Introduction

Habanero chili (Capsicum chinense Jacq.) Is traditionally produced in the Yucatan Peninsula in the open sky (^{Macías et al., 2013}); however, with this system the crop is negatively affected by various environmental factors, capable of reducing the product quality, yield and profitability of the crop (^{Lugo-Jiménez et al., 2010}), in addition to the characteristics habanero chilli such as the flavor, aroma, pungency, color and shelf life depend on the weather, soil and location of the region (^{Borges-Gómez et al., 2014}).

Some recommendations of the nutritional requirements of Capsicum chinense, especially when the crop is established in the open, indicate the use of fertilization doses to obtain the best yields (^{Borges-Gómez et al., 2010}; ^{Noh-Medina et al., 2010}). However, the results of field fertilization are not entirely satisfactory since it depends on the type of soil (^{Borges-Gómez et al., 2014}).

On the other hand, information on nutrient solutions for greenhouse-grown habanero chilli is scarce. ^{Tucuch-Haas et al. (2012)} have used the universal nutrient solution (SNU, ^{Steiner, 1984}), modifying concentrations of N-NH₄ ⁺: N-NO₃ ^-, indicate that with the ratio 0% NH₄ ⁺:100% NO₃ ^- plants of greater height and of stem diameter until the end of the crop cycle and that the ratio 20% NH₄ ⁺:80% NO₃ ^- provides better results in yield and fruit quality.

However, it has been reported that habanero chili can be nourished according to the phenological stage of the crop. ^{López-Gómez et al. (2017)} evaluated three concentrations of nitrate in the vegetative stage (10, 12 and 14 meq L^-1), each combined with three ratios of nitrate: phosphate: sulfate in the flowering stage (14:1.25:4.75, 12:1:7 and 14:1.25:4.75 meq L^-) and with three nitrate ratios: potassium in the fruiting stage (14:5, 14:5 and 12:7 meq L^-1).

The results indicated that due to the nutritional regime of 14 meq L^-1 of NO₃ ^- (vegetative stage), 14:1.25:4.75 meq L^-1 of NO₃ ^-:H₂PO₄ ^-:SO₄ ^2- (flowering stage) and 14:5 meq L^-1 de NO₃ ^-:K⁺ (fruiting stage), there was an increase in the number of flowers plant^-1, number of fruits plant^-1 and yield, which was 1054 g plant^-1 in six fruit cuts, 33% higher than the yield obtained from plants that are fed with SNU during the entire crop cycle, while the accumulation of dry matter was also higher 20.3%. In plants of the Capsicum genus, information about the effect of pruning on yield is scarce.

In the chilli (Capsicum annuum) different recommendations are indicated (^{Jaimez et al., 2002}). According to ^{Cruz et al. (2009)}, in the north of Europe and America the production of chilli in greenhouse conditions is generally based on the 'Dutch' type pruning, which consists of the use of undetermined cycle cultivars that are driven to two stems until reaching 2 to 3 m high, which can increase the yield.

Similarly, ^{Villegas et al. (2004)} point out that, in the tomato crop of undetermined growth habit, the plants are pruned to two stems when the first inflorescence begins and they are allowed to grow freely until they reach 2 m in height, eliminating the lower leaves and sprout lateral.

However, information on the types of pruning that the crop requires is scarce in habanero chilli. According to ^{Macías et al. (2013)}, in the production of habanero chili in the greenhouse, the plants are pruned to three stems during the whole crop cycle. On the other hand, ^{Jaimez et al. (2002)}, when evaluating the effect of different pruning intensities (at 10 and 15 knots) carried out in habanero chilli plants (Capsicum chinense).

On the dynamics of production of flowers and fruits, they observed that an increase in the weight of the fruits can be achieved, obtaining fruits of greater commercial quality, although this can cause decreases between 12-14% in the total yield. The importance of pruning is that sometimes a rapid increase of some organ can compete with the leaves for nutrients that can easily be translocated, which causes foliar senescence and reduction in its photosynthetic capacity. There is also competition between the bodies whose growth and development are simultaneous; such is the case of apex growth with foliar differentiation.

