Abstract
Fruit drop from pear trees causes serious losses in income. However, the application of plant bio-regulators improves the internal physiology of developing fruit by ensuring that they receive an adequate supply of water, nutrients, and other compounds necessary for their proper growth and development, which leads to improved size, quality, and ultimately better yield in a variety of fruit crops. This study investigated the foliar application of three plant growth regulators: CPPU at 10, 15, and 20 ppm, GA3 at 25, 50, and 75 ppm and NAA at 25, 50, and 75 ppm. The pear trees were sprayed four times: before flowering, full bloom, after three weeks, and after six weeks. The results showed that the spray of GA3 at 50 and 75 ppm gave the highest effect in increasing the shoot length, shoot thickness, leaf area, and leaf total chlorophyll. The spraying of NAA at 50 and 75 ppm was the best treatment in increasing the fruit set percentages, fruit yield, fruit weight, and fruit dimensions as well as the fruit content from soluble solids, and fruit sugars, while they reduced the fruit drop percentages comparing with the other applied treatments.
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Improving the Productivity and Reducing the Drop Percentages of Fruits in Pear by the External Application of Some Plant Growth Regulators
Adel M. Al-Saif,a,* Lidia Sas-Paszt,b Ahmed Ayoub,c Hesham S. Abada,d and Walid F. A. Mosa e
Fruit drop from pear trees causes serious losses in income. However, the application of plant bio-regulators improves the internal physiology of developing fruit by ensuring that they receive an adequate supply of water, nutrients, and other compounds necessary for their proper growth and development, which leads to improved size, quality, and ultimately better yield in a variety of fruit crops. This study investigated the foliar application of three plant growth regulators: CPPU at 10, 15, and 20 ppm, GA3 at 25, 50, and 75 ppm and NAA at 25, 50, and 75 ppm. The pear trees were sprayed four times: before flowering, full bloom, after three weeks, and after six weeks. The results showed that the spray of GA3 at 50 and 75 ppm gave the highest effect in increasing the shoot length, shoot thickness, leaf area, and leaf total chlorophyll. The spraying of NAA at 50 and 75 ppm was the best treatment in increasing the fruit set percentages, fruit yield, fruit weight, and fruit dimensions as well as the fruit content from soluble solids, and fruit sugars, while they reduced the fruit drop percentages comparing with the other applied treatments.
DOI: 10.15376/biores.19.3.5880-5894
Keywords: GA3; NAA; Fruit set; Pyrus communis; Yield; Fruit quality
Contact information: a: Department of Plant Production, College of Food and Agriculture Sciences, King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia; b: The National Institute of Horticultural Research, Konstytucji 3 Maja 1/3, 96-100 Skierniewice, Poland; c: Project Management Department, Arid Lands Cultivation Research Institute (ALCRI), City of Scientific Research and Technological Applications (SRTA-City), New Borg Al-Arab City, Egypt; d: Plant Production Department, Arid Lands Cultivation Research Institute, City of Scientific Research and Technological Applications (SRTA-City), New Borg El-Arab City 21934, Egypt; e: Plant Production Department (Horticulture-Pomology), Faculty of Agriculture, Saba Basha, Alexandria University, Alexandria 21531, Egypt;
* Corresponding Author: adelsaif@ksu.edu.sa
INTRODUCTION
Pear (Pyrus communis L.) belongs to the Rosaceae family and the Pyrus genus, which includes twenty-two species found in Asia, Europe, and northern Africa. ‘Le-Conte’ is the essential pear cultivar grown in Egypt and it resulted from a hybridization between Pyrus communis x Pyrus serotina. It is one of the most important pear trees in the world, and it is cultivated in whole temperate-zone countries. The cultivated area in Egypt is approximately 5154 hectares, which has resulted in approximately 74,000 tons (FAO 2021). The productivity of pear cv. ‘Le-Conte’ in Egypt changes from year to year, and this may be as a result of a reduction in ovules viability and stigma receptivity, pollen development rates, ovule abortion, increased flower abscission, and reduced fruit reservation (Yehia and Hassan 2005). In general, pear is the 3rd largest crop from the cultivated area among the deciduous fruit trees.
Plant growth regulators (PGRs) play a vital part in improving horticultural crops’ yield and fruit quality (Velasquez et al. 2016). The exogenous spraying of PGRs is used often to improve the fruit size, increase the cell division, and minimize the fruit number by encouraging flower formation and reducing the flower and fruit shedding (Davenport 2011; Agustí et al. 2022). Additionally, they are organic chemical compounds, which regulate the plant’s physiological processes when they are applied in small concentrations, where they can induce the fruit set, minimize the fruit drop and raise the productivity and quality characteristics (Bons and Kaur 2020). PGRs are also signaling molecules that influence fruit growth, blooming rates, and plant cell division (Cutler and Nelson 2017; Talat et al. 2020).
