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Pak. J. Agri., Agril. Engg., Vet. Sci., 2013, 29 (1)
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ISSN 1023-1072
Pak. J. Agri., Agril. Engg., Vet. Sci., 2013, 29 (1): 13-23
HETEROSIS OF SOME YIELD AND ITS RELATED CHARACTERS IN AROMATIC
RICE (ORYZA SATIVA L.) VARIETIES AND THEIR F1 HYBRIDS UNDER
LOWLAND
AND UPLAND ENVIRONMENTS 1
A. D. Jarwar1, Q. D. Dela Cruz2 and G. S. Junejo1
1Rice Research Station, Thatta Sindh, Pakistan 2Department of
Crop Sciences, Institute of Graduate Studies, Central Luzon
State University, Nueva Ecija Philippines
ABSTRACT
Heterotic performance of twenty-one F1 hybrids and their 10
parents were evaluated in a randomized complete block design with
three replications in two environments. Significant differences
were observed among parents, hybrids and hybrids versus parents for
most of the yield and yield related characters in both
environments. Under lowland environment, grain yield showed the
high relative mid parent heterosis that varied from 12.69 to
17.45%. F1 hybrids, Sugdasi x Basmati 370 (16.52%), Bengalo x
Pandan (16.39%), JJ77 x Pandan (12.88%) and DR65 x Vertin (12.69%)
showed high mid parent heterosis. Under upland environment, grain
yield showed the high relative mid parent heterosis that varied
from 13.37 to 27.69%. F1 hybrids, Bengalo x Pandan (27.69%), DR65 x
Vertin (24.27%), Rataria x Vertin (21.25%), Sugdasi x Pandan
(17.38%), Sugdasi x Basmati 370 (13.42%) and LR2 x Basmati 370
(13.37%) showed high mid parent heterosis. F1 hybrids, Sugdasi x
Pandan, LR2 x Basmati 370, Bengalo x Pandan, Bengalo x Basmati 370
and DR65 x Vertin showed higher yield ha-1 in both environments.
Keywords: Aromatic rice, environments, F1 hybrids, heterosis, yield
traits.
INTRODUCTION The current levels of rice production do not meet
future demand. Since 2000, annual withdrawals from rice stocks have
been necessary to bridge the gap between rice production and
demand. The world population is projected to increase from 6.13
billion in 2001 to 7.21 billion in 2015 and 8.27 billion in 2030,
indicating a corresponding increase in rice demand from 680 million
tons in 2015 to 771 million tons in 2030 (Badawi, 2004). The
challenge of overcoming hunger, poverty and malnutrition in
rice-consuming countries while maintaining productivity and
protecting the environment will require coordinated efforts.
Corresponding author: [email protected]
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Increased awareness at national, regional and global efforts to
secure sustainable rice production. In addition, rice research
plays a major role in the efficient utilization of cultivated area,
improved rice varieties, and the minimization of losses during
milling. The major focus of rice research in the next decade must
emphasize on the development of high-yielding and early-maturing
varieties in order to ensure sustainable production of rice (Swain,
2005). Rice, the second most widely-grown cereal crop after wheat
and gifted with rich genetic repositoire, is the staple food for
more than half of the global human population. More than one
hundred thousand landraces and improved cultivar collections
available in the rice germplasm world wide largely contribute to
the rich genetic diversity of rice. Driven by natural selection of
varieties distributed in diverse agro-ecoclimatic conditions
coupled with continuous selection by man for his diverse in quality
and aesthetic preferences, a unique rice varietal group has
emerged, which became known as basmati rice, a specialty rice all
over the world (Singh et al., 2000). Heterosis is a phenomenon in
which F1 hybrids derived from diverse parents show superiority over
their parents. Two major hypotheses have been proposed to explain
the genetic basis of heterosis: the dominance hypothesis
(Davenport, 1908) and over dominance hypothesis (East, 1908, 1936).
The heterozygote (Aa) is more vigorous and productive than either
homozygote (AA or aa). This over- dominance theory is proven for
traits controlled by a single or a few genes. The heterozygote
performs a given function over a range of environments more
efficiently than either homozygote (East, 1936). Studies on the
genetic basis of heterosis for polygenic traits in various crops
have shown that heterosis is the result of partial to complete
dominance, over dominance, epistasis, and may be a combination of
all these (Comstock and Robinson, 1952). Evidence of real over
dominance for quantitative traits is hard to find. However,
apparent overdominance caused by non allelic interaction and
linkage disequilibrium are common contributors to heterosis (Jinks,
1983). The presence of heterosis and SCA effects for yield and its
related traits in rice are reported by Saleem et al. (2008). Faiz
et al. ( 2006) evaluated four genotypes (2 lines and two testers)
and their F1’s to estimate heterosis and combining ability effects
in yield and yield influencing traits like plant height, number of
productive tillers plant-1, number of spike-lets panicle-1, number
of filled grains panicle-1, sterility %age and grain yield.
