Commercial productivity and quality of pitaya as a function of number of fruits per cladode

ABSTRACT Increasing orchard productivity is among the main objectives of pitaya producers. However, the commercial productivity may reduce due to reduction of fruit size as a function of the high amount per plant. This study evaluated the influence of the number of fruit per cladode in commercial productivity and in quality of fruits of two pitaya species at different harvest times. The experiment was carried out in a six-year-old orchard formed by the species Selenicereus undatus and Hylocereus polyrhizus. At each flowering time, the number of fruits set per cladode was counted and plants with two, four, five and six fruits per cladode were selected, and surplus fruits removed. The evaluations followed a split plot design over time, with the main plot as the number of fruit per cladode and the subplot as the harvest seasons: December, February and March, with four replicates and one plant per plot. Plants grown with two fruits per cladode presented the highest percentage of fruits with commercial size and commercial productivity. Both species showed fruits with commercial size in the first harvest of the cycle (December). S. undatus fruits classified as Class I and H. polyrhizus fruits classified as Extra and Class I showed the best quality.


INTRODUCTION
The quality of fruit is essential for commercialization.
The quality standard of pitaya classifies the lots in three classes, which considers the variation of mass and defects (FAO, 2004;Asean Stan 42, 2015).However, the quality of fruit depends on intrinsic and extrinsic factors that affect the growth and production of plants.
Size is one of the most important quality variables, and in the case of pitaya, it is decisive for classification, because the largest size fruits are classified in the categories that achieve the best prices on the market (Then, 2013).However, information lacks on the number of fruit produced per plant related to commercial quality and productivity, which is important for the management of pitaya orchards.
In research studies, variation in productivity has been attributed to the uneven size of fruits, demonstrating that the number of fruits per plant is related to its composition, quality and productivity (Fernandes et al., 2018;Rabelo et al., 2020a;Rabelo et al., 2020b;Alves et al., 2021).
According to these reports, the variations occur due to nutrient availability, so that the nutritional management of the orchard is one of the factors responsible for the commercial production of pitayas with quality.
Núbia Cassiana Santos et al.However, when the number of fruits affects commercial productivity, the best course of action is to adopt management practices to reduce the number of fruits in the plant (Cruz et al., 2011); or increase the supply of pollen at the time of pollination (Silva et al., 2011;Lone et al., 2017), aiming to improve uniformity in size and increase yield.
Specifically for pitayas in Brazil, further studies are needed on management practices relating quality variables and commercial productivity.In this sense, this study evaluated the effect of the number of fruit per cladode on the commercial productivity and the quality of fruits of two pitaya species at different harvest times.

