Genetic Diversity Studies in Popular Rice ( Oryza Sativa L.) Varieties of India

The success of any breeding programme depends upon the selection of suitable parents for developing elite recombinants. The eighty seven popular rice varieties of India were grouped into ten clusters using Mahalanobis D 2 statistics which revealed the presence of substantial diversity among the genotypes. The characters viz., kernel length, protein content, days to 50 per cent flowering, 100-grain weight, kernel breadth, single plant yield, plant height, number of grains per panicle and L/B ratio contributed maximum towards divergence. Maximum intra cluster distance was observed in cluster X. Cluster II showed maximum inter cluster distance with cluster IX. Most of the long slender grain types are included in the cluster X, which is having highest desirable mean values for most of the characters. The superior performing genotypes from the divergent clusters II, III, VI, VIII, IX and X can be used as parents to exploit maximum heterosis for improving productivity along with fine grain quality.

Rice is the most important staple cereal foodstuff which forms the daily bread for more than three billion people around the world.Thus, the slogan "Rice is Life" aptly suits to the present day scenario where roughly half of the planet's population depends on rice.To meet the demands of increasing population and to maintain selfsufficiency, the present production level needs to be increased enormously which is possible through heterosis breeding and other innovative breeding approaches.To increase the present levels of heterosis for yield, there is a need to identify and utilize genetically divergent parents for inter and intra sub-specific crosses in rice.
A systematic evaluation and characterization of germplasm lines not only help in identification of superior and genetically divergent germplasm lines but also provide information on the utility of the genetic resources.Success of any breeding programme depends upon the amount of genetic variability available in the crop species besides the efficiency of selection techniques adopted by the plant breeder.Quantification of degree of divergence in a given material is of immense value in identification of divergent genotypes for further use in hybridization to create new variability.Mahalanobis D2 statistics has been proved to be a powerful tool for quantifying genetic diversity in a given population.Divergent genotypes could be obtained by collection from different eco-geographical regions or it could be induced by combination breeding.Therefore, the present investigation was carried out to generate 1*Corresponding author email: rrsunkara@yahoo.co.in the information on genetic divergence in the popular rice varieties cultivated in different regions of India.

Materials and Methods
A field experiment was conducted with eighty seven genotypes of rice collected from Plant Breeding Division, Crop Improvement Section, Directorate of Rice Research, Rajendranagar, Hyderabad in a randomized block design with three replications at Directorate of Rice Research Farm, ICRISAT, Patancheru, Hyderabad, Andhra Pradesh, India, situated at 17.53oN latitude, 78.27oE longitude and altitude of 545 m above mean sea level.Thirty days old seedlings were transplanted 20 cm apart between rows and 15 cm within the row in three blocks.All the necessary precautions were undertaken to maintain uniform plant population in each treatment.All the recommended package of practices was adopted besides providing necessary prophylactic plant protection measures to raise a good crop.Single plant observations on yield and its contributing characters were recorded on five randomly selected plants in each genotype from the middle row in each replication as per standard techniques for plant height, number of productive tillers per plant, panicle length, single plant yield, spikelet fertility.Days to 50 per cent flowering was computed on plot basis.Seed weight was recorded by weighing 100-grains of each genotype.Mean kernel length and breadth of ten polished kernels from their bulk sample from each replication of each genotype were measured using a steak grain shape tester.L/B ratio was computed by dividing mean kernel length with mean kernel breadth.Protein content was determined by the Micro-Kjeldhal method described by Pregl (1930).The mean data after computing for each character was subjected to standard methods of statistical analysis.The genetic divergence between the rice varieties was estimated using Mahalanobis (1936) D2 statistics and grouping of genotypes into different clusters was carried out by using Tocher's method as described by Rao (1952).

