescence length, inflorescence width and stem diameter. For the interaction of species by environment, significant differences were obtained for most variables, except for plant height, inflorescence length and seed diameter. This indicates a differential response of species to these sources of variation, coinciding with what was previously reported (^{Präger et al., 2018}; ^{Tiwari et al., 2018}).

Table 2 presents the comparison of means between species. In the phenological variables, amaranth presented a greater number of days to the emergence of panicle and days to flowering. However, for grain filling period and maturity, quinoa presented a greater number of days.

Although in quinoa the inflorescence emerges first and flowering begins, this species takes longer to reach maturation, this is due to the longer period of grain filling, but still quinoa is less late than in its places of origin. In Bolivia and Peru, it matures in up to more than 200 days (^{Rojas et al., 2013}; ^{Chura et al., 2019}), this because it grows there near 4 000 masl, while in Mexico it was sown at 2 250 masl.

In the size variables, amaranth has an advantage in length and diameter of the inflorescence and stem diameter, while both species presented the same plant height. In the seed variables, quinoa presented a larger seed diameter, a greater weight of one thousand grains, therefore, amaranth has a greater hectoliter weight; it should be clarified that this value is of quinoa without benefiting; that is, still with the pericarp attached to the seed. In yield, amaranth presented higher grain yield per day and higher grain yield. This can be explained because the evaluation sites are places where amaranth is traditionally sown (^{Espitia, 1992}; ^{Espitia, 1994}) and quinoa is introduced into them.

The size of the seed is of the most contrasting characteristics. The seed diameter of the three quinoa varieties evaluated ranged from 1.8 to 1.9 mm, being classified as large grain (^{Murphy et al., 2019}). Grain size is also related to utilization, large grains larger than 1.8 mm are used for cooked consumption, which is the most widespread form worldwide (^{INDECOPI, 2014}). Quinoa, due to its larger seed size, presents fewer agronomic management problems, as it germinates after three or four days, while amaranth germinates after eight or ten days, so quinoa presents better emergence of seedlings. The values obtained here for weight of one thousand grains (2.67 g) is comparable to those reported (2.3 to 3.2 g) in South America (^{Curti et al., 2014}).

In relation to the yield per day, amaranth had 25.42 kg per day, almost five more than quinoa; while in grain yield, amaranth also presented a higher yield than quinoa, almost 800 kg ha^-1 more on average of the three varieties of each crop. The yield values for quinoa in the three environments of the present study are higher than those reported in a test for 12 genotypes in northern Argentina (^{Curti et al., 2014}), they report 654 to 1 703 kg ha^-1 in environments exposed to drought.

In general, it can be established that both amaranth and quinoa have the potential to be grown under the conditions evaluated. Quinoa, due to its origin, is likely to show better performance as it is grown in environments closer to 3 000 masl (^{Zurita-Silva et al., 2014}). On the contrary, as one descends in altitude, quinoa is likely to present problems, especially if temperatures of 30 ^oC occur during flowering, as this causes sterility since grain formation reduces (^{Bertero, 2013}).

Table 3 shows the means for the three varieties of amaranth studied in the present experiment. The experimental lines Tlahuicole and L-145 were the ones with the highest yield (4 097 kg ha^-1), while Nutrisol, which is a commercial variety, yielded a little less than one tonne. It is worth mentioning that the latter showed a maturity 15 days less than the first two, as did the rest of the phenological variables that are inversely correlated with yield (^{Espitia et al., 1992}).

Table 4 shows the comparison of means for the three varieties of quinoa evaluated, Suyana presented higher yield, greater size and weight of seed and greater plant size, yielded more than the variety of amaranth Nutrisol and only 300 kg less than the best varieties of amaranth. The information on mildew (Peronospora variabilis) is not shown, but this variety was the one that presented the lowest incidence of this disease, which is one of the adverse factors for the production of quinoa worldwide (^{Murphy et al., 2019}). Similarly, the content of saponins is an important aspect in the production of quinoa (^{Zurita-Silva et al., 2014}), Suma was the variety with the lowest content followed by Suyana.

Due to the performance of both species, a slight advantage for amaranth is clearly seen, as it has a higher yield and a shorter crop cycle. Quinoa, on the other hand, has a great advantage, which is the size of the grain, which facilitates the agronomic management of the crop. If we look more specifically at the level of individual varieties, the variety of quinoa Suyana has very good performance, comparable to those of amaranth.

A disadvantage of quinoa would be the perigonium of the seed, in which the saponins are found, this forces that in the post-harvest management, the seed has to be scarified or pearled to remove the ‘shell’ and then washed to eliminate all the saponins (^{Zurita-Silva et al., 2014}). These post-harvest management processes make quinoa grain more expensive. On the contrary, amaranth is harvested, cleaned and is ready to use because it has no perigonium. Therefore, and in accordance with the stated objective, it can be established that amaranth has the agronomic characteristics to expand its cultivation, similarly as has happened with quinoa. The limitations of amaranth may be of a different nature, such as political will, because being in a more westernized region, local consumption has not become as popular as quinoa in its places of origin.

