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Introduction
Cucumis melo L. (melon) is a perishable fruit due to its high moisture content, hence the importance of finding new ways to preserve it for its storage and transportation. Freezing is one of the most widely used methods, but it reduces its quality by causing irreversible damage (Ayala-Aponte & Cadena, 2014). Identifying the exact point of fruit cooling for its conservation without degrading its cellular structure is very difficult (Chassagne-Berces et al., 2009). Post-harvest storage of melon requires low temperatures (2.2 to 5.0 °C) that enable preserving it for up to 21 days; however, if lower temperatures are applied, they can cause freeze damage (Suslow, Cantwell, & Mitchell, 2002), which is why it is important to find different ways of preserving the fruit to avoid economic losses.
Control of environmental variables such as relative humidity and temperature help to reduce damage caused by rottenness, as well as the use of natural alternatives such as chitosan (Bautista-Baños, Hernández-Lauzardo, Velázquez-del Valle, Bosquez-Molina, & Sánchez-Domínguez, 2005; de Oliveira et al., 2014). Several technologies have been evaluated to preserve the firmness and quality of melon for a longer period of time, including the regulation of temperatures at low levels, the application of waxy mixtures and the use of 1-methylcyclopropene (1-MCP) as an inhibitor of ethylene to delay maturation (Alanís-Guzman, García-Díaz, Reyes-Avalos, & Meza-Velázquez, 2013; García-Robles, Quintero-Ibarra, Mercado-Ruiz, & Báez-Sañudo, 2016; Li et al., 2011).
To avoid disease and obtain good melon quality and greater post-harvest life, good fertilization is needed before harvest (Alves-Ferreira et al., 2015; Flores et al., 2013). Among the cucurbits, the melon crop has demanding fertilization needs (Lima-de Deus, Soares, Lima-Neves, Francismar-de Medeiros, & Rodrigues-de Miranda, 2015); therefore, products based on carboxylic acids and calcium are applied to increase the quality, amount and shelf life of the fruit (Román-Moreno & Gutiérrez-Coronado, 1998), although obtaining a long post-harvest life is also linked to good crop management.
Consumption of melon is related to the content of total soluble solids (TSS), which is responsible for the sweet taste since it has been established that if a melon fruit has less than 9 °Brix, it is not marketable; if it contains between 9 and 12 °Brix, it is marketable, and if it contains more than 12 °Brix, it possesses an extra quality (Vargas, Castoldi, de Oliveira-Charlo, & Trevizan-Braz, 2008). In addition to the TSS, high quality standards with characteristics such as the internal and external appearance of the fruit and the thickness of the pulp are what determine consumer acceptance (Vargas et al., 2008). The different melon genotypes have different organoleptic characteristics, yields, resistance to pests and diseases, fruit quality, adaptation to the environmental conditions of the site, acceptance in the market and post-harvest life (Bianchi et al., 2016; Monge-Pérez & Loría-Coto, 2017).
One of the regions that produces the most melon in Mexico is the Comarca Lagunera, where in the months of June, July and August there is an excess of supply resulting in low prices (Ramírez-Barraza, García-Salazar, & Mora-Flores, 2015). In Mexico, the Cantaloupe-type melon, also known as Chinese melon, which is rough or reticulated, accounts for 70 % of all melon production, followed by the Honeydew melon, also known as Honeymelon, with 28 %; other types of melon make up the remaining 2 % (Espinoza-Arellano, Orona-Castillo, & Cano-Ríos, 2002). Each country has its own cultural traditions in terms of preferred tastes; consequently, while Harper / Cantaloupe melons account for 85 % of all melon exports to the United States and Honeydew melons only 15 %, Europe’s imports are substantially different: 58 % Honeydew melons, 39 % Harper melons and 3 % Galia melons (Monge-Pérez, 2014).
The supply situation in the melon export market requires evaluating recently created cultivars, including those of interest to new markets. The Korean, Japanese and Singaporean markets have great importance, with the melon as either a fresh or frozen product (Laínez & Krarup, 2008). Therefore, it is important for the producer to choose a good genotype with quality characteristics and a long post-harvest life that can reach distant markets, which can yield good profits (Espinoza-Arellano, Lozada-Cota, & Leyva-Nájera, 2011; Espinoza-Arellano et al., 2009).
