Response of strawberry cv. winter dawn to plant growth regulators for growth, yield and quality under protected conditions

Introduction

Strawberry (Fragaria x ananassa Duch.) belongs to family Rosaceae. The origin of the cultivated Strawberry can be traced to the hybridization of two wild species, Fragaria cheloensis Duch. from South America and Fragaria Virginiana Duch. from North America during the 18 th century. The chromosome number of Strawberry is 2n = 2x = 56. This is an octaploid species. It holds a prominent place among small fruits due to its short cropping period, high market demand, and economic profitability. Strawberry is a highly nutritious fruit, valued not only for its sensory appeal but for its rich nutrient profile. Strawberries are mainly composed of about 91% water making them an ideal choice for hydration and weight management. Strawberries are a good source of dietary fibre (2.0 g/100 g), which supports digestive health. In addition to this, strawberries are rich in bioactive compounds such as anthocyanins, ellagic acid, and other polyphenols which contributes to strong antioxidant and anti-inflammatory properties. The application of Plant Growth Regulators like GA3 can effectively promote vegetative growth by stimulating cell elongation and division, resulting in increased plant height, larger leaves and overall canopy development. Paclobutrazol acts as a growth retardant by inhibiting gibberellin biosynthesis, resulting in more compact plant, while it significantly alters plants metabolic and physiological processes. Triacontanol, a naturally occurring plant stimulant, enhances physiological efficiency by stimulating photosynthesis, enzymatic activity and nutrient uptake. It enhances overall plant vigor, increases fruit number by increasing biomass and improves both yield and quality attributes, including color, taste and sweetness. It is also known to increase chlorophyll content and improve stomatal conduction which affects photosynthetic efficiency and energy availability for fruit development.

Materials and Methods

Climatic Conditions and Geographical Location at the Experimental Site

The experimental site is located at a latitude of 25.57° North and longitude of 81.51° East, with an altitude of 98 meters above the mean sea level. The region is characterized by extremely hot summers and fairly cold winters. Temperatures can rise upto 46-48 °C and it may ocassionally drop to 4-5°. The relative humidity fluctuates between 20% and 94%, and the area receives an average rainfall of approximately 1013.4 mm.

Experimental Details

Studies on response of strawberry to plant growth regulators for growth, yield and quality under Protected Conditions was conducted on cv. Winter Dawn during 2024-2025 in the naturally ventilated polyhouse of Horticulture Research Field of the Department of Horticulture, Naini Agricultural Institute, SHUATS, Prayagraj, (Uttar Pradesh). The experiment was laid out in RBD with ten treatments (9+1) control and these are mentioned as T0: Control, T1: Gibberellic acid @ 50 ppm, T2: Gibberellic acid @ 75 ppm, T3: Gibberellic acid @ 100 ppm, T4: Paclobutrazol @ 25 ppm, T5: Paclobutrazol @ 50 ppm, T6: Paclobutrazol @ 75 ppm, T7: Triacontanol @ 30 ppm, T8: Triacontanol @ 40 ppm, T9: Triacontanol @ 50 ppm. The runners were transplanted on 30 th Nov. 2024 in the naturally ventilated polyhouse. The last harvesting was performed on 17 th March 2025.

Results and Discussions

Response of Strawberry cv. Winter Dawn to Plant Growth Regulators on Plant height, Number of leaves and Number of runners under Protected Conditions

The maximum plant height 26.81 cm was recorded with the treatment T1 (Gibberellic acid @ 50 ppm) and it was followed by T2 (Gibberellic acid @ 75 ppm) with 26.66 cm. The minimum plant height was recorded under the treatment T8 (Triacontanol @ 40 ppm). This increase in height of the plant with the application of GA3 @ 50 ppm during the research period has got the support of Swamy (2013) in Strawberry, Sakamoto et al., (2004) [15] in rice, Weaver and McCune (1959) [16] in grapes, Amin et al., (2008) [17] in papaya. The increased plant height in strawberry may be due to modifying gene expression related to cell wall loosening and expansion enabling cells to elongate more rapidly (Sponsel and Hedden, 2004) [18] .

Number of leaves per plant

Maximum number of leaves (27.17) per plant was recorded in treatment T1 (Gibberellic acid @ 50 ppm), followed by T8 (Triacontanol @ 40 ppm) with (26.05), while as the minimum number of leaves (20.80) was observed with treatment T3 (Gibberellic acid @ 100 ppm). The increase in number of leaves may be due to enhanced chlorophyll content and accelerated meristematic activity. These observations are in close agreement with the findings of (Kumar et al., 2012) [19] , in tomato, (Panse et al., 2013) [20] in brinjal, 9 Meena et al., 2015) [21] in okra.