MATERIALS AND METHODS
The study was carried out in an orchard in Minas Gerais, The soil in the experimental area is a Typic Haplorthox (Santos et al., 2018), with 60% sand, 27% clay, and 13% silt.Fertilization management was according to the soil chemical analysis and the age of the plants, with three applications of 300 g of N, 300 g of K 2 O, and 90 g of P 2 O 5 per plant, during the flowering and fruiting period.to determine the relationship between the number of fruits in each class and the total production in each treatment.
The fruits in each class, were grouped in categories from A to I, or without classification, according to the mass, for later chemical evaluation.The chemical characteristics were evaluated immediately after the classification, using representative samples of the fruits composed by four replicates, of each category, in each harvest season, determining the content of total soluble solids (ºBrix) and titratable acidity (% malic acid).
The soluble solids content was measured using a digital refractometer with automatic temperature compensation, model PR-100 pallete (Atago Co Ltd., Japan).Titratable acidity was based on the neutralization of acids present in the fruit with a standardized alkali solution of 0.1 mol L -1 sodium hydroxide by titration (IAL, 2008).The ratio (SS / TA ratio) was calculated from the results of the titratable acidity (TA) and the soluble solids (SS) content.
Total production per plant was calculated by multiplying the mass of commercial class fruits, including fruits that were outside the commercial standard, by the total number of fruits harvested per plant and the total productivity from production per plant multiplied by the density of plants per Commercial productivity and quality of pitaya as a function of number of fruits per cladode hectare (1,111).The production and commercial productivity was calculated in the same way, but fruits that did not reach the minimum standard for commercialization, with mass below 135 g, were disregarded (FAO, 2004;Asean Stan 42, 2015).
The data were subjected to analysis of variance.The unfolding of the interaction was carried out to study the effect of the number of fruits per cladode in the different seasons, comparing the means with the Tukey test, with a 5% probability of error.The variables showing significant differences between the number of fruits per cladode subjected to regression analysis, considering a 5% probability of error.The analyses were performed using the Sisvar statistical software (Ferreira, 2011).1).
The results of thinning suggest that the number of fruits per plant should be reduced by around 41% in both species conducted with two fruits per cladode (Table 1).However, this percentage must be evaluated in the field, as well as the the number of productive cladodes per plant.In addition, to ensure efficiency of thinning, all flowering times or thinning seasons must be considered, as the species develops flowers and fruits simultaneously, with a short period between anthesis and fruit ripening (Marques et al., 2011;Silva et al., 2015), thus, there is high competition between Núbia Cassiana Santos et al.
sink for assimilates.
These results are important and demonstrate that S undatus plants presented a higher percentage of fruits meeting the marketing standards, including the Extra class, compared with H. polyrhizus (Table 1).The differences between the pitaya species may be related to genetic characteristics and the number of cladodes per plant, which influence the number of floral buds and pollination efficiency.The selected plants of H. polyrhizus had mean of 120 cladodes per plant, while S. undatus had mean of 50 cladodes, with different demand for photoassimilates and pollen, considering that the flower fertilization in this species depends on cross-pollination, whereas S. undatus can present self-pollination (Muniz et al., 2019).In addition, the greater the number of floral buds, requires eficiency pollination to set fruits and to produce larger fruits.
Regarding the harvest season, it was observed in both species a lower number of fruits per plant in the first harvest of the cycle, in December 2018, resulting in fruits of greater mass and longitudinal and cross diameters, regardless of the number of fruits per cladode (Table 2).
This increased mass may be due to the greater availability of photoassimilates, which may favor the increase in fruit mass because of the less competition between the sinks.
The greater number of fruits per plant and the smaller sizes observed in the harvests of February and March resulted from the greater amount of flowers in the plants in the second and third flowering times that occurred in January and February, respectively.At that time, the temperature and low precipitation in the crop site favored floral induction and natural pollination.The conditions were different from those prevailed in the flowering that occurred in November 2018 and contributed to reduce the fruiting index due to the lower availability of pollen and/or a decrease in the presence of pollinators (Silva et al., 2011).This is because the temperature, light and absence of rain are the main climate elements responsible for flowering and natural pollination of pitaya (Marques et al., 2011;Silva et al., 2015, Muniz et al., 2019).
These results are relevant for the management of orchards that do not manage artificial pollination, aiming to establish practices to avoid plant wearing out or increase the availability of photoassimilates, as it is essential that fruits reach mass for commercial classification.In addition, as new flowers bloom, the reserves seem to wear off and depending on the quantity of fruit that simultaneously grows in the plant, the competition between the sinks is greater, which explains the smaller sizes in the February and March harvests.
Regarding the total number of fruits, production per plant and total productivity, no differences were observed in function of the number of fruits per cladode, in the two species.S. undatus showed means of 58 fruits per plant, 10.5 kg per plant, and total productivity of 11.7 t ha -1 , while H. polyrhizus showed means of 70 fruits per plant, 10.9 kg per plant, and total productivity of 12.1 t ha -1 (Table 3).
These results show that a greater number of fruits per cladode does not result in greater productivity and, although H. polyrhizus produces a greater number of fruits per plant, the difference in productivity is not significant because of the lower mass of fruits, showing a relationship between the number of fruits per plant and the size of the fruits.
Considering only fruits that meet the commercial standard, the results show that the number of fruits per cladode influences production, with reduction in commercial number of fruits per plant from 43.9 to 29 and from 34 to 26, commercial production per plant from 11.6 kg to 6.2 kg and from 9.6 kg to 4.9 kg, and commercial productivity from 12.9 t ha -1 to 6.8 t ha-1 and from 10.7 t ha -1 to 5.4 t ha -1 for S. undatus and H. polyrhizus, respectively (Table 3).This is caused by the lower mean mass of fruits in plants conducted with six fruits per cladode.A relevant point observed was that the commercial productivity in plants conducted with two fruits per cladode (12.9 t ha -1 and 10.7 t ha -1 ) is similar to the total productivity (11.7 t ha -1 and 12.1 t ha -1 ), showing that fruit size uniformity, even with a smaller number of fruits per plant, compensates for commercial productivity.
In the analyses of fruit quality, in all harvest seasons, non-commercial fruits showed the lowest soluble solids concentrations and ratio and the highest acidity, for the two species (Tables 4 and 5).The exception was observed in fruits of S. undatus classified as extra A in the March harvest, which showed no difference from non-commercial fruits, with mean of 14.5° Brix.This result may be related to the maturation stage and the high demand for photoassimilates.
The pitayas of S. undatus ranked in class I presented the best results in the two categories (D and E) for soluble solids concentrations, varying between 16.8° Brix to 18.1° Brix, titratable acidity from 0.26% to 0.3%, and SS/TA ratio from 53.1 to 67.3 (Table 4).Fruits of H. polyrhizus in the Extra class and class I showed the best results for soluble solids concentrations with variation between 19.5° Brix to 22.3° Brix, the acidity between 0.19% and 0.29%, and the SS/TA ratio between 67.2 and 111.6 (Table 5).The results observed for the fruits of the two species in all seasons, including the non-commercial fruits (Tables 4 and 5), show they are satisfactory for consumption, comparing the values considered acceptable of 12.2° Brix, titratable acidity less than 1%, and SS/TA ratio of 40 (To et al., 2002;Wanitchang et al., 2010;Ortiz & Takahashi, 2015).The low percentage of acids in pitayas imparts their mild flavor, which generally have a titratable acidity of less than 1% when ripe, being one of the variables used to assess the stage of fruit ripeness (Ortiz & Takahashi, 2015).Means followed by the same lower case letters in the columns, do not differ by the Tukey test, at 5% probability.CV1 (%) = coefficient of variation of the classes.CV2 (%).= coefficient of variation of the interaction between classes and harvest times; SC = unrated.
Commercial productivity and quality of pitaya as a function of number of fruits per cladode Means followed by the same lower case letters in the columns, do not differ by the Tukey test, at 5% probability.CV1 (%) = coefficient of variation of the classes.CV2 (%).= coefficient of variation of the interaction between classes and harvest times; SC = unrated.
Fruits with the lowest mass were those lowest in taste, indicating that, probably, the competition for photoassimilates depends on the sink force, which is responsible for the amount of photoassimilates that is partitioned to each fruit.
Therefore, in absence of interference with the amount of fruit produced per plant, there is high competition between the sinks for the available photoassimilates.

