GENETIC DIVERSITY FOR COLD TOLERANCE IN RICE (Oryza sativa L.)
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Date
2013
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ACHARYA N.G. RANGA AGRICULTURAL UNIVERSITY
Abstract
In the present investigation, 76 rice genotypes were evaluated for diversity to cold
tolerance by employing morphological traits and SSR markers. The experiment was laid out in
RBD with three replications at college farm, as well as in CRD at the laboratory, Institute
of Biotechnology, College of Agriculture, Rajendranagar, Hyderabad during rabi 2011.
In the study the genotypes showed significant differences for days to germination,
germination percentage, growth rate and seedling vigour at seedling stage. The highest
germination percentage was observed with genotype Pusa superfast followed by IR-83222-
174 indicating their tolerance to cold. Gedanzipeton has the lowest germination percentage.
Among 76 genotypes tested for various parameters the genotypes Pusa superfast,
Emergency, IR-83222-174 and Tellahamsa exhibited tolerance to cold temperature
prevailing at seedling stage in terms of leaf yellowing score. The seedlings of these
genotypes remained green with higher growth rate.
Analysis of variance indicated the existence of significant difference among
genotypes for all the characters observed. Studies of genetic variability revealed high
phenotypic and genotypic coefficients of variation, heritability and genetic advance as per
cent of mean for the traits viz., number of tillers per plant, grain yield per plant, number of
filled grains per panicle and total number of grains per panicle indicating simple selection
can be practiced for improvement of these characters. Detection of minor differences
between GCV and PCV for all the characters indicated less influence of environment on
these characters.
Morphological divergence by Euclidian2 method indicated the existence of
significant diversity among genotypes which were grouped into nine clusters. Days to 50
percent flowering, unfilled grains per panicle, filled grains per panicle and panicle length
contributed maximum towards genetic diversity. Maximum difference among the
genotypes within the same cluster was shown by cluster VII. The maximum inter cluster
distance was noticed between the cluster VI and IX. From the inter cluster D2 values of
nine clusters the highest divergence occurred between cluster VI and IX indicating their
importance to contributing genetic diversity. Cluster VI and IX were represented by single
genotype indicating high degree of heterogeneity among the genotypes. The genotypes
showing cold tolerance in terms of leaf yellowing score, germination percentage, days to
germination and growth rate at seedling stage were grouped in cluster I, II, III and V
indicating their divergence to cold tolerance from other clusters.
Character association studies revealed that the character grain yield per plant
showed significant positive association with filled grains per panicle, number of tillers per
plant, total number of grains per panicle and panicle length. This indicated that
simultaneous selection of all these characters were important for yield improvement.
A critical analysis of the results by path analysis revealed that the traits number of
filled grains per panicle, number of tillers per plant, panicle length and plant height were
directly influencing the grain yield per plant. Hence, these traits were considered as
important attributes in formulating selection criterion for achieving desired targets.
Diversity analysis for cold tolerance through molecular markers was carried out
employing 12 SSR markers. The number of alleles ranged from 2 to 8 with a mean of 4.08
indicating greater magnitude of diversity among the genotypes. The PIC value ranged from
0.688 to 0.943 with an average of 0.855, conformed the markers used were highly
informative. Cluster analysis using SSR markers revealed a dendrogram with range of 0.51
to 0.96 similarity indicating considerable amount of diversity among the genotypes. Cluster
analysis was done with cold tolerant QTL linked markers. Cluster analysis using SSR
markers revealed a dendrogram with range of 0.51 to 0.96 similarity index. The genotypes
were grouped into two main clusters. Cluster I consisted of single genotype while the
remaining 75 genotypes were accommodated in the cluster II, which was the major cluster.
Cluster II was classified into two sub-clusters IIA and IIB. Cluster IIA consisted of single
genotype while IIB had 74 genotypes. Cluster IIB sub grouped into IIB1 and IIB2.Cluster
IIB1 consisted of single genotype while IIB2 had 73. IIB2 was a major cluster sub grouped
into IIB2a and IIB2b. Cluster IIB2a contains 31 genotypes while cluster IIB2b had 42.
Molecular and morphological analysis did not give similar results, but molecular
markers (SSR) were more informative and could group the genotypes into different clusters
based on their genetic constituency. But both can be complementary for assessment of
diversity for cold tolerance and genotype identification in breeding programme.
Based on the present study, cold tolerant (Tellahamsa, IR-83222-174,Emergency and
Pusa superfast) and susceptible genotypes were identified. The findings of this study can be
utilised in Breeding programmes and marker assisted Breeding for development of cold
tolerant varieties for the benefit of the farmers.
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Keywords
rice, genetics, grain, genotypes, developmental stages, planting, tolerance, yields, biological phenomena, genetic structures