In general terms, pruning can influence the number and quality of flowers and fruits. Such is the case of ^{Ponce et al. (2012)}, who report that, in the cultivation of peel tomatoes, if the number of fruits is reduced, they will be of greater size and quality; however, excessive apical pruning can further promote vegetative growth and suppress flowering.

Based on the above, it is convenient to analyze the effects of the nutrition provided in accordance with the phenological stage of the crop along with the type of conduction pruning on the yield and physical quality of the fruit of habanero chili grown under plastic cover in a system hydroponic.

Materials and methods

The experiment was carried out in a greenhouse of the experimental field of the Faculty of Agricultural Sciences (18° 58’ 51” north latitude, 99° 13’ 57” west longitude, 1 868 masl) at the Autonomous University of the State of Morelos, Cuernavaca, Morelos, Mexico.

Results and discussion

The plants with 2, 3 and 4 stems nourished with RN2 were of greater height and with more resistant stems; however, the development of the plants in most of the evaluated variables was better because of RN2 without pruning. The flower abortion was greater when the plants were not pruned (Table 3).

^{Ramírez-Luna et al. (2005)} report more than 40% of flower abortion, while ^{Medina-Lara et al. (2008)} have described up to 85% of flower abortion in this crop. On the other hand, ^{Cruz et al. (2012)} indicate that high temperatures cause physiological disorders in habanero chili plants (Capsicum chinense Jacq.) causing a high abortion of flowers.

^{Patiño-Torres and Jaimez-Arellano (2016)} point out that high temperatures cause an increase in ethylene production, which causes abortion of flowers, also mentioning that high densities of plants per surface induces floral abortion due to a low intensity of light. Similarly, ^{Jaimez et al. (2010)} attribute to the high temperatures the same effect on paprika (Capsicum annuum), but argue that the phenomenon is due to an affectation of the germination process of the pollen and of the pollen tube, in addition to the fact that this process can also be different between cultivars

On the other hand, when the plants were treated with RN2, but not pruned, the highest values were obtained in terms of root volume and dry matter weight of the plant organs (leaf, stem and root) as well as of total dry matter (Table 4).

The total dry matter weight of the plants (leaf + stem + root) nourished with the RN2 and without pruning was 29.5% higher than the weight of the plants that were nourished with RN1 and also did not receive pruning. The percentage of dry matter of the aerial part of the plants nourished with the treatment without pruning/RN2 was 79.9% while the production of dry matter of root corresponded to 20.1%. Due to the same treatment, the highest yield was also obtained (Figure 1).

Figure 1 Yield of habanero chilli due to the effect of driving pruning and the nutritional regime. RN1= supply of the universal nutrient solution (^{Steiner, 1984}) throughout the crop cycle. RN2= supply of specific nutrient solution for each phenological stage of habanero chilli (^{López-Gómez et al., 2017}). Means with the same literal are statistically equal according to the Tukey test (p≤ 0.05). 

These results seem to be related to what ^{Peña and Zenner (2015)} point out, who state that high percentages of dry matter from the aerial part of Capsicum annuum plants indicate a greater number of leaves, source and production of photoassimilates for filling demanding organs. In addition, ^{Peil and Gálvez (2005)} show that, under the conditions of cultivation in artificial substrates under greenhouse, with a contribution of water and nutrients close to the optimum, maximum growth of plants with a reduced radical system can be achieved.

In the case of cucumber, this fraction varies between 8 and 15%, in the vegetative growth stage and between 3 and 7% during the reproductive stage. In the case of tomato, the fraction of dry matter destined for the roots varies between 17 and 20% in the vegetative stage; and between 1 and 10% in the reproductive stage. In terms of yield, the highest value was 616.9 g per plant in six fruit cuts due to the treatment without pruning/RN2, exceeding 22.8% of the yield of the plants pruned to four stems and fed with the regime.