Number of runners per plant

At last harvest the maximum number of runners (2.67) was recorded in treatment T2 (Gibberellic acid @ 75 ppm), the minimum number of runners recorded was (0.87) in treatment T4 (Paclobutrazol @ 25 ppm). However, no runners were produced in treatments T5 (Paclobutrazol @ 50 ppm), T6 (Paclobutrazol @ 75 ppm), T7 (Triacontanol @ 30 ppm), T8 (Triacontanol @ 40 ppm), T9 (Triacontanol @ 50 ppm). Highest number of runners are produced due to the promotion of cell elongation and enhanced activity of the apical meristem. This hormonal stimulation promotes the outgrowth of lateral buds into runners instead of flowering shoots. The results were further supported by (Rajesh et al., 2012) [22] . Response of Strawberry cv. Winter Dawn to Plant Growth Regulators on First flower appearance (days), Number of flowers per plant, Duration of Harvesting (days), Polar Diameter (mm), Radial Diameter (mm), Number of Fruits Per Plant, Fruit Weight (g), Yield Per Plant (g) under protected conditions.

First Flower Appearance

Minimum days taken to first flower appearance (48.00) was noted with treatment T2 (Gibberellic acid @ 75 ppm), maximum number of days to flower appearance (63.67) was found with treatment T6 (Paclobutrazol @ 75 ppm). These findings have got the support from (Paroussi et al., 2022) [23] , and (Kumar et al., 2014) [24] . Minimum number of days required to produce first flower is due to that GA3 increases the activity of hydrolytic enzymes, like amylases, enhancing sugar mobilization to growing points, thus supplying energy for floral initiataion.

Number of Flowers per Plant

The maximum number of flowers (31.27) was seen in treatment T2 (Gibberellic acid @ 75 ppm), then followed by treatment T3 (Gibberellic acid @ 100 ppm) as (27.92). The minimum number of flowers per plant was recorded in treatment T0 (Control) with 16.35. The maximum number of flower production may be due to the effect of plant growth regulators that encourages rapid growth of plant tissues by promoting cell elongation, shoot growth and floral initiation. By stimulating stem elongation and leaf expansion, GA3 improves overall plant vigor, which supports a higher capacity for flower production. These results were also in obtained by (Thakur et al., 2017) [25] .

Duration of Harvesting

The maximum duration of harvesting (29.00) was recorded in treatment T7 (Triacontanol @ 30 ppm), followed by (28.33) in treatment T9 (Triacontanol @ 50 ppm).The minimum duration of harvesting was seen in treatment T5 (Paclobutrazol @ 50 ppm) with (23.67). These results have got the support from (Pang et al., 2020) [26] . The results showed that foliar application of triacontanol significantly extended the harvesting period by enhancing photosynthetic activity, improving nutrient assimilation, and promoting hormonal balance, especially of auxins and cytokinins (Kumar et al., 2013) [27] .

The maximum polar diameter of (47.15 mm) was recorded in treatment T7 (Triacontanol @ 30 ppm), followed by (42.14 mm) in in treatment T9 (Triacontanol @ 50 ppm. The minimum polar diameter was seen in treatment T3 (Gibberellic acid @ 100 ppm) with 32.75 mm.

The maximum radial diameter (29.10 mm) was recorded in treatment T7 (Triacontanol @ 30 ppm), closely followed by (23.23 mm) in treatment T9 (Triacontanol @ 50 ppm). However, the minimum radial diameter was found in treatment T3 (Gibberellic acid @ 100 ppm) with (11.15mm). The increased dimensions in strawberry are due to enhanced physiological and biochemical processes essential for fruit development, by boosting photosynthesis and chlorophyll content. Triacontanol also improves nutrient uptake and translocation, supplies essential elements that supports the fruit enlargement. These results have found the support from Choudhary, Ashima (2023) [28] and similar to those of Khunte et al., (2014) [29] .

Number of Fruits per Plant

The maximum number of fruits per plant (25.08) was found in treatment T7 (Triacontanol @ 30 ppm), which is followed by (22.67) in treatment T8 (Triacontanol @ 40 ppm). Whereas, the minimum number of fruits per plant (13.75) was recorded in treatment T1 (Gibberellic acid @ 50 ppm). These results are consistent with those of Rani et al., (2005) in strawberry, Singh et al., (2016) [31] . (Sharma and Singh, 2009) [3] , reported that the increased number of fruits are due to enhanced photosynthetic efficiency, which results in more production of carbohydrates and energy needed for flower initiation and fruit development.

