1 Introduction

Strawberry (Fragaria ananassa) is a naturally occurring hybrid (Fragaria chelonesis × Fragaria virginiana) and a highly appreciated crop, grown in cooler regions worldwide for their delicious fruits, high nutrient value, various bioactive compounds, and medicinal attributes (Oszmiański and Wojdylo, 2009). Strawberries have a base chromosome number X=7 and are octoploid (2n=8x=56) which belongs to the family Rosaceae. Strawberry plants are perennial, herbaceous with fruits etaerio of achenes and edible parts as succulent receptacles. Strawberry fruits are popular among consumers because of their delicious blends of acid and sweetness, glamorous red color, volatiles, and phenols that give them pleasant flavors (Sharma and Yamdagni, 2000).

They are also high in nutrition, a rich source of niacin, vitamin A, vitamin C, and minerals such as calcium, potassium, phosphorus, and iron (Karakara and Dwivedi, 2002). Among different fruit crops grown, strawberries provide great benefits for small and large farmers in sub-tropical and temperate regions as they provide a quick return in a short time approximately six months (Biswas et al., 2009). The worldwide strawberry production is 8 885 028 tons per year with China, the United States of America, and Mexico contributing more than half of global strawberry production. The top five strawberry producers in the world are China which produces 3 221 557 tons, the United States which produces 1 021 490 tons, Mexico 861 337 tons, Turkey 486 705 tons and Egypt with the production of 460,245 tons (FAOSTAT, 2021). The area, production, and productivity of strawberries in Asia are 164 204 ha, 4 336 603 Mt, and 264,098 Mt/ha respectively (FAOSTAT, 2020).

In Nepal, the cultivation of strawberries is limited to the Nuwakot district and its periphery covering approximately 55 ha of area with the production of around 495 Mt. The productivity of Nepal’s strawberry is very low 9 Mt/ha as compared to the global productivity of 23.58 mt/ha. Nepal imports worth NRs 2.1 million of strawberries annually i.e. 10 826 kg. The cultivation of strawberries is concentrated in hilly regions with the preoccupied mindset of strawberries being a temperate crop. The varieties used to cultivate strawberries in Nepal were limited to Nyho, Ahime, Iberry, and Ohno (Dhakal et al., 2002). Despite its nutritional value and high demand, the cultivation of strawberry is concentrated in hilly areas of Nepal and its potential areas have not been identified yet. The production of strawberries is flourishing according to the increasing consumer demand, thus spreading to Kathmandu, Biratnagar, Chitwan, and Dharan since 2018 but has not been established yet (https://english.onlinekhabar.com/returning-home-from-the-us-to-cultivate-his-dreams-and-strawberries.html).

Strawberries are taken as a temperate crop, but this concept is not the same worldwide. Many tropical areas in the world are successfully cultivating strawberries. Under such conditions, identification of suitable variety and study of varietal performance for tropical and subtropical regions in Nepal is needed. The current global strawberry diversity includes 500 cultivated varieties and countless wild varieties. The investigation of varietal evaluation is imperative to assess them on various characters and parameters for selection for further breeding programs and production (Asrey and Singh, 2004). Thus, this experiment was designed to study the comparative growth and yield performance of different strawberry varieties under low chilling conditions to identify the commercial strawberry varieties suitable for tropical and subtropical regions of Nepal.

2 Materials and Methods

2.1 Research location and duration

The experiment was conducted at the Research Field of Nepal Agrovine Private Limited, Bharatpur-5, Chitwan for over two years during the winter-summer season of the planting years 2020 and 2021. The first-year experiment was conducted from October 2020 to March 2021 and the postharvest study took place from January 2021 to April 2021. Similarly, the second-year experiment was conducted from October 2021 to March 2022 and the postharvest study was conducted from January 2022 to April 2022.

2.2 Treatment details

In the present study, various varieties of strawberries were cultivated to assess their performance on growth and yield. The study consisted of eight varieties as treatments with seven low-chilling strawberry varieties developed in the United States and one widely cultivated Japanese variety as a control or check variety (Table 1).

3 Results and Analysis

3.1 Vegetative parameters

The results showed that significant variations were found among the different strawberry varieties at 30, 45, 60, 75, 90, 105, and 120 DAT in terms of plant height (Table 2). At 30 DAT, the variety Florida Festival showed the maximum plant height (15.30 cm) which was on par with the variety Sweet Sensation (15.08 cm) and Ruby Gem (14.64 cm) while the minimum plant height (5.24 cm) was recorded in variety Nyho. At 45 DAT, variety Florida Festival had the highest plant height (23.41 cm) followed by variety Sweet Sensation (19.06 cm) and Ruby Gem (18.82 cm), whereas variety Nyho recorded the lowest plant height (6.35 cm). Similar results were observed at 60, 75, 90, 105, and 120 DAT with the maximum plant height in the variety Florida Festival followed by Sweet Sensation and Ruby Gem whereas the minimum plant height was recorded in the variety Nyho. At the final growth stage i.e., 120 DAT the maximum plant height (44.95 cm) was measured in variety Florida Festival, whereas the minimum plant height (13.45 cm) was measured in Nyho, respectively.