CPPU (Sitofex) is a synthetic cytokinin that plays a paramount role in increasing fruit size by inducing cell division or cell increase in many fruits such as sweet cherry, apple, kiwifruit, grape, and pear (Zhang and Whiting 2011). Cytokinins have the ability to increase the fruit soluble solids and reduce the coloration of the exocarp. As cytokinins induce the growth of the floral meristem, it increases the flower number (Li et al. 2019). Aremu et al. (2020) found that cytokinins are critical for enhancing fruit development, floral and fruit growth, and fruit weight. They also help to preserve and enhance the texture, flavour, and aroma of fruit in a variety of fruits, including raspberries, kiwis, litchi, grapes, sweet cherries, and strawberries.
Gibberellins have the ability to ameliorate the fruit set percentages and growth in apple (Watanabe et al. 2008). Moreover, they are mostly applied to reduce the drop percentage and to increase the quality of fruit (Kumari et al. 2018). Aremu et al. (2020) reported that gibberellins enhance physiological functions such as fruit production, flower initiation, leaf elongation, and stem development. By promoting photosynthetic enzymes and increasing the efficacy of mineral utilization, they also enhance the process of photosynthesis. Additionally, they noticed that in grapes, sweet cherries, strawberries, kiwifruit, and raspberries, gibberellins improve fruit set percentages, growth, size, fruit preservation, and fruit quality attributes, such as fruit weight, hardness, length, and diameter.
As a broad-spectrum regulator of plant growth, NAA is an auxin analogue that stimulates cell division and expansion (Gill and Bal 2009). The synthetic auxin NAA helps to promote root development, vascular tissue differentiation, cell lengthening, apical control, fruit setting percentage, and the prevention of leaf or fruit loss (Mehraj et al. 2015). Additionally, the foliar spraying of NAA at 25 to 50 ppm on apple markedly enhanced the fruit set and retention (Osama et al. 2015). It is mostly utilized to improve the production of strawberries like improving the fruit from total sugars, ascorbic acid, and on the opposite side to lessen the titratable acidity (Bhople et al. 2020). So, the purpose of this study was to find out how foliar application of CPPU, GA3, and NAA could improve vegetative growth, and increase fruit set percentages, productivity, and quality while decreasing fruit drop percentages.
EXPERIMENTAL
Treatments, Location and Design
The experiment was conducted in 2022 and 2023 on 10-year-old pear trees (Pyrus communis L.) budded on Pyrus betulifolia rootstock. The trees were planted at 4*4 meters in sandy soil within a private orchard under drip irrigation, in Nubaria region, El-Beheira governorate, Egypt. The analysis of the soil is shown in Table 1 (Sparks et al. 2020).
Table 1. Physiochemical Soil Analysis
Sixty uniform trees, selected for their similar growth and size, received consistent agricultural practices throughout the two-year experiment. The trees were sprayed four times: before flowering, during full bloom, three weeks after the full bloom spray, and three weeks after the third spray, using water as the control, 10, 15 and 20 ppm CPPU, 25, 5 and 75 ppm GA3 and 25, 50, and 75 ppm NAA. The trees were randomly distributed and arranged in a Randomized Complete Block Design (RCBD) in six replicates (six trees).
Vegetative Parameters
At the end of the vegetative time, the shoot diameter was in cm and the shoot thickness was measured by using a vernier caliper. Total chlorophyll (SPAD) was measured in fresh leaves by taken from 10 mature leaves located in the middle section of the shoots surrounding the trees. The average leaf area (cm²) was determined using the below equation (Mosa et al. 2022),
LA = 0.70 (L × W) – 1.06 (1)
where LA is the leaf area, L is the leaf length, and W is the leaf width.
Fruit Set Percentages and Fruit Drop Percentages
In March of 2022 and 2023, four carefully selected branches from each side of the experimental trees were labeled, and the number of blooms on each branch was recorded. The fruit set percentage was then calculated using Eq. 2 (El-Hady et al. 2007).
(2)
By computing the quantity of dropped fruits from fruit planting until the harvesting date in June of each year, pre-harvest fruit drops were estimated. Next, the fruit drop’s proportion was determined using the formula below.
(3)
Fruit Yield
During the July 2022 and 2023 seasons, the yield in kg for each tree was weighted and then by multiplying the yield of the tree * the number of trees in a hectare to calculate the yield of hectare in ton.
Fruit Quality
Fruit physical characteristics
Thirty fruits were randomly selected from each replicate (tree). Measurements were made of the average of their weight (g), fruit length, and fruit diameter by using a vernier caliper. Fruit firmness (Ib/inch²) was determined using a Magness and Taylor pressure tester equipped with a 7/18-inch plunger. Fruit size (cm³) was assessed by measuring the volume of displaced water after immersing the fruit.
Fruit chemical characteristics
Total soluble solids percentages were measured by using the hand refractometer (ATAGO Co. LTD., Tokyo, Japan). Ascorbic acid content (VC) in the juice was assessed through titration with 2,6-dichloro phenol-indo-phenol and expressed in milligrams per 100 mL of juice. Total and reducing sugars were quantified calorimetrically using the Nielsen’s method (Nielsen 2010). Non-reduced sugars percentage is the difference between total sugars and reduced sugars. Fruit acidity, expressed as a percentage of malic acid content, was determined in fruit juice through titration with 0.1 N sodium hydroxide, using phenolphthalein as an indicator (A.O.A.C. 2005).
