Establishment and management of progenitors and populations derived from F₁

The seed of the parents and of the populations derived from the resulting crosses of the first generation, was extracted and conditioned for sowing on May 10, 2017. The seed of the 17 genotypes was sown in polystyrene trays of 200 cavities, depositing two to three seeds per cavity, using as substrate Peat (Premier Sphagnum Peat Moss, from Angeles Millwork & Lumber Co) and mineral perlite (Hortiperl from Termolite) in a 70:30 ratio respectively.

At 50 days after sowing, the transplant was carried out in beds with white plastic padding and a strip for localized irrigation, the beds with 25 cm high and a separation of 1.60 m and 30 cm between plants, establishing a double row in a staggered pattern, resulting in a plantation density of 41 667 plants ha^-1. Two-stem pruning and Dutch-type tutoring were carried out. The initial drip irrigation was 0.5 L plant^-1 day^-1, with a gradual increase to 3.5 L plant^-1 day^-1, the nutrition was based on a nutrient solution proposed by ^{Steiner (1984)} applied to irrigation water, modifying it throughout the crop cycle according to the phenological stages of the genotypes.

A sanitary control and foliar applications were carried out to correct any type of deficiencies. The work was established under a randomized block experimental design with three repetitions. Each experimental plot consisted of 12 plants. Irrigation was carried out every third or fourth day depending on the needs of the crop, foliar fertilizer was applied to correct deficiencies due to some nutritional element. A sanitary control was carried out applying biweekly active ingredients such as Imidacoprid, abamectin, thiamethoxam, chlorpyrifos, among others, against white fly, paratrioza, jumping aphid and thrips, in addition to Bacillus subtilis and Trichoderma harzianum against fungal diseases.

Yield and yield components

The variables evaluated were: total fruit yield (RTF) in kg, adding the weight of fruit obtained throughout the crop cycle, the average fruit weight (PPF) in grams and the total number of fruits per plant (NFP) was estimated by counting all the fruits harvested throughout the production cycle and divided by the number of plants harvested. The three variables were estimated from a random sample of 12 plants in each one of the treatments and in the three repetitions in twenty cuts at intervals of 10 to 11 days.

Fruit quality measurements

The fruit quality variables were determined in fresh fruits, in the Laboratory of Plant Nutrition and Tissue Culture of the Department of Horticulture of the UAAAN. The content of ascorbic acid (CAA) in the fruits of the parents and F2 populations was estimated using the ^{AOAC (2000)} methodology by means of color change titration.

For the quantification of total carotenes (CT), the technique described by ^{Silverstein et al. (1998}), based on the colorimetric method, with a Genesys 10S UV-Vis spectrophotometer (Thermo Scientific, Waltham, MA USA 0245.1) which was adjusted to a wavelength of 454 nm to quantify the absorbance of the analyzed samples, which were read in triplicate and the content was obtained by the following formula

Where: %Abs454= percentage of absorbance at 454 nm; V= volume measured in the specimen; P= weight of the sample in grams.

The quantification of the content of capsicinoids (CAPs) was determined in pepper fruits in the stage of physiological maturity by the method described by ^{Bennett and Kirby (1968}), in a Bio-145025 BIOMATE-5 spectrophotometer (Thermo Electron Corporation, Madison, USA) at a wavelength of 286 nm. To determine the concentration of capsaicin in the samples, a calibration curve of this compound (Sigma, Co.) was constructed within a range of 0 to 1.2 mg ml^-1. The readings were made in triplicate for each sample and the capsaicin content was expressed in Scoville units (SHU).

Estimation of agronomic variables

To estimate the days to flowering (DAF) and days to harvest (DAC), the days from transplanting to the first flowering and the first fruit harvest were counted. Plant height (ADP) was measured with a tape measure, at the end of the production cycle (240 ddt), it was taken from the base of the stem to the apex of the plant. The basal stem diameter (DBT) was measured at 3 cm above the soil surface with an Autotec digital Vernier.

