Introduction

Chilhuacle is one of the oldest dried chilis in Oaxaca (^{López et al., 2016}) and is the main ingredient to prepare Oaxacan black mole (^{García-Gaytán et al., 2017}; ^{Martínez-Gutiérrez et al., 2021}). In recent years, this variety has positioned itself commercially as one of the dried chilis of greatest economic value in regional and national markets. Its high price is due to the lack of improved cultivars, high susceptibility to pests and diseases, ignorance of nutritional requirements, low yield and high production costs (^{López et al., 2016}; ^{García-Gaytán et al., 2017}). As for nutrition, it is relevant to satisfy the nutritional demand of chilhuacle in order to obtain high yields and the quality of the fruits demanded by the market.

In this way, the nutritional regime aims to provide essential nutrients in sufficient quantity and in the ionic form absorbed by plants in order to cover the requirements by phenological stage (^{Valentín-Miguel et al., 2013}; ^{Nieves-Gonzales et al., 2015}; ^{Siles, 2019}), and increase productive potential, fruit quality (^{Valentín-Miguel et al., 2013}) and appropriate development from seedling to fruit filling (^{Sieiro et al., 2020}), in addition to reducing susceptibility to pests, diseases and deficiencies. By means of nutrient solutions, the supply of both macro and micronutrients can be manipulated (^{Steiner, 1984}).

In relation to the former, Nitrogen (N), phosphorus (P) and potassium (K) are the most demanded by the plant. N is required in high quantities during the early stages of growth; if the demand is not met, the plant manifests chlorotic leaves and dwarfism, which affects the yield (^{Eguez et al., 2022}). P is a constituent of adenosine triphosphate (ATP) (^{Siles, 2019}), nucleic acid former and transfer of genetic information (^{Díaz-Durán et al., 2022}). Deficiency symptoms are a purple coloration on stems and leaf ribs (^{Eguez et al., 2022}). K is an element of fruit quality; the deficiency is manifested by the tendency of the plant to wither on dry and sunny days, short internodes and leaf fall (^{Eguez et al., 2022}).

Calcium (Ca), magnesium (Mg) and sulfur (S) are elements required in less quantity than N, P and K; however, they have important functions in plants. Ca is the second messenger in signal transduction; the deficiency presents itself as apical rot (^{Sun et al., 2010}), Mg is a constituent of chlorophyll, so it is related to the production of carbohydrates (^{Pinilla et al., 2011}), in insufficiency, chlorotic leaves appear in the middle third of the leaf.

S in the form of SO₄ ^2- stimulates growth, increases the quality and uniformity of the fruits, favoring resistance to cold, tolerance to drought and salts (^{Nazar et al., 2011}), the deficiency causes the young leaves to turn yellow and, in pepper, growth is reduced (^{Silva et al., 2017}). The response of plants to the supply of nutrients during the production cycle is modified by the environment in which they grow, for this reason, the objective of the research was to evaluate the effect of different nutritional regimes on the yield and quality of chilhuacle fruits, grown in the autumn-winter cycle.

Materials and methods

Results and discussion

The cycle of chilhuacle from transplantation to harvest of the last fruit was 168 days, with an average temperature of 20.2 °C, average relative humidity of 73.83% and average luminous intensity of 2 252.1 lux. If the duration of the seedling phase is considered, which also belongs to the vegetative stage (44 days), the full duration of the crop was 212 days. ^{López-López and Pérez-Bennetts (2015}) reported for chilhuacle, 35 to 45 days of seedling stage, 90 days of growth-development and 60 days of harvest, to have a cycle of 185 to 195 days in open field.

The ideal average temperature to grow chilhuacle is 28 °C so that the phenological stages occur favorably. ^{Mármol (2010}) a temperature ±20 °C causes a delay in flowering, fruiting and anomalies in the fruits. In relation to morphological variables of chilhuacle plants, the different regimes supplied had a statistically similar effect (p≤ 0.05) on the relative concentration of chlorophyll, stem diameter and root volume (Table 2), the average values were 75.87 SPAD units, 16.97 mm and 97.75 cm³, respectively. Regarding the stem diameter, in Capsicum, it represents the ability of the plant to support the weight of branches, flowers and fruits, as well as reducing the risk of breakage of the aerial part.

