Effect of growth regulators and manual thinning of fruits on the quality of guava cv. Taiwan lite pink super gold

Introduction

Guava (Psidium guajava L.), popularly known as the "apple of the tropics," is an important tropical and subtropical fruit crop valued for its nutritional richness, adaptability and pleasant flavour. The fruit is particularly valued for its high vitamin C content, dietary fibre, sugars, minerals and bioactive compounds, making it an important component of a healthy diet (Semwal et al., 2024) [1] . Among the commercially cultivated cultivars, newer selections with attractive fruit colour, large size and improved eating quality have gained considerable importance. Fruit quality in guava is influenced by genetic characteristics, environmental conditions, crop load and cultural practices. Excessive fruiting increases competition among developing fruits for assimilates, water and nutrients, which may result in smaller fruits, reduced total soluble solids, sugars, colour development and other desirable quality attributes. Therefore, regulation of crop load is important for improving the quality and market value of guava fruits. Fruit thinning is an important crop management practice that involves the removal of excess young fruits to reduce competition among the remaining fruits. It can be carried out manually or through chemical growth regulators such as naphthalene acetic acid (NAA) and ethephon (Ethrel). Chemical thinning promotes fruit abscission by modifying hormonal balance and enhancing ethylene-mediated separation of young fruits. The effectiveness of thinning depends on the concentration of the growth regulator, degree of manual thinning and stage of application. Appropriate thinning can improve the allocation of assimilates towards the retained fruits, thereby enhancing fruit size, total soluble solids, sugars, vitamin C, colour, firmness and other biochemical constituents. It may also influence titratable acidity and the overall balance between sugars and acids, which are important determinants of consumer acceptability and eating quality. Thus, optimizing crop load through manual and chemical thinning can be an effective approach for producing larger, nutritionally superior and more marketable guava fruits. The cultivar Taiwan Lite Pink Super Gold is characterized by attractive fruit appearance and desirable eating quality, but information on the influence of different thinning levels and growth regulator concentrations on its quality attributes is limited. Hence, the present investigation was undertaken to evaluate the effect of growth regulators and manual thinning of fruits on the quality attributes of guava cv. Taiwan Lite Pink Super Gold.

Materials and Method

Experimental site

The study was conducted during 2025-26 at a farmer's field in Kallaganguru village, Shivamogga district, Karnataka. The experimental site is situated at 13°56′ N latitude and 75°33′ E longitude, at an elevation of about 569 m above mean sea level and falls under the Southern Transition Zone of Karnataka. The region experiences a tropical monsoon climate with distinct summer, monsoon and winter seasons. The soil of the experimental site was red loamy to red lateritic, acidic and non-saline in nature.

Experimental design and treatment details

The experiment was laid out in a Randomized Complete Block Design (RCBD) with three replications. The experiment comprised ten treatments with four plants per treatment in each replication, resulting in 120 plants in total. Four-year-old healthy and uniform guava plants of cv. Taiwan Lite Pink Super Gold, spaced at 2.4 × 2.4 m, were selected for the experiment. NAA @ 50 ppm T 6

Treatment imposition

The treatments were imposed one month after fruit set at the pea stage during the last week of December. Manual fruit thinning was carried out by removing the required proportion of young fruits using a secateur at 20, 40 and 60 per cent levels. Chemical thinning treatments were imposed using NAA at 50, 100 and 150 ppm and Ethrel at 500, 1000 and 1500 ppm concentrations (Table 1).

Observations recorded

Observations on fruit quality parameters were recorded at commercial maturity. Physical quality parameters, viz., fruit length, fruit diameter, fruit weight, fruit volume, fruit firmness and shelf life were recorded, while chemical quality parameters viz., total soluble solids, titratable acidity, TSS ratio, total sugars, reducing sugars, non-reducing sugars, vitamin C and lycopene content were estimated.

The data on all quality parameters were subjected to analysis of variance (ANOVA) for a Randomized Complete Block Design. Significant differences between treatment means were compared using the critical difference (CD) at 5 per cent level of significance.

Results and Discussion

The results obtained from the present investigation are presented and discussed in this chapter. The findings are interpreted based on the effects of manual fruit thinning and growth regulator treatments on fruit quality and are compared with the findings of earlier researchers.

Physical parameters

The physical characteristics of fruits, viz., fruit length, fruit diameter, fruit weight and fruit volume, were significantly influenced by manual fruit thinning and growth regulator treatments (Table 2). The highest fruit length (8.93 cm), fruit diameter (10.12 cm), fruit weight (369.50 g) and fruit volume (399.94 cc) were recorded in T 4 (60% fruit thinning), followed by T 3 (40% fruit thinning), whereas the lowest values were recorded in T 1 (control). The improved fruit size under higher thinning levels might be attributed to reduced crop load and better partitioning of assimilates towards the developing fruits. Similar improvement in fruit growth with crop-load regulation and growth regulator application has been reported by Tahir et al. (2002) [2]

, Mishra et al. (2020) [3] and Lal et al. (2023) [4] .

