Assessment of Genetic Diversity in Taro Using Morphometrics

Taro is an important tropical tuber crop, used as a staple food or subsistence food by millions of people in the developing countries. A program was done to analyze and identify the same promising 20 selected local and Indian accessions taro, aiming at the characterization of the extent and distribution of genetic diversity using morphological marker with the define objectives ‘to find genetic variability amongst the 20 taro genotypes collected from different agro-climatic zones in India, in respect of plant physical (like length of main sucker, no of petioles, length of leaf lamina, wt. of side tuber, number of side tuber, estimated Corm yield, breadth of leaf lamina)’. The present study revealed that the genetic diversity recorded through physical parameters corresponded with the genetic diversity revealed through molecular data analysis. On the basis of D2 statistics the 20 genotypes were grouped into six different clusters (I-VI). Most of the local taro genotypes collected from different locations (BCC-1, BCC-2, BCC10, BCC15, BCC18, BCC-21, BCC24 and BCC-25) were placed in Cluster II with moderate intra cluster distance indicating their closeness, and showed similar phenotypic characters. The genotypes viz. FC-4, FC-11 and PKS1 were found to distantly relate to other genotypes and were grouped into Cluster III.

Taro [Colocasia esculenta (L.) Schott] is one of the oldest cultivated crops grown for its edible corms and leaves (Plucket, 1976;Kuruvilla & Singh, 1981; Coates et al., 1988).It is an important tropical tuber crop, used as a staple food or subsistence food by millions of people in the developing countries in Asia, Africa and Central America.World-wide it is the fifth most consumed root vegetable (FAOSTAT, 2005) with over 25% produced in Oceania and South-East Asia.The corms, leaves and petioles are used as a vegetable and considered as a rich source of carbohydrates, proteins, minerals and vitamins.They are a good source of thiamin, riboflavin, iron, phosphorus, zinc and a very good source of vitamin B6, vitamin C, niacin, potassium, copper, and manganese.Taro corms are very high in starch, and are a good source of dietary fiber.Oxalic acid may be present in the corm and especially in the leaf and these foods should be eaten with milk or other foods rich in calcium.Taro corms and leaves are also credited with having medicinal values.In India, two taro types, i.e., Colocasia esculenta var esculenta (Dasheen type) and C. esculenta var antiquorum (Eddoe type), are commonly cultivated throughout the country.Like most other root and tuber crops, taro is vegetatively propagated, although seeds are also naturally formed.Taro is a member of the Araceae family, which is made up of at least 100 genera and more than 1500 species.Colocasia is the most important edible genus while Colocasia esculenta being the most important species (Maga, 1992).Germplasm characterization and evolutionary process in viable populations are important links between the conservation and utilization of plant genetic resources.Taro cultivars in the Asia Pacific regions exhibit remarkable morphological variation.This variation may be associated with cross-pollination and sexual recombination, and perhaps mutation, followed by intensive selection by isolated human communities in diverse environments (Rao et al. 1998).It is also likely that continuous vegetative propagation and selection has contributed to the phenotypic diversity observed.The origin of existing landraces or farmer varieties can only be elucidated by assessing genetic diversity to establish varietal identity and the extent and distribution of genetic variation.The study of agro-morphological variability is the traditional method of assessing genetic diversity.Agro-morphological characterization, however, is often hindered by the limited number of polymorphic features and the need for multiple test environments (Kresovich et al. 1997).The present investigation was done to analyze and identify some promising local collections and genotypes of taro, aiming at the characterization of the extent and distribution of genetic diversity using D 2 statistics based on agromorphological parameters.

MATERIALS METHODS
The experiment was conducted at the Central Horticultural Research Station, Mondouri, Bidhan Chandra Krishi Viswavidyalaya, Nadia, West Bengal.The site is situated at 9.75MSL, at approximately 22057' N latitude and 88020'E longitude.Topographical situation of the experimental site is under gangetic new alluvial plains of West Bengal.The soil is sandy loam and slightly acidic.
The total of twenty Colocasia esculenta (L.) Schott accessions were considered in this study.The accessions were collected from different parts of West Bengal and other states (Assam, Orissa, Kerala) India.An overview of the genotypes that have been studied is given below in Table -1.Representative samples were collected based on traditional knowledge of inhabitants and phenotypic variations observed.The experiment was laid out in randomise complete block design using 10m x 5m plots with three replications.Corms of the same size were used as a planting material and planted on a ridge during onset of rainy season.One month after planting, after the crop was well established, the plants were earthed up.Cultivation and weeding were carried out when necessary.
Descriptor of taro (Colocasia esculenta) developed by IPGRI (IPGRI, 1999) were followed for data collection.There were two sets of data's (qualitative and quantitative) collected for assessing the diversity and to find key morphological traits in taro cultivars.In regarding to the qualitative traits, only the first replication of the experiment was considered, whereas, for quantitative characters the entire replications were considered.Both foliar and subterranean data's were considered.For foliar traits, scored at five months after planting, while, subterranean traits were evaluated at harvest (8 months).Most of the data (qualitative and quantitative traits) were recorded on individual plant basis using sample averages of six plants selected at random from the row.The data were analysed for coefficient of variation (Burton and De Vane, 1953), heritability (Hanson et al., 1956), genetic advance (Johanson et al., 1955), D2 statistics by P. C. Mahalanobis (1936) and clusters analysis through Tocher method (Rao, 1952).

Leaf colour and shape
Diversity in leaf colour and shape is considered to be most important as it is the primary  2. A wide degree of variation in leaf colour existed among the genotypes.BCC-1, BCC-2, BCC-10, BCC-15, BCC-21, BCC-25, Sonajuly, Muktakeshi and PKS-1 had deep green leaf colour while the leaves of BCC-32 and BCC-38 were bass green.GK-1 had yellow green and BCC-18, FC-4, FC-11 had light green leaves.Variation in leaf shape was also observed.BCC-1, BCC-2, BCC-18, BCC-21, BCC-30, Topi and PKS-1 had lanceolate leaf shape while the leaves of BCC-10, BCC-15, BCC-24, BCC-32 and Muktakeshi were cup shaped.BCC-25, Sonajuly, FC-4, FC-11 and GK-1had cordate and Telia had oval shaped leaves.It is quite evident that based on leaf colour and shape though some of these genotypes could be identified, but the genotypes belonging to same colour group might not always be easily identifiable as there was no clear colour variation amongst them.

Variation in physical parameters
Mean value of the genotypes for different character and estimates of different genetic variability parameters are presented in Table 3

Table 4 : Distribution of 20 genotypes of taro into different cluster based on D 2 Values Cluster No of genotypes Name of the genotype
Yared Dagne, (2007)clump, number of side tuber/plants, weight of side tubers/plants and corm yield had high GCV and PCV (>30%) with high heritability (>80%) and high GA % over mean indicating greater variability of the characters and greater possibility of improvement through selection.Length of leaf and breath of leaf lamina had moderately low GCV and PCV indicating less variability for the character but had high heritability with moderate GA% over mean indicating less possibility of improvement.This results also supported byYared Dagne, (2007).