Heterosis Studies for Yield and its Components in Rice Hybrids using CMS system
Realizing the potential of hybrid rice to increase productivity, the present experiment was undertaken with a fixed model i.e. line x tester mating design involving 3 CMS lines and 20 elite restorers to identify the best heterotic combination. The results indicated that the manifestation of heterobeltiosis for grain yield was significantly superiority of 43 hybrids ranging from 11.63 to 113.04% and 46 hybrids over standard variety (Sarjoo-52) 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 per panicle. These crosses also possessed about 80% pollen viability. Besides grain yield, considerable heterosis was observed for other characters also but its degree varied from character to character. The best cross combination in order of merit grain yield and other yield components were IR58025AxIR48749-53-2-2-2R, NMS4AxIR633-76-1R, IR58025AxIR54853-43-1-3R, IR58025AxIR19058-107-1R and PMS10AxIR54853-43-1-3R. Considering the heterosis more than 60% as well as significant sca effects for major components, the NMS4AxIR633-76-1R, IR58025AxIR19058-107-1R and IR58025AxIR32419-28-3-1-3R were most promising combinations and need to be tested on large scale. Besides these, some other crosses viz., NMS4AxIR52256-9-2-2-1R, NMS4AxIET 9352 and IR58025AxIET201102, which expressed more than 50% heterosis along with desirable significant sca effects for more than six important yield components, may be considered for commercial exploitation.
Rice (Oryza sativa L.) is the most important food crop of India with
world ranking first in area and second to China in production. At the current
growth of population rice requirement increases dramatically; hence, it is challenging
task to ensuring food and nutritional security to the country. Therefore, enhancing
productivity of rice through novel genetic approaches like hybrid rice was felt
necessary. Exploitation of heterosis is considered to be one of the outstanding
achievements of plant breeding. The presence of sufficient hybrid vigour is
an important pre-requisite for successful production of hybrid varieties. Hybrid
vigour in rice was first reported by Jones (1926). According
to Malthus (1989) the food grains increase in arithmetical
progressions while the population increases in geometrical progression, thus
improved technologies are required to bridge the gap to feed the increasing
population. Therefore, for breaking the yield barrier level and make rice cultivation
more attractive, it is now necessary to explore alternative approaches. Among
the all possible alternatives, heterosis is an important approach for increasing
rice production. It has not only contributed to food security, but has also
benefited the environment (Duvick, 1999). The various
crop species in which hybrid varieties are used commercially, rice ranks very
high. Heterosis has been commercially exploited in rice with a yield advantage
of 20-25% over the best pure lines (Rather et al.,
2001). Hybrids offer opportunity to break through the yield ceilings of
semi dwarf rice varieties. Hybrids have already been successfully used in maize,
pearl millet and sorghum. The discovery of Cytoplasmic Male Sterility (CMS)
in rice (Athwal and Virmani, 1972; Erickson,
1969; Shinjyo, 1969) suggested that breeders could
develop a commercially viable F1 hybrid, but little serious interest
was paid until Chinese scientists reported successful production of F1
rice hybrids in China (IRRI, 1977). Those hybrids
yielded 20-30% higher than conventionally bred varieties (Lin
and Yuan 1980; Shen 1980). Significant heterosis,
heterobeltiosis and standard heterosis have been reported in rice by a number
of workers (Nijaguna and Mahadevappa, 1983; Panwar
et al., 1983; Yoshida and Fujimaki, 1984;
Devarathinam, 1984; Cheema and Awan,
1985; Peng and Virmani, 1991; Vivekanandan,
1991; Lokaprakash et al., 1992; Wilfred
and Prasad, 1992; Watanesk, 1993; Patel
et al., 1994; Zhang et al., 1994;
Ali and Khan 1995; Rao et al.,
1996; Mishra and Pandey, 1998; Nuruzzaman
et al., 2002; Li et al., 2002; Faiz
et al., 2006; Saleem et al., 2008;
Rashid et al., 2007; Bagheri
and Jelodar, 2010; Rahimi et al., 2010).
The increased yield of rice hybrids alone does not ensure profitability to farmers
if their grain quality is not acceptable and if they fetch a low price in the
market. Khush et al. (1988) studied this subject
intensively and concluded that hybridity per se did not harm grain quality
in terms of physical and chemical characteristics as long as both parents possess
acceptable grain quality, hybrid rice breeding programs must give emphasis (if
they have not done so in the past) to the critical evaluation of parental lines
and hybrids for grain quality before these are released for commercialization.
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. 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. 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. Identifying high yielding hybrids is expensive
and involves testing large number of hybrid combinations in multi environmental
trials therefore; the present investigation was aimed to evaluate rice hybrids
for yield, adaptability and grain quality for successful commercial utilization.