Mineral content in the apricot leaves
From the middle part of the shoots, 30 leaves were collected in July after fruit picking from each tree (Arrobas et al. 2018) to analyze macronutrients (nitrogen, phosphorus, potassium) and micronutrients (iron, zinc, manganese, boron). The leaves were washed with tap water, then distilled water, and dried in an oven at 70 °C until they reached a consistent weight before being thoroughly crushed. The samples were then digested using 2 mL of H2SO4 and H2O2. The nitrogen content in the leaves was measured using the micro-Kjeldahl method (Wang et al. 2016). Phosphorus was determined by the Vanadomolybdate method (Weiwei et al. 2017), and potassium was assessed using a flame photometer (SKZ International Co., Ltd., Jinan Shandong, China) (Chapman 2021). The concentrations of zinc, manganese, and iron were measured with an Atomic Absorption Spectrophotometer, while boron was quantified using a spectrophotometer at 430 nm.
Statistical analysis
The results were statistically analyzed using One Way ANOVA for a Randomized Complete Block Design (RCBD). The means of the treatments were compared using the Least Significant Difference at 0.05 (LSD0.05) (Snedecor and Cochran 2021).
RESULTS AND DISCUSSION
Vegetative Growth Parameters
Table 2 reveals that external application of CPPU, GA3, and NAA on pear trees can enhance shoot length, thickness, leaf area, and total chlorophyll content compared to unsprayed trees. The highest significant improvements were observed with foliar spraying of GA3 at 75 ppm, followed by 50 ppm. Moreover, spraying pear trees with 75 ppm NAA and CPPU at 20 ppm significantly increased these vegetative parameters. The differences between the influence of 75 and 50 ppm from GA3 were not significant in the shoot length and leaf total chlorophyll in both seasons and also there were insignificant differences between them in the first season in shoot thickness, and leaf are but in the second seasons the differences were significant.
Table 2. Effect of the Foliar Spraying of CPPU, GA3, and NAA on Shoot Length, Shoot Thickness, Leaf Area, and Leaf Total Chlorophyll of Pear Trees during 2022 and 2023
The treatments with the same letters in each column do not significantly differ from one another.
Fruit Set and Fruit Drop Percentages, and Fruit Number
Table 3 indicates that the application of plant growth regulators such as NAA, GA3, and CPPU enhanced both the fruit set percentages and the number of fruits while decreasing the rate of fruit drop across both experimental seasons. Furthermore, the application of 75 ppm NAA resulted in the most obvious increases in both fruit set percentages and fruit numbers, proving to be the most effective treatment across both experimental seasons.
Table 3. Effect of the Foliar Spraying of CPPU, GA3 and NAA on Fruit Set and Fruit Drop Percentages and Fruit Number per Tree of Pear Trees during 2022 and 2023
The treatments with the same letters in each column do not significantly differ from one another.
This treatment also notably reduced the percentage of fruit drop during the two testing periods. Additionally, significant improvements in fruit quantity and fruit set ratio were achieved compared to untreated trees through the foliar applications of 50 ppm NAA, as well as 75 and 50 ppm GA3, and 20 ppm CPPU throughout both seasons. The reduction in fruit drop percentage by 50 and 75 ppm NAA was similarly effective across the two seasons.
Fruit Weight and Fruit Yield
Table 4 shows that, across both seasons, foliar applications of 75, 50, and 25 ppm NAA, 75 and 50 ppm GA3, and 10, 15, and 20 ppm CPPU significantly increased fruit weight and yield, both in kg per tree and tonnes per hectare when compared to untreated trees.
Additionally, the spraying of 75 ppm NAA was the superior treatment that gave the highest notable increments in both studying seasons over the other sprayed treatments. The spraying of 50 ppm NAA, 75 GA3 and 20 ppm CPPU were more efficient in increasing the fruit weight, and fruit yields in kg or ton rather than the other sprayed treatments.
Table 4. Effect of the Foliar Spraying of CPPU, GA3, and NAA on Fruit Weight, Fruit Yield in kg and in ton per Hectare of Pear Trees during 2022 and 2023
The treatments with the same letters in each column do not significantly differ from one another.
Fruit Quality
Physical fruit characteristics
According to Table 5, the application of 75 and 50 ppm NAA, 75 and 50 ppm GA3, and 20 and 15 ppm CPPU significantly enhanced the physical characteristics of the fruits, including size, length, and firmness, compared to trees that were not sprayed across the two seasons.
The most significant increments in these parameters were significantly noticed when the trees were sprayed at 75 ppm NAA in the two seasons. The fruit diameter was remarkably increased by the spraying of the pear trees with 75, 50, and 25 ppm NAA and 20 ppm CPPU significantly improved it in the two seasons.
Table 5. Effect of the Foliar Spraying of CPPU, GA3, and NAA on Fruit Size, Length, Diameter and Firmness of Pear Trees during 2022 and 2023
The treatments with the same letters in each column do not significantly differ from one another.