The Cruiser hybrid is supplied to both domestic and export markets and is one of the main hybrids planted in the Comarca Lagunera (Chew et al., 2010); however, this hybrid has an intermediate post-harvest life, meaning it is unable to reach distant markets in tradable conditions (Suslow et al., 2002). The objective of this research was to identify new Harper-type melon hybrids that have a longer post-harvest life that enables producers to access the aformentioned markets.
Materials and methods
The experiment was carried out in the José María Morelos ejido’s El Progreso field located at km 20 of the toll-free Torreón-Saltillo (25° 23’ and 25° 48’ NL and 103° 23’ and 103° 03’ WL, at an elevation of between 1,100 and 1,700 masl), in the municipality of Matamoros, Coahuila, Mexico, within the Comarca Lagunera, during the spring-summer agricultural cycle of 2014.
Four Harper-type melon hybrids (Alaniz Gold, Queen RZ, King RZ and Cruiser) were evaluated for which a randomized block design with three replications was used. Experimental plots of 2 x 8 m were formed to carry out the test. Planting started on March 16, 2014, with a density of 20,000 plants per hectare. All the preparatory work was carried out prior to sowing: fallowing, tracing, leveling, and tracing of beds; the latter were established in the month of February with a distance of 2 m in width, in a mulching system with strip irrigation. The drippers were 30 cm apart whereas the distance between plants was 25 cm. Pollination was carried out by means of beehives, placing 3 colonies per hectare four days after the onset of male flowering.
Since the soil analysis showed a low percentage of organic matter (1.2 %), the following fertilization plan was chosen: a base fertilization to the soil supplied before sowing of 52-75-0 (N-P-K), continuing with a total fertilization by fertigation of 120-100-200-40-40 (N-P-K-Ca-Mg) divided in all of the vegetative cycle starting from the first flowering. It was complemented with three foliar applications of organic fertilizer containing auxins, gibberellins, cytokinins, and micronutrients in chelated form.
Irrigation was carried out every third day at the beginning of the crop and increased to a daily basis at the appearance of the fruit. A pest and disease control system was implemented using products based on fipronil for soil pests, products based on lambda-cyhalothrin and thiamethoxam for the control of aphids, products with an active ingredient of carbendazim or methyl thiophanate for root diseases, and agrochemicals with the active ingredients difenoconazole and azoxystrobin for the control of molds.
The harvest was carried out on May 17, 2014, cutting 30 fruits of each hybrid. The fruits of the Harper-type hybrids do not detach themselves from the peduncle, so a knife was used to cut them. All fruits were harvested on the same date, according to the treatments.
The variables evaluated were fruit yield (t·ha-1), fruit weight (g), polar diameter (PD, cm), equatorial diameter (ED, cm), total soluble solids (TSS, °Brix) and post-harvest life (h), thickness of the epicarp and mesocarp (ET and MT [cm]), and cavity diameter (CD, cm) and firmness of the epicarp and mesocarp (EF and MF [N]), the latter were measured with a Fruit Hardness Tester (FHT 200, Extech® Instruments, USA) using a tip of 6 mm in diameter; the firmness in the epicarp was taken in the equatorial zone, whereas in the mesocarp the average of three measurements of the firmness of the middle part of the pulp was calculated. TSS was determined with a hand refractometer (Master 53α, Atago®, USA).
For post-harvest life, 15 fruits of each hybrid were sampled and stored at 18 °C without applying any previous treatment or washing. The weight of the fruits was taken every five days until completing 30 days. Every 10 days the weight loss percentage (WL) and the speed factor (SF) were determined for two fruits of each hybrid using the following equation:
Statistical analysis
The data obtained were subjected to an analysis of variance, and in cases where significant differences were found a Fisher mean comparison was performed (P ≤ 0.05). In addition, a regression analysis was performed to assess fruit weight loss. All analyses were performed using the Statistical Analysis System ver. 9.0 (SAS, 2004).