On the other hand, ^{Tucuch-Haas et al. (2012)} reported yield of habanero chili of 302 g/plant in three fruit cuts, providing the Steiner solution with an NH₄ ⁺/NO₃ ^- ratio of 10/90%, respectively, in combination with a mixture of coconut fiber tezontle substrate (75-25% respectively) and with 10-20 mm tezontle granulometry.

On the other hand, ^{Alejo-Santiago et al. (2015)} evaluated four concentrations of NO₃ ^- in the nutrient solution (5, 10, 15 and 20 meq L^-1), based on what was proposed by ^{Steiner and Van Winden (1970)}. They point out that by increasing the concentration of NO₃ ^- in the nutritive solution, the production of dry matter in the different organs of the habanero chili plant var. ʻBig Brotherʼ, increased significantly, observing that with the dose of 20 meq L^-1, the dry matter corresponding to leaves, stems and flowers was the highest with respect to the other treatments, while the highest total dry matter production was recorded in the treatment of 15 meq L^-1.

This is due to the fact that from 20 meq L^-1, the production of dried fruit matter decreases. As a consequence, they also observed that the increase in the concentration of NO₃ ^- in the nutrient solution, up to a dose of 15 meq L^-1, caused an increase in yield. However, from the dose of 20 meq L^-1, the yield decreases. This increase in organ dry matter and yield coincides with the results obtained in the present investigation, since the applied RN2 had a higher concentration of nitrate (14 meq L^-1) in all the phenological stages of the culture, unlike the solution Steiner (12 meq L^-1).

Due to the effect of RN2 without the need to prune the plant, the highest number of fruits per plant was also obtained (Table 6), surpassing with 35.5% more fruits than the plants nourished with RN1 without pruning and up to 61% the amount of fruits produced by plants pruned to 4 stems regardless of the nutrition applied. However, from the plants that were pruned to two main stems nourished with RN2, fruits 47.1% heavier than those obtained from plants without pruning plus RN2 were obtained (Table 6).

As for the length and diameter of the fruit, the highest values were presented in most of the treatments where pruning was performed unlike the plants that were not pruned (Table 6). However, a trend is observed, especially in the diameter of the fruits, that when the plants are pruned and also receive RN2, the diameter is larger.

According to ^{Ramírez-Luna et al. (2005)} habanero chili plants developed in the greenhouse have a greater number of flowers and fruits, but with small fruit size, in contrast to the production in the field, where larger fruits are obtained, attributing the smaller fruit size, to the low intensity of light in the greenhouse. Condition that favors larger plants, thinner stems, but small fruits.

However, in tomato cultivation (Lycopersicon esculentum Mill.), ^{Aldana et al. (2007)} state that the size of the fruit depends directly on the amount of pollen grains deposited in the stigma; that is, with less pollen, smaller, deformed fruits or with few seeds are produced. This problem is of great importance since increasing the quality parameters can increase the shelf life; therefore, their economic value (^{Chamu-Baranda et al., 2011}).

Conclusions

The fruit size of habanero chili is increased by the effect of pruning to 2, 3 and 4 stems together with the nutritional regimens RN1 or RN2 compared to the simultaneous effect of unpruned plants with the same regimes. The number of fruits and yield per plant of habanero chili was favored by the joint effect of not pruning the plant with the nutritional regime two (RN2), although the yield was statistically similar to that of plants driven to four stems with the same regime.

The nutritional regime based on the phenological stage of the crop (RN2) together with the driving pruning does affect the yield and quality of the fruits of habanero chilli.

The yield of habanero chilli was higher when the alternative nutritional regime (RN2) was applied without pruning the plant.

The size and weight of the fruits of habanero chilli is greater when the plants are nourished based on their phenological stage (RN2) and are pruned to 4, 3 and 2 stems; however, with this pruning the total yield decreases from 22.8% to 53.7%, compared to unpruned plants.