Fruit chemical characteristics
In comparison to the trees that were not sprayed throughout the two seasons, the findings in Table 6 showed that the foliar spraying of NAA, GA3, and CPPU significantly increased the fruit content from TSS percentages and from vitamin C. Additionally, the treating of pear trees with 75 ppm NAA, 75 ppm GA3 and 20 ppm CPPU gave the highest remarkable values in the fruit content from soluble solids in the two seasons. The application of 75 and 50 ppm from NAA and also 20 ppm CPPU extremely increased the fruit content from vitamin C during two test seasons. Concerning the fruit content from acidity, it was noticed that it was notably minimized by the spraying of 25, 50, and 75 ppm NAA, 50 and 75 ppm GA3, and 15 or 20 ppm CPPU with respect to not treated trees.
Table 6. Effect of the Foliar Spraying of CPPU, GA3 and NAA on Fruit Content from Soluble Solids, Acidity and VC of Pear Trees during 2022 and 2023
The treatments with the same letters in each column do not significantly differ from one another.
Total and reduced sugars percentages were markedly increased by spraying the pear trees with 50 and 75 ppm NAA, 50 and 75 ppm GA3, and 15 and 20 ppm comparing with untreated trees in 2022 and 2023 (Table 7). Moreover, the notable and most significant percentages were obtained by the spraying of pear trees with 75 ppm NAA, then by 50 NAA, 75 ppm GA3, and 20 ppm in both experimental seasons. Moreover, the differences between the effects of 50 ppm NAA, 75 ppm GA3, and 20 ppm CPPU were not significant on the fruit content from total and reducing sugars content in both testing season. Non-reducing sugars content in pear fruits were not significantly affected by the spraying of the foliar application of the tree applied PGRs compared to untreated trees.
Table 7. Effect of the Foliar Spraying of CPPU, GA3 and NAA on Fruit Content from Total, Reduced, and Non-Reduced Sugars of Pear Trees during 2022 and 2023
The treatments with the same letters in each column do not significantly differ from one another.
Mineral Content from Macro and Micronutrients
Leaf mineral content from macronutrients such as nitrogen, phosphorous, and potassium was positively affected by the spraying of NAA, GA3 and CPPU in the two seasons (Table 8).
Table 8. Effect of the Foliar Spraying of CPPU, GA3 and NAA on the Leaf Mineral Content from Nitrogen, Phosphorous and Potassium of Pear Trees during 2022 and 2023
The treatments with the same letters in each column do not significantly differ from one another.
The most significant increment was obtained by the spraying of 75 ppm NAA compared to untreated trees. Spraying the pear trees with 25 and 50 ppm GA3, 50 and 75 ppm, as well as 15 and 20 ppm significantly increased the leaf content of nitrogen compared to the control. The phosphorous concentration in the leaves of pear was markedly increased by the spraying of 75 ppm GA3 and 20 ppm CPPU as compared to the control. The potassium percentage was remarkably increased by the spraying of 20 ppm CPPU, 50 and 75 ppm GA3, and 50 ppm NAA as compared to untreated trees.
Table 9 demonstrates that the foliar application of 50 and 75 ppm NAA, 50 and 75 ppm GA3, and 20 ppm CPPU significantly enhanced the leaf content from Fe, Zn, Mn, and B compared to untreated trees. The most effective treatment, yielding the best results, was the application of 75 ppm NAA, which outperformed the other treatments. Conversely, the effects of spraying 25 ppm NAA, 25 ppm GA3, and 15 and 10 ppm CPPU on increasing leaf nutrient content were not significant in the years 2022 and 2023.
Table 9. Effect of the Foliar Spraying of CPPU, GA3, and NAA on the Leaf Mineral Content from Iron, Zinc, Manganese, and Boron of Pear Trees during 2022 and 2023
The treatments with the same letters in each column do not significantly differ from one another.
DISCUSSION
The data showed that CPPU, GA3, and NAA external spraying was beneficial for enhancing pear tree vegetative growth, fruit set percentages, fruit productivity, fruit quality, and nutritional status.
These findings align with those of Guirguis et al. (2003), which indicated that applying a 20 ppm CPPU treatment at full bloom significantly increased both the fruit set percentage and fruiting. The treatment of CPPU at 10 mg/L on blueberries cv. ‘Elliott’ during 10 to 15 days after 50% bloom revealed a remarkable increase in fruit set and berry size (Serri and Hepp 2006). Xiao et al. (2007) indicated that the spraying of CPPU at 10 to 25 mg/L after full bloom on Diospyros Kaki cv. ‘Zenjimaru’ increased the fruit weight, as well as fruit content by reducing TSS content TSS-acid ratio, and starch degradation. CPPU effectively increased fruit weight in pear and kiwifruit by encouraging cell division and growth (Zhang et al. 2008). Banyal et al. (2013) reported that applying CPPU to Royal Delicious apple trees when the fruit size reaches 10 mm significantly improves fruit set and retention, reduces fruit drop, and maximizes both fruit weight and yield. This treatment also enhances fruit size and overall quality, particularly in terms of fruit weight, compared to other treatments examined in the study. Cytokinin induces the prolongation of inflorescences and the flooring meristems by enhancing the flower number and developing the flower formation as well as raising the sing flower number (Li et al. 2019). Banyal and Banyal (2020) stated that CPPU effectively promotes cell division and elongation, leading to increased fruit weight and productivity. Apricot trees of the Zaghinia cultivar, treated with 0, 7.5, and 15 mg/L Sitofex, showed significant increases in fruit set percentage, productivity, fruit weight, firmness, and size. Additionally, there were notable enhancements in the fruit content of TSS, and TSS-TA ratio (Medan and Al Douri 2021).
