1 Introduction

Litchi (Litchi chinensis Sonn.) is one of the most important subtropical fruit crops cultivated worldwide for its attractive appearance, pleasant aroma, excellent flavor, and high nutritional value. The fruit is rich in sugars, vitamin C, phenolic compounds, and antioxidants, making it highly valued for both fresh consumption and processing. South and Southeast Asia account for a major proportion of global litchi production, with Nepal being one of the important producing countries in the Himalayan region. In Nepal, litchi is predominantly cultivated in the Terai belt, where favorable climatic conditions support its commercial production. According to the Ministry of Agriculture and Livestock Development (MoALD, 2023), litchi occupies approximately 5,769 ha, with an annual production of 42,736 metric tons and an average productivity of 7.41 t/ha. Among the major production districts, Sarlahi has emerged as an important litchi-growing area because of its subtropical climate, fertile alluvial soils, and increasing commercial orchards, contributing substantially to local livelihoods and the regional fruit economy.

The commercial value of litchi is largely determined by fruit quality attributes rather than yield alone. Consumers generally prefer fruits with larger size, higher fruit weight, greater edible aril proportion, smaller seeds, attractive peel color, and higher total soluble solids (TSS), as these characteristics directly influence market acceptability, consumer preference, shelf value, and profitability (Menzel, 2005). Small-seeded or "chicken-tongue" seed cultivars are particularly desirable because they possess a greater edible portion and fetch premium market prices (Singh et al., 2012). Likewise, TSS is one of the most important quality indicators because it reflects sugar accumulation and sweetness, thereby influencing fruit taste and overall eating quality (Hussain et al., 2021). Therefore, systematic evaluation of fruit morphological and quality traits is essential for identifying superior cultivars suitable for commercial cultivation, breeding programs, and orchard improvement.

Fruit characteristics in litchi are strongly influenced by cultivar genetics and their interaction with environmental conditions. Previous studies have documented considerable variation among cultivars in fruit size, fruit weight, seed morphology, aril development, and physicochemical quality (Nacif et al., 2001; Singh et al., 2012; Wang et al., 2017; Nath et al., 2022). Similarly, Chaudhary et al. (2023) evaluated major litchi cultivars in the central Terai of Nepal and reported significant differences in several fruit quality traits, highlighting the importance of cultivar selection for commercial production. However, most published studies have focused on general varietal descriptions or evaluations conducted under different agroecological conditions. Because fruit quality is influenced by both genetic background and environmental factors, cultivar performance may vary considerably across production regions. Consequently, findings from other countries or even other regions of Nepal cannot be directly extrapolated to the orchards of Sarlahi.

Sarlahi represents one of Nepal's important commercial litchi-producing districts, yet comprehensive comparative information on the fruit morphological and quality characteristics of its major cultivated varieties remains limited. Scientific evaluation under local agro-climatic conditions is necessary to identify cultivars with superior commercial traits, provide reliable recommendations to growers, and support evidence-based orchard management. Furthermore, understanding varietal differences in fruit quality can assist breeding programs, improve cultivar selection, and enhance the competitiveness of Nepalese litchi in domestic and potential export markets.

Therefore, this study aimed to evaluate the differences in fruit morphological and quality characteristics among seven major litchi cultivars grown under the agro-climatic conditions of Sarlahi, Nepal. The study specifically compared fruit morphology, fruit size, fruit weight, pericarp weight, aril weight, seed characteristics, and total soluble solids (TSS) to identify superior cultivars with greater commercial potential. The findings are expected to provide valuable scientific information for cultivar selection, orchard management, future breeding programs, and the sustainable development of the litchi industry in Nepal.

2 Materials and Methods

2.1 Study site

The experiment was conducted during the 2024 fruiting season at the Tropical Horticulture Center (THC), Sarlahi District, Madhesh Province, Nepal (26.4703° N, 86.7325° E). The experimental site is located in the subtropical Terai region of Nepal at an altitude of approximately 85 m above sea level. The area experiences a humid subtropical climate characterized by hot summers, mild winters, and a distinct monsoon season. The average annual temperature ranges from 10 °C–38 °C, with an annual rainfall of approximately 1,400–1,800 mm, most of which occurs from June to September. The orchard soil is deep, well-drained alluvial loam with good fertility, which is considered suitable for commercial litchi production.