Significant differences were observed in lines, testers and line x
testers. The highest positive heterosis over better parents was
observed for grain yield (41.83 %), number of productive tillers
plant-1 (11.04 %) and number of filled grains panicle-1 (7.39 %) in
the cross IR69616A x Basmati 385. GCA effects were found higher for
filled grains and number of spike-lets panicle-1. Except plant
height, mean performance of the parents was positively and strongly
correlated with GCA effects. Nuruzzaman et al. (2002) reported the
presence of heterosis and SCA effects for yield and its related
traits. Vanaja and Babu (2004) pointed out that yield increase in
rice was due to favorable heterosis in flag leaf area, number of
spikelets panicle-1 and number of grains panicle-1. Tiwari et al.
(2011) studied three CMS lines and 20 elite restorers to identify
the best heterotic combination. Their results indicated
manifestation of heterobeltiosis in grain yield for 43
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hybrids ranging from 11.63 to 113.04% and 46 hybrids over
standard variety, ranging from 10.48 to 71.56%. Most of the crosses
which exhibited superiority over better parent or standard variety
for grain yield also showed significant heterosis for number of
fertile spikelets and number of spikelets panicle-1. The hybrid
rice programe depends upon the magnitude of heterosis which also
helps in the identification of potential cross combinations to be
used in the conventional breeding programes to create wide array of
variability in segregating generations. A good hybrid should
manifest high heterosis for commercial exploitation. This study is
therefore aimed at estimating the heterotic effects and aids in
selecting the desirable parents and crosses for the exploitation of
heterosis in newly introduced basmati varieties of Indica rice.
MATERIALS AND METHODS This study was conducted at the experimental
area of the Research office, Central Luzon State University,
Science city of Munoz, Nueva Ecija, Philippines. Hybridization was
done to produce F1 hybrid seed during summer and wet seasons of
April, 2010. Evaluation of genotypes was carriedout during the dry
season of July 2011. Ten selected genotypes of which seven were
used as lines and three as testers while one was kept as check.
Line (males) Local Roosi-2, Sugdasi, Mehak, JJ77, Rataria, DR65,
and Bengalo were originated from Pakistan through selection.
Whereas Testers (Females) Pandan and Vertin were originated from
Philippines and Basmati 370 from India through selection. Variety
Basmati 370 was used as check. The seeds were sown in plastic pails
for the production of crosses in the dry/summer season-2010.
Staggard planting was done to synchronize flowering, to obtain the
planned crosses. Hybridization was done as soon as the flowering
appeared in the parental material. The crosses were made in line x
tester mating fashion, thus 21 F1 hybrids were developed. The pails
were filled with garden soil and organic compost in a ratio of 9:1
which was thoroughly mixed. Approximately 10 kg of the medium was
used in each pail. Three to five seeds were hand dibbled in each
pail. The seeds were covered with thin layer of fine soil and kept
wet to the level of saturation. Four to five days after emergence
watering was done when required. Fertilizers were applied following
the recommended rate into two splits 1st at seedling and 2nd at
panicle initiation stage. Flowers of female parents were
emasculated by cutting the tip of each floret with scissor and the
immature anthers were removed with an automatic sucker or by hand
with forceps, taking care that stigma is not damaged. Emasculation
was done in the afternoon between 4-6 p.m, one day before the
anther is expected to dehisce and the stigma is likely to become
fully receptive. The emasculated flowers were then covered with
butter paper bags to avoid natural cross pollination. Pollination
of emasculated flowers of each floret was done in the morning
between 10 and 11 a.m. when the anthers were fully matured and
ready to dehisce. Dehisced anthers were collected from the male
parents and were shed onto the female parents (emasculated
panicle). After pollination, the panicles were again properly
covered, to protect from foreign pollen and were tagged just after
bagging. The tags were marked with the date of
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emasculation, date of pollination, and the names of male and
female parents. Seeds of the crossed material were harvested after
21-25 days of pollination and kept in the cold storage. Harvesting
of the crossed plants were done 25 days after pollination.
