STUDY OF GENETIC PARAMETERS IN THERMO-SENSITIVE GENIC MALE STERILE LINES (TGMS) OF RICE (Oryza sativa L.)

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B. MEENA KUMARI*, S. MANONMANI AND K. GANESAMURTHY
Centre for Plant Breeding and Genetics, Tamil Nadu Agricultural University, Coimbatore – 3.

ABSTRACT

Twenty eight suspected TGMS lines in rice developed from various sources were evaluated for genetic variability and
heritability parameters along with correlation coefficients based on morphological traits and pollen fertility studies. Highest
PCV and GCV were observed for pollen fertility, spikelet fertility and number of productive tillers suggesting that these characters
are under the influence of genetic control. High heritability was recorded for stigma length and panicle length. High heritability
coupled with high genetic advance as per cent of mean was observed for panicle length. Pollen fertility was positively and
significantly associated with panicle exertion, spikelet fertility, number of seeds per panicle and single plant yield at genotypic
level. Emphasis may be given on characters like stigma length, panicle length and single plant yield for improvement of these
lines, since majority of other traits are environment dependant.
KEY WORDS: Correlation, Genetic advance, Heritability, Rice, TGMS lines, Variability

INTRODUCTION

Today, rice is synonymous with food security in most parts of the Asia. Recent progress in plant breeding research indicated that a significant shift in the yield frontier could be made possible through hybrid rice. Three-line breeding utilizing the Cytoplasmic Genic Male Sterility (CMS) system has been found to be effective in the development of commercial hybrids, but this system has some constraints such as a yield plateau in rice hybrids, dependency on a single CMS source, restriction on the choice of male parents due to problems associated with fertility restoration, complex seed production procedures, and high seed cost (Yuan, 1998). To overcome these problems, the two-lineĀ  ystem of hybrid breeding utilizing Environment Sensitive Genetic Male Sterility (EGMS) especially the Thermo Sensitive Genetic Male Sterile lines (TGMS) is considered as an alternative to CGMS system. Use of the thermo sensitive genic male sterility system in two line breeding is simple, inexpensive, efficient and
eliminates the limitations associated with the cytoplasmicgenetic
male sterility (CGMS) system in rice due to the
different weather conditions prevailing in India. Hence,
an understanding of genetic variability, heritability and
correlation of pollen fertility with other traits will help in
the effective selection of parents to exploit the maximum
heterosis.
MATERIAL AND METHODS
A total of 28 medium and late maturing TGMS lines
were selected for the present study. They were evaluated
at Paddy Breeding Station, Tamil Nadu Agricultural
University, Coimbatore during Rabi, 2009-10, in a
randomized block design with three replications. The data
was recorded for twelve traits viz., days to first flowering,
plant height (cm), number of productive tillers per plant,
panicle length (cm), spikelet fertility (%), grain yield per
plant (g), angle of glume opening, stigma exertion (%),
stigma length (cm), pollen fertility (%), panicle exertion
(%) and no. of spikelets per primary panicle in five
randomly selected plants of each genotype.
The analysis of variance was carried out statistically
utilizing the mean values (Panse and Sukhatme, 1995)
for the twelve characters studied in selected 28 TGMS
lines. GCV and PCV were calculated using the formula
suggested by Burton (1952). The heritability estimate in
the broad sense was calculated by the method proposed
by Lush (1940).
RESULTS AND DISCUSSION
The analysis of variance revealed the significant
difference among 28 TGMS lines for the twelve characters
studied, indicating sufficient scope for further
improvement. The mean, GCV, PCV, heritability (broad
sense) and genetic advance as percentage of mean worked
out for twelve characters are presented in Table 1. The
mean values of panicle exertion (50.94%), panicle length
(20.90) and stigma length (2.27) were good, indicating
that the genotypes were of superior quality for executing
the hybrid breeding in rice. To have more outcrossing
rate in male sterile lines of rice, in turn for more hybrid
seed set, the traits panicle exertion, angle of glume
opening, stigma exertion and stigma length are important.
PCV was higher than GCV for all the characters studied.
PCV ranged from 9.94 (panicle length) to 127.98 per cent
(number of productive tillers) and GCV ranged from 3.07