GA3 directly organizes the elongation, extension, and development of the plant cells consequently increasing the fruit length and diameter of the olive fruits (Ramezani et al. 2010). The external spraying of GA3 resulted in greater shoots, leaves, stems and roots by stimulating cell expansion and division in numerous plants (Bose et al. 2013). The external application of GA3 ameliorates cell extension (Erogul and Sen 2015) and fosters fruit mineral absorption (Fortes et al. 2015), and cell divide (Zhang et al. 2020), which consequently increases the fruit weight and its size. Ozkan et al. (2016) documented that the use of GA3 substantially enhanced pollen grain germination and the growth of pollen tubes. The external application of GA3 affects the hormonal balance in the plants, fruit growth and seed formation (Zang et al. 2016). Additionally, the same authors reported that spraying rabbiteye blueberry with GA3 at 500 mg/L dramatically raised return bloom, inflorescences number, area, leaf fresh weight, photosynthetic rate, fruit weight, and number of fruitful seeds. Additionally, GA3 can increase the fruit size, fruit firmness, vitamin C, TSS, total sugars, and sweetness indicators of apple (Hajam et al. 2017). The usage of GA3 is very important in the transport from the vegetative to the propagative phase and this consequently is paramount for the development of the flowers, fertilization, and fruit growth (Plackett and Wilson 2018; Prakash et al. 2022). GA3 can stimulate fruit development by precisely promoting cell expansion (Khan et al. 2020; Zhang et al. 2020). GA3 promotes cell extension, division, and fruit growth by regulating various cellular activities, including protein synthesis, the efficacy of photosynthesis, nutrient absorption, phytohormonal equilibrium, and antioxidant defense mechanisms (Gacnik et al. 2021; Talaat et al. 2023). The foliar application of GA3 on olive promoted cell enlargement and mesocarp development, which reflected in increasing the fruit quality (Yadav et al. 2021).
NAA has the ability to encourage cell elongation in mesocarp cells, thus increasing fruit size and yield (Stern et al., 2007). Additionally, Agrawal and Dikshit (2008) indicated that the exo spray of NAA raised the fruit’s weightiness and productivity because it can activate cell prolongation, vacuole size, and cell wall flexibility. Anawal et al. (2015) reported that external spraying of 40 ppm NAA on pomegranate cv. ‘Bhagwa’ significantly enhanced the fruit weight, number, length, diameter, volume, soluble solids, and total, reducing, and non-reducing sugars compared to untreated trees. NAA has the ability to encourage the rapid formation of roots in the cuttings of many crops such as vines (Rademacher 2015). The effectiveness of NAA on plant growth is largely attributed to increased cellulose production and reduced fruit drop (Suman et al. 2017). The foliar spray of NAA can improve the fruit quality and productivity in numerous fruit crops; plums, blueberries, guavas, and berry (Singh et al. 2017; Milić et al. 2018). Besides, NAA is crucial in preventing preharvest fruit drop percentage, promoting cell division, elongation, and membrane permeability, and enhancing flowering rates, fruit productivity, and fruit size (Thiruppathi 2020).
CONCLUSIONS
- Spraying of plant growth regulators (PGRs) greatly reduced the fruit drop and thus improved the obtained yield and its productivity per hectare.
- The most notable influence resulted from the spraying of 75 ppm NAA in improving the fruit set percentages, reducing the fruit drop percentages, and raising fruit productivity in the 2022 and 2023 seasons.
- The exogenous application of 50 NAA, 75 GA3 and 20 ppm CPPU were also effective treatments in reducing the fruit drop and raising the fruit yield compared to the not sprayed trees.
ACKNOWLEDGMENTS
The authors extend their appreciation to the Researchers Supporting Project number (RSP2024R334), King Saud University, Riyadh, Saudi Arabia.
FUNDING
This research was funded by Researchers Supporting Project number (RSP2024R334), King Saud University, Riyadh, Saudi Arabia.
REFERENCES CITED
Agrawal, S., and Dikshit, S. (2008). “Studies on the effect of plant growth regulators on growth and yield of sapota (Achras sapota L.) cv. Cricket Ball,” Indian Journal of Agricultural Research 42(3), 207-211.
Agustí, M., Reig, C., Martínez-Fuentes, A., and Mesejo, C. (2022). “Advances in citrus flowering: A review,” Frontiers in Plant Science 13, article 868831. DOI: 10.3389/fpls.2022.868831
Anawal, V. V., Narayanaswamy, P., and Ekabote, S. D. (2015). “Effects of plant growth regulators on fruit set and yield of pomegranate cv. Bhagwa,” International Journal of Scientific Research 9(4), 220-222.
