Evaluation of genetic diversity of cherry tomato (Solanum lycopersicum L. var. cerasiforme) germplasm under West Garo Hills, Meghalaya

Introduction

Vegetables are edible parts of plants commonly used in cooking, though some are consumed raw in smaller amounts. Various plant parts serve as vegetables, including leaves (e.g., leafy greens), stems (such as knolkhol, asparagus, cauliflower), fruits (like melons, gourds, brinjal, tomato, capsicum, and okra), immature flower buds and thick stalks (e.g., broccoli), heads or buds (such as cabbage, globe artichoke, and Brussels sprouts), underground parts (like potato, sweet potato, onion, garlic, colocasia, ginger, and turmeric), fleshy leaf stalks (e.g., celery), and storage roots (including radish, carrot, turnip, and beetroot) (Arya, 2013) [1] . Vegetable cultivation plays a significant role in agriculture due to their richness in essential nutrients such as carbohydrates, proteins, vitamins, and minerals. Regular consumption of vegetables not only enhances taste and appetite but also contributes dietary fiber, aiding digestion and preventing constipation. Economically, vegetables are among the most affordable sources of natural food and serve as excellent dietary supplements alongside staple cereals. Tomato (Solanum lycopersicum L.), a key vegetable crop, belongs to the Solanaceae family, which includes around 90 genera. This family is divided into two main subfamilies: Solanoideae and Cestroideae. The genus Lycopersicon, part of the Solanoideae subfamily, has a diploid chromosome number of 2n = 2x = 24 (basic number x = 12). Within Solanoideae, Lycopersicon is categorized under the large tribe Solaneae, which includes 18 genera the largest being Solanum, and Lycopersicon being one of the smallest yet closely related (Swarup, 2014) [19] . Tomato (Solanum lycopersicum L.) is the second most produced vegetable inthe world, with relevant participation in human diet (Barankevicz et al., 2015) [3] . Cherry tomato (Solanum lycopersicum L. var. cerasiforme) is recognized as a botanical type within the broader category of cultivated tomatoes (Najeema et al., 2018) [11] . It is believed to be the wild ancestor from which all domesticated tomato varieties have evolved (Ramya et al., 2016) [14] . Both the cherry tomato and the modern cultivated tomato (Solanum lycopersicum L.) are capable of crossbreeding (Swarup, 2014) [19] . Characterized by its small, bright red, and flavorful fruits, the cherry tomato is commonly consumed fresh and is known for its resemblance to cherries in appearance (Charlo et al., 2007) [6] . Cherry tomato plants are generally classified by their growth habit either determinate or indeterminate. Determinate types grow as compact bushes, producing a single harvest during the season, while indeterminate types develop long vines that continue producing fruit over an extended period (Hancock et al., 1984) [7] . This tomato variety has seen rising popularity worldwide due to its desirable traits, including being rich in vitamins A and C, natural sugars, and having a low calorie content. It also performs well under high temperatures and contains beneficial antioxidants and phytochemicals such as lycopene, beta-carotene, flavonoids, and essential nutrients (Prema et al., 2011; Rosales et al., 2011) [13,16] . Given the growing demand, it has become increasingly important to breed high-yielding cherry tomato cultivars that are resilient to both biotic and abiotic stresses and are well-suited for both fresh consumption and processing.

Given the rising demand and potential of cherry tomato, there is a need to improve the crop by developing highperforming varieties suited to specific agro-ecological conditions and market needs. Evaluating cultivated cherry tomato genotypes for desirable traits across different environments can reveal the extent of genetic variability, which is crucial for crop improvement. Understanding genetic parameters and character associations helps in identifying traits that significantly influence yield and adaptability. The greater the genetic diversity in the germplasm, the higher the chances of selecting superior types for breeding. Selection remains a core component of vegetable crop improvement. To select effectively, it is essential to assess the extent and nature of variation among genotypes and how environmental factors influence trait expression. Genotypes with desirable traits and high variability can serve as valuable parents in breeding programs for better yield, stress tolerance, and nutritional quality. In the West Garo Hills of Meghalaya, diverse landraces of cherry tomato are cultivated and preserved by local farmers using traditional practices. Recognizing this diversity, the present study was undertaken to assess genetic divergence among cherry tomato accessions using Mahalanobis D² statistics.

Materials and Methods

A field experiment was conducted at the Departmental Research Farm, Horticulture Department, NEHU Tura Campus, West Garo Hills, Meghalaya. The site, located at 25°31' N latitude and 90°13' E longitude, stands at 527 m above sea level. Climatic data during crop growth were recorded by the Agro-meteorological Division, Ministry of Earth Sciences, and are summarized in Table-1. The study involved 15 cherry tomato germplasm lines collected from various locations within West Garo Hills. The trial followed a randomized block design (RBD) with three replications.