(angle of glume opening) to 59.39 (pollen fertility). GCV
was found to be moderate (10-20%) for plant height,
stigma length, panicle exertion, panicle length and number
of seeds per panicle. Similar findings of moderate GCV
was reported earlier for plant height and panicle length
(Umadevi et al., 2009). Difference between the PCV and
GCV was low for panicle length and stigma length
indicating the less influence of environment. The
quantitative traits, viz., pollen fertility (109.67), spikelet
fertility (106.02), number of spikelets per panicle (82.86),
plant height (82.14), number of productive tillers (127.98)
and days to first flowering (78.21) expressed high variability
at phenotypic level and low variability at genotypic level.
This shows the high influence of environment for the
expression of these traits in the TGMS lines studied.
The heritability and genetic advance estimates were
interpreted as low, medium and high as per the
classification of Johnson et al. (1955). Broad sense
heritability ranged from 0.206 (angle of glume opening)
to 88.55 per cent (stigma length). As heritability alone
cannot serve as an indication of the expected genetic
improvement, the genetic advance is also taken into
consideration. High heritability estimates coupled with
high genetic advance was observed for stigma length and
panicle length. This indicated the lesser influence of
environment in expression of these characters and
prevalence of additive gene action in their inheritance
which is amenable for direct selection. It was earlier
reported for panicle length by Ushakumari et al. (2002)
and Umadevi et al. (2009). High heritability coupled with
very low genetic advance as per cent of mean was recorded
for single plant yield indicating the non additive gene
action hence, selection for this trait may not be rewarding.
Low heritability with low genetic advance observed for
days to first flowering, plant height, panicle exertion, angle
of glume opening and number of spikelets per panicle
indicated the high influence of environment in the
expression of these traits.
The genotypic correlations were of higher magnitude
than the corresponding phenotypic correlation coefficients
for the majority of trait combinations observed (Table 2).
This is due to the predominant role of heritable factors.
This study revealed that the pollen fertility had significant
and positive correlation with panicle exertion, spikelet
fertility, number of seeds per panicle and single plant yield
at genotypic level. The observation supports earlier
findings by Borbora et al. (2005) and Panwar and Mashiat
Ali (2007) for number of filled grains per panicle. Highly
significant and negative correlation of pollen fertility was
observed with plant height, stigma exertion and stigma
length at genotypic level. This indicates the traits panicle
exertion, spikelet fertility, number of seeds per panicle
and single plant yield are to be concentrated for the
selection of plants while improving the TGMS lines.
Path coefficient analysis was worked out to get an
insight into the direct and indirect effects of different
characters on pollen fertility and the results are presented
in Table 3. The moderate residual effect of 0.4551 in the
present study indicated that some more characters are to
be included for accounting purpose. Spikelet fertility
(0.6482), panicle exertion (0.4456), number of seeds per
panicle (0.1573) and single plant yield (0.1385) had the
positive direct effect on the expression of pollen fertility.
Days to fifty per cent flowering is having the highest
negative direct effect on the expression of pollen fertility.
The traits number of productive tillers, panicle exertion,
stigma exertion, stigma length and single plant yield are
having both positive direct and indirect effects on pollen
fertility. Though plant height (-0.1849), angle of glume
opening (-0.1625) and panicle length (-0.0164) are having
negative direct effect on pollen fertility, these traits are
having the positive indirect effect through majority of
other traits studied. Similarly, number of seeds per panicle
and spikelet fertility are having negative indirect effect,
though the traits are having positive direct effect on the
expression of pollen fertility.
The materials used for this study are the thermo
sensitive genic male sterile lines, where majority of the
reproductive traits are determined by environment. This
study suggested that due emphasis may be given on
characters like stigma length, panicle length and single
plant yield for improvement of these lines, since majority
of other traits are environment dependant.