Aremu, A. O., Fawole, O. A., Makunga, N. P., Masondo, N. A., Moyo, M., Buthelezi, N. M., Amoo, S. O., Spíchal, L., and Doležal, K. (2020). “Applications of cytokinins in horticultural fruit crops: Trends and future prospects,” Biomolecules 10(9), article 1222. DOI: 10.3390/biom10091222
Arrobas, M., Afonso, S., and Rodrigues, M. Â. (2018). “Diagnosing the nutritional condition of chestnut groves by soil and leaf analyses,” Scientia Horticulturae 228, 113-121. DOI: 10.1016/j.scienta.2017.10.027
Association of Official Analytical Chemists-International, A.O.A.C. (2005). “Official Methods of Analysis. 18th Ed., W. Hortwitz, and G. W. Latimer (eds.), AOAC-Int. Suite 500, 481 North Frederick Avenue, Gaithersburg, Maryland 20877–2417, USA.
Banyal, A. K., and Banyal, S. K. (2020). “Forchlorfenuron (CPPU): A promising plant growth regulator augments fruit size, fruit weight, quality and yield of kiwifruit (Actinidia deliciosa) cv. Hayward,” International Journal of Current Microbiology and Applied Sciences 9, 2091-2101. DOI: 10.20546/ijcmas.2020.905.240
Banyal, A. K., Raina, R., and Kaler, R. K. (2013). “Improvement in fruit set, retention, weight and yield of apple cv. Royal delicious through foliar application of plant growth regulators,” Journal of Krishi Vigyan 2(1), 30-32.
Bhople, A.A., Kullarkar, P.P., Singh, S.K., Singh, S.K., and Saxena, D. (2020). “Studies on impact of growth regulators on performance of strawberry cv. Camarosa under polyhouse condition”, Annals of Agri Bio Research 25 (2), 234-238.
Bons, H. K., and Kaur, M. (2020). “Role of plant growth regulators in improving fruit set, quality and yield of fruit crops: A review,” The Journal of Horticultural Science and Biotechnology 95(2), 137-146. DOI: 10.1080/14620316.2019.1660591
Bose, S. K., Yadav, R. K., Mishra, S., Sangwan, R. S., Singh, A., Mishra, B., Srivastava, A., and Sangwan, N. S. (2013). “Effect of gibberellic acid and calliterpenone on plant growth attributes, trichomes, essential oil biosynthesis and pathway gene expression in a differential manner in Mentha arvensis L,” Plant Physiology and Biochemistry 66, 150-158. DOI: 10.1016/j.plaphy.2013.02.011
Chapman, D. (2021). Water Quality Assessments: A Guide to the Use of Biota, Sediments and Water in Environmental Monitoring (2nd ed.), CRC Press, Boca Raton, FL, USA. DOI: 10.1201/9781003062103
Cutler, S. R., and Nelson, D. C. (2017). “Plant hormones,” in eLS (pp. 1-11), Wiley. DOI: 10.1002/9780470015902.a0002091.pub2
Davenport, T. L. (2011). “Citrus flowering,” Horticultural Reviews 12, 349-408. DOI: 10.1002/9781118060858.ch8
El-Hady, S., Eman, L.; Haggag, M., Abdel-Migeed, M., and Desouky, I. (2007). “Studies on sex compatibility of some olive cultivars,” Research Journal of Agriculture and Biological Sciences 3, 504-509. Available online: https://www.researchgate.net/ publication/281265322.
Erogul, D., and Sen, F. (2015). “Effects of gibberellic acid treatments on fruit thinning and fruit quality in Japanese plum (Prunus salicina Lindl.),” Scientia Horticulturae 186, 137-142. DOI: 10.1016/j.scienta.2015.02.019
FAO (2021). “Food and Agriculture Organization of the United Nations,” Available online: http://faostat-fao.org (accessed on 19 December 2021).
Fortes, A. M., Teixeira, R. T., and Agudelo-Romero, P. (2015). “Complex interplay of hormonal signals during grape berry ripening,” Molecules 20(5), 9326-9343. DOI: 10.3390/molecules20059326
Gacnik, S., Veberič, R., Hudina, M., Marinovic, S., Halbwirth, H., and Mikulič-Petkovšek, M. (2021). “Salicylic and methyl salicylic acid affect quality and phenolic profile of apple fruits three weeks before the harvest,” Plants 10(9), article 1807. DOI: 10.3390/plants10091807
Gill, P., and Bal, J. (2009). “Effect of growth regulator and nutrients spray on control of fruit drop, fruit size and quality of ber under sub-montane zone of Punjab,” Journal of Horticultural Sciences 4(2), 161-163. DOI: 10.24154/jhs.v4i2.536
Guirguis, N., Attala, E. S., and Ali, M. (2003). “Effect of Sitofex (CPPU) on fruit set, fruit quality of Le Conte pear cultivar,” Annals of Agricultural Sciences Moshtohor, 41(1), 271-282.
Hajam, M. A., Hassan, G., Bhat, T., Bhat, I., Rather, A., Parray, E., Wani, M., and Khan, I. (2017). “Understanding plant growth regulators, their interplay: For nursery establishment in fruits,” International Journal of Chemical Studies 5(5), 905-910.