2.2 Plant materials and experimental design

Seven commercially important litchi (Litchi chinensis Sonn.) cultivars, namely Shahi, China, Seedless, Early Large Red (ELR), Calcuttia, Muzaffarpur, and Bombai, were selected for evaluation. The cultivars were maintained in the experimental orchard of the Tropical Horticulture Center, Sarlahi. Uniform, healthy, air-layered trees aged 15–20 years with comparable canopy size and vigor were selected for the study. The orchard was established under a square planting system with uniform spacing of 10 m × 10 m. Standard orchard management practices, including irrigation, fertilizer application, weed management, pruning, and plant protection measures, were uniformly followed throughout the experimental period to minimize management-related variation.

The experiment was laid out in a Randomized Complete Block Design (RCBD) with four replications. Each tree represented one experimental unit, resulting in a total of 28 experimental trees (7 cultivars × 4 replications).

2.3 Fruit sampling

Fruits were harvested at commercial maturity based on uniform peel colour development, characteristic cultivar appearance, and market harvest stage. Twenty fruits were randomly collected from each experimental tree, representing all four canopy directions (north, south, east, and west) and different canopy heights to minimize sampling bias. Damaged, diseased, insect-infested, and malformed fruits were excluded from sampling. Immediately after harvest, the samples were transported to the laboratory for morphological and physical analyses.

2.4 Determination of fruit morphological characteristics

Fruit morphological characteristics, including fruit colour, fruit shape, fruit size, seed colour, seed shape, seed size, and aril colour, were recorded using freshly harvested mature fruits. Fruit maturity was identified based on characteristic peel colour and varietal appearance. Morphological descriptors were evaluated following the standard litchi descriptor guidelines described by Nacif et al. (2001) and Saikia and Kotoky (2022).

2.5 Determination of fruit physical characteristics

Fruit length, fruit width, fruit weight, pericarp weight, aril weight, seed length, seed width, and seed weight were determined using twenty representative fruits from each experimental unit. Fruit and seed length were measured from the base to the apex, while width was measured at the widest portion using a digital Vernier caliper with an accuracy of 0.01 cm. Fruit, pericarp, aril, and seed weights were measured using a calibrated digital electronic balance with an accuracy of 0.01 g.

Total soluble solids (TSS) were determined using freshly extracted juice obtained from the edible aril. The juice was filtered through muslin cloth and a few drops were placed on the prism of a hand-held digital refractometer (0–32 °Brix range). The instrument was calibrated with distilled water before each measurement, and TSS values were expressed as °Brix at room temperature. Three independent measurements were recorded for each experimental unit, and their average value was used for statistical analysis.

2.6 Statistical analysis

The collected data were entered into Microsoft Excel and analyzed using R software version 4.4.0. Analysis of variance (ANOVA) was performed to determine the significance of differences among cultivars. Mean separation was carried out using Duncan's Multiple Range Test (DMRT) at the 5% level of significance (p ≤ 0.05). Coefficient of variation (CV%) and overall treatment means were also calculated to assess experimental variability and trait performance.

3 Results and Analysis

3.1 Fruit morphology of tested varieties

Significant variation was observed in fruit morphological characteristics among the seven evaluated litchi cultivars (Table 1). Fruit colour varied from red, crimson red, pinkish red, and tyrian rose to brownish-green. Likewise, fruit shape ranged from oval and cordate to conical, oblong, and globose, while fruit size was classified as medium or large depending on the cultivar. Seedless, Calcuttia, and Muzaffarpur produced comparatively larger fruits, whereas Shahi, China, Early Large Red (ELR), and Bombai produced medium-sized fruits.