Table 2 Plant Height (cm) of eight strawberry varieties evaluated under low-chilling conditions in Chitwan, Nepal (2020-2021) Note: In the DMRT, the significance level is as follows: ns=Not significant at 5% (p≤0.05). *=Significant at 5% (p≤0.01), **=Significant at 1% (p≤0.001), ***=Significant at less than1% (p<0.001). SEM: Standard error of the mean, LSD: Least significant difference, CV: Coefficient of variation

There was significant variation among different strawberry varieties at 30, 45, 60, 75, 90, 105, and 120 DAT in number of trifoliate leaves (Table 3). At 30 DAT, the variety Sweet Sensation had the maximum number of trifoliate leaves (9.01), which was at par with Florida Festival (8.51) and Florida Beauty (8.31). The minimum number of trifoliate leaves (4.08) was observed in Winter Dawn. At 45 DAT, the Florida Festival had the maximum number of trifoliate leaves (16.32), while Winter Dawn had the minimum (7.11).

Table 3 Number of trifoliate leaves of eight strawberry varieties evaluated under low-chilling conditions in Chitwan, Nepal (2020-2021) Note: In the DMRT, the significance level is as follows: ns=Not significant at 5% (p≤0.05). *=Significant at 5% (p≤0.01), **=Significant at 1% (p≤0.001), ***=Significant at less than1% (p<0.001). SEM: Standard error of the mean, LSD: Least significant difference, CV: Coefficient of variation

At 60 DAT, the maximum number of trifoliate leaves (22.47) was observed in a variety that was comparable to Sweet Sensation (22.15), and the minimum number of trifoliate leaves (11.37) was observed in Nyho. The same trend was observed at 75 DAT and 90 DAT. Florida Festival had the maximum number of trifoliate leaves (30.06) at 75 DAT, comparable to Sweet Sensation (29.04), while Nyho had the minimum (13.66). At 90 DAT, Florida Festival and Sweet Sensation both had the maximum number of trifoliate leaves (34.61 and 33.24, respectively), and Nyho had the minimum (15.36). At 105 DAT, 120 DAT with the maximum number of trifoliate leaves was observed in Sweet Sensation which was at par with Florida Festival whereas the minimum number of trifoliate leaves was observed in Nyho.

The study revealed significant variations in all DATs in terms of canopy spread (Table 4). At 30 DAT, the variety Ruby Gem had the widest canopy spread (19.90 cm), while Nyho had the narrowest canopy spread (13.51 cm). At 45 DAT, Sweet Sensation had the maximum canopy spread (27.84 cm), which was comparable to Ruby Gem (27.41cm) and Florida Festival (27.39 cm), whereas Nyho had the minimum canopy spread (17.50 cm). At 60 DAT, Sweet Sensation had the maximum canopy spread (37.96 cm), which was comparable to Florida Festival (37.62 cm) and Ruby Gem (36.26 cm), whereas Nyho had the minimum canopy spread (23.24 cm). At 75 DAT, Sweet Sensation had the maximum canopy spread (45.54 cm), which was comparable to Florida Festival (44.63 cm), and Ruby Gem (44.60 cm), whereas Nyho had the minimum canopy spread (28.94 cm). The same trend continued at 90 DAT, 105 DAT, and 120 DAT, with Florida Festival having the maximum canopy spread, and Nyho having the minimum canopy spread.

Table 4 Canopy Spread (cm) of eight strawberry varieties evaluated under low-chilling conditions in Chitwan, Nepal (2020-2021) Note: In the DMRT, the significance level is as follows: ns=Not significant at 5% (p≤0.05). *=Significant at 5% (p≤0.01), **=Significant at 1% (p≤0.001), ***=Significant at less than1% (p<0.001). SEM: Standard error of the mean, LSD: Least significant difference, CV: Coefficient of variation

3.2 Phenological parameters

Days to first flowering, number of flowers per plant, and fruit set (%) of sample plants were recorded, and significant differences were observed (Table 5). The maximum number of days to first flowering (58.57) was recorded in Ruby Gem and the minimum number of days to first flowering (34.56) was recorded in Winter Dawn. The highest average number of flowers per plant (36.38) was observed in Winter Dawn and the lowest was in Nyho (13.33). The highest number of fruits per plant was observed in Winter Dawn (25.98) and the lowest was observed in Nyho (8.56). Ruby Gem had the highest fruit set % (83.98) and Nyho had the lowest (64.45).

Table 5 Phenological characteristics of eight strawberry varieties evaluated under low-chilling conditions in Chitwan, Nepal (2020-2021) Note: In the DMRT, the significance level is as follows: ns=Not significant at 5% (p≤0.05). *=Significant at 5% (p≤0.01), **=Significant at 1% (p≤0.001), ***=Significant at less than1% (p<0.001). SEM: Standard error of the mean, LSD: Least significant difference, CV: Coefficient of variation

3.3 Yield parameters

The average weight of a fruit (g) of the different varieties was analyzed, revealing a highly significant difference (Figure 1). The highest average weight of fruit (g) was recorded in Florida Beauty (37.62 g) which was at par with Sweet Sensation (37.53 g) and the lowest was in Nyho (16.50 g).