The maximum fruit weight of (28.40 g) was recorded in treatment T7 (Triacontanol @ 30 ppm), followed by (25.53 g) in treatment T8 (Triacontanol @ 40 ppm). However, the minimum fruit weight (14.02 g) was found in treatment T0 (control). The increased fruit weight in strawberry is due to the increased levels of natural growth hormones, promoting rapid cell division and enlargement in fruit tissues, increasing fruit size and weight. These results are in close context with Mehta et al., (2012) [32] . Triacontanol could promote fruit development by upregulating factors related to fruit ripening related growth and development in strawberry Pang et al., (2020) [26] .

The maximum fruit yield per plant (314.90 g) was found to be in treatment T7 (Triacontanol @ 30 ppm), which was followed by (296.43 g) in treatment T8 (Triacontanol @ 40 ppm). The minimum fruit yield was seen in treatment T0 (control) with (146.05 g). The increase in fruit yield per plant is due to enhanced photosynthetic efficiency by increasing chlorophyll content, which boosts carbohydrate production and translocation to the Verma et al., (2020) [33] .

TSS (° Brix)

The TSS was found maximum in treatment T3 (Gibberellic acid @ 100 ppm) with 9.27 °Brix, followed by 8.03 in treatment T7 (Triacontanol @ 40 ppm). Whereas, the minimum TSS 3.10 was recorded in treatment T5 (paclobutrazol @ 50 ppm). The observed rise in TSS may be attributed to the breakdown of cell walls as suggested by (Anitha et al., 2005) [34] , along with a reduction in respiration and an increase in dry matter due to water loss. The reduction in TSS levels could be due to sugar dilution caused by water spraying during the first ripening phase. This has got the support from (Khatoon et al., 2021) [35] .

The maximum acidity (%) was found highest in treatment T7 (Triacontanol @ 30 ppm) with 1.70%, closely followed by 1.30%, in treatment T4 (Paclobutrazol @ 25 ppm). The minimum acidity (%) 0.50% was found to be in the fruits with treatment T1 (Gibberellic acid @ 50 ppm). The reduction in titrable acidity is likely due to reduced respiration and slower accumulation of organic acids, this result has got the support from (Sharma et al., 2018) [36] , and in contrast to increasing acidity may be attributed to enhanced metabolic activity and organic acid biosynthesis during early fruit development and has got the support from (Singh et al., 2016) [37] .

The maximum sugar percentage (8.40) was found in treatment T7 (Triacontanol @ 30 ppm), followed by (8.27) in treatment T8 (Triacontanol @ 40 ppm) and the minimum 6.27) was recorded in treatment T1 (Gibberellic acid @ 50 ppm). These results have got the support from (Singh et al., 2017) [38] and (Mandal et al., 2020) [39] . They reported that the respective increase in total sugar is attributed to enhanced photosynthesis, chlorophyll content, and activity of sugar metabolizing enzymes.

Ascorbic acid

The maximum ascorbic acid content (4.87) was found in treatment T6 (Paclobutrazol @ 75 ppm), then followed by (4.07) in treatment T2 (Gibberellic acid @ 75 ppm). Whereas, the minimum ascorbic acid content was found in treatment T8 (Triacontanol @ 40 ppm) with (2.46). This finding correlates with the findings of (Kumar and Singh, 2019) [40] .

pH

The maximum pH of 5.49 was found in the fruits of treatment T4 (Paclobutrazol @ 25 ppm), followed by 5.22 found with treatment T9 (Triacontanol @ 50 ppm). The minimum pH was found in treatment T1 (Gibberellic acid @ 50 ppm) which is (3.00). The respective increase in pH is due to slowed synthesis of organic acids like citric acid and malic acid, which are responsible for the sour taste and low pH in fruits. As same was reported by (Sharma et al., 2018) [

Conclusion

According to our experimental results it is concluded that the treatment T1 (Gibberellic acid @ 50 ppm) performed best in terms of plant height and number of leaves. However, treatment T2 (Gibberellic acid @ 75 ppm) had the maximum number of runners, earliness in flowering and number of flowers. The maximum duration of harvesting was seen in treatment T7 (Triacontanol @ 30 ppm) and it was also found best for other yield parameters. The treatment T3 (Gibberellic acid @ 100 ppm) was found to be effective in terms of TSS° Brix. While as, the treatment T7 (Triacontanol @ 30 ppm) was found best for acidity and total sugar content. Moreover, treatment T6 (Paclobutrazol @ 75 ppm) showed the best performance for Vitamin C content.

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