Statistical analysis

For each variable, an analysis of variance and a comparison of means were performed using the Tukey test (p( 0.01) using the statistical program SAS^® V. 9.0 (^{SAS Institute Inc., 2002}). The statistical model was in accordance with the experimental design of complete random blocks, using the general linear model (PROC GLM). Inbreeding depression (DEP, in%) was estimated with the averages of the differences (F₁-F₂) /F₁, expressed in percentage, and multiplied by (-1) to indicate a decrease in the magnitude of the variable to be evaluated (^{Hernández-Leal et al., 2013}).

Yield and yield components

The analysis of variance applied to parents and F2 populations, exhibited significant differences (p< 0.01) between genotypes in RTF, NFP and PPF. The comparison of means (Table 2) shows that the populations F2, P_{1, 5} and P_{3, 4} were the ones that presented the highest yield per plant with 2 735.5 and 2764.0 g pl^-1 respectively.

The aforementioned populations were significantly superior to the maternal and paternal parents under study; however, they do not differ significantly from the rest of the F2 populations, even so, they are promising for the development of varieties of Jalapeño and Serrano pepper. The genotype that presented the lowest RTF was P_{1, 6} with a yield of 1 338.2 g pl^-1. It should be noted that there are differences compared to its first filial generation (F1), due to the fact that most of the F2 populations show a loss of vigor, clearly caused by homozygosity (Table 3).

The results obtained allow to indicate that the generational advance, caused inbreeding depression, which resulted in the decrease of the average yield of the F2 populations in 19.1% compared to their F1; however, the maximum yields of 2 764 g pl^-1, obtained from the population F2(P₃, ₄) with a density of 41 667 plants ha^-1, allowed to estimate yields of up to 115 167 t ha^-1, where even having 10% of failures or 10% of non-usable space exceed 100 t ha^-1, therefore the F2 populations (P_{1, 5}; P_{2, 6}; P_{3, 4} and P_{3, 8}) are considered promising for commercial production In protected environments, this characteristic is maintained in the segregating F2 generation, so that small pepper producers could use the F2 seed for commercial plantings, without the fruits significantly detracting from the yield, although morphological variability was observed, which is why recommends continuing to work with the advancement of filial generations in order to standardize these characteristics.

These results coincide with ^{Gaytán-Bautista et al. (2009}) in the cultivation of corn, who mentions that the generational advance from F1 to F2 reduced the average yield of corn grain and dry forage by 22 and 8%, respectively, in 22 commercial hybrids studied. In this sense, ^{Hernández-Leal et al. (2013}) mentions that the yield reduction in the F2 generations in saladette tomato was minimal, when evaluating seven commercial genotypes and their respective F2, finding DEP for total weight between 17.5 and 66.1%, which suggests that the inbred depression of one generation F2 depends particularly on the genetic makeup of the lines that have given rise to the commercial hybrid.

In this research, the highest DEP observed was -55.3%, which according to what was indicated by ^{Hernández-Leal et al. (2013}) is minimal, it is also important to note that the populations P₁,₇ and P₃,₄ did not show PED, they exhibited an increase of 7.22 and 5% respectively in RTF when going from F1 to F2 (Table 3), this also it may be due to the fact that the genotypes adapted well to the greenhouse conditions, although heterozygosity was reduced, which efficiently exploits hybrid vigor, coinciding with ^{Martínez et al. (2010}); ^{Duarte et al. (2012}). These authors mentioned that the plants studied under controlled conditions favor the expression of genes related to fruit yield or that the inbreeding depression in autogamous species is relatively small compared to what would be expected in cross-pollinated species (^{Charlesworth and Charlesworth, 1987}), this is because in self-pollinated species the self-fertilization process has a purifying effect of deleterious recessive alleles.

It should be noted that together with the improvement and selection of hybrids and their respective F2 populations, progress was also made in the improvement of the parents originally used, as mentioned in (Table 3) that the parents do not present an adverse effect due to inbreeding depression, on the contrary, with the exception of P2 (Mirador), all present positive PED values, which indicates that as generational advances they adapt better to the protected environment or progress was made in the intra-family selection process that led to the selection of the best individuals within each family, reducing genetic variability but conserving the best individuals.