Figure 1 Average weight of the fruit (g) of eight strawberry varieties evaluated under low-chilling conditions in Chitwan, Nepal (2020-2021)

The analysis of yield per plant (g), yield per plot (kg), and yield per hectare (mt) across different varieties revealed highly significant differences (Table 6). The highest yield per plant (g) was recorded in Winter Dawn (713.23 g) and the lowest was in Nyho (123.27 g). Similarly highest yield per plot was recorded in Winter Dawn (35.66 kg) and the lowest was recorded in Nyho (6.16 kg). In terms of yield per hectare, Winter Dawn performed the best with 48.50 mt production and Nyho had the poorest result on compared varieties with yield per hectare of 8.38 mt.

4 Discussion

The variation in these varieties may be ascribed to the variable expression of the genetic constitution responsible for vegetative characters due to varying agroclimatic conditions, a finding that is consistent with Rahman et al. (2013). The variations in plant height between strawberry varieties can be influenced by different components, including genetic characteristics, growth habits, and environmental conditions. Sweet Sensation might grow taller than Winter Dawn at a certain stage of development, i.e., up to 90 DAT but as they progress in growth, their relative heights might change as there was no significant difference in plant height after 90 DAT throughout the experiment. In an experiment conducted in Morang, Nepal, the variety ‘Sweet Sensation’ demonstrated greater plant height when compared to the ‘Ruby Gem’ variety at 45, 60, and 90 days after transplanting (Katel et al., 2023).

The variation involving several leaves may be because different varieties react differently to light, photoperiod, temperature, available metabolites, soil nutrient status, and how those metabolites are distributed to the above-ground plant parts (Tanaka and Muzata, 1974; Strik, 1988). Research has indicated that inherent genetic variation may result in fluctuation in leaf number leading to varied growth patterns even if varieties are grown under constant environmental parameters. Furthermore, different varieties may respond differently to photoperiod, light, temperature, and other factors, which could explain the variation in leaf numbers observed by Ashan et al. (2014).

Singh et al. (2008) observed variations in plant canopy spread and plant height among different varieties which corroborates the current observation that the tropical and subtropical climatic conditions enhance the vegetative growth of strawberries resulting in higher vegetative growth. Earlier flowering in the variety ‘Winter Dawn’ might be due to its short-day behavior. According to Joolka and Badiyala (1983), variations in the chilling hours of different varieties also account for variations in the initiation of flowers as well as the duration of flowering. There is a positive correlation between vegetative characteristics like canopy, number of leaves, number of crowns, and number of flowers per plant (Girijalba et al., 2015). The favorable climatic conditions in the research area may have influenced early flowering.

Differentiation in the number of flowers and variation in fruit set percentages was the major cause of variation in the amount of fruit per plant. The genetic composition and adaptability to the environment may also be the cause of varied fruit set percentages. Temperature had a marked effect on the number of flowers and fruits per plant. Elevated air temperatures during fruit setting and fruiting have been shown to harm fruit volume in sensitive cultivars (Das et al., 2015; Jami et al., 2015). Variety Winter Dawn exhibited precocious flowering and fruiting which might be due to its genetic makeup. This precocious flowering and fruiting have resulted in exceptionally high yields of Winter Dawn (Whitaker et al., 2015). Similarly higher average weight of fruits may be the result of balanced vegetative growth and the number of fruits in the plant. The balanced vegetative and reproductive growth leads to the

A variety with a longer flowering period produces more fruit due to having a greater number of flowers. The shorter days to the first flowering and first fruit set in Winter Dawn may explain its higher flower and fruit count compared to other varieties. Higher fruit numbers have also resulted in higher yields in the variety Winter Dawn. Several authors supported our findings indicating that the choice of varieties can influence the fruit set and yield of strawberries (Simkova et al., 2023). Therefore, genetic makeup is a prime factor that impacts on quantity and quality of strawberry fruits.

5 Conclusion

The findings of the research indicate that there were significant variations in different parameters for strawberry varieties. Among the tested varieties, Florida Festival and Sweet Sensation stood out as prominent in terms of vegetative parameters. However, for phenological and yield characteristics like number of flowers, number of fruits, and yield per plant Winter Dawn was found superior. These results can be milestones for selecting strawberry varieties suitable for the sub-tropical and tropical regions of Nepal.

Authors’ contributions

The conduction of research, data collection, and analysis was done by Bishal Shrestha, Prof. Kalyani Mishra Tripathi contributed to the research concepts, and Prof. Arjun Shrestha and Rajendra Gautam, PhD participated in the interpretation, and organization of the manuscript. All authors read and approved the final manuscript.

Acknowledgments

We would like to acknowledge Mr. Shashan Devkota for his guidance in strawberry cultivation and Nepal Agrovine Private Limited for all the inputs provided for the research.

Conflict of Interest Disclosure

The authors affirm that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest.

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