In pepper, the growth rate occurs at 6 cm per unit of time using complete nutrient solutions than in solutions with -N and -K that delay the stem diameter, leaf area and number of leaves (^{Eguez et al., 2022}). In Chilhuacle, it is possible that the stems have the same mechanical strength regardless of the nutritional regime due to the statistically similar percentage (p≤ 0.05) of dry matter destined for this organ.

The nutritional regime (R7) with 14 mEq L^-1 of NO₃ ^-, 10:0.75:9.25 mEq L^-1 of NO₃ ^-:H₂PO₄ ^-:SO₄ ^2- and 12:7 mEq L^-1 of NO₃ ^-:K⁺ in the vegetative, reproductive and fruiting stages, respectively, increased the leaf area by 110.35% in relation to that of the plants that received a regime (R6) with 14, 12:1:7 mEq L^-1 of NO₃ ^-:H₂PO₄ ^-:SO₄ ^2- and 14:9 mEq L^-1 of NO₃ ^-:K⁺ and even the control regime (R1:12, 12:17, 12:7), which showed the largest leaf area. In this sense, the requirements (R7: 10:0.75: 9.25 and 12:7 mEq L^-1) for flowering and fruiting with respect to the leaf area are lower to increase in this variable, as the formation of fruits.

Measuring leaf area and chlorophyll concentration can indicate the nutritional state of the plant, the interception of solar radiation, CO₂ exchange, evapotranspiration and photosynthetic efficiency (^{Misle et al., 2013}). The regimes (R7) 14, 10:0.75:9.45, 12:7 and (R6) 14, 12:1:7, 14:9 mEq L^-1 were statistically similar (p≤ 0.05) in the relative chlorophyll content, however, the leaf area was completely different, as was the height of the plant, and there were no statistical differences in root length. These data suggest different photosynthetic capacity, which may have been modified by the variation of nutrition in the reproductive and fruiting stages (Table 2).

In plant height, the regime (R3) with 12 (NO₃ ^-), 10:0.75:9.25 (NO₃ ^-:H₂PO₄ ^-:SO₄ ^2-) and 12:7 (NO₃ ^-:K⁺) mEq L^-1 induced plants 18.62% higher than the regimes (R6) 14, 12:1:7, 14:9 and (R8) 14, 10:0.75:9.25, 14:9, which were statistically similar (Table 2). Chilhuacle has an average height of 128.30 to 152.18 cm with topping to 10 internodes, while to 20 internodes, it could reach values of up to ± 170 cm, this variation could be an effect of environmental conditions and a management without pruning, where the plant has a free growth of stems, leaves, flowers and fruits.

In Capsicum, nutrition particularly affects stem diameter and leaf number (^{Eguez et al., 2022}). Therefore, knowing the phenological stages and identifying the ideal moment of application of nutrient solutions (^{Valentín-Miguel et al., 2013}) would allow reaching the maximum yield potential of a crop.

Regarding the production of dry matter, in root it was statistically similar (p≤ 0.05) with any of the regimes evaluated, with an average of 16.80 g. In stem, in the regime (R3) with 12, 10:075:9.25, 12:7 and (R7) 14, 10:075:9.25, 12:7 mEq L^-1, an average value of 135.5 g was obtained, which represented an increase of 41.45% compared to plants with the lowest accumulation of dry matter (Table 3). The dry matter of leaf was similar in plants nourished with 12, 12:1:7, 14:9 (R2); 12, 10:0.75:0.95, 12:7 (R3); 14, 10:0.75:9.25, 12:7 (R7) and 14, 10:0.75:9.25, 14:9 (R8) mEq L^-1, with an average of 135.5 g; the increase was 80.91% compared to plants nourished with the regime (R6) 14, 12:1:7, 14:9 mEq L^-1.

By implementing all the indispensable elements in nutrition, the obtaining of fresh and dry matter increases in a balanced way between the aerial and root parts (^{Eguez et al., 2022}). The lack of N (in root) and K (in leaf) significantly reduces the production of dry matter when these elements are insufficient. The dry matter of the fruits per plant and that of the whole plant increased 165.93% and 78.3%, respectively, with the regime (R8) 14, 10:0.75:9.25, 12:7 mEq L^-1 compared to (R6) 14, 12:1:7, 14:9 mEq L^-1.

