Genetic diversity of Dimocarpus longan Lour., in Southern Western Ghats

Abstract

Longan (Dimocarpus longan Lour.), is an important commercially cultivated fruit tree, belonging to the family Sapindaceae. It is commonly known as dragon-eye. In Kerala, it is known by the names chempoovam, mullai etc. It is widely cultivatedin many Asian countries like China, Thailand, and Taiwan etc. Recently many other countries including India, Sri Lanka etc. have started cultivating longan tree as a commercial fruit tree. Longan is used as a traditional medicine in China due to its high medicinal and nutraceutical value. The global demand for longan fruit has hiked rapidly due to its sweet taste and nutritional value. Fruit consist of a white edible juicy aril which is surrounded by a leathery pericarp. The fruit is rich in various bioactive polyphenols, vitamin C, volatile compounds, minerals, amino acids, proteins, fats, carbohydrates etc. Longan leaf, fruit pericarp, seed and pulp were used for extracting various polyphenols. Extracts from various parts of longan have shown pharmaceutical properties like antioxidance, anti-tyrosinase, anti-cancerous, anti-glycated, immunomodulatory activity, antihypertensive etc. Thus the importance of fruit can also be emphasized due to its richness in nutritional value. The longan tree is a subtropical fruit tree native to the southern regions of China and Indo-Burma. D. longan is indigenous to India's Western Ghats, ranging from Konkan to Tinnevelly. Other distributions in India include Eastern Bengal and Western Peninsular regions. In the Western Ghats region of Kerala, longan is a species widely distributed in evergreen forests. There is a small distribution in the semi-evergreen forests of Kerala as well. The diversity of indigenous longan populations in Western Ghats has never been studied before. In this study, morphological and genetic diversity of longan populations from six different locations in the Western Ghats regions of Kerala were selected. Among these six locations, three were located in the north of Palghat gap and three were in the South ii of Palghat gap. Morphological parameters like crown shape, branching pattern, tree height, tree girth, leaf length and leaf width was considered for studying the morphological diversity. Results from morphological traits revealed that the population from Meppadi region from north of Palghat gap stood different from other longan populations. Cluster analysis conducted using UGPMA method based on the morphological traits showed that population from Mankulam was closely related to the Meppadi population. The populations from six locations were divided into two major clusters. ISSR primers were used to investigate the genetic diversity existing among the six populations. 15 ISSR primers screened from total of 19 primers were used to amplify the DNA sample from different longan populations. Average polymorphism rate of 69.51% was observed. Matrix data was obtained and hierarchical dendrogram was produced using UGPMA method in NTsys pc 2.02 and DARwin software which clusters the populations into two major groups. Jaccard’s dissimilarity index was calculated using R software and the values ranged from 0.00 to 0.51. Genetic relation existing between the natural populations of longan in Kerala, cultivated longan cultivars and litchi were identified. Cluster analysis using UGPMA method pooled different populations into four major clusters and study proved that litchi is genetically more related to the cultivated longan variety rather than the wild populations. This is the first report on the molecular characterization of D. longan from Western Ghats regions in India. The results from this research study can provide valuable information to distinguish, classify and identify the origin of longan populations in India and can be applied for future breeding programs.