Calcium and boron interactions affecting fruit quality and yield of apple under temperate conditions

An observation common among apple growers in the Marathwada highlands is that fruit firmness and shelf life have declined over the past decade despite no change in variety or rootstock. Calcium and boron, two nutrients that share a role in cell-wall integrity and pollen tube growth, are often overlooked in apple nutrition programmes. This research investigated the individual and combined effects of pre-harvest calcium chloride (CaCl2, 0.5% w/v) and borax (0.2% w/v) sprays on fruit quality, yield, and post-harvest shelf life of apple cv. Royal Delicious at the university highland research block, Parbhani, during 2022 and 2023. Four treatments (control, Ca only, B only, Ca + B) were applied as three foliar sprays at petal fall, fruit set, and 30 days before harvest in a RCBD with five replications. The combined Ca + B treatment raised TSS to 15.8 deg Brix (control: 12.5), fruit firmness to 7.8 kg/cm2 (control: 6.1), and shifted 38.7% of fruit into the premium grade (>70 mm) compared with 18.3% in the control. Yield increased by 19.4% and shelf life extended by 8 days. These results indicate a strong synergy between calcium and boron for improving apple marketability.

Illustrations explain the paper; charts are replotted from the paper's own table values.

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Cell Wall SynergyClose ×

AI-generated conceptual illustration (apple fruit cell wall). It explains the idea and does not show study data.

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TSS (°Brix): Control vs Ca only vs B only vs Ca + BClose ×

Replotted from Table 1 (page 2) of the original paper. Every bar is the paper's own table value.

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Yield (t/ha): Control vs Ca only vs B only vs Ca + BClose ×

Replotted from Table 1 (page 2) of the original paper. Every bar is the paper's own table value.

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Introduction

Experienced apple growers in Marathwada's highland pockets have noticed a worrying pattern: fruit that once held firm for four weeks in ambient storage now softens within two, and bitter pit incidence has risen from 5% to over 15% in some orchards. Both symptoms point to calcium deficiency in the fruit, a condition exacerbated by heavy nitrogen fertilization and vigorous vegetative growth that diverts calcium away from developing fruit [1, 2] . Boron interacts with calcium at the cell-wall level by cross-linking pectic polysaccharides via the rhamnogalacturonan-II complex, and B-deficient fruit typically show corky internal browning alongside reduced firmness [3] . Foliar application during fruit development can bypass poor xylem delivery, placing both nutrients directly on fruit surfaces where they are absorbed through lenticels [4] . Yet most Indian apple nutrition research has focused on nitrogen and potassium, leaving the Ca-B interaction largely unexplored under local conditions [5,6] . This research was conducted at the Vasantrao Naik Marathwada Agricultural University highland research block, Parbhani (19.27 deg N, 76.77 deg E; altitude 821 m), to quantify the individual and combined effects of foliar calcium and boron on fruit quality, grade distribution, yield, and post-harvest shelf life of Royal Delicious apple [7,8] .

Material and Methods

Material and Methods

Material

Twelve-year-old Royal Delicious trees on M.9 rootstock at 3 m x 2 m spacing were used. CaCl 2 (food grade, 77% purity) and borax (Na 2 B 4 O 7 .10H 2 O, 11.3% B) were dissolved with Tween-20 (0.05% v/v) as surfactant. Four treatments were tested in a RCBD with five replications (three trees per replicate): T 1 control (water spray), T 2 CaCl 2 0.5% w/v, T 3 borax 0.2% w/v, T 4 CaCl 2 0.5% + borax 0.2% w/v. Sprays were applied at petal fall (mid-April), fruit set (early May), and 30 days before anticipated harvest (mid-September) in both 2022 and 2023.

Methods

At harvest, 30 fruit per replicate were sampled. Fruit weight, equatorial diameter, flesh firmness (penetrometer, 11 mm tip), TSS (digital refractometer), titratable acidity (0.1N NaOH to pH 8.1), and bitter pit incidence (%) were recorded. Fruit were graded: Premium (>70 mm), Grade A (65-70 mm), Grade B (60-65 mm), Cull (<60 mm). Shelf life was assessed on 10 fruit per replicate stored at 25 +/-2 deg C; the endpoint was defined as the day when firmness fell below 4.5 kg/cm2 [9] . Yield per tree was recorded and converted to t/ha. Fruit tissue Ca and B concentrations were determined by AAS and azomethine-H methods, respectively [10] . Two-year pooled data were analysed by ANOVA in SAS 9.4; means separated by DMRT at p<0.05 [11] .

Results

Table The line chart (Figure 1) shows the Ca + B curve diverging from others after the fruit-set spray, with the gap widening progressively. The donut charts (Figure 2) contrast the control's dominant Grade B fraction with the Ca + B treatment's shift toward Premium and Grade A, illustrating the commercial value of the combined spray.

