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Highlights
‘Yashar’ mandarin containing less seeds were produced using pollen grains of different citrus cultivars and copper sulfate.
Produced ‘Yashar’ mandarin containing less seeds had more antioxidant capacity than other treatments.
Introduction
‘Yashar’ mandarin (Citrus tangerine ‘Tanaka’) was produced in 2009 through the intersection of ‘Minneola’ tangelo tangerine (C. paradisi cv. ‘Duncan’ × C. reticulata cv. ‘Dancy’) as a mother parent and ‘Changsha’ mandarin (C. changsha tangerine) as a father parent in the Citrus Research Institute in Khorramabad, Tonekabon, Iran (Golein, Alian, Ebrahimi, & Nazerian, 2012) (Figure 1). ‘Yashar’ mandarin is one of the serotinous cultivars (mostly yields in May) with high performance and appropriate quantitative and qualitative characteristics. It has large fruit with sufficient fruit juice, dark orange flesh, and a desirable smell and taste. ‘Yashar’ mandarin is a seeded cultivar, and it shows biennial bearing, and resistance to the cold condition. ‘Yashar’ mandarin trees have a wide and broad crown, and their branches are almost without thorns (Golein et al., 2012).
Figure 1 Origin of hybrid ‘Yashar’ mandarin through hybridization between ‘Minneola’ tangelo and ‘Changsha’ mandarins.
Being full of seeds is one of the most important disadvantages of ‘Yashar’ mandarin. Cross-pollination and using chemical compounds are some techniques to reduce the number of seeds in various plants such as citrus. Hybridization among different genus is one of the corrective techniques to produce new citrus cultivars. Consumers have always been cautious about different characteristics of citrus cultivars, such as being totally seedless or having fewer seeds, having thin skin and desirable taste. Citrus breeders have always try to create such characteristics in new genotypes and cultivars.
The use of suitable pollinators can be one of the most impressive and safest farming methods from an environmental point of view to improve fertility level and the quality of fruits which are self-incompatible cultivars (Ioannis, Papadakis, Protopapadakis, & Ioannis, 2009). Different effects of pollen grain sources on quantitative, qualitative, physical and biochemical characteristics of citrus fruits has been reported (Wallace & Lee, 1999; Wallace, King, & Lee, 2002; Talaie, Golein, Ebrahimi, & Vezvaei, 2002; Alinezhad-Jahromi, Zarei, & Mohammadkhani, 2019). The effect of pollination on the number of seeds in an incompatible variety of mandarin ‘Afourer’ showed that few seedless fruits were formed on free-pollinated trees. At the same time, the use of anti-bee nets resulted in producing a high percentage of seedless fruits (Gambetta et al., 2013). Appropriate management of pollinators increased the quantity and quality of mandarins (Wallace et al., 2002).
A study on the effect of ‘Balady’ mandarin pollen grains on ‘Balady’ sour lemon, ‘Agamy’ and ‘Hosni’, revealed that no significant differences were observed in total soluble solids (TSS), acidity (TA) and vitamin C content of fruits (Kitat, El-Azad, & Wehida, 1994). The pollination with ‘Moro’ blood orange pollen grains on ‘Clementine’ mandarin significantly reduced the number of seed (Alinezhad-Jahromi et al., 2019). Different sources of pollen grains had a significant effect on the fruits of three mandarin cultivars, such as their sugar content, acidity and number of seeds and their weight (Wallace & Lee, 1999).
The results of controlled pollination on ‘Clementine’ mandarin showed that the highest percentage of fruits were related to pollinated flowers with sweet lemon pollen grains. The lowest percentage of them were related to self-pollinated flowers. Furthermore, the highest and lowest live seeds were gained from flowers pollinated with ‘Lisbon’ lemon pollen grains and self-pollinated pollen grains (Alinezhad-Jahromi et al., 2019). The effects of pollen grains of nine cultivars of citrus on ‘Page’ mandarin demonstrated that ‘Hamlin’ orange is the best pollinator (Goleine et al., 2012). Local mandarins and clustered lemon are the best pollinators for ‘Clementine’ mandarins according to the weather conditions of the northern part of Iran (Alinezhad-Jahromi et al., 2019).