Fruit firmness and shelf life

Fruit firmness and shelf life were significantly influenced by the treatments (Table 3). The highest fruit firmness (8.68 kg cm⁻²) and shelf life (10.53 days) were recorded in T 4 (60% fruit thinning), followed by T 3 (40% fruit thinning), whereas the lowest firmness (5.93 kg cm⁻²) and shelf life (7.10 days) were recorded in T 10 (Ethrel @ 1500 ppm). The enhanced firmness and shelf life under higher thin-ning may be attributed to reduced crop load, improved assimilate and mineral partitioning, particularly calcium and delayed cell-wall degradation. In contrast, the lower firmness and shelf life under higher Ethrel concentration may be due to its ethylene-releasing action, which accelerates ripening and softening (Fig. 1). Similar findings were reported by Deshmukh et al. (2022) [5] , Jemric et al. (2005) [6] , Devlal et al. (2017) [7] , Kumar et al. (2017) [8] and Kaur et al. (2024) [9] .

TSS, acidity and TSS:acid ratio

The TSS, acidity and TSS ratio of fruits were significantly influenced by manual thinning and growth regulator treatments (Table 4). The highest TSS (12.33 °Brix) and TSS:acid ratio (41.40), along with the lowest acidity (0.30%), were recorded in T 4 (60% fruit thinning), whereas the lowest TSS (10.20 °Brix) and TSS ratio (22.63) were recorded in T 1 (control). The increase in TSS and TSS:acid ratio with higher thinning may be attributed to reduced crop load and improved source-sink balance, resulting in greater accumulation of soluble solids, while the reduction in acidity may be associated with increased utilization of organic acids during fruit maturation. Similar results were reported by Tahir et al. (2002) [2] , Mishra et al. (2020) [3] , Rahman et al. (2017) [10] , Lal et al. (2023) [4] and Makvana et al. (2024) [11] .

Sugar composition

The reducing sugars, non-reducing sugars and total sugars were significantly influenced by the treatments (Table 5). The highest reducing sugars (5.03%), non-reducing sugars (3.21%) and total sugars (8.24%) were recorded in T 4 (60% fruit thinning), while the lowest values (3.73, 2.43 and 6.17%, respectively) were recorded in T 1 (control). The higher sugar accumulation under fruit thinning may be attributed to reduced competition among developing fruits and greater availability of assimilates for individual fruits, together with enhanced conversion of stored carbohydrates into soluble sugars during ripening (Fig. 2). Similar findings were reported by Tahir et al. (2002) [2] , Patel et al. (2014) [12] , Jain et al. (2011) [13] , Silva et al. (2022) [14] and Kumari et al. (2023) [15] .

Bioactive compounds

The bioactive compounds, viz., vitamin C and lycopene, were significantly influenced by manual fruit thinning and growth regulator treatments (Table 6). The highest vitamin C (231.01 mg/100 g) and lycopene (5.23 mg/100 g) contents were recorded in T 4 (60% fruit thinning), which were at par with T 9 (Ethrel @ 1000 ppm), whereas the lowest values were recorded in T 1 (control). The enhancement in bioactive compounds under higher thinning may be attributed to improved source-sink balance, greater assimilate availability and advanced physiological maturity of the fruits. Similar improvements in vitamin C and lycopene content with crop-load regulation and growth regulator application have been reported by Tahir et al. (2002) [2] , Santos et al. (2023) [16] , Singh (2019) [17] , Silva et al. (2022) [14] , Kumari et al. (2023) [15] and Presman et al. (2020) [18] .

Conclusion

The present investigation revealed that manual fruit thinning and growth regulator treatments significantly influenced the quality attributes of guava cv. Taiwan Lite Pink Super Gold. Among the treatments, 60 per cent manual fruit thinning was most effective in improving overall fruit quality, recording the highest fruit weight, firmness, shelf life, TSS, sugars, vitamin C and lycopene, along with the lowest titratable acidity. The improvement in quality may be attributed to reduced crop load and better allocation of assimilates towards the retained fruits, resulting in enhanced fruit development and bio-chemical quality. Ethrel @ 1000 ppm also showed comparatively better performance for several quality attributes. Thus, 60 per cent manual fruit thinning can be recommended as an effective practice for producing larger, firmer and nutritionally superior guava fruits of cv.

Taiwan Lite Pink Super Gold under the conditions of the present study.