Results
The coefficient of variation (CV) showed values below 23 %. The analysis of variance detected differences among the hybrids in fruit shape, shown by the significance (P ≤ 0.05) of the epicarp thickness (CV = 22.7 %), mesocarp thickness (CV = 7.7 %), and cavity diameter (CV = 8.2 %), as well as in quality, due to epicarp firmness (CV = 12.5 %), mesocarp firmness (CV = 15.9 %) and concentration of TSS (CV = 18.4 %). No significant difference among the hybrids in the variables fruit weight and yield were observed (Table 1).
Table 1 Mean comparisons of fruit weight and yield in Cucumis melo L. hybrids.
| Cruiser F1 | Alaniz Gold | Queen RZ | King RZ | LSD1 | |
|---|---|---|---|---|---|
| Fruit weight (kg) | 1.762 abz | 1.641 b | 1.924 a | 1.935 a | NS |
| Yield (t·ha-1) | 45.291 a | 33.894 a | 41.303 a | 43.532 a | NS |
1LSD = least significant difference; NS = not significant. zMeans with different letters within each line do not differ statistically (Fisher, P ≤ 0.05).
Parameters of fruit shape and quality
It is necessary to specify that in the CD and ET variables, the smaller the cavity and thickness the better, contrary to the MT. Alaniz Gold hybrid showed a higher MF value than EF one (Table 2). This may be due to the fruits being harvested when they were not yet ripe enough, resulting in a low TSS value.
Table 2 Mean comparisons of the physical parameters evaluated in hybrids of Cucumis melo L at the time of harvest.
| Cruiser F1 | Alaniz Gold | Queen RZ | King RZ | LSD | |
|---|---|---|---|---|---|
| PD1 (cm) | 15.99 az | 14.06 b | 16.55 a | 16.01 a | NS |
| ED (cm) | 14.69 a | 14.98 a | 14.92 a | 15.02 a | NS |
| ET (cm) | 0.54 c | 0.88 a | 0.56 bc | 0.65 b | 0.09 |
| MT (cm) | 3.71 ab | 3.40 c | 3.81 a | 3.63 b | 0.15 |
| CD (cm) | 6.03 b | 6.62 a | 6.33 ab | 6.68 a | 0.46 |
| EF (N) | 44.46 c | 46.95 c | 62.52 a | 55.36 b | 4.74 |
| MF (N) | 38.67 c | 64.30 a | 49.62 b | 28.66 c | 7.88 |
| TSS (°Brix) | 6.54 b | 6.80 b | 13.62 a | 13.42 a | 1.43 |
1PD = polar diameter; ED = equatorial diameter; ET = epicarp thickness; MT = mesocarp thickness; CD = cavity diameter; EF = epicarp firmness; MF = mesocarp firmness; TSS = total soluble solids; LSD = least significant difference; NS = not significant. zMeans with different letters within each line do not differ statistically (Fisher, P ≤ 0.05).
Figure 1 shows the performance of the hybrids over 30 days. The hybrid with the highest weight loss was Cruiser F1, without reaching the end of the experiment. The fruits of this hybrid were only evaluated until day 20 because the commercial maturity of the fruits had already passed.
The regression equations showed that the Queen RZ and King RZ hybrids have similar weights, as well as Alaniz Gold and Cruiser F1; however, the fruit weight loss in Cruiser F1 was higher (1.088 g·h-1) compared to the others, and less with Queen RZ with (0.547 g·h-1). The initial weight of the King RZ’s fruit (2,086 g) was the highest, and its final weight at 30 days was similar to that of Queen RZ (1,614 g). The initial weight of Alaniz Gold's fruit (1,785 g) was the lowest of the hybrids; however, its final weight was more than that of Cruiser F1 (1,488 and 1,371 g, respectively) 20 days after harvest.
Tables 3, 4 and 5 show the means of the fruit shape parameters, firmness and concentration of TSS evaluated at 10, 20 and 30 days post-harvest, respectively. The quality of the fruits of the Cruiser F1 hybrid decreased considerably after 20 days; therefore, only results of this hybrid until this date are shown (Table 4).