In both variables (R8 and R6), they were affected by the variation of the nutrient solution of the reproductive stage and the fruiting stage since the concentration of NO₃ ^- in the vegetative stage was 14 mEq L^-1. In the chili known as chile de agua, the production of dry matter (66.7 g plant^-1) increased according to the osmotic potential (0.09 MPa), being significant in the yield and the harvest index (^{Valentín-Miguel et al., 2013}). In leaves such as roots, the accumulation of dry matter is found in a higher concentration of P than with -N and -K (^{Eguez et al., 2022}). P, in addition to being a former of the ATP molecule (^{Siles, 2019}), nucleic acids and transfer of genetic information (^{Díaz-Durán et al., 2022}), its concentration of accumulable dry matter in the plant is higher.

Regarding the physical quality of the fruits, these were analyzed in two categories: large (> 4 g) and medium (2 to 3.9 g). In this study, 884 fruits of chilhuacle were evaluated, of which 64.03% corresponded to the first and 35.97% to the second. Studies conducted by ^{Vázquez-Vázquez et al. (2011}) in jalapeño pepper determined that the percentage of first quality fruits is from 46.1 to 50.5%, while the second from 43.4 to 46.9%, third of 7% and only from 0.2 to 0.9% of fourth quality. As for large fruits of chilhuacle, they had an average length of 50.35 mm, there were no significant differences between the nutritional regimes, the same happened for the diameter of the base of the fruit (42.85 mm), average weight of fresh matter (27.95 g) and dry matter (5.45 g) of the fruit (Table 4).

The results present similarity in weight of fresh and dry matter of fruits, indicating the ability of the plant to maintain itself in different nutritional regimes; however, due to the impact on other components of the yield (number of fruits plant^-1, among others), it is possible to propose modifications in agronomic management that generate a higher yield, with fewer resources. Regarding the number of fruits per plant, the control (12, 12:1:7, 12:7 mEq L^-1) and the regimes (R4) 12, 10:0.75:9.25, 14:9 and (R7) 14, 10:0.75:9.25, 12:7 mEq L^-1 had 171.71% more than the plants nourished with (R6) 14, 12:1:7, 14:9 mEq L^-1 corresponding to the vegetative, reproductive and fruiting stages.

The ratio between the nutrient solution (15, 1.25, 8.75 mol of NO₃ ^-:H₂PO₄ ^-:SO₄ ², 11.25, 5 and 8.75 mol of Ca²⁺:Mg²⁺: K⁺) and the osmotic potential (0.090 MPa) in chile de agua increased the fruits plant^-1 (100.3) and the yield (2601.5 g plant^-1), recommending 0.036 MPa up to 75 dat, subsequently 0.054 MPa to harvest 2 kg plant^-1 (^{Valentín-Miguel et al., 2013}). Regarding the yield of fresh and dry matter of chilhuacle fruits, it increased by 207.5 and 212.06%, respectively, with the regime (R7) 14 (NO₃ ^-), 10:0.75:9.25 (NO₃ ^-:H₂PO₄ ^-:SO₄ ^2-) and 12:7 (NO₃:K⁺) mEq L^-1 compared to plants that received 14, 12:1:7, 14:9 (R6) mEq L^-1 (Table 4).

From the above data, it is deduced that the yield component number of fruits plant^-1 is the one that had the most influence on the yield of fresh and dry matter of large fruits. Considering this, it is convenient to implement and evaluate agronomic practices aimed at increasing this variable, such as manipulating the number of stems per plant, foliar fertilization with the aim of increasing the set and the size of flowers and fruits, among others.

In the category of medium fruits, the diameter of the base of the fruit, the weight of fresh and dry matter were statistically similar (p≤ 0.05), regardless of the nutritional regime; the average values were 34.46 mm, 15.35 g and 2.36 g. The opposite happened with the length of the fruit, number of fruits per plant and the yield of fresh and dry matter of fruits (Table 5). The first variable was favored 50.9% with the regime (R4) of 12, 10:0.75:9.25, 14:9 mEq L^-1 compared to the fruit length of plants nourished with (R3) 12, 10:0.75:9.25, 12:7 mEq L^-1. In chilhuacle, the requirements of P (0.75 mEq L^-1) were lower during the course of the phenological stages.