Evaluation of hybrids alongwith their parents and a check variety
was done in two environments, low land and upland conditions in
three replications, during the dry season in December 2010. Lowland
conditions were characterized by continuous presence of water
during the growing period, while in the upland condition, the
genotypes were grown under controlled irrigation. In each
environment, each genotype was planted in a row plot of 1 meter
length with a distance of 30 cm between rows and 20 cm between
plants. The field was prepared thoroughly by alternate plowing and
harrowing until the desired soil tilth was attained under lowland
environment, whereas in upland environment, field was prepared with
disc plowing and harrowing twice. Thirty day- old seedlings were
pulled and one seedling hill-1 were transplanted in the prepared
plots and sprayed with mollusicide at the rate of 1L ha-1 right
after transplanting in the lowland. Whereas in the upland
condition, irrigation was applied in the prepared plots at the time
of transplanting. The experimental plots in both the environments
were fertilized at the rate of 132-42-42 NPK kg ha-1 at 7 days
after transplanting, while the remaining dose was applied into two
splits at 30 and 45 DAT. During transplanting, water level was
maintained at 2-3cm depth until 25-30 DAT in the lowland condition.
In upland condition, irrigation was applied as alternate dry and
wet. Aside from irrigation, weeding and appearance of insect pests
and diseases were monitored regularly and no infestation was
observed in the experiments. In the upland condition, manual
weeding was done to control the weeds. Harvesting was done when the
plants reached at maturity. Five plants were randomly selected by
cutting the stem close to the soil surface for determining the
agronomic traits and yield components. Proper labels were used to
tag the index plants. The data were collected for panicle length
(cm), number of spikelets panicle-1, number of filled grains
panicle-1, percent filled grains, weight of 1000 grains (g) and
grain yield (kg ha-1). Data for yield and its related characters
were subjected to the following biometrical analysis methods. The
data collected from the experiment were subjected to statistical
analysis for analysis of variance appropriate for RCBD. Mean
squares were tested against error variance by the usual “F” test.
The least significant difference (LSD) was computed by multiplying
the standard error of the difference with “t” values for (r-1)
(t-1) degres of freedom at 5% and 1% level of significance.
Heterosis was expressed as the percent deviation of the hybrids
(F1) from each of the relative parent i.e. increased or decreased
vigor of the F1 hybrids over their mid parent value as under:
Where: = Mean performance of F1 hybrids
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Pak. J. Agri., Agril. Engg., Vet. Sci., 2013, 29 (1)
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= Mean value of the two corresponding parents
P1 = mean performance of male parent, P2 = mean performance of
female parent Estimates of heterosis was tested for their
significance by the following formula:
Where:
r = number of replications
f = number of female (testers)
m = number of males (lines)
Means were compared with least significant difference (LSD)
which was computed by multiplying the standard error of the
difference with the respective “t” value for error degree of
freedom at 5% and 1% levels of significance.
RESULTS AND DISCUSSION One of the essential factors needed in
hybrid development is the high magnitude of heterosis available
through specific combinations. In the present study, heterosis was
calculated as deviation of hybrids from mid parental values of each
of the crosses for yield and its component. Significant variation
for all characters studied except for number of non-productive
tillers plant-1 and length of panicle among the crosses. For
parents versus crosses, all the characters were significant except
percent filled grains panicle-1. In the present study, the parents
of diverse origin were used which indicate a variable heterosis
from higher to lower degrees in their F1 hybrids under lowland and
upland environments. The heterotic effect of the crosses for
different yield traits, for two environments studied are presented
in Table 1. The character wise results are given here under:
Panicle length Under lowland conditions, heterotic values ranged
from -8.03 to 7.64. Out of 21 crosses, seven showed significantly
positive heterosis over their mid parents, while eight crosses
showed significantly negative heterosis. The highest positive
heterosis was observed on the cross combinations Sugdasi x Basmati
370 (7.64%) followed by cross Rataria x Vertin (6.51%). The
significant positive heterotic effect indicates that those hybrids
gave increased panicle length.
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Under upland conditions, heterosis values varied from -10.27% to
7.23%. Six crosses exhibited significantly positive heterosis and
five exhibited significant negative heterosis among 21 F1 hybrids.