As can be deduced from the magnitude of the mean squares presented in the analysis of variance (Table 1), the variation due to species x environment interaction is comparable to the variation due to the sources of variation of environment and species. Figures 1 and 2 presented the performance of the species through the evaluated environments. It can be observed that there were changes in magnitude and order in variables, such as days to flowering, grain filling period, panicle length (Figure 1), stem diameter and yield (Figure 2).

Figure 1 Species-by-environment interaction of six variables of the comparison of three amaranth genotypes (continuous line) and three quinoa genotypes (dashed line) in three environments. S-S 2019. 

In the variables associated with phenology, there was variation through environments, in days to flowering and grain filling period there were changes in order and magnitude when changing environment, with amaranth tending to present higher values of these variables when the environment improves, while in emergence of panicle, amaranth remained above quinoa in the three test environments, the opposite happened in days to maturity, these results agree with what was previously reported (^{Espitia 1992}; ^{De Santis et al., 2018}).

In variables of size length of panicle (Figure 1) and diameter of stem (Figure 2), changes in magnitude and order occurred, with amaranth presenting higher values, in plant height (Figure 1) and panicle width (Figure 2) changes in magnitude were obtained, with amaranth being the one that presented the highest values through the evaluated environments, these results are consistent with what was previously reported (^{Tiwari et al., 2018}; ^{Thiam et al., 2021}).

Figure 2 Genotype-by-environment interaction of the yield of the comparison of three amaranth genotypes (continuous line Tlahuicole, dashed line L-145 and dotted line Nutrisol) and three quinoa genotypes (continuous line Suyana, dashed line Tokyo and dotted line Suma) in three environments. S-S 2019. 

For the variables related to the seed, changes in magnitude in seed diameter, weight of one thousand grains and hectoliter weight were obtained (Figure 2), with quinoa having the largest seed size, although for seed diameter, the environment x species interaction was not significant, which indicates that this variable is controlled mainly by genetic effects, this is demonstrated since in the analysis of variance only the source of variation species was significant, while environments and environments x species were non-significant. This indicates that the significance in species is due to the expression of the seed diameter so different between the two species since quinoa has a seed diameter almost twice that of amaranth.

This difference is also noticeable in the weight of 1 000 seeds since quinoa has a value three times higher than that of amaranth. The opposite happens in hectoliter weight, where amaranth presented a value of 81.71 kg and quinoa of 62.2 kg, which was expected due to the smaller seed size that gives greater density and fewer spaces between seeds. These results are consistent with what was reported by ^{Thiam et al. (2021}) for quinoa and for amaranth by ^{Espitia (1992}); ^{Tiwari et al. (2018}).

For yield, changes in order and changes in magnitude occurred; quinoa showed better yield in the most unfavorable environment that was Santa Lucía de Prías second date, while amaranth presented better yield in Boyeros and in Santa Lucía de Prías first date, this indicates that the performance of amaranth improves as the environment improves (^{Tiwari et al., 2018}), quinoa, on the contrary, presented a slight decrease, this is perhaps due to the incidence of mildew (Peronospora variabilis) on earlier sowing dates, this disease is one of the limitations worldwide for quinoa production (^{Khalifa and Thabet, 2018}).

That amaranth has resulted in a yield advantage is normal, as the evaluations were conducted in its naturally adaptation environment, while quinoa is being introduced. Due to its resistance to low temperatures, quinoa in Mexico can be used in crop rotation in cereal areas where barley, wheat and oats are produced since it is a broadleaf plant, which would allow reducing pests and diseases of cereals by being incorporated into the crop pattern of these regions. The soil would also be improved since the quinoa stubble would be incorporated in its entirety, the straw of the cereals is harvested in bales, increasing the content of organic matter and the cation exchange capacity.

In the three environments evaluated, it can be seen that, in general, amaranth showed better performance than quinoa; however, the variety of quinoa Suyana presented a performance very similar to the best varieties of amaranth (Tlahuicole and L-145), so it can be established that selecting the appropriate genotypes, good yields of both crops can be obtained.

One of the important characteristics for the commercialization and consumption of quinoa is the size of the seed, the Peruvian technical standard reports that the grains classified as large are those greater than 1.7 mm, medium between 1.7 and 1.4 and small grains less than 1.4 mm in diameter (INDECOPI, 2014), the results obtained with the genotypes evaluated were satisfactory since they presented large grain. A disadvantage of quinoa is the fact of having a perigonium, which is where the saponins are found, compounds that give a bitter taste, these must be eliminated by physical methods such as scarification, wet methods such as washing or the combination of both (^{Zurita-Silva et al., 2014}), amaranth did not present perigonium and the seed is ready to be used when harvested, this is an advantage of amaranth. Agronomically, it can be established that both crops have good potential; that is, they complement each other since amaranth is more adapted to climates from temperate to hot and quinoa from temperate to cold.

Conclusions

In general, amaranth performed better in the environments evaluated than quinoa. Amaranth surpassed quinoa in inflorescence length, inflorescence width, stem diameter, hectoliter weight and yield, whereas quinoa showed higher values for seed diameter and weight of one thousand seeds. The Tlahuicole and L-145 amaranth genotypes were the ones that present the best performance, followed by the variety of quinoa Suyana. Amaranth observed the characteristics to be a worldwide phenomenon, as has happened with quinoa.