An important component of yield is the number of fruits per plant. Table 2 shows that the Tampiqueño maternal parent has a greater quantity of fruits per plant; however, it should be noted that the average weight of these fruits is 8.28 g, therefore the total yield is low; however, in the same statistical group are the populations F2, P_{3, 4} and P_{3, 8}, which share the Tampiqueño as a maternal parent, which indicates that said parent is very productive, a characteristic that was inherited from their descendants who in this case they presented 95 and 93.5 fruits per plant respectively.

The average NFP of the female parents is 107.5, the male parents 14.7 and the F2 populations is 64.6, so it can be observed that they have an increasing trend compared to their paternal parents; however, they do not reach the NFP of the maternal parents, but they do exceed their PPF. The F2 P₂,₆ population stands out in the NFP with 100 fruits per plant, however, it does not exceed the average of the female parents, but that of the male parents in 85%, therefore, this segregating that also presents low depression inbred, it may be one of the most promising for the development of a new variety of C. annuum for greenhouse production.

The results indicate that there was high production of fruits, with respect to the paternal parents. Researchers such as ^{May et al. (2010}) report that they obtained from 5.8 to 12.2 pepper fruits per plant and in this investigation, they were obtained from 11.31 to 18.5, which represents more than 51% the highest value recorded.

For the PPF variable, it was found that the male parents continue to show the highest weights as expected; however, the UANShw, had a value of 197.44 and was significantly higher than the rest of the male parents, the female parents and the F2 populations. The PPF of female parents was 11.46 g while of the male parents 151.09 g and the F2 populations have an average of 37.52 g. The progeny is outside the range of both parents for this characteristic, this great difference may be due to the fact that transgressive segregation can be very common in some self-pollinated species such as pepper and tomato.

Fruit quality

The analysis of variance applied to the fruit quality variables, show significant differences between parents and F2 populations (p≤ 0.01). Regarding the content of CT, the comparison of means (Table 4) shows that the populations P_{2, 4,} P_{2, 5} and P_{2, 6,} were significantly higher than the rest of the F2 populations, and parents, where the mean of the three F2 indicated exceeded the female parents by 320.9% and the male parents by 249.9%.

In this sense, it is possible to mention that the mean CT content of the female parents was 1 411.9 mg/0.1 kg, that of the male parents was 1 663.7 mg/0.1 kg, and that of the F2 populations was 5 531.7 mg/0.1 kg, which is summarized in that the F2 populations contain 292% more CT content compared to the female parents and 232.5% more than the male parents. It should be noted that the F2 populations show more promise regarding this antioxidant pigment, effective in the prevention of certain degenerative diseases of the human being.

The most outstanding F2 populations have the same maternal parent in common, however, the mirador pepper does not present high amounts of CT (1 363.8 mg/0.1 kg), which we can attribute to the presence of genes that combined favorably to present high CT values. Table 5 shows that the genotypes (F1 and F2 populations) had positive DEP % values for CT, which indicates that they all increased the content of this antioxidant from one generation to another (F1 to F2), with the F2 populations being P_{1, 4} and P_{1, 6} those with the lowest values 19.4 and 31.6% respectively, with respect to the rest of the populations; however, the rest of the populations had a 208.5 to 426.3% increase in these important pigments for human health, with respect to their first filial generation, which makes them attractive for their advancement and selection in later generations.

Regarding the content of CAPs, it is possible to observe that the female parents, especially the Serrano pepper, was significantly higher than the rest of the parents and F2 populations under study, with 14 532 SHU, which was 94.83% hotter than the paternal parents, the which present an average of 751.2 SHU, being these significantly lower than the rest of the genotypes studied. The F2 populations have an average of 8 160.33 SHU, the population P_{3, 8} excelling with 10 866.7 SHU.

As can be seen, the F2 populations are not hotter than the maternal parents, however, they do present more itching when compared to the paternal parents, which is promising if it is intended to commercialize these peppers within the Mexican Republic, since the demand for high-heat products is becoming higher and Capsicum oleoresins have had to be imported from Africa for industrial uses (^{Cruz-Pérez et al., 2007}).