Copper sulfate (CuSO4) has played different roles in agriculture for different purposes. Some of its important applications are as follow: a pesticide, a stimulator to form some vitamins (also its metabolic role in some enzyme systems), and its role as biosynthesis and the effects of ethylene and also its role in the process of producing seedless fruits (Kyamarsi, & Eshghi, 2011; Mesejo, Martínez-Fuentes, Reig, Rivas, & Agustí, 2013). The aforementioned salt is mainly absorbed from the soil as Cu2+ ion, and it has also been used as foliar spraying. The application of copper sulfate in seed reduction has been reported in cultivar ‘Fortune’ mandarin, cultivar ‘Clemenules’ of the ‘Clementine’ mandarin and cultivar ‘Afourer’ tangor. Copper sulfate can have inhibitory effects on pollen tube growth and seed formation (Mesejo et al., 2013). It has also been reported that copper sulfate caused ‘Shiraz’ black grapes cultivar to become seedless (Kyamarsi & Eshghi, 2011).
The present study aimed to evaluate the sprays with cooper sulfate and pollination impacts regarding different sources of pollen grains (‘Valencia’ orange, ‘Hamlin’ orange, sour orange and free pollination) on ‘Yashar’ mandarin characteristics particularly seed number to choose the best pollinator.
Materials and methods
Place of research
This study was carried out on ‘Yashar’ mature mandarin trees grafted on identical and healthy sour orange rootstocks regarding their growth condition at the Citrus Research Institute of Ramsar city, Mazandaran, Iran. Ramsar is considered one of the subtropical regions regarding climate, and its altitude is -20 m a. s. l. Its longitude is 50.65° from the east, and its latitude is 36.90° from the north. The average, maximum and minimum, temperatures are 35 and -2 °C, respectively, and the annual rainfall is 800-1,500 mm.
First experiment
In the first experiment (done on 2018), the effect of pollen grains of different citrus cultivars (‘Valencia’ orange, ‘Hamlin’ orange and sour orange) and free pollination (control group) on the carpel of the ‘Yashar’ mandarin was evaluated in a randomized completely block design with four treatments and three replications.
Selection of ‘Yashar’ mandarin trees for pollination
From the trees in the ‘Yashar’ plot, 12 healthy trees (Figure 2A) were selected and marked in terms of growth rate, size and shape of the crown and even equality of the rootstocks. These trees were reproduced by grafting the scion on a sour orange tree as a rootstock.
Selecting pollinator trees
In order to choose pollinator cultivars, those cultivars that were free of pests and diseases were used and were either low-seeded or high-seeded (full of seeds).
Performing manual pollinating operations
For pollination, 100 flowers were selected in each combination, and the flowers were isolated in clear wax bags 24 h before the petals were supposed to open. At the same time, the blossoms of the ‘Valencia’, ‘Hamlin’ and sour orange cultivars were separated while their opening stage was close enough. They were collected, their anthers were separated and kept in Petri dishes. The anthers were split after 24 h at ambient room temperature (24 to 26 °C), and their pollen grains were released (Figures 2B and C). By selecting the flowers from the desired trees, the flowers were castrated (Figure 2D) and then the packing operation was performed. After the pistil preparation in ‘Yashar’ mandarin, the pollen of the cultivars was transferred to them (Figure 2E), and they were covered again with paper bags (Figure 2F). Four to five days after inoculation, the bags were opened, and the numbers of formed fruits were counted. In order to prevent fruits from falling or being picked, they were covered with plastic nets (Figure 2G).
Measured characteristics
The fruits were harvested after ripening (harvest index was proportion of TSS to TA), and they were transferred to the Plants Breeding and Seed and Scion Preparation laboratory of the Department of Citrus Research Institute, Ramsar, Iran. At the laboratory, different characteristics such as weight, length, diameter, skin thickness and fruit volume, number of seeds, percentage of fruit juice, vitamin C in fruit flesh, total phenol in the flesh, the antioxidant capacity of flesh, TSS, TA, technology index and vividness of fruit skin were measured.