Results and Discussion
Genetic divergence analysis quantifies the genetical distance among the selected genotypes and reflects the relative contribution of specific traits towards the total divergence.The genetic divergence among the genotypes is very much essential since a cross involving genetically divergent parents is likely to produce high heterotic effects and variability in the segregating generations.Analysis of variance indicated the existence of significant variability for all the characters studied except 100 grain weight, kernel length, kernel breadth and L/B ratio.Based on relative magnitude and D2 estimates, all the genotypes under study were grouped into ten clusters (Table 1).Among the different clusters, cluster IX consisted of a maximum of 19 varieties and cluster II VIII contained a minimum of 2 varieties each.A wide range of variation was observed in cluster means for all the characters studied (Table 2).Clusters with high cluster mean and high genetic divergence should be considered while selecting parents for hybridization programme.Most of the genotypes with long slender grains were included in Cluster X, which was found to be the superior group by recording highest cluster mean values for maximum number of yield contributing characters viz., number of grains per panicle (106.00),number of filled grains per plant (970.00),number of chaffy grains per plant (80.50), total number of grains per plant (1050.50),single plant yield (19.95) and L/B ratio (4.84) and lowest cluster mean value for two traits i.e., spikelet fertility (82.13) and kernel breadth (1.63).Hence, genotypes of cluster X can be selected as parents in hybridization programme for developing superior hybrids having high yield coupled with fine grain quality.
Cluster IX had highest mean for number of productive tillers per plant (11.80), 100-grain weight (2.61) and kernel length (8.08) and least mean value for number of grains per panicle (53.60).The cluster II was found to exhibit highest cluster mean values for panicle length (27.83) and least cluster mean value for 100-grain weight (1.50), kernel length (4.37) and L/B ratio (2.35).Maximum cluster mean value for plant height (170.67) and days to 50 per cent flowering (124.89) were recorded in cluster III.Cluster I and cluster VI showed maximum mean values for kernel breadth (2.03) and protein content (11.16), respectively.Minimum cluster mean values for plant height (100.98) and days to 50 per cent flowering (94.68) were recorded in cluster VI and cluster V, respectively.Cluster IV was found to exhibit as parents to develop high yielding rice varieties.The inter cluster distances were higher than the intra cluster distances reflecting the presence of wider diversity among the genotypes of the distant group.Similar results were obtained by Anuradha and Reddy (2003), Rao (2004) and Raghuwanshi and Duhoon (2005).The greater the distance between two clusters, the wider will be the genetic diversity among the genotypes of those clusters.Maximum intra cluster distance (1836.70)was observed in cluster X (Table 3) indicating that some genetic divergence still existed among these genotypes and hence these can be used for yield improvement through recombination breeding.The intra cluster distance was minimum (624.34)for cluster I revealing greater uniformity as a consequence of less divergence among the genotypes of this group.Highest inter cluster distance was noticed between cluster II and IX (11942.41)indicating the existence of maximum

Table 2 . Cluster means for different characters (in cluster analysis)
highest mean for spikelet fertility (99.52) and least cluster mean for protein content (7.49), while cluster VII was characterized by its lowest mean for panicle length (23.10) and single plant yield (11.99).However, lowest mean values for number of filled grains per plant (584.94),number of chaffy grains per plant (49.19) and total number of grains per plant (633.43)were noticed in cluster VIII.Therefore, genotypes with high mean values for the above yield contributing traits from different clusters may be used

Table 4 . Relative contribution of different traits to genetic diversity in rice
per cent flowering (12.96 %), 100-grain weight (4.92 %), kernel breadth (2.99 %), single plant yield (1.71 %), plant height (1.47 %), number of grains per panicle (1.42 %), L/B ratio (0.59 %), number of filled grains per plant (0.43 %) and number of chaffy grains per plant (0.11 %).However number of productive tillers per plant, panicle length, total number of grains per plant and spikelet fertility did not contribute towards genetic divergence among the genotypes under study.In the present study, seven superior genotypes, viz., ASG-4013, CN-1039-9, Dinesh, Varalu, Birupa, Erramallelu and Basumathi-386 with outstanding mean performance from the divergent clusters II, III, VI, VIII, IX and X were found to have immense potential for utilization as parents in heterosis breeding.