In the F2 generation, the populations P_{1, 5} and P_{1, 7} not only maintained the F1 itch, but increased it more than 20%, however, populations such as P_{1, 4}, P_{1, 6}, P_{2, 4} and P_{3, 4} maintained values lower than 20% but are still positive, which indicates an increase in itching in relation to the first generation, contrary to the rest of the populations, which reduced their itching in the F2.

Agronomic variables

The analysis of variance applied to parents and F2 populations showed significant differences (p≤ 0.01) between the two regarding DAF and DAC. The comparison of means (Table 6) shows that in the DAF variable the F2 populations were significantly earlier than the parents, both maternal and paternal.

The maternal parents presented an average of 64.4 days to flowering after transplantation, the paternal parents 48.77 days, while the F2 populations obtained their first flower on average at 29.37 days. F2 stocks follow the same trend as their first filial generation showing high precocity. The F2 populations achieved 54.33% more precocity in relation to their female parents and 39.77% in relation to their paternal parents, while in the F1 generation they presented around 54% precocity.

The F2 P_{1, 6} population presented higher precocity, reaching flowering 23.3 days after transplantation; however, it does not differ significantly from the rest of the F2 populations. The latest female parent was the lookout, reaching its first flowering at 88 days, while the later males were UANOg and UANRd, both presenting their first flowering after 56 days.

These results differ greatly from the parameters of the crop since it is mentioned that in bell pepper the flowering period ranges between 70 and 93 days; however, in practice it is different, since in this research the paternal parents had their first flowering between 37 and 56 days, similar data obtained by ^{Moreno-Pérez et al. (2011}) who evaluated 13 bell pepper hybrids in the greenhouse under hydroponic conditions, finding that most of their hybrids had their first flowering 30 days after transplantation and in their latest hybrid up to 45 days after transplantation.

This can be attributed to what was described by ^{Montes et al. (2004}) who point out that the accumulation of heat units during the different development stages of Capsicum spp. It shows a difference between types of pepper and this is more evident between the different levels of domestication, which means that wild variants show a slower start in their development, compared to domesticated cultivars, so this crop is already well adapted to the greenhouse conditions and with its development during the hottest months of the year, had a greater accumulation of heat units, which were reflected in the earliness of the crop.

Therefore, the results obtained indicate that sowing in May and transplantation in June, allow flowering in July, achieving greater precocity and favorable development of the plant, and fruit production is achieved for a longer time (up to 8 months) and harvest in the coldest months of the year thus achieving high prices in greenhouse production.

It should be noted that the Jalapeño in its first filial generation only reached 117 cm in height, while in this generation it exceeded 206 cm, which may suggest that in this genotype and in this variable there was the presence of transgressive inheritance manifesting in a degree higher than the F1 generation or else this population is adapting well to greenhouse conditions, which allow greater control of environmental factors, very different conditions to which it was acclimatized or adapted, since commercially it is managed under conditions open sky. The F2 populations have a positive trend in relation to their parents, presenting higher ADP, exceeding the mean of male parents by 47.24% and 5.45% of female parents.

The analysis of variance applied to the DDT variable shows that the F2 populations were statistically equal, with the Jalapeño Mitla and the F2 P₂,₆ population showing the highest values, although they were significantly equal to the F2 populations and six parents, with the exception of the Mirador progenitor, which shows the thinnest stem, which was reflected in the anatomy of the plant as it is the lowest, thinnest and most fragile genotype, which limits it to an adequate option for greenhouse production, since it is still under conditions of controlled environment, adequate irrigation and optimal health, the plant cannot develop properly.

On the other hand, the F2 populations studied indicate that as generational progresses, the plants are adapting better to greenhouse conditions, although it is soon to be certain, since they have only been a generation, but they do allow us to observe that, as in In the first generation, the plants show an indeterminate growth tendency, thicker stems, better anatomy, more rigid, erect, well-defined plants with good foliar coverage.