Second experiment
In the second experiment (done on 2019), the impact of foliar spraying of copper sulfate at the rate of 25 mg·L-1 was conducted at stages of 30, 60 and 80 % of blossoming fruit flowers and a free pollination treatment (control) was evaluated in randomized completely block design with four treatments and three replications.
Selecting ‘Yashar’ mandarin trees for foliar spraying
From the trees in the ‘Yashar’ plot, 12 healthy and uniform trees with the age of 15-16 years were marked in terms of growth rate, size and shape of the crown and even equality in the rootstocks. All of these trees were reproduced by bud grafting on a sour orange tree.
Time of spraying
Foliar spraying of 25 mg·L-1 copper sulfate (with the use of water) was conducted in May at three different times. The first time was done on May 10th, while 30 % of the flowers were opened. The second time was on May 14th, when 60 % of the flowers were opened. The last time was on May 17th, when 80 % of the flowers were opened. Foliar spraying was done in the morning while it was sunny and there was no wind, and it was done by using low-pressure hand sprayer.
Measured characteristics
In this experiment, the same characteristics were evaluated as in the previous one. A digital caliper (Digit-Cal, Switzerland) with an accuracy of 0.01 mm was used to measure length, diameter and thickness characteristics. Fruit weight was measured with a digital scale with an accuracy of 0.01 g. To measure fruit volume, water displacement was used as well. In order to measure the volume of fruits, each fruit was immersed in a beaker containing 1 L of water one by one. Then the content of each fruit in mL was obtained by measuring the amount of water poured down with the help of a measuring cylinder. At the midpoint of the fruit, the vividness of the skin was measured by using a chromometer (CR400-Minolta, Japan) (Alinezhad-Jahromi et al., 2019).
With the help of a juicer, the fruit extract was extracted, and its amount was measured using a measuring cylinder. In order to measure TSS, optical refractometer (Atago-ATC-20E, Japan) with a range of 0 to 20 % was used. In this regard, a drop of fruit extract was placed on the device, and its Brix degree was read. To measure titrable acidity, 10 mL of fruit juice was mixed with 20 mL of distilled water, and two-three drops of phenolphthalein were added to it. Then the resulting mixture was titrated into pink by using a digital burette (Rudolf Brand) containing sodium hydroxide 0.1 N. By placing the volume of sodium hydroxide 0.1 N in the following formula, the titrable acidity was obtained based on the percentage of citric acid (Alinezhad-Jahromi et al., 2019).
The technology index was obtained by multiplying the percentage of the extract in TSS divided by 100 (Castricini, Silva, Silva, & Rodrigues, 2017).
After some initial evaluations, an amount of the fruit flesh was sampled for chemical tests, and then it was placed in a freezer at -80 °C. The 1 g of flesh tissue was mixed separately in 2 mL of methanol, and after being squished, the samples were kept in a refrigerator for 24 h. Then, the samples were centrifuged for 10 min at 6,000 rpm. The supernatant of the samples was gently removed with a sampler, and it was placed in tubes with lids, and it was kept at -20 °C for further measurements.
Total phenol was measured by the Folin-ciocalteu method (Aksoy, Kolay, Ağılönü, Aslan, & Kargıoğlu, 2013). In this regard, 250 μL of 10 % Folin was added to 200 μL of centrifuged methanolic extract. After 5 min, 200 μL of 7 % sodium carbonate was added to the mixture. After keeping it at room temperature for 90 min in a dark condition. The absorbance rate of the extract was read at 675 nm using a Nano-drop spectrophotometer (1000-ND, USA). Total phenol content obtained from the standard curve equation was measured as milligrams of gallic acid (mg·g-1).
The antioxidant capacity of fruit flesh (%) was measured by the free radical scavenging of DPPH (2, 2-diphenyl, 1-picryl hydrazyl) method (Aksoy et al., 2013). Therefore, 50 μL of methanolic extract extracted from fruit flesh were diluted in 450 μL of distilled water. After vortexing, 25 μL of the resulting dilution was removed and poured into a tube with a lid. Then, 100 μL of DPPH was added to the aforementioned solution, and the resulting solution was kept at room temperature for 20 min in a dark condition. The absorption rate of DPPH and the prepared samples at 517 nm were read by using a Nano-drop spectrophotometer (ND-1000 model, USA). Vitamin C was used to prepare standard curve (Brand-Williams, Cuvelier, & Berset, 1995).