3.2 Seed morphology of tested varieties

Considerable variation was also observed in seed morphology among the studied cultivars (Table 2). Seed colour ranged from light brown to dark chocolate, whereas seed shape varied between elliptic oblong and elliptic oval. Seedless was the only cultivar possessing small seeds, while Calcuttia and Muzaffarpur had large seeds. Differences were also recorded in aril colour, varying from grayish white and creamy white to dirty creamy white among the evaluated cultivars.

3.3 Fruit length, fruit width and fruit weight

Fruit length, fruit width, and fruit weight differed significantly among the evaluated cultivars (Table 3). Fruit length ranged from 3.25 to 3.64 cm. Early Large Red recorded the greatest fruit length (3.64 cm), which was statistically comparable with China (3.61 cm) and Muzaffarpur (3.60 cm), whereas Bombai produced the shortest fruits (3.25 cm).

Fruit width varied significantly from 2.90 to 3.30 cm. China exhibited the highest fruit width (3.30 cm), followed by Bombai (3.17 cm) and Seedless (3.16 cm), while Shahi recorded the lowest value (2.90 cm).

Fruit weight also differed significantly among cultivars, ranging from 18.85 to 23.10 g. Seedless produced the heaviest fruits (23.10 g), followed by China (21.96 g), whereas Shahi recorded the lowest fruit weight (18.85 g).

3.4 Pericarp weight, aril weight, seed length, seed width and seed weight

Pericarp weight, aril weight, seed length, seed width, seed weight, and total soluble solids (TSS) differed significantly among the evaluated cultivars (Table 4).

Pericarp weight ranged from 1.38 to 3.58 g. Muzaffarpur recorded the highest pericarp weight (3.58 g), followed by Bombai (2.68 g), whereas Shahi exhibited the lowest value (1.38 g).

Aril weight ranged from 10.72 to 15.14 g. Seedless produced the highest aril weight (15.14 g), followed by Calcuttia (13.24 g) and China (13.17 g), whereas Muzaffarpur recorded the lowest aril weight (10.72 g).

Significant differences were also observed in seed dimensions. Muzaffarpur produced the longest seeds (2.79 cm), while Seedless recorded the shortest seed length (1.85 cm). Seed width ranged from 1.04 to 1.70 cm, with Bombai producing the widest seeds (1.70 cm) and Seedless the narrowest (1.04 cm). Seed weight varied between 1.20 and 4.29 g. China produced the heaviest seeds (4.29 g), whereas Seedless had the lightest seeds (1.20 g).

Total soluble solids ranged from 18.25 to 21.50 °Brix. Shahi recorded the highest TSS (21.50 °Brix), followed by China (19.75 °Brix), whereas Early Large Red and Calcuttia exhibited the lowest values (18.25 °Brix).

4 Discussion

The present study demonstrated significant variation in fruit morphological and quality characteristics among the seven evaluated litchi cultivars, indicating that fruit traits are largely governed by genetic differences among cultivars and their interaction with the growing environment. Fruit morphology, including colour, shape, and size, varied considerably across cultivars, reflecting differences in genetic makeup that determine fruit development and external appearance. Environmental factors such as temperature, solar radiation, soil fertility, and orchard management may further influence the expression of these traits, although cultivar genetics remain the primary determinant. Similar variation in fruit morphology among commercial litchi cultivars has been reported by Nacif et al. (2001) and Nath et al. (2022), who concluded that fruit appearance is predominantly cultivar dependent.

Significant differences were also observed in fruit length, fruit width, and fruit weight among the evaluated cultivars. Seedless produced the highest fruit weight, whereas Early Large Red and China recorded superior fruit dimensions. Fruit size is a complex quantitative trait regulated by cell division and cell expansion during fruit development and is influenced by the availability of carbohydrates and assimilates during the fruit growth period. Cultivars possessing greater sink strength generally accumulate more assimilates, resulting in larger and heavier fruits. Comparable variation in fruit size among litchi cultivars has been documented by Wang et al. (2017) and Chaudhary et al. (2023). Minor differences between the present findings and previous reports may be attributed to variations in environmental conditions, orchard management practices, tree age, and regional agroecological characteristics.