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Figure 2Close ×

Fruit grade distribution (%) under control and combined Ca + B treatment

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Original paper figureSource PDF · page 3 ↗

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Figure 1Close ×

Total soluble solids (°Brix) progression from pre-bloom to harvest under four treatments

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Original paper figureSource PDF · page 2 ↗

Discussion

The synergy between Ca and B can be explained by their shared role in cell-wall architecture. Calcium cross-links pectin chains in the middle lamella, while boron stabilises the rhamnogalacturonan-II dimer that anchors pectin networks [3] . When both are adequate, cell walls are stronger and less prone to the enzymatic softening that occurs during ripening [12] . The 74% reduction in bitter pit confirms calcium's direct role in preventing this disorder, which arises from localised Ca deficiency in the calyx end of the fruit [2] . The shelf-life extension (21 to 29 days) is commercially meaningful for Marathwada growers, who often lack coldstorage access and must sell through ambient-temperature supply chains [13] . And the grade shift toward premium fruit (18.3% to 38.7% above 70 mm) translates to a price premium of 25-40% in domestic wholesale markets [14] . One limitation: Royal Delicious is a relatively soft-fleshed variety, and the response may differ in firmer cultivars like Fuji or Gala [15,16] .

Conclusion

Conclusion

Acknowledgement

Acknowledgements Funding sourcesThis research was supported by the departmental budget of the Department of Plant Physiology and Nutrition, Vasantrao Naik Marathwada Agricultural University, Parbhani. Institutional supportThe authors thank the Director of Research for providing access to the highland research block and laboratory facilities.

Figures and tables from the paper

Treatment	Wt. (g)	Firmness (kg/cm²)	TSS (°Brix)	Bitter pit (%)	Yield (t/ha)	Shelf life (days)
Control	156.3	6.1	12.5	14.7	18.4	21
Ca only	168.7	7.1	13.4	7.3	20.6	27
B only	163.4	6.7	13.9	11.2	19.8	24
Ca + B	181.2	7.8	15.8	3.8	22.0	29
CD (p<0.05)	8.9	0.4	0.7	2.4	1.3	3

Table text extracted from the original PDF; superscript letters are shown inline. The original table image is below.

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Table 1Close ×

Fruit quality and yield of royal delicious apple under calcium and boron treatments (two-year mean)

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Original paper tableSource PDF · page 2 ↗

1. Ferguson IB, Watkins CB. Bitter pit in apple fruit. Horticultural Reviews. 1989;11:289-355.
2. De Freitas ST, Amarante CVT, Labavitch JM, Mitcham EJ. Cellular approach to understand bitter pit development in apple fruit. Postharvest Biology and Technology. 2010;57(1):6-13.
3. O'Neill MA, Ishii T, Albersheim P, Darvill AG. Rhamnogalacturonan II: Structure and function of a borate cross-linked cell wall pectic polysaccharide. Annual Review of Plant Biology. 2004;55:109-139.
4. Wójcik P, Lewandowski M. Effect of calcium and boron sprays on yield and quality of Elstar apple. Journal of Plant Nutrition. 2003;26(5):1049-1059.
5. Peryea FJ, Neilsen D, Neilsen G. Boron maintenance sprays for apple: Early-season applications and tankmixing with calcium chloride. HortScience. 2003;38(4):542-546.
6. Deka U, Gogoi C. Apple nutrition in Marathwada highlands: A status review. Journal of Maharashtra Agricultural Universities. 2021;46(2):134-139.
7. ICAR-CITH. Package of Practices for Temperate Fruits. Srinagar: Central Institute of Temperate Horticulture; 2020.
8. SAS Institute. SAS/STAT User's Guide. Version 9.4. Cary: SAS Institute; 2017.
9. Saure MC. Calcium translocation to fleshy fruit: its mechanism and endogenous control. Scientia Horticulturae. 2005;105(1):65-89.
10. Kader AA. Postharvest Technology of Horticultural Crops. 3rd ed. Oakland: UC Agriculture and Natural Resources; 2002.
11. APEDA. Export Statistics for Fresh Fruits 2022-23. New Delhi: Agricultural and Processed Food Products Export Development Authority; 2023.
12. Fallahi E, Conway WS, Hickey KD, Sams CE. The role of calcium and nitrogen in postharvest quality and disease resistance of apples. HortScience. 1997;32(5):831-835.
13. Wojcik P, Wojcik M. Effects of boron fertilization on Conference pear tree vigor, nutrition, and fruit yield and storability. Plant and Soil. 2003;256(2):413-421.
14. Shear CB, Faust M. Nutritional ranges in deciduous tree fruits and nuts. Horticultural Reviews. 1980;2:142-163.