The positive significant heterotic effect indicates the length of
panicle has increased. In upland environment, the highest
significant positive heterosis was found in cross combinations JJ77
x Vertin (7.23%) followed by LR2 x Basmati 370 (6.82%) and Sugdasi
x Vertin (6.65%). The average heterosis in two environments ranged
from -5.74 to 4.95. Out of 21 hybrids, 10 exhibited positive
heterotic effects and the rest exhibited negative effects. Number
of spikelet panicle-1 Under lowland condition, only one cross
Sugdasi x Basmati 370 showed significantly positive heterotic
effect (23.66%), while hybrid DR65 x Vertin was recorded
significantly negative heterosis (-24.69%).While under upland
conditions, the heterosis ranged from -22.72 to 27.04. The highest
positive heterosis was shown by cross of Bengalo x Pandan (27.04%)
followed by Sugdasi x Basmati 370 (12.73%). Out of 21 crosses, 12
showed positive heterotic effects and nine expressed negative
effect. The positive heterotic effect exhibited increase in the
number of spikelets panicle-1 due to hybrid vigour. Average values
of two environments ranged from -18.30 to 18.19. Out of 21 cross
combinations, 11 showed mean positive heterotic effects while 10
showed negative effects. Hybrid Sugdasi x Basmati 370 exhibited the
highest average heterotic value of 18.19%. These results agreed
with the findings of Faiz et al. (2006) who observed highest
positive heterosis for this trait. Number of filled grains
panicle-1 Under lowland environment, the heterotic effects showed
that among the crosses, Sugdasi x Basmati 370 and DR65 x Pandan
exhibited maximum significant positive heterosis (27.03 and 27.06%,
respectively). Such higher values indicated complete dominant gene
action in these crosses. Under upland environment, out of 21 cross
combinations, only Bengalo x Pandan showed highest positive
heterosis (34.73%), while JJ77 x Basmati370 showed the highest
negative heterosis (-30.87%) over their mid parental values. The
heterosis values ranged from -30.87 to 34.73%. In combined
environments, mean values ranged from -23.25 to17.00. Out of 21 F1
hybrids, 11 hybrids exhibited positive heterotic effect. The
highest mean value (20.21%) was observed in cross Sugdasi x Basmati
370, followed by Bengalo x Pandan (17.00%) and DR65 x Pandan
(12.87%). Percent filled grains panicle-1 Under lowland condition,
all cross combinations showed insignificantly negative and also
positive heterotic effects, except cross of DR65 x Pandan, which
exhibited significantly positive heterosis over their mid parental
value (5.09%).
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Table 1. Heterotic effects for different yield and its related
characters under two environments.
F1 hybrids Length of panicle (cm) Number.of spikelets
panicle-1
Number of filled grains panicle-1
Lowland Upland Mean Lowland Upland Mean Lowland Upland Mean
LR2 x Pandan -3.47** -2.73 -3.10 -4.73 -10.37 -7.55 -10.04
-10.71 -10.37
LR2 x Basmati 370 3.09* 6.82** 4.95 4.69 3.15 3.92 5.10 6.87
5.98
LR2 x Vertin -2.82* -5.23** -4.02 1.85 5.87 3.86 3.07 5.17
4.12
Sugdasi x Pandan -5.56** -2.11 -3.83 -7.91 -7.26 -7.58 -9.67
-6.55 -8.11
Sugdasi x Basmati 370 7.64** -4.19* 1.72 23.66* 12.73 18.19
27.03* 13.40 20.21
Sugdasi x Vertin -0.58 6.65** 3.03 -0.32 1.97 0.82 0.37 2.84
1.60
Mehak x Pandan 0.89 -7.48** -3.29 -0.02 -8.95 -4.48 -2.75 -14.41
-8.58
Mehak x Basmati 370 0.05 0.13 0.09 -15.75 7.74 -4.01 -15.83
11.26 -2.28
Mehak x Vertin -4.35** -1.11 -2.73 -2.18 -1.11 -1.64 -0.55 -2.22
-1.38
J J 77 x Pandan -8.03** -3.45* -5.74 -2.61 4.58 0.98 -5.33 5.97
0.32
J J 77 x Basmati 370 5.69** -10.27** -2.29 -13.00 -22.72* -17.86
-15.63 -30.87 -23.25
J J 77 x Vertin -2.63* 7.23** 2.30 -12.54 -11.07 -11.80 -14.78
-11.19 -12.98
Rataria x Pandan 3.54** 4.67** 4.10 -1.71 -4.79 -3.25 -0.62
-9.24 -4.93
Rataria x Basmati 370 -2.67* -0.45 -1.56 5.73 2.67 4.20 5.02
5.23 5.12
Rataria x Vertin 6.51** 1.95 4.23 0.41 7.79 4.10 1.71 9.06
5.38
Bengalo x Pandan 2.79* 0.41 1.60 1.20 27.04 14.12 -0.73 34.73**
17.00
Bengalo x Basmati 370 -0.91 5.07** 2.08 9.74 3.27 6.50 10.61
1.96 6.28
Bengalo x Vertin 0.33 -3.29 -1.48 -3.79 -9.29 -6.54 -1.39 -10.78
-6.08
DR 65 x Pandan -2.98* 1.27 -0.85 21.20 0.32 10.76 27.06* -1.32
12.87
DR 65 x Basmati 370 -1.19 0.82 -0.18 -24.69* -11.91 -18.30
-26.12* -10.48 -18.30
DR 65 x Vertin 3.88** 4.34* 4.11 15.64 5.72 10.68 15.88 4.25
10.06
S.E 1.21 1.64 - 10.91 10.73 - 10.64 10.79 - LSD at 0.5 2.44 3.31
- 22.06 21.69 - 21.50 21.81 - LSD at 0.1 3.26 4.43 - 29.51 29.02 -
28.77 29.19 -
** = Significant at1% level * = Significant at 5% level
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Table 1. Continued.
