STUDIES ON GENETIC DIVERSITY IN RICE (Oryza sativa L.)

Studies on Genetic Divergence in

Rice (OryzasativaL.)

Praveen Kumar Pandey

Department of Genetics and Plant Breeding

Allahabad Agricultural Institute–Deemed University, Allahabad – 211007 (U.P.) INDIA.

Email: pandeypraveen1986@yahoo.com

ABSTRACT

Genetic diversity is pre-requisite for any crop improvement programme as it helps in the development
of superior recombinants. In the present study the nature and magnitude of genetic diversity was
assessed among 40 rice genotypes for 12 quantitative characters. From the experimental results it was
observed that NDR-6117 recorded to be the best performer for ‘seed yield’ with good ‘harvest index’
followed by Pusa-44, Sarju-52 and Mala. On the basis of Mahalanobis D² statistics the genotypes were
grouped into seven clusters. The geographical diversity has not been found related to genetic diversity.
Plant height, biological yield and test weight contributed considerably, accounting for 86.16 % of total
divergence. The highest intra-cluster distance was recorded for cluster-VII. Highest intercluster
distance was observed between cluster II and VII , therefore the genotypes from cluster II (Triguna,
MAUB-15, Pant dhan-6) having desired mean values for characters like; days to 50% flowering, panicle
length and harvest index; and from cluster VII (Sonachur and Mala) having desired mean for plant
height, flag leaf width, spikelets per panicle, biological yield and test weight, may be used in future
hybridization programme to achieve desired segregants for early rice varieties with higher yield.

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INTRODUCTION

Rice is the world's largest food crop, providing the caloric needs of millions of people daily. There
are two distinct types of domesticated rice, Oryza sativa, or Asian rice and Oryza glaberrima, African rice.
The genus Oryza contains 21 wild relatives of the domesticated rices. The genus is divided into four species
complexes: the O. sativa, O. officialis, O. ridelyi and O. granulata species complexes. All members of the
Oryza genus have n = 12 chromosomes and while interspecific crossing is possible within each complex, it
is difficult to recover fertile offspring from crosses across complexes. Oryza sativa is distributed globally
with a high concentration in Asia. (Vaughan et
al., 2003).
The current global population of 6.4 billion is expected to reach 7.5 billion by 2020 and 9.0 billion
by 2050 AD. Most of this population increase will occur in developing countries of Asia and Africa, where
rice is the staple food. Globally, rice is cultivated now on 154 million hectares with annual production of
around, 600 million tones and average productivity of 3.9 tons/ha. More than 90% of the rice is produced
and consumed in Asian countries. The other continents in which rice is grown are Africa (7.78% of the
global area), South America (6.4%) and North America (1.4%). (Viraktamath, 2007). Rice plays a pivotal
role in Indian economy being the staple food for two third of the population. In India During 2007-08 the
production of rice was 96.4 million tons and it stands second in position in production as China occupies
the first place with 125.36 million tonnes in the world’s production table of 2,038.9 million tonnes
(USDA. March 2006).
India is the largest rice growing country in the world. However, its productivity per unit area by
world standard is low. In order to increase rice productivity, high yielding and disease resistant varieties
should be developed. Grain quality in rice has been assuming an increasingly important issue particularly
since last decade due to change in the consumer preference for better quality rice as a result of changed
life style of the consumers and India’s emergence as one of the major exporter of rice in the international
markets. Large scale food shortage was experienced in India and in several neighboring countries in Asia
during late 50s and early 60s. Frequently there were warnings of impending wide spread famines. During
this grim scenario, the semi dwarf, fertilizer responsive, high yielding genotypes of rice and wheat were
introduced which led to phenomenal increase in production and productivity of these crops. This
phenomenal turn around a food front from scarcity to self sufficiency and in the few cases, even to
exportable surplus is referred to as “Green Revolution”.
Most of the Asian countries have been able to keep pace between rice production growth rate and
that of population during the last four decades. This has been mainly possible due to the contributions
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made by the green revolution technologies. However, it is of great concern to note that the rate of growth
in rice production has started declining during 90s and there has been a plateauing effect. The population
growth in most of the Asian countries, except China, continues to be around 2% per year. Hence it is very
pertinent to critically consider whether the rice production can be further increased to keep pace with
population growth. With the current green revolution technologies it is estimated that by 2020 at least
115-120 million tons of milled rice is to be produced in India to maintain the present level of self
sufficiency. Is there a need for a paradigm shift in rice research to meet the challenges of the future
decades for ensuring food security. After a brief review of rice research in India and considering the gains
obtained through green revolution technologies, the possibilities and prospects of utilizing the gene
revolution technologies are considered for further enhancing the production and productivity of rice for
not only ensuring food security but also nutritional security.
Knowledge on the genetic architecture of genotypes is necessary to formulate efficient breeding
methodology. It is essential to find out the relative magnitude of additive and non additive genetic
variances, heritability and genetic gain with regard to the characters of concern to the breeder. The
systematic breeding programme involves the steps like creating genetic variability practicing selection and
utilization of selected genotypes to evolve promising varieties. The large spectrum genetic variability in
segregating populations depends on the level of genetic diversity among genotypes offer better scope for
selection. Estimates of GCV, PCV, heritability and genetic advance will play an important role in exploiting
future research projections of rice improvement.
In a rice improvement programme, it is the germplasm, which virtually determine the success and
nature of end product. The development of superior rice population involved the intelligent use of
available genetic variability both indigenous as well as exotic to cater the need of various farming
situations of rice. The grain yield is the primary trait targeted for improvement of rice productivity in both
favourable and unfavourable environments from its present level. Rigorous efforts are needed to improve
the production of rice in the country by diversifying its uses and by developing rice hybrids for specific
traits of economic importance. Breeding strategies is chiefly influenced by the choice of germplasm. Any
wrong choice of germplasm to initiate the selection process results in the vastage of resources.