Genetic divergence (D 2 analysis)

Genetic divergence in cherry tomato was assessed using Mahalanobis D² statistics as proposed by Rao (1952). The analysis followed these steps:  A set of uncorrelated linear combinations (y's) was derived from the common dispersion matrix of correlated variables (x's) through pivotal condensation.  Genotypic means for 15 traits (x₁ to x₁₅) were transformed into uncorrelated values (y₁ to y₁₅).

iii. D² values between the ith and jth genotypes were calculated as: D²ᵢⱼ = ∑(yᵢₜₕ-yⱼₜₕ)², for t = 1 to K characters.

Clustering

Genotypes were grouped into clusters based on D² values, following Rao's method. Genotypes within a cluster had smaller average D² values than those in different clusters, indicating greater similarity within than between clusters.

Results and Discussion

The experiment was conducted to evaluate 15 cherry tomato germplasm lines for genetic divergence and trait characterization, aiming to identify superior genotypes for future breeding programs. Data collected on various traits were analyzed for genetic variability using Mahalanobis D² statistics.

Genetic divergence analysis

Genetic divergence plays a crucial role in crop improvement. Understanding the extent and nature of genetic variability helps in selecting promising lines from existing germplasm, thereby enhancing the effectiveness of breeding programs.

Grouping of genotypes into different clusters (D 2 analysis)

Based on genetic divergence analysis, the clustering pattern of the fifteen cherry tomato genotypes is shown in Table 2.

The genotypes were divided into two distinct clusters:

Cluster II contained the majority with eleven genotypes, while Cluster I included four. The grouping did not reflect any correlation between genetic and geographic origin. Similar findings were reported by Spaldon et al. (2017) [18] . Hence, genotype selection for hybridization should prioritize genetic variability over geographic distribution. [10] .

In tomato, yield results from the combined influence of several contributing traits (Bernousi et al., 2011) [4] . Key characteristics such as number of flowers per cluster, days to first fruit ripening, fruit weight, length, and breadth play a significant role and should be evaluated for genetic divergence to identify superior genotypes with desirable traits (Hussain et al., 2018) [8] . [18,15,10] . The contribution of 15 traits to genetic divergence is presented in Table 4.9. Among them, number of fruits per cluster contributed the most (12.23%), followed by number of fruits per plant (11.23%), days to first fruit set (9.89%), number of clusters per plant (9.45%), days to first fruit harvest (8.89%), days to first fruit maturity (7.89%), fruit yield per plant (6.97%), fruit length (4.76%), and number of flowers per cluster (4.55%). Similar major contributions of traits like days to 50% flowering, flowers per cluster, and fruits per plant were reported by Khanna and Misra (1977) [9] , Bhattacharya et al. (1979) [5] , and Prasanth (2003) [12] . In contrast, Sekhar et al. (2008) [17] and Spaldon et al. (2017) [18] noted a lower contribution from traits such as days to 50% flowering and marketable yield. Traits with relatively lower contributions included fruit weight (3.23%), days to last fruit harvest (2.88%), seeds per fruit (2.67%), fruit breadth (2.56%), days to 50% flowering (2.34%), stem thickness (2.22%), 1000-seed weight (2.12%), locule number per fruit (1.45%), plant height and peduncle length (1.23% each), primary (0.98%), secondary branches (0.89%), and pericarp thickness (0.34%). Overall, traits such as fruits per cluster, fruits per plant, days to first fruit set, clusters per plant, and earliness-related traits accounted for 59.58% of the total divergence. These traits should be prioritized in parent selection for hybridization. Supporting this, Babu et al. (2018) [2] also found that average fruit weight, number of fruits per plant, and locule number per fruit made significant contributions to genetic diversity in tomato.

Rescaled Distance Cluster Combine

Conclusions

This study revealed significant genetic diversity among 15 cherry tomato genotypes from West Garo Hills, Meghalaya, using Mahalanobis D² analysis. The genotypes were grouped into two clusters, with divergence unrelated to geographic origin, highlighting the importance of genetic variability in breeding. Cluster I showed higher fruit yield and average fruit weight, while Cluster II exhibited greater diversity and early maturity traits. Key traits contributing most to genetic divergence included number of fruits per cluster, fruits per plant, and earliness traits. These findings support the use of genetically diverse local landraces in breeding programs to develop high-yielding, stress-tolerant cherry tomato varieties suited to regional conditions.

Acknowledgement

AcknowledgementThe author sincerely thanks the institutional head, lab assistant, co-workers, and field assistants for their support during the study. Gratitude is also extended to the local people for their valuable cooperation and assistance in the field.

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