F1 hybrids Percent filled grains
panicle-1 Weight of 1000 grains (g) Yield (kg ha-1)
Lowland Upland Mean Lowland Upland Mean Lowland Upland Mean LR2
x Pandan -4.95 -0.66 -2.80 0.71 3.21** 1.96 -3.15 -0.01 -1.58 LR2 x
Basmati370 0.45 3.34 1.89 -6.69** -8.84** -7.76 16.42 13.37 14.89
LR2 x Vertin 0.45 0.06 0.25 -1.57* -4.60** -3.08 -21.05 -24.42
-22.73 Sugdasi x Pandan -1.29 0.84 -0.22 4.53** 3.71** 4.12 16.52
17.38 16.95 Sugdasi x Basmati 370 2.75 1.33 2.04 -3.36** -3.54**
-3.45 17.45 13.42 15.43 Sugdasi x Vertin 1.11 0.78 0.94 7.80**
11.01** 9.40 -13.29 -7.69 -10.49 Mehak x Pandan -2.28 -4.98* -3.63
3.74** 4.71** 4.22 9.42 -3.26 3.08 Mehak x Basmati 370 -0.23 3.46
1.61 -5.38** -7.02** -6.20 -43.71 -34.58 -39.14 Mehak x Vertin 1.80
-0.66 0.57 -1.91** 3.46** 0.77 -9.25 -9.94 -9.59 J J 77 x Pandan
-2.68 2.35 -0.16 0.18 -5.54** -2.68 12.88 -12.91 -0.01 J J 77 x
Basmati 370 -2.27
-9.20** -5.73 -3.78** -0.16 -1.97 -29.97 -48.61 -39.29
J J 77 x Vertin -2.25 -0.54 -1.39 -1.81* -3.56** -2.68 -3.75
-7.04 -5.39 Rataria x Pandan 1.57 -4.81* -1.62 2.30** 6.07** 4.18
-2.23 -11.96 -7.09 Rataria x Basmati 370 -0.50 3.17 1.33 1.66*
-8.11** -3.22 -18.99 9.25 -4.87 Rataria x Vertin 1.52 1.45 1.48
1.05 6.97** 4.01 7.01 21.25 14.13 Bengalo x Pandan -1.57 6.86**
2.64 7.98** 0.62 4.30 16.39 27.69 22.04 Bengalo x Basmati 370 1.26
-0.79 0.23 -2.24** -3.20** -2.72 7.56 10.78 9.17 Bengalo x Vertin
2.46 -1.36 0.55 -7.36** 3.89** -1.73 5.01 -14.31 -4.65 DR 65 x
Pandan 5.09* -1.39 1.85 5.32** 5.08** 5.20 -1.75 3.41 0.83 DR 65 x
Basmati 370 -1.44 1.48 0.02 -2.36** -2.02 -2.19 6.43 3.66 5.04 DR
65 x Vertin 0.57 -1.05 -0.24 -1.10 -5.47** -3.28 12.69 24.27 18.48
S.E 2.31 2.32 - 0.71 1.05 - 711.00 492.29 - LSD at 0.5 4.67 4.70 -
1.43 2.13 - 1436.94 994.90 - LSD at 0.1 6.25 6.25 - 1.19 2.85 -
1922.55 1331.15 - * = Significant at 1% level * = Significant at 5%
level
The heterosis values however ranged from -4.95 to 5.09%. Under
upland condition, heterosis values for this trait ranged from -9.20
to 6.86. Among 21 crosses, only Bengalo x Pandan showed
significantly highest positive heterosis (6.86%), while cross
combination JJ77 x Basmati 370 showed highest negative
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heterosis (-9.20%), followed by hybrid Mehak x Pandan (-4.98%).