Table 3 Mean comparisons of physical parameters evaluated at 10 days post-harvest in hybrids of Cucumis melo L.
| Cruiser F1 | Alaniz Gold | Queen RZ | King RZ | LSD | |
|---|---|---|---|---|---|
| PD1 (cm) | 19.50 az | 14.50 b | 16.25 b | 16.50 b | 2.64 |
| ED (cm) | 14.15 a | 15.65 a | 14.60 a | 15.20 a | NS |
| ET (cm) | 0.80 a | 0.70 ab | 0.45 c | 0.50 bc | 0.22 |
| MT (cm) | 3.00 a | 3.60 a | 3.50 a | 3.75 a | NS |
| CD (cm) | 7.15 a | 7.15 a | 6.50 a | 7.15 a | NS |
| EF (N) | 49.31 b | 49.75 b | 61.81 a | 52.42 ab | 9.76 |
| MF (N) | 42.63 b | 67.11 a | 44.90 b | 21.32 c | 12.70 |
| TSS (°Brix) | 6.25 b | 10.25 a | 12.90 a | 12.10 a | 2.67 |
1PD = polar diameter; ED = equatorial diameter; ET = epicarp thickness; MT = mesocarp thickness; CD = cavity diameter; EF = epicarp firmness; MF = mesocarp firmness; TSS = total soluble solids; LSD = least significant difference; NS = not significant. zMeans with different letters within each line do not differ statistically (Fisher, P ≤ 0.05).
Table 4 Mean comparisons of physical parameters evaluated at 20 days post-harvest in hybrids of Cucumis melo L.
| Cruiser F1 | Alaniz Gold | Queen RZ | King RZ | LSD | |
|---|---|---|---|---|---|
| PD1 (cm) | 16.93 az | 15.45 a | 16.15 a | 16.65 a | NS |
| ED (cm) | 13.75 b | 15.80 a | 15.40 a | 15.60 a | 1.58 |
| ET (cm) | 0.39 a | 0.55 a | 0.35 a | 0.30 a | NS |
| MT (cm) | 2.79 b | 3.40 ab | 4.00 a | 3.75 a | 0.63 |
| CD (cm) | 6.46 a | 6.50 a | 6.25 a | 6.75 a | NS |
| EF (N) | 28.52 b | 45.12 a | 53.71 a | 57.32 a | 16.37 |
| MF (N) | 14.69 b | 47.88 a | 23.23 b | 19.58 b | 18.77 |
| TSS (°Brix) | 7.23 b | 8.80 b | 11.65 a | 12.35 a | 1.71 |
1PD = polar diameter; ED = equatorial diameter; ET = epicarp thickness; MT = mesocarp thickness; CD = cavity diameter; EF = epicarp firmness; MF = mesocarp firmness; TSS = total soluble solids; LSD = least significant difference; NS = not significant. zMeans with different letters within each line do not differ statistically (Fisher, P ≤ 0.05).
Table 5 Mean comparisons of physical parameters evaluated at 30 days post-harvest in hybrids of Cucumis melo L.
| Cruiser F1 | Alaniz Gold | Queen RZ | King RZ | LSD | |
|---|---|---|---|---|---|
| PD1 (cm) | - | 14.19 bz | 15.74 a | 16.03 a | 0.66 |
| ED (cm) | - | 14.20 a | 14.54 a | 14.65 a | NS |
| ET (cm) | - | 0.44 a | 0.35 a | 0.26 a | NS |
| MT (cm) | - | 3.39 b | 3.70 a | 3.66 a | 0.22 |
| CD (cm) | - | 6.39 a | 5.95 a | 6.37 a | NS |
| EF (N) | - | 51.66 a | 50.95 a | 48.37 a | NS |
| MF (N) | - | 39.92 a | 20.65 b | 21.09 b | 12.35 |
| TSS (°Brix) | - | 7.39 b | 10.25 a | 10.44 a | 1.05 |
1PD = polar diameter; ED = equatorial diameter; ET = epicarp thickness; MT = mesocarp thickness, CD = cavity diameter; EF = epicarp firmness; MF = mesocarp firmness; TSS= total soluble solids; LSD = least significant difference; NS = not significant. zMeans with different letters within each line do not differ statistically (Fisher, P ≤ 0.05).