Seed characteristics showed marked differences among cultivars, with Seedless exhibiting significantly smaller and lighter seeds than the remaining cultivars. Small-seeded cultivars are highly desirable because reduced seed size increases the proportion of edible aril, thereby improving consumer acceptance and market value. The larger aril weight recorded in Seedless further supports this relationship, indicating that suppression of seed development allows greater allocation of assimilates toward aril growth. Similar observations have been reported by Singh et al. (2012), who described "chicken-tongue" seeded cultivars as commercially superior because of their higher edible portion. Nath et al. (2022) also emphasized that seed morphology is genetically controlled and serves as an important criterion in cultivar selection and breeding programmes.

Total soluble solids (TSS), an important indicator of fruit sweetness and eating quality, differed significantly among cultivars. Shahi recorded the highest TSS, suggesting superior sugar accumulation during fruit maturation. The accumulation of soluble sugars in litchi fruit is regulated by genotype and influenced by physiological processes such as carbohydrate translocation, photosynthetic efficiency, enzyme activity, and fruit maturity at harvest. Climatic conditions during fruit development, particularly temperature and light intensity, may further influence sugar accumulation. Hussain et al. (2021) similarly reported that cultivar genetics play a dominant role in determining soluble solids, while environmental conditions modify the extent of sugar accumulation. The relatively high TSS of Shahi indicates its suitability for fresh consumption and premium fruit markets.

The observed varietal differences have important implications for commercial litchi production in Nepal. Seedless combined high fruit weight, greater aril weight, and reduced seed size, making it an attractive cultivar for consumers and the fresh fruit market. In contrast, Shahi exhibited superior sweetness, while China and Early Large Red performed well for fruit size. These findings suggest that cultivar selection should be based on the intended market, with Seedless being preferable where edible portion is prioritized and Shahi being suitable where sweetness is the primary quality attribute. Region-specific evaluation of cultivars is essential because fruit quality is influenced by genotype × environment interactions, and cultivar performance may vary under different agro-climatic conditions (Menzel, 2002).

Although the present study provides valuable baseline information on the fruit quality characteristics of major litchi cultivars grown in Sarlahi, it was conducted at a single location during one fruiting season. Consequently, seasonal variation and environmental effects could not be fully evaluated. Future studies should include multi-location and multi-year trials to assess the stability of cultivar performance under diverse agroecological conditions. In addition, integrating physiological, biochemical, molecular, and postharvest quality analyses would provide a more comprehensive understanding of varietal performance and support the development of improved litchi cultivars for commercial production in Nepal.

5 Conclusion

This study demonstrated significant variation in fruit morphological and quality characteristics among seven major litchi (Litchi chinensis Sonn.) cultivars grown under the agro-climatic conditions of Sarlahi, Nepal. Among the evaluated cultivars, Seedless exhibited superior commercial attributes, including higher fruit weight, greater aril weight, and smaller seed size, indicating a higher edible portion and greater consumer preference. Shahi recorded the highest total soluble solids (TSS), reflecting superior sweetness and eating quality, whereas China and Early Large Red produced comparatively larger fruits. These findings confirm that cultivar selection plays a crucial role in determining fruit quality and market value.

The results provide valuable scientific information for growers, researchers, and orchard managers in selecting cultivars according to market demand and production objectives. Based on the overall evaluation of fruit quality traits, Seedless appears to be the most promising cultivar for commercial cultivation in the Terai region of Nepal, while Shahi is particularly suitable for fresh fruit markets where sweetness is a key quality attribute.

Since the present investigation was conducted at a single location during one fruiting season, further multi-location and multi-year evaluations are recommended to validate the stability of cultivar performance under diverse agroecological conditions. Future research should also integrate physiological, biochemical, molecular, and postharvest quality assessments to support breeding programmes and the sustainable development of the litchi industry in Nepal.

Authors’ contributions

AA and AP were involved in conceptualization, conducting the experiment, data curation, editing, data analysis, writing the original draft, manuscript revision and providing the final structure to the manuscript. Both authors read and approved the final manuscript.

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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