Out of 21 crosses, 11 hybrids showed positive heterosis, whereas 10
showed negative heterosis. Averaged over two environments ranged
from -5.73 to 2.64%. Out of 21F1 hybrids, 13 hybrids showed
positive effects. Positive heterotic effect revealed that hybrids
had increased percent filled grains panicle-1. Among the average
positive heterotic effect, the highest value was exhibited by cross
Bengalo x Pandan (2.64%), followed by Sugdasi x Basmati 370
(2.04%). However, cross combination DR65 x Basmati 370 showed the
lowest heterotic value (0.02%). Weight of 1000 grains Under lowland
condition, estimates of heterotic effect for this trait ranged from
-7.36 to 7.98%. Significant positive heterosis over mid parent
values was observed in seven hybrids out of 21 and 10 expressed
significantly negative heterosis. The significantly positive
heterotic effects could reflect towards higher grain yield. This
also suggests that cross combinations with highest magnitude of
positive heterosis like Bengalo x Pandan (7.98%), Sugdasi x Vertin
(7.80%) and DR65 x Pandan (5.32%), have heavier seed weight and
could be utilized for the exploitation of heterosis in grain
weight. Under upland condition, the heterosis values ranged from
-8.84 to 11.01. Out of 21 F1 hybrids, 10 showed significantly
positive heterotic effect over mid parental values, while eight
showed significantly negative heterosis. Hybrid of Sugdasi x Vertin
exhibited highest significant positive heterosis (11.01%), followed
by Rataria x Vertin (6.97%), Rataria x Pandan (6.07%) and DR65 x
Pandan (5.08%). Above crosses, showed higher values for their
average performance for this trait. Significantly positive
heterosis indicates the heavier weight of 1000 grains, resulting
higher yields for these hybrids. Averagedover environments, mean
values ranged from -7.76 to 9.40. However positive heterosis values
were observed in nine out of 21 F1 hybrids. The positive heterotic
effects of those crosses could be reflected for higher grain yield
under lowland and upland conditions which suggest that cross
combinations with highest magnitude of positive heterotic effects
like Sugdasi x Vertin (9.40%), DR65 x Pandan (5.20%), Bengalo x
Pandan (4.30%) and Mehak x Pandan (4.22%) have heavier seed weight
and can be utilized for the exploitation of heterosis to improve
grain weight over both the environments. Yield (kg ha-1) Under
lowland conditions, all crosses showed non-significant positive as
well as negative heterotic effects. Out of 21cross combinations, 11
crosses exhibited positive heterosis and 10 manifested negative
heterotic effects. The heterotic values ranged from -43.71to 17.45.
Cross of Sugdasi x Basmati 370 showed highest positive heterosis
(17.45%), followed by Sugdasi x Pandan (16.52%) and LR2 x Basmati
370 (16.42%). Under upland condition, all hybrids showed
non-significant heterosis. Out of 21, ten crosses showed positive
heterosis and 11 negative effects. The heterosis values ranged from
-48.61 to 27.69%. Cross combination Bengalo x Pandan, showed
highest positive heterosis (27.69%), followed by DR65 x Vertin
(24.27%) and Rataria x Vertin (21.25). Over the
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environments, the mean values ranged from -22.73 to 22.04%,
however hybrid Bengalo x Pandan exhibited highest heterotic value
(22.04%) followed by cross combinations DR65 x Vertin (18.48%),
Sugdasi x Pandan (16.95%), Sugdasi x Basmati 370 (15.43), LR2 x
Basmati 370 (14.89) and Rataria x Vertin (14.13). Heterosis in
grain yield is attributable to increases in number of spikelets and
number of filled grains. Most of the parents involved in the
crosses showed higher mean values over their parents for those
characters. CONCLUSION The increased yield of hybrids with the high
heterotic effects observed in this study under lowland environment
of growing basmati rice, suggests that these hybrids could be
utilized for the exploitation of heterosis.
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(Received September 05, 2012; Accepted December 26, 2012)