Vitamin C was measured by titration with dichlorophenol-indophenol solution (Mazumdar, & Majumder, 2003). At first, 1 g of the sample was weighed, and it was poured into a Falcon 15 mL tube; then, 3 mL of 3 % metaphosphoric acid was added and squished. Then, it was stored in a refrigerator for 15 to 20 min at 4 °C. The aforementioned solution was centrifuged, and 3 mL of it was taken. It was poured into a beaker and a magnet was placed in it. With a digital burette, dichloroindophenol solution was added until pink appeared, and the burette number was recorded. The amount of vitamin C (mg·100 g-1 fresh weight) was calculated using the following formula:
where a is the weight of the sample, b is metaphosphoric volume used for extraction, c is the volume of solution consumed for titration, d is the colour factor (amount of solution used for titration), and e is the volume of colour solution used for each sample.
Data analysis
The obtained data were first recorded in Excel software. Then, the statistical analysis was performed using MSTATC software (MSTAT-C, 1991). Duncan test (P < 0.05) was used to find out the significance of differences among the mean value.
Results
First experiment
Number of seed
The mean comparison showed that the lowest number of seeds was obtained in ‘Yashar’ mandarin pollinated by ‘Valencia’ orange (Table 1). This result showed that compatible pollen grains and sufficient pollinators were available in the plot where the experiment took place.
Table 1 Mean comparison of the effect of pollination by pollen grains of ‘Valencia’ orange, ‘Hamlin’ orange and sour orange on seed number and some morphologic and physiologic traits of ‘Yashar’ mandarin.
| Treatment | Fruit weight (g) | Fruit length (mm) | Fruit diameter (mm) | Fruit skin thickness (mm) | Fruit volume (mL) | Seed number | Fruit juice (%) | Flesh vitamin C (mg·100 g-1) | Flesh total phenol (mg∙100 g-1) | Flesh antioxidant capacity (%) | Total soluble solids (%) | Titrable acidity (%) | Technology index | Skin vividness |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Control | 130.80 az | 56.54 b | 56.75 a | 3.06 a | 110.00 a | 24.07 a | 52.30 a | 65.47 a | 84.23 a | 0.51 a | 13.17 b | 1.94 a | 6.89 b | 57.72 a |
| ‘Hamlin’ | 142.10 a | 57.72 b | 67.87 a | 2.03 b | 133.60 a | 19.47 a | 71.45 a | 45.09 b | 77.43 a | 0.65 a | 13.61 a | 2.12 a | 9.72 a | 60.58 a |
| ‘Valencia’ | 171.00 a | 65.13 a | 73.14 a | 2.59 a | 167.00 a | 18.73 a | 63.32 a | 45.72 b | 90.13 a | 0.55 a | 12.28 d | 2.12 a | 7.78 ab | 58.30 a |
| Naranja agria | 168.20 a | 61.45 ab | 70.31 a | 3.08 a | 150.70 a | 20.77 a | 77.56 a | 42.60 c | 88.33 a | 0.57 a | 12.86 c | 1.86 a | 9.97 a | 56.88 a |
| CV (%) | 11.30 | 5.01 | 4.49 | 14.56 | 20.45 | 9.30 | 13.53 | 12.84 | 7.43 | 20.99 | 1.80 | 11.38 | 12.69 | 3.32 |
zMeans with different letters on the same column are significantly different (Duncan, P ≤ 0.05).
Morphological characteristics
In the present study, there was no significant difference between weight, diameter and volume of fruit and fruit juice percentage in pollinated flowers by different pollen grains and self-pollinated flowers. However, the highest fruit weight, fruit diameter and fruit volume were obtained in fruits pollinated with ‘Valencia’ orange pollen grains, and the highest percentage of juice was recorded in pollinated flowers with sour orange pollen grains (Table 1). Free-pollinated or self-pollinating flowers had the lowest values for characteristics like weight, length, diameter and volume of fruit and the percentage of fruit juice.