References

1. Semwal DP, Longkumer S, Chandra PRS, Rai KM, Arya M, Ahlawat SP, Singh PK. Diversity distribution analysis of guava (Psidium guajava L.) populations in cultivated and wild habitats in the midhills of Uttarakhand, India. Agriculture. 2024;14(4):575.
2. Tahir FM, Hamid K. Studies of physico-chemical changes due to fruit thinning in guava (Psidium guajava L.). OnLine Journal of Biological Sciences. 2002;2(11):744-745.
3. Mishra M, Lal S, Kumar R. Effect of fruit thinning on growth, yield and quality of rainy season crop of guava (Psidium guajava L.). Journal of Pharmacognosy and Phytochemistry. 2020;9(5):3214-3217.
4. Lal M, Bahadur V. Effect of different chemicals and manual thinning on crop regulation in guava. International Journal of Plant & Soil Science. 2023;35(18):141-148.
5. Deshmukh NA, Rymbai H, Verma VK, Jha AK. Crop regulation studies in guava (Psidium guajava L.) at higher altitude of Northeast India. International Journal of Agricultural Sciences. 2022;14(4):11243-11246.
6. Jemric T, Pavicic N, Skenderovic M. Influence of thinning method on postharvest quality of 'Golden Delicious Cl. B' apple (Malus domestica Borkh.). Agriculture Conspectus Scientificus. 2005;70(1):11-15.
7. Devlal S, Bhardwaj VK, Uniyal S. Response of fruit thinning on yield and quality of peach cv. Red June. Journal of Hill Agriculture. 2017;8(3):297-301.
8. Kumar R, Rimpika, Sharma N, Shylla B, Thakur A, Sharma DP. Influence of manual and chemical thinning on yield and quality of nectarine [Prunus persica (L.) Batsch var. nucipersica] cv. Snow Queen. International Journal of Bio-Resources and Stress Management. 2017;8(5):601-604.
9. Kaur N, Singh A. Effect of pre-harvest application of potassium nitrate, naphthalene acetic acid and ethephon on ripening and shelf-life of guava cv. Allahabad Safeda. Indian Journal of Horticulture. 2024;81(3):261-265.
10. Rahman H, Akter A, Rahman J, Riad MI, Rahman MM. Effect of fruit thinning and bagging on the yield and quality of guava. Journal of Agricultural Science and Technology. 2017;6(1):20-27.
11. Makvana AG, Bhuva SK, Makwana PS, Thumar JM. Impact of leaf to fruit ratio on physico-chemical traits of guava cv. Lalit under high density planting. International Journal of Advanced Biochemistry Research. 2024;8(11):268-272.
12. Patel RK, Meitei SB, Kumar A, Srivastava K, Deka BC, Deshmukh NA, Verma VK. Effect of leaf and fruit thinning on yield and quality of peach cv. Flordasun. Ecoscan. 2014;6:467471.
13. Jain MC, Dashora LK. Effect of plant growth regulators on physico-chemical characters and yield of guava cv. Sardar under high density planting system. Indian Journal of Horticulture. 2011;68(2):259-261.
14. Silva MS, Leonel S, Leonel M, Souza JMA, Ferreira RB, Martins RC, Ferraz RA. Plant growth regulators as thinners in guava orchards increase larger fruits with higher nutritional value. Emirates Journal of Food and Agriculture. 2022;34(2):107-116.
15. Kumari THL, Vardhan AH, Omprasad J, Krishna KU. Studies on foliar application of growth regulators on fruit quality of guava cv. Taiwan Pink. Biological Forum. 2023;15(10):432-435.
16. Santos DSA, Pereira GA, Fonseca WL, Zuffo AM, Cunha JGD, Soares NP, Morais EM, Nascimento AAS, Santos DP, Almeida MD, Aguilera JG, Aranibar LM, Salcedo EP, Chura RMM, Contreras WC, Alejo RC. Photosynthetic assimilation of guava (Psidium guajava L.) cv. Paluma under different pruning and fruit thinning intensities. Agronomy. 2023;13:299.
17. Singh VK. Effect of plant growth regulator (NAA) in guava. Journal of Pharmacognosy and Phytochemistry. 2019;8(6):17291730.
18. Presman ZM, Tuvia AS, Chalupowicz D, Beniches M, Gamliel A, Fallik E. Watermelon rootstock/scion relationships and the effects of fruit-thinning and stem-pruning on yield and postharvest fruit quality. Agriculture. 2020;10(9):366.
19. How to cite this article: Adithya K, Thippesha D, Umamaheswarappa P, Sridhar R, Nagaraja M, Renukaswamy N. Effect of growth regulators and manual thinning of fruits on the quality of guava cv. Taiwan lite pink super gold. International Journal of Advanced Biochemistry Research. 2026;SP10(9):1886-1890. doi: https://www.doi.org/10.33545/26174693.2 026.v10.i9Sw.10101