As for TSS at 10, 20 and 30 days after harvest, it is noticeable that as days go by the value of °Brix decreases, in the case of the Queen RZ and King RZ hybrids, this value reaches approximately 10 °Brix, while Alaniz Gold goes down to 7.4 °Brix. This performance was observed in most of the variables evaluated.
Table 6 shows that the Cruiser F1 hybrid has the highest weight loss speed, which was to be expected due to its short shelf life, while the rest of the hybrids had a similar speed factor. On the other hand, the Queen RZ hybrid showed the lowest percentage of weight loss in the three dates evaluated, followed by King RZ and Alaniz Gold.
Table 6 Fruit weight loss speed factors in fruits at 10, 20 and 30 days post-harvest in Cucumis melo L. hybrids.
| IW1 (g) | WL (%) | W (g) | SF (g·h-1) | |
|---|---|---|---|---|
| 10 days post-harvest (240 h) | ||||
| Cruiser F1 | 2,044 | 9.78 | 200 | 0.83 |
| Alaniz Gold | 1,859 | 7.21 | 134 | 0.56 |
| Queen RZ | 1,995 | 6.27 | 125 | 0.52 |
| King RZ | 2,165 | 7.53 | 163 | 0.68 |
| 20 days post-harvest (480 h) | ||||
| Cruiser F1 | 1,859 | 26.14 | 486 | 1.01 |
| Alaniz Gold | 2,091 | 12.67 | 265 | 0.55 |
| Queen RZ | 2,175 | 11.08 | 241 | 0.50 |
| King RZ | 2,282 | 12.58 | 287 | 0.60 |
| 30 days post-harvest (720 h) | ||||
| Cruiser F1 | - | - | - | - |
| Alaniz Gold | 1,707 | 23.73 | 405 | 0.56 |
| Queen RZ | 1,994 | 20.66 | 412 | 0.57 |
| King RZ | 2,035 | 21.43 | 436 | 0.61 |
1IW = initial weight; WL = percentage of fruit weight loss; W = fruit weight loss; SF = weight loss speed factor.
Discussion
Fruit weight and fruit yield did not show significant differences among hybrids. The largest production was presented by the hybrid Cruiser F1 (45.29 t·ha-1), followed by King RZ (43.53 t·ha-1), Queen RZ (41.30 t·ha-1) and finally Alaniz Gold (33.89 t·ha-1). Most of the yields obtained are higher than those observed in a study conducted at the University of Costa Rica where 59 genotypes were evaluated, 18 of them Harper type, and obtained an average of 0.584 kg per fruit with a yield of 34.34 t·ha-1 (Monge-Pérez & Loría-Coto, 2017). On the other hand, the results compiled by Monge-Pérez (2016) indicate a yield of 41.30 t·ha-1 with the hybrid Harper JMX-1001, with a harvest start of 62 days after planting; this value is equal to the one reported with Queen RZ.
In the first evaluation of the 120 fruits, it was found that the hybrid that has the best fruit shape characteristics is Queen RZ, with polar and equatorial diameters of 16.55 and 14.95 cm, respectively. In addition it also had the thickest mesocarp (3.81 cm), small cavities (6.33 cm) and not very thick epicarps (0.56 cm), good firmness in the epicarp and mesocarp (62.52 and 49.62 N, respectively), and the highest concentration of TSS (13.62 °Brix). In addition, this hybrid reached 30 days of post-harvest life at 18 °C. Nunes et al. (2004) evaluated different genotypes of Red Fresh in Brazil and obtained a yield of 32.54 t·ha-1 with an average weight of 1.254 kg in fruits with a mesocarp thickness of 3.18 cm, cavity diameter of 6.55 cm, mesocarp firmness of 42.80 N and TSS of 10.89 °Brix; these results are slightly lower than those obtained in this experiment
Laínez and Krarup (2008) evaluating the Glamor cultivar in Chile, and equatorial and polar diameters of 13 and 13.5, respectively, were obtained, with a 4.8 cm cavity diameter, 12.4 °Brix TSS and 18.7 N mesocarp firmness (Laínez & Krarup, 2008). The genotypes evaluated by Monge-Pérez and Loría-Coto (2017) showed 14.54 °Brix and 19.12 N mesocarp firmness. In an evaluation of the genotype Bonus n° 2, Rizzo and Braz (2001) obtained average fruit weight of 693.25 g with polar and equatorial diameters of 10.20 and 10.48 cm respectively, with mesocarp and epicarp thicknesses of 2.80 and 0.209 cm, respectively, and 13.15 °Brix TSS. These results are also below those obtained in this experiment.