Khan, A., Bilal, S., Khan, A. L., Imran, M., Shahzad, R., Al-Harrasi, A., Al-Rawahi, A., Al-Azhri, M., Mohanta, T. K., and Lee, I.-J. (2020). “Silicon and gibberellins: Synergistic function in harnessing ABA signaling and heat stress tolerance in date palm (Phoenix dactylifera L.),” Plants 9(5), 620. DOI: 10.3390/plants9050 620
Kumari, S., Bakshi, P., Sharma, A., Wali, V., Jasrotia, A., and Kour, S. (2018). “Use of plant growth regulators for improving fruit production in sub-tropical crops,” International Journal of Current Microbiology and Applied Sciences 7(3), 659-668. DOI: 10.20546/ijcmas.2018.703.077
Li, S.-j., Xie, X.-l., Liu, S.-c., Chen, K.-s., and Yin, X.-r. (2019). “Auto-and mutual-regulation between two CitERFs contribute to ethylene-induced citrus fruit degreening,” Food Chemistry 299, article 125163. DOI: 10.1016/j.foodchem. 2019.125163
Medan, R. A., and Al Douri, E. S. (2021). “Improving the productivity of Zaghinia apricot trees by foliar application of Sitofex and L-arginine,” Annals of the Romanian Society for Cell Biology 25(6), 7066-7075.
Mehraj, H., Taufique, T., Ali, M., Sikder, R., and Jamal Uddin, A. (2015). “Impact of GA3 and NAA on horticultural traits of Abelmoschus esculentus,” World Applied Sciences Journal 33(11), 1712-1717. DOI: 10.5829/idosi.wasj.2015.33.11.12590
Milić, B., Tarlanović, J., Keserović, Z., Magazin, N., Miodragović, M., and Popara, G. (2018). “Bioregulators can improve fruit size, yield and plant growth of northern highbush blueberry (Vaccinium corymbosum L.),” Scientia Horticulturae 235, 214-220. DOI: 10.1016/j.scienta.2018.03.004
Mosa, W. F., Abd EL-Megeed, N. A., Ali, M. M., Abada, H. S., Ali, H. M., Siddiqui, M. H., and Sas-Paszt, L. (2022). “Preharvest foliar applications of citric acid, gibberellic acid and humic acid improve growth and fruit quality of ‘Le Conte’pear (Pyrus communis L.),” Horticulturae 8(6), 507. DOI: 10.3390/horticulturae80 60507
Nielsen, S. S. (2010). “Phenol-sulfuric acid method for total carbohydrates,” in: Food Analysis Laboratory Manual, S. S. Nielsen, (ed.), Food Science Texts Series, Springer, Boston, MA. DOI: 10.1007/978-1-4419-1463-7_6. 47-53.
Osama, H., Amro, E., and Saber, M. (2015). “Effect of growth regulator, antioxidant and application date on fruiting and fruit quality of mango trees cv. Keitt,” Journal of Agriculture and Veterinary Science 8(12), 87-95. DOI: 10.9790/2380-081218795
Ozkan, Y., Ucar, M., Yildiz, K., and Ozturk, B. (2016). “Pre-harvest gibberellic acid (GA3) treatments play an important role on bioactive compounds and fruit quality of sweet cherry cultivars,” Scientia Horticulturae 211, 358-362. DOI: 10.101 6 /j.scienta.2016.09.019
Plackett, A. R., and Wilson, Z. A. (2018). “Gibberellins and plant reproduction,” Annual Review of Plant Biology, 323-358. DOI: 10.1002/9781119312994.apr0540
Prakash, R., Jokhan, A. D., and Singh, R. (2022). “Effects of foliar application of gibberellic acid, boric acid and sucrose on noni (M. citrifolia L.) fruit growth and quality,” Scientia Horticulturae 301, article 111098. DOI: 10.1016/j.scienta.2022. 111098
Rademacher, W. (2015). “Plant growth regulators: Backgrounds and uses in plant production,” J. Plant Growth Regul. 34, 845-872. DOI: 10.1007/s00344-015-9541-6
Ramezani, S., Shekafandeh, A., and Taslimpour, M. R. (2010). “Effect of GA3 and zinc sulfate on fruit yield and oil percentage of ‘Shengeh’olive trees,” International Journal of Fruit Science 10(3), 228-234. DOI: 10.1080/15538362.2010. 510418
Serri, H., and Hepp, F. (2006). “Effect of the growth regulator cppu on fruit quality and fruit ripening of highbush blueberries,” Acta Horticulturae 715, 279-283. DOI: 10.17660/ ActaHortic.2006. 715.40
Singh, K., Sharma, M., and Singh, S. K. (2017). “Effect of plant growth regulators on fruit yield and quality of guava (Psidium guajava) cv. Allahabad Safeda,” Journal of Pure and Applied Microbiology 11(2), 1149-1154. DOI: 10.22207/JPAM. 11.2.61
Snedecor, G. C., and Cochran, W.G. (2021). Statistical Methods, Iowa State University Press, 8th ed., Ames, IA, USA.