Based on the results of the analysis of variance, fruit length and thickness of fruit skin were significantly affected by pollen grain sources (P < 0.01 and P < 0.05). The highest fruit length and the highest thickness of fruit skin in pollinated flowers with ‘Valencia’ oranges and sour oranges were obtained, respectively. The minimum thickness of the fruit skin was estimated in pollinated flowers with ‘Hamlin’ orange pollen grains (Table 1).
Physiological characteristics
There was no significant difference between skin vividness, total phenol content, and antioxidant capacity in flowers pollinated by different pollen grains and self-pollinated flowers. The highest antioxidant capacity with the highest vividness of skin was recorded in pollinated flowers with ‘Hamlin’ orange pollen grains as well (Table 1).
Based on the results of the analysis of variance, the amount of vitamin C and SST as well as the technology index (sequentially, P < 0.01, P < 0.01 and P < 0.05) were influenced by pollen grain sources (Table 1). The highest amount of vitamin C and SST, respectively, were found in self-pollinated flowers and pollinated flowers with ‘Hamlin’ orange pollen grains. The highest technology index was recorded in pollinated flowers with sour orange and ‘Hamlin’ orange pollen grains. Also, the lowest technology index was obtained in pollinated flowers with free pollen grains.
Second experiment
Number of seed
The results of analysis of variance showed that foliar spraying with copper sulfate at different stages of flower opening had a significant effect on seed number (P < 0.01). The analysis of mean comparison showed that the seed number produced in fruits of flowers treated with copper sulfate in all stages of flower opening (30, 60 and 80 %) were less than the number of seeds produced in fruits from flowers in the control group (Table 2, Figure 3). The lowest number of seeds was obtained in ‘Yashar’ mandarin while they were treated with copper sulfate at the stage when 30 % of flowers were opening.
Table 2 Mean comparison of the effect of spraying copper sulfate (25 mg·L-1) in three times (30, 60, and 80 % flowers opening) on seed number, and some morphologic and physiologic traits of ‘Yashar’ mandarin.
| Treatment | Fruit weight (g) | Fruit length (mm) | Fruit diameter (mm) | Fruit skin thickness (mm) | Fruit volume (mL) | Seed number | Fruit juice (%) | Flesh vitamin C (mg·100 g-1) | Flesh total phenol (mg∙100 g-1) | Flesh antioxidant capacity (%) | Total soluble solids (%) | Titrable acidity (%) | Technology index | Skin vividness |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Control | 165.20 az | 60.21 a | 71.06 a | 2.58 a | 153.50 a | 25.93 a | 73.15 a | 58.19 a | 67.83 a | 0.48 a | 13.02 a | 1.86 a | 9.52 a | 59.38 bc |
| 30 | 150.40 a | 58.28 a | 67.65 ab | 2.76 a | 140.00 a | 17.48 c | 60.02 b | 47.23 a | 68.32 a | 0.60 a | 12.20 a | 1.84 a | 8.21 b | 59.95 b |
| 60 | 167.20 a | 61.44 a | 71.49 a | 2.52 a | 195.60 a | 19.05 bc | 76.42 a | 50.80 a | 85.28 a | 0.51 a | 13.10 a | 1.87 a | 10.01 a | 57.62 c |
| 80 | 140.50 a | 56.56 a | 65.04 b | 2.35 a | 121.40 a | 20.42 b | 55.62 b | 57.53 a | 81.17 a | 0.58 a | 12.99 a | 1.79 a | 7.24 b | 62.09 a |
| CV (%) | 16.09 | 3.98 | 3.23 | 13.55 | 27.90 | 5.15 | 10.21 | 22.25 | 13.80 | 29.67 | 3.44 | 4.31 | 10.61 | 1.69 |
zMeans with different letters on the same column are significantly different (Duncan, P ≤ 0.05).
Morphological characteristics
The highest fruit length, fruit weight and fruit volume were recorded in flowers sprayed with copper sulfate at the stage when 60 % of flowers were opening, y the highest fruit skin thickness was recorded in flowers sprayed at the stage when 30 % of flowers were opening (Table 2). Changes were insignificant regarding the characteristics of those products sprayed with copper sulfate and those in the control group. The lowest fruit length, fruit weight and fruit skin thickness were observed in flowers sprayed with copper sulfate in the stage when 80 % of flowers were opening.