The hybrid Alaniz Gold did not present favorable results in the variables studied, possibly because its fruits were harvested when they were not yet at their point of maturation. In the evaluation of hybrids at 10 days after harvest, it is shown that Queen RZ continues to maintain quality characteristics. In general, the four hybrids showed a decrease in TSS and in most of the variables evaluated. In the evaluation after 20 days, the Queen RZ hybrid remains outstanding in terms of TSS (11.65 °Brix); however,it was surpassed by the King RZ hybrid, which obtained 12.35 °Brix. In the last evaluation carried out at 30 days, only Alaniz Gold, Queen RZ and King RZ fruits were available. The last two were the ones that obtained the most favorable values, reaching 10.25 and 10.44 °Brix, respectively.
It can be affirmed that as days go by, the amount of °Brix decreases, with the Queen RZ and King RZ hybrids having around 10 °Brix, while Alaniz Gold drops up to 7.4 °Brix. The above, according to the literature, indicates that the hybrids Queen RZ and King RZ can be commercialized after 30 days of storage at 18 °C; this is due to the fact that they present TSS values in the range considered as marketable (between 9 and 12 °Brix) (Vargas et al., 2008).
Mesocarp firmness in the Queen RZ hybrid was 44.90 N at 10 days after harvest, decreasing to 20.65 N at 30 days. Laínez and Krarup (2008), in evaluating fruits of Oriental-type cantaloupes stored at 0 and 10 °C for 21 days, found that the fruits of the cultivar Glamour underwent a reduction in quality with a firmness of 41.8 and 16 N and TSS of 11.4 and 10.5 °Brix, at 0 and 10 °C, respectively. Gomes, Menezes, Nunes, Costa, and Souza (2001) analyzed two cutting dates (when the fruit is not ripe [II] and when the fruit is fully ripe [IV]) in Cantaloupe-type fruits stored for 25 days at 20 °C and obtained firmness values of 30.07 and 17.87 N for II and IV, respectively, at the beginning of storage, and 5.32 and 3.50 N at the end of the storage period.
Brackmann et al. (2006) evaluated the hybrid Torreon grown hydroponically and stored in polyethylene packages for 25 days at 2 °C, and observed that the mesocarp firmness was initially 17.4 ± 2.4 N and ended at 16.9 N (Brackmann et al., 2006).
The Queen RZ hybrid stands out among the four hybrids by obtaining the least fruit weight loss with an average speed factor of 0.55 g·h-1. The fruit weight loss percentages incurred by the Queen RZ hybrid fruits were 6.27, 11.10 and 19.80 % at 10, 20 and 30 days respectively with a speed factor of 0.52, 0.50 and 0.57 g·h-1 respectively. These values are lower than those reported by Cano-Ríos, Theran-Kruger, and Esparza-Martínez (2004) in a study conducted in the Comarca Lagunera with cross-linked hybrids, because fruit weight loss percentages of 16.80 and 13.60 % were obtained for Hy Mark and Cruiser, respectively, with a speed factor of 1.55 and 1.24 g·h-1, at 6 storage days.
Conclusions
Fruit shape parameters (equatorial and polar diameter) in the Harper-type melon hybrids were not significantly modified by the fruit weight loss caused by the passage of time; however, the quality of the fruit is diminished by the effect of storage (30 days, 18 °C), since the fruit weight loss causes reduced firmness and TSS. According to the results obtained, we can affirm that the Queen RZ and King RZ Harper-type hybrids were marketable after 30 days post-harvest, sufficient to reach distant markets. These hybrids also had better fruit shape parameters, greater firmness and a higher concentration of TSS compared to the control of the region (Cruiser F1).
Harper-type melon hybrids represent an opportunity for melon producers to venture not only into distant markets, but to introduce this type of melon in the national market and change the planting and marketing paradigm.