Sparks, D. L., Page, A. L., Helmke, P. A., and Loeppert, R. H. (2020). Methods of Soil Analysis, Part 3: Chemical Methods (Vol. 14), John Wiley and Sons, Hoboken, NJ, USA.
Stern, R. A., Flaishman, M., Applebaum, S., and Ben-Arie, R. (2007). “Effect of synthetic auxins on fruit development of ‘Bing’ cherry (Prunus avium L.),” Scientia Horticulturae 114(4), 275-280. DOI: 10.1016/j.scienta.2007.07.010
Suman, M., Sangma, P. D., Meghawal, D. R., and Sahu, O. P. (2017). “Effect of plant growth regulators on fruit crops,” Journal of Pharmacognosy and Phytochemistry 6(2), 331-337.
Talaat, N. B., Nesiem, M. R., Gadalla, E. G., and Ali, S. F. (2023). “Putrescine, in combination with gibberellic acid and salicylic acid, improves date palm fruit quality via triggering protein and carbohydrate accumulation and enhancing mineral, amino acid, sugar, and phytohormone acquisition,” Journal of Plant Growth Regulation 1-17. DOI: 10.1007/s00344-023-11134-5
Talat, H., Shafqat, W., Qureshi, M. A., Sharif, N., Raza, M. K., ud Din, S., Ikram, S., and Jaskani, M. J. (2020). “Effect of gibberellic acid on fruit quality of Kinnow mandarin,” Journal of Global Innovations in Agricultural Sciences 8(2), 59-63. DOI: 10.22194/JGIASS/8.901
Thiruppathi, M. (2020). “Effect of foliar application of micronutrients and PGRs on yield and growth characteristics of guava (Psidium guajava L.) cv. BanarasiInt,” International Journal of Current Microbiology and Applied Sciences 9(8), 1486-1490. DOI: 10.20546/ijcmas.2020.908.171
Velasquez, S. M., Barbez, E., Kleine-Vehn, J., and Estevez, J. M. (2016). “Auxin and cellular elongation,” Plant Physiology, 170(3), 1206-1215. DOI: 10.1104/pp. 15.01863
Wang, H., Pampati, N., McCormick, W. M., and Bhattacharyya, L. (2016). “Protein nitrogen determination by Kjeldahl digestion and ion chromatography,” Journal of Pharmaceutical Sciences 105(6), 1851-1857. DOI: 10.1016/j. xphs.2016.03.039
Watanabe, M., Segawa, H., Murakami, M., Sagawa, S., and Komori, S. (2008). “Effects of plant growth regulators on fruit set and fruit shape of parthenocarpic apple fruits,” Journal of the Japanese Society for Horticultural Science 77(4), 350-357. DOI: 10.2503/jjshs1.77.350
Weiwei, C., Jinrong, L., Fang, X., and Jing, L. (2017). “Improvement to the determination of activated phosphorus in water and wastewater by yellow vanadomolybdate method,” Indus Waters Treaty 37(2), 95-97.
Xiao, H., Wang, J., and Huang, M. (2007). “Influence of CPPU on sugar and acid content of Diospyros kaki cv. Zenjimaru fruit,” Journal of Zhejiang Forestry Science and Technology 27(5), article 28.
Yadav, S., Singh, J., Gupta, S., and Yadav, J. S. (2021). “A study on foliar feeding of GA3 and NAA on fruit drop, retention, yield and quality of ber fruit (Ziziphus mauritiana Lamk.) cv. ‘Banarasi Karaka’,” Biological Forum – An International Journal 13(3), 608-612.
Yehia, T. A., and Hassan, H. (2005). “Effect of some chemical treatments on fruiting of Leconte pears,” Journal of Applied Sciences Research 1(1), 35-42.
Zang, Y.-X., Chun, I.-J., Zhang, L.-L., Hong, S.-B., Zheng, W.-W., and Xu, K. (2016). “Effect of gibberellic acid application on plant growth attributes, return bloom, and fruit quality of rabbiteye blueberry,” Scientia Horticulturae 200, 13-18. DOI: 10.1016/j.scienta.2015.12.057
Zhang, C., Lee, U., and Tanabe, K. (2008). “Hormonal regulation of fruit set, parthenogenesis induction and fruit expansion in Japanese pear,” Plant Growth Regulators 55, 231-240. DOI: 10.1007/s10725-008-9279-2
Zhang, C., and Whiting, M. (2011). “Pre-harvest foliar application of Prohexadione-Ca and gibberellins modify canopy source-sink relations and improve quality and shelf-life of ‘Bing’ sweet cherry,” Plant Growth Regulators, 65, 145-156. DOI: 10.1007/s10725-011-9584-z
Zhang, L., Wan, X., Xu, Y., Niyitanga, S., Qi, J., and Zhang, L. (2020). “De novo assembly of transcriptome and genome-wide identification reveal GA3 stress-responsive WRKY transcription factors involved in fiber formation in jute (Corchorus capsularis),” BMC Plant Biology 20(1), 1-15. DOI: 10.1186/s12870-020-02617-8
Article submitted: March 30, 2024; Peer review completed: May 18, 2024; Revised version received and accepted: May 24, 2024; Published: July 15, 2024.
DOI: 10.15376/biores.19.3.5880-5894