CONCLUSIONS
Plants of the species S. undatus and H. polyrhizus conducted with two fruits per cladode presented the highest percentage of fruits that reach the commercial size and the highest commercial productivity.
Both pitaya species had most of the fruits meeting the commercial size in the first harvest of the cycle (December).
Pitayas of S. undatus classified as class I and H. polyrhizus classified as Extra and class I showed the best quality.
The orchard was formed by six-year-old Selenicereus undatus (Haw.)D.R.Hunt and Hylocereus polyrhizus (F.A.C.Weber) Britton & Rose spaced at 3.0 x 3.0 m, without management of artificial pollination.The training system consisted of "T" trellis of eucalyptus posts of 1.80 m high with a 1 m long cross arm.The plants were pruned for training of the main cladode and productive cladodes, ensuring light penetration to the stems and cleaning pruning to balance the numbers of cladodes and favor flowering, when necessary.S. undatus plants were kept with around 45 cladodes and in the H. polyrhizus with 130 cladodes per plant.Irrigation management was carried out during the period of low rainfall to maintain soil moisture for nutrient absorption at the time of fertilization, with 20 L per plant, weekly.The weed control was carried out within a radius of 40 cm from the stem by hand weeding, and the remainder of the area was mowed.

Table 1 :
Number of fruits per plant of the species Selenicereus undatus (1) and Hylocereus polyrhizus (2), conducted with two, four, five and six fruits per cladode, classified in different classes and categories according to the international standard

Table 3 :
Total number of fruits per plant, total production per plant, total productivity, number of commercial fruits, commercial production per plant and commercial productivity of Selenicereus undatus and Hylocereus polyrhizus species according to number of fruits per cladode

Table 4 :
Content of soluble solids (SS), titratable acidity (TA) and SS / TA ratio of Selenicereus undatus fruits, in different categories of Extra, I and II classes e no commercial standard

Table 5 :
Content of soluble solids (SS), titratable acidity (TA) and SS / TA ratio of Hylocereus polyrhizus fruits in different categories of Extra, I and II classes e no commercial standard