Based on the results of the analysis of variance, fruit diameter and fruit juice percentage were significantly (P < 0.05) affected by foliar spraying with copper sulfate at different stages. The highest fruit diameter (71.49 mm) and the percentage of fruit juice (76.42 mL) were obtained in flowers sprayed with copper sulfate in the stage when 60 % of flowers were opening (Table 2). The differences were insignificant in these two characteristics of flowers sprayed with copper sulfate with the highest value and those in the control group. The lowest fruit diameter (65.04 mm) and fruit juice percentage (55.62) were recorded in flowers sprayed with copper sulfate at the stage when 80 % of flowers were opening.
Physiological characteristics
There was no significant difference between vitamin C of fruit flesh, total phenol of fruit flesh, the antioxidant capacity of fruit flesh, SST and TA of the fruit in flowers that were sprayed with copper sulfate in different stages when the different percentage of flowers were opening. However, the highest phenols of fruit flesh, SST and TA were found in flowers sprayed with copper sulfate at the stage when 60 % of flowers were opening (Table 2). The highest oxidative capacity was found in flowers sprayed with copper sulfate at the stage when 30 % of flowers were opening, and the highest amount of vitamin C was observed in the fruits of the control group.
The lowest phenol and antioxidant capacity of fruit flesh in the control group, the lowest SST and vitamin C in flowers sprayed with copper sulfate at the stage when 30 % of flowers were opening, and the lowest titrable acidity in flowers sprayed with copper sulfate at the stage when 80 % of flowers were opening were recorded (Table 2).
The flowers sprayed with copper sulfate in the stage when 60 % of the flowers were opening had the highest technology index (10.01). In comparison, the flowers sprayed with copper sulfate in the stage when 80 % of the flowers were opening had the lowest index of technology. Furthermore, the highest degree of fruit skin vividness was recorded in flowers that were sprayed with copper sulfate in the stage when 80 % of them were opening. In comparison, the lowest degree of fruit skin vividness was reported in flowers sprayed with copper sulfate at the stage when 60 % of them were opening (Table 2).
Discussion
First experiment
The direct impacts of pollen grains on fruit characteristics and seed formation were reported in other kinds of citrus. According to the results of the study of Alinezhad-Jahromi et al. (2019), the most and the least number of seeds were obtained from pollinated flowers by ‘Lisbon’ lemon pollen grains and self-pollinated flowers, respectively. According to Vithanage (1991), the self-pollinating tangor ‘Ellendale’ produced fewer fruits and seeds, while pollinating with pollen grains of ‘Murcott’ and ‘Emperor’ resulted in larger fruits with more seeds. ‘Shaddock’ fruits showed the highest number of seeds after cross-pollination with ‘Balady’ mandarin, while grapefruit-pollinated flowers had larger, heavier and highest quality (Atawia et al., 2016).
According to the outcomes of the present study, with increasing the quantity of characteristics in ‘Yashar’ mandarin, ‘Valencia’ orange and in most physiological characteristics, ‘Hamlin’ orange and sour orange are suggested as suitable pollinators. Fruits with free-pollinated or self-pollinated flowers had the lowest values in most morphological and physiological characteristics. Similar results were reported from some other citrus fruits (Talaie et al., 2002; Mesejo et al., 2013; Atawia et al., 2016; Alinezhad-Jahromi et al., 2019). The type of pollen grain plays an important role in the number of seeds produced in hybrid fruits and the quantitative and qualitative characteristics of the fruit (Atawia et al., 2016; Alinezhad-Jahromi et al., 2019).
Direct impacts of pollen grain sources on qualitative fruit characteristics of other citrus fruits including C. reticulata (Wallace & Lee, 1999), C. aurantifolia ‘Swingle’ (Kitat et al., 1994), C. maxima (Atawia et al., 2016) and Citrus tangerina ‘Clementine’ (Alinezhad-Jahromi et al., 2019) were reported. The impacts of different pollen grains on the quantitative and qualitative characteristics of ‘Yashar’ mandarin and other citrus fruits can be attributed to the phenomena of xenia and metaxenia.