In habanero pepper var Big Brother, the optimal requirements of P were with 1.5 mEq L^-1, however, the accumulation of P is concentrated in greater proportion in roots, mainly affecting the production of fruits (^{Nieves-González et al., 2015}). The number of fruits increased 156.52%, the yield of fresh matter of fruits 176.87% and the yield of dry matter of fruits 200% with the regime (R7) 14 (NO₃ ^-), 10:0.75:9.25 (NO₃ ^-:H₂PO₄ ^-:SO₄ ^2-) and 12:7 (NO₃ ^-: K⁺) mEq L^-1 in relation to the plants that received (R4) 12, 10:0.75:9.25, 14:9 mEq L^-1. ^{Vázquez-Vázquez et al. (2011}) reported a similar percentage of first and second quality fruits, regardless of fertilization.

In chilhuacle, the addition of ammonium in 3 mEq L^-1 in the NS, the yield increased by 54.1% in the black cultivar (434.34 g plant^-1) than in the red cultivar (274.14 g plant^-1) (^{Urbina-Sánchez et al., 2020}). Chile de agua requires high amounts of K (until 90 days), then of N (next 150 days) and to a lesser extent of P (^{Valentín-Miguel et al., 2013}). In this sense, Capsicum require more N and K in the early stages of the crop, while P, K and Mg increase as flowering and fruiting begin.

The different response of the plant to nutrition may be related to the regime, species and environmental variables of the production region, such as temperature as it can increase or decrease the quality and yield of a crop. In pepper, a daytime temperature <18 ºC produces parthenocarpic fruits, while <10 ºC reduces their growth, causing an excess of small, poorly set, poor quality, pointed, seedless and deformed as type ‘cookies or balls’ fruits (^{Mármol, 2010}). In the present experiment, the average temperature during the fruiting stage (116 d) was 18.27 ºC, it is possible that this environmental condition is part of the explanation for the presence of small fruits (< 2 g of dry matter) deformed in the form of ‘wings’.

In relation to the percentage production of large fruits (> 4 g) and medium fruits (2 to 3.9 g), the regimes with 12, 10:0.75:9.25, 14:9 (R4); 14, 12:1:7, 12:7 (R5); 14, 10:0.75:9.25, 12:7 (R7) and 14, 10:0.75:9.25, 14:9 (R8) (mEq L^-1) made the plants have on average 71.6% of large fruits and 28.4% of medium fruits. The opposite happened in the plants nourished with 14, 12:1:7, 14:9 mEq L^-1 (R6), which had 35.8% of large fruits and 64.11% of medium fruits (Table 6). The above data indicate that the concentration of phosphorus in the reproductive stage and that of potassium in the fruiting stage are important; however, the relationship with other anions affects the final response, in this case, the weight of the dry matter of the fruits.

In the regional markets of Oaxaca, chilhuacle is marketed as large and medium fruits. Large fruits are considered of first quality, while medium fruits, of second quality. Chilhuacle is not considered in the Official Mexican Standard NMX-FF-107/1-SCFI-2014 (^{SEGOB, 2014}) for the production of dried chilis, such as cascabel, ancho, mulato and pasilla chilis, where in the quality standards, size (length), color, appearance, spiciness, weight and health predominate, so it represents an opportunity to generate quality parameters for chilhuacle.

Conclusions

The nutrition of chilhuacle through a regime based on a specific solution for the vegetative, reproductive and fruiting stages benefited growth variables and yield components such as fresh and dry matter of the fruit. In the autumn-winter cycle, the nutrition of chilhuacle with the regime 14 mEq L^-1 of NO₃ ^- in the vegetative stage, 10:0.75:9.25 mEq L^-1 of NO₃ ^-:H₂PO₄ ^-:SO₄ ^2- in the reproductive stage and 12:7 mEq L^-1 of NO₃ ^-:K⁺ in the fruiting stage significantly increased the leaf area, dry matter of stem, of leaf, of fruit, of the whole plant, the number of fruits per plant and the yield of fresh and dry matter of fruits per plant, while the percentage of large fruits (> 4 g) was 63.64% and of medium fruits (2 to 3.9 g) was 36.36%.

Recommendations

It is proposed to continue carrying out studies to determine the factors that influence the quality of chilhuacle fruits in relation to size, appearance, physical and organoleptic characteristics as determined by the Official Mexican Standard NMX-FF-107/1-SCFI-2014 for the production of commercial dried chilis in our country.