Grain yield is a complex character, which depends on its main components viz; number of spikes
per plant, spike length, number of grains per spike and 1000 grain weight. These components are further
dependent for their expression on several morphological and developmental traits, which are interrelated
with each other and therefore, the parents selected for the breeding programmes aimed at increased seed
yield should possess wide range of genetic variation for the above said morphological and developmental
characters. Besides, it could be of interest to know the magnitude of variation due to heritable component,
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which in turn would be a guide for selection for the improvement of a population. In other words, for the
improvement in any crop species, the knowledge of genetic variability for characters of economic
importance and their heritability and genetic advance is of utmost importance in planning future breeding
programme.
Efficient and economic crop improvement scheme refers to the collection of superior alleles into a
single population. Over the past century selection of desirable parents for hybridization programme has
been found as an effective operating implement in developing high yielding crop varieties upon which, the
modern agriculture can rely. Though, it is a difficult task for a plant breeder but several biometric
techniques suggested by various workers from time to time has been useful in selection of parents which
in turn would effect the crosses and ultimately generates a population true to the breeding value. The
availability of the above information greatly aids in the formulation of breeding scheme as well as in the
choice of appropriate selection method.
Progenies originating from the crosses involving diverse parents exhibit greater heterosis and
provide broad spectrum of variability in segregating generations. Such crosses not only results in inducing
variation but also provide new recombination of the genes in the gene pool, which may have great impact
on future breeding programme. Choice of parents is not only based on desirable agronomic traits,
components of yield and extent of diversity but also on heritability of yield contributing traits. The
environment, in which selection is made, is also important because heritability and genetic advance
estimates vary with change in environment.
Genetic improvement mainly depends upon the amount of genetic variability present in the
population. In any crop, the germplasm serves as a valuable source of base population and provides scope
for wide variability. Information on the nature and degree of genetic divergence would help the plant
breeder in choosing the right parents for breeding programme. (Vivekanandan and Subramanian, 1993).
It is well known that all plant breeding programmes involve selection at one stage or other. Genetic
variances serve as a basis for major plant breeding decision; they provide a greater array of genotypes
among which selection can be practiced to develop still new varieties or breeding materials. Success in
recombination breeding depends on the suitable exploitation of genotypes as parents for obtaining high
heterotic crosses and transgressive segregants. For this, the presence of genetic variability in a base
population is essential. Heritability and genetic advance are other important selection parameters. The
estimates of heritability help the plant breeder in determining the character for which selection would be
rewarding. The breeders are interested in selection of superior genotypes based on their phenotypic
expression. The major function of heritability estimates is to provide information on transmission of
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characters from the parents to the progeny. Heritability estimates can anticipate improvement by selection
of useful characters.
Genetic diversity is pre-requisite for any crop improvement programme as it helps in the
development of superior recombinants. The crosses between parents with maximum genetic divergence
are generally the most responsive for genetic improvement (Arunachalam, 1981). A quantitative
estimation of genetic diversity guides the breeder for rapid progress of the breeding programme. The
selection of agronomically suitable diverse parents for hybridization is important for getting desired
recombinants segregating generations. Hybrids showing strong heterosis are usually developed from the
parental lines that are diverse in relatedness, ecotype, geographic origin etc (Lin and Yaun, 1980).
Genetic diversity can be evaluated with morphological traits, seed protein, isozymes and DNA
markers. Conventionally, it is estimated by the D
² analysis metroglyph and principal component analysis
using morphological traits. The D² technique is based on multivariate analysis developed by Mahalanobis
(1936) had been found to be a potent tool in quantifying the degree of divergence in germplasm. This
analysis provides a measurement of relative contribution of different components on diversity both at intra
and inter-cluster level and genotypes drawn from widely divergent clusters are likely to produce
hecterotic combinations and wide variability in segregating generation.
Recognizing the importance of genetic diversity in plant breeding experiments, the present
research work was taken up with the following objectives:

1. To estimate genetic variability, heritability and genetic advance for quantitative characters.
2. To assess genetic diversity in different accessions of rice for different Agro-economically important

characters and group them into clusters.
3. To identify suitable parents for future breeding programme.