The sour orange and ‘Duncan’ grapefruit pollen had more impacts on increasing the average length of ‘Page’ mandarin in comparison with the pollinating with the pollen grains of local mandarin, sweet lemon, ‘Hamlin’ orange and ‘Mars’ orange. The effect of ‘Duncan’ grapefruit pollen grain on the enhancement of SST in ‘Page’ mandarin fruit was higher than the pollen grain effect of ‘Mars’ orange, sour orange and sweet lemon (Golein et al., 2012). The impacts of pollination with different citrus seeds on quantitative characteristics such as weight, volume, length, the diameter of the fruit and fruit skin thickness had been shown (Golein et al., 2012).
Manual cross-pollination of ‘Clementine’ mandarin with a cluster lemons pollen increased the TSS in ‘Clementine’ mandarins compared to pollination with pollen grains of frost ‘Valencia’ orange, ‘Siaervaz’ local orange and sweet lemon (Alinezhad-Jahromi et al., 2019).
The technology index is an important indicator in the citrus industry. A higher amount of it shows the better quality of produced fruit juice, and it also indicates its suitability for conversion industries (Kluge, 2003). Due to the high technology index and the ripening time of ‘Yashar’ mandarin, it proves that it is the best for conversion industries. The effect of ‘Salustiana’ orange, ‘Siaervaz’ orange, and ‘Shel Mahaleh’ natural hybrid pollen has impacts on the increment of the vitamin C in ‘Page’ mandarin more than the effect of pollen grains of sweet lemons, local mandarin, sour oranges, ‘Duncan’ grapefruit, and ‘Hamlin’ oranges (Golein et al., 2012).
Second experiment
In the present study, the positive effect of foliar spraying of copper sulfate on reducing the number of seeds in ‘Yashar’ mandarin was demonstrated. Foliar spraying at a concentration of 25 mg·L-1 copper sulfate on the ‘Afourer’ mandarin tree at full flowering stage, decreased the number of seeds in each fruit and increased the percentage of seedless fruits (Mesejo et al., 2013). Copper sulfate treatment on ‘Shiraz’ black grape cultivar reduced the percentage of becoming seedless compared to the control group; besides, it increased vitamin C (Kyamarsi & Eshghi, 2011). In some studies, enhancement in seedless fruit percentage was reported while they are sprayed with copper sulfate (Ikeda, Ishikawa, Yazawaand, & Baba, 2002).
Foliar spraying with copper sulfate reduced the size and weight of some fruits, including grapes and wheat (Kyamarsi, & Eshghi, 2011; Yadavi, Maghsoudi, & Janzadeh-Deh Sheikh, 2019). Since, gibberellin is also produced in seeds, the reduction of seeds in the fruit has a negative effect on the production of gibberellin; in this regard, the reduction of seeds reduces the production and effect of gibberellin hormone; thus, it will reduce the weight and size of the fruit (Kyamarsi, & Eshghi, 2011). Applying copper sulfate in wheat reduced seedling weight and increased the amount of TSS in the fruit (Yadavi et al., 2019).
The use of copper in some plants stimulated the production of various secondary metabolites (Bamneshin, Hatamzadeh, Naqavi, & Mirjalili, 2019). Accordingly, copper has direct and indirect impacts on different genetic and epigenetic stages, and it causes changes in the quantitative and qualitative characteristics of plants.
Conclusions
The result of current study demonstrated that ‘Valencia’ orange pollen grains produced ‘Yashar’ mandarin fruits with fewer seeds. The number of seeds produced in fruits of foliar sprayed flowers with copper sulfate at all stages when flowers were opening was less than the number of seeds in fruits of the control group (not being foliar sprayed with copper sulfate). The lowest number of seeds was obtained in ‘Yashar’ mandarin sprayed with copper sulfate when 30 % of flowers were opening.
In designing the ‘Yashar’ mandarin garden, it is necessary to evaluate the appropriate distance of this tree from other citrus trees. Also, the pollinators and other factors affecting pollination in the garden should be carefully managed.