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REVIEW OF LITERATURE

The literature relevant to the present study has been reviewed briefly in this chapter under the
following heads:
2.1 Genetic variability and genetic parameters
2.2 Genetic divergence
2.1 Genetic variability:
Variability refers to the presence of differences among the individuals of plant population.
Variability results due to differences either in the genetic constitution of the individuals of a population or
in the environment in which they have grown. The existence of variability is essential for resistance to
biotic and abiotic factors as well as for wider adoptability.
Variance is the amount of variation present among the member of a population. Fisher (1918) partitioned
the total phenotypic variance into genotypic variance and environmental variance. He further divided the
genotypic variance in to additive, dominance and epistatic effects. However, it is only the genetic variation
which is heritable. Selection is also effective when there is significant amount of generic variability among
the individuals in a population. Hence insight into the magnitude of generic variability present in a
population is of paramount importance to plant breeder for staring a breeding programme in any crop
including rice.
Bhattacharaya and Mishra (1981) found high heritability and genetic advance for plant height,
number of ear bearing tillers per plant, panicle weight and number of grains per panicle in 22 rice
varieties.
Denge (1981) reported high heritability value for 1000-grain weight, palnt height, grain
number per panicle, number of tiller, grain weight per plant, panicle length and panicle number per plant.
Singh and Sharma (1982) recorded high hetitability values for plant height and 1000 grain
weight and high expected genetic advance for plant height and number of grains per panicle.
Maurya et al. ( 1986) found high heritability coupled with high genetic advance for kernal
length, L/B ratio, flag leaf width, flag leaf length, plant height, grains per panicle and test weight.

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Reddy (1992) reported highest genotypic and phenotypic coefficient of variability for number of
grains per panicle. All the traits exhibited moderate to high estimates of heritability ranging from 67.9%
for grain yield per hill to 99.5% for days to 50% flowering. Plant height and number of grains per panicle
showed high estimates of genetic advance. Among with high estimates of heritability.
Singh (1992) observed high magnitude of heritability along with high genetic advance fro fertile
spikelets per panicle, grain yield, number of tillers per panicle, plant height and spikelets per panicle. High
heritability coupled with low genetic advance recorded for 1000- grain weight and panicle length
revealed the major role of non –additive gene action in transmission of these characters from parents to
offspring.

Ali, etal. (1993) Broad sense heritability and relative expected genetic advance were computed far
plant height, number of tillers per plant, panicle length, number of spikelets per panicle, number of grains
per panicle, spikelets density, 100 – grain weight and grain yield per plant from F₂ population obtained
from twelve rice crosses involving Basmati 385, 4439, 4048 – 3 and IR-6 rice varieties/lines, exhibited
high heritability and greater relative expected genetic advance which offered promise for effective
selection and high yield potential.

Sharma and Roy (1993) recorded high heritability and genetic advance for panicle per m2 grains per
panicle and grain weight. Plant height, flag leaf length, flag leaf width, panicle length and grains per
panicle were significantly and positively correlated with grain yield.

Chaubey and Singh (1994) evaluated Twenty rice varieties for yield related traits and observed that
phenotypic coefficient of variation was greater than the genotypic coefficient of variation for all the traits
studied and heritability was highest for total number of spikelets followed by grain yield per plant and 100
– grain weight. Genetic advance as percent of mean was highest for grain yield per plant followed by
panicle weight and total number of spikelets.
Ganesan (1994) evaluated 28 rice hybrids and their seven very early and four early maturing
parents for genetic variability. The characters, grains per panicle, grain yield per plant and dry matter
production showed high genotypic co-efficient of variation, indicating the predominance of additive gene
effects. Days to panicle emergence showed moderate genetic variability, indicating the existence of scope
for further improvement through phenotypic selection.
Genetic variability for thirty nine rice genotypes were assessed by Sarma and Richharia (1995) and
reported that secondary branches per panicle, spikelets per panicle, grain yield, panicle weight and
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effective tillers per plant exhibited high genotypic coefficient of variation and observed high heritability
for secondary branches per panicle and spikelets per panicle.
Reddy and De (1996) studied that there were significant differences among 36 genotypes for the
12 characters. Grain yield per hill, grain per panicle and panicle weight had the highest estimates of
genotypic and phenotypic variability. They observed high heritability for grain length, followed by 1000 –
grain weight, grain breadth, plant height, panicle weight, grain yield and grain per panicle.
Sharma et al. (1996) assessed 39 upland rice genotypes for 12 yield components. Genotypic
coefficient of variation (GCV) was highest for effective tillers per meter row length, followed by panicle
weight, secondary branches per panicle, grain yield per meter row length and spikelets per panicle. They
recorded broad sense heritability which ranged from 42.2% for grain yield per meter row length to 99.9%
for grain length. Effective tillers per meter row length, panicle weight, secondary branches per panicle and
spikelets per panicle had high GCV and high heritability. Genetic advance as a percent of mean was
highest for effective tillers per meter row length followed by panicle weight
Ashvani et. al. (1997) reported highest genotypic variation for straw yield per plant followed by
grain yield per panicle, grain yield per plant, height of plant, total biological yield per plant and number of
fertile florets per panicle in 22 genotypes of rice, growing in India. They observed high heritability
coupled with high genetic advance for 1000 – grain weight, height of plant, flag leaf area, grain yield per
panicle and straw yield per plant.
Borbora and Hazarika (1998) evaluated thirty genotypes of rice for 11 yield related traits. Highly
significant variation among the genotypes was observed for different characters. The differences between
genotypic and phenotypic coefficient of variation were relatively low for almost all the characters except
grain yield per plant. They recorded high to moderate genotypic coefficient of variation together with high
heritability and genetic advance for number of filled grains per panicle and 1000 – grain weight, grain
yield per panicle and number of secondary branches per panicle.
Rather etal. (1998) evaluated 56 rice cultivars belonging to three different eco-geographical races
viz. India Javanica and Japonica for genetic variability and genetic parameters with respect to 14 traits.
Spikelets sterility and grains per panicle exhibited high genotypic coefficient of variation associated
moderate heritability and high genetic advance.
Lalitha and Sreedhar (1999) studied 50 genotypes of groa (upland) rice for 10 quantitative traits in
Kharif 1995. The genotypic coefficient of variation was highest for grain yield per plant and also high
for 1000-grain weight.
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Kumar etal.(1999) noted significant variation for plant height, number of tillers per plant, flag leaf
length, flag leaf width, number of panicle per plant, Number of spikelets per plant, yield per plant and test
weight.
Pushpa et al. (1999) found that the genotypic coefficient of variation was highest for grain
yield/plant and also high for spikelets per panicle and grain yield per panicle in 50 genotypes of gora
(upland) rice. High heritability was observed for 1000-grain weight, days to hundred percent flowering,
grain yield per plant and days to 50% flowering.
Rasyad (1999) estimation of genetic component of variances and heritability in a reference
population is very crucial if it is utilized for a breeding programme. We were particularly interested in
assessing variation for several agronomic traits in a reference population of rice (Oryza sativa L.)
commonly grown in considerably high level of soil salinity. Fourteen adopted cultivars selected from the
area and two high yielding cultivars were evaluated at two levels at salinity in a green house experiment
in 1997.
Verma etal. (2000) observed relatively low magnitude of differences between PCV and GCV for all
the traits, except number of sterile spikelets per panicle.
Yadav (2000) reported high genotypic and phenotypic coefficient of variation for spikelets per
panicle, grain yield and harvest index in nine rice cultivars at Chattisgarh. High heritability coupled with
high genetic advance for total seeds per panicle, total seeds per plant and seed yield per plant in a study
including 15 genotypes of rice.
Yadav etal. (2002) genetic variability for yield and its components was studied in 15 genotypes of
rice during Kharif 1997-98 in Raigarh, Madhya Pradesh. Observation on 5 competitive plants were
recorded for 10 characters (days to 50 flowering, days to maturity, plant height, tiller per plant, panicle
length, spikelets per panicle, total seeds per panicle and per plant, 1000-seed weight, and seed yield per
plant). Appreciable amount of genotypic coefficient of variation, heritability and genetic advance were
observed for total grains per panicle, total grains per plant and grain yield per plant. This indicated the
role of additive genetic component controlling these traits and scope for selection.

Bidhan et al. (2001) evaluated 25 medium duration genotypes for eight traits and observed high
phenotypic and genotypic variances for grain yield, followed by number of filled grains per panicle. They
recorded heritability which ranged from 50% (grain yield per hill) to 90% (grain breadth). Genetic
advance as percent of mean was highest for number of filled grains per panicle (70.34), followed by grain

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