MATERIALS AND METHODS
The parental material comprised 3 CMS lines viz; IR58025A, NMS4A and PMS10A
used as females (lines) were crossed with 20 diverse genotypes used as male
(testers) in a line x tester mating design in 2001-02. Thus, the resultant sixty
hybrids along with their 23 parents and one standard check variety (Sarjoo-52)
were evaluated in a randomized block design with three replications at Crop
Research Station-Masodha, Narendra Deva University of Agriculture and Technology,
Kumarganj, Faizabad during 2002-03. Each genotype was raised in 2.5 m long single
row plot keeping 20x15 cm spacing. The recommended agronomic practices followed
to raise good crop stand. The data were recorded on 10 randomly selected plants
from each replication for various quantitative traits studied were viz., days
to 50% flowering, plant height (cm), pollen fertility (%), effective tillers
per plant, panicle length (cm), number of spikelets per panicle, number of fertile
spikelets, spikelet fertility (%), 100 grain weight (g), grain yield per plant
(g), biological yield (g) and harvest index (%). The general reference for data
collection was standard evaluation system for rice (Anonymous,
2002; Virmani et al., 1997). The percent increase
or decrease of F1 hybrids over better parent as well as standard
check was calculated to estimate possible heterotic effects for above mentioned
parameters (Fonseca and Patterson, 1968):
where, Hbt = Heterobeltiosis, Hs = Standard Heterosis. To estimate significant
differences among hybrids and parents, the mean data of each character were
subjected to Analysis of Variance (ANOVA) as suggested by Steel
and Torrie (1980). The characters showing significant differences were subjected
to heterosis calculation. Deviation of F1 from its either of the
parental values was interpreted by Mather and Jink (1977)
depicting type of gene action operating for controlling the trait. The t
test was applied to determine significant difference of F1 hybrid
means from respective mid parent and better parent values using formulae as
reported by Wynne et al. (1970).
RESULTS AND DISCUSSION
The analysis of variance (Table 1) revealed that highly significant
differences among lines (females) for various characters under studied i.e.,
days to 50% flowering, effective tillers per plant, panicle length (cm), number
of spikelets per panicle, number of fertile spikelets, spikelet fertility%,
grain yield per plant, biological yield, harvest index except plant height,
pollen fertility and 100 grain weight while, variance among males (testers)
were highly significant for all traits. The variances among crosses due to males
and females (linesxtesters) interaction component, indicating their sca
effects were highly significant for all the traits except for 100 grain weight.
The predominance of sca effects suggested that dominance and epistatic
gene interactions were important for controlling these traits confirming the
earlier findings of Janardhanam et al. (2000),
Satyanarayana et al. (2000), Panwar
(2005), Saravanan et al. (2006), Kumar
et al. (2006) and Salgotra et al. (2009).
|| Analysis of variance for combining ability for different
characters in rice
|* Significant at 5% level and **1% probability level of significance
Estimation of heterosis: Heterosis was computed as percent increase or decrease in F1 value over better parent (heterobeltiosis) and over best commercial variety (standard heterosis) were presented in Table 2. The relative magnitude of heterosis over better parent and standard variety, (Sarjoo-52) were studied for 12 characters viz., days to 50% flowering, plant height, pollen fertility, panicle bearing tillers (i.e., effective tillers) per plant, panicle length, number of spikelets per panicle, number of fertile spikelets, spikelet fertility percent, 100 grain weight, grain yield per plant, biological yield per plant and harvest index in 60 crosses. The nature and magnitude of hybrid vigour differed for different traits in various hybrid combinations. The five best cross combination and per se performance were given in Table 3. The salient results obtained on different aspects and conclusions drawn from the experiment are summarized below.
Days to 50% flowering: Negative heterosis is desirable for days to flowering
because this will make the hybrids to mature earlier as compared to parents.
Almost all the crosses had either equal or early flowering than the standard
variety (Sarjoo-52). When compared to better parent, significant earlier flowering
plants were observed in thirty one crosses while; eight crosses were identified
for late flowering. The magnitude of heterosis observed over better parent ranged
from -16.57% (IR58025AxIR 35454-18-1-1-2R) to 7.27% (NMS4AxIR 53480-8-39-3-1-2R)
with a mean of -3.04% over the better parent, the magnitude of standard heterosis
ranged from -4.22% (IR58025AxIR 58110 -114-2-2-2R) to -16.57% (IR58025AxIR 35454-18-1-1-2R)
with mean value of -9.67%. In general, all the sixty crosses exhibited early
flowering over standard variety (Sarjoo-52), while thirty one crosses exhibited
significantly early flowering and eight crosses were late flowering as compared
over the better parent. The five superior crosses having heterobeltiosis for
early flowering were IR58025AxIR 35454-18-1-1-2R, NMS4AxIET 9352, NMS4AxIR 35454-18-1-1-2
R, NMS4AxIR 42686-2-118-6-2R and IR58025AxIR 32419-28-3-1-3R. In respect of
standard heterosis the most promising cross combinations for early flowering
were IR58025AxIR32419-28-3-1-3R, NMS4AxIR 42686-2-118-6-2R, PMS 10 AxIR 633-76-1
R, PMS 10 AxIR 54853-43-1-3R and PMS10AxNDR358. Heterosis in both negative and
positive directions for days to flowering have also been reported by Peng
and Virmani (1991), Murthy and Kulkarni (1996).
Most data have indicated negative heterosis in days to flowering in hybrids
(Chang et al., 1971, 1973;
Dhulappanavar and Mensikai, 1967; Fujimaki
and Yoshida, 1984; Mallick et al., 1978;
Namboodri, 1963; Purohit, 1972;
Xu and Wang, 1980) found that days to maturity in hybrids
depend on the male plant. Most hybrids have long growth duration (Deng,
1980; Lin and Yuan, 1980; Tian
et al., 1980; Wu et al., 1980).
Plant height: Semi-dwarf plant height (80-100 cm) is desirable for recording
high yield in rice variety as vigour in plant height may lead to unfavourable
grain/straw ratios and below optimum yield due to lodging.
||Estimation of heterosis over better parent (BP) and standerd
variety (SV) for yield and yeild components in rice
|*Significant at 5% 11 and **1% probablity level of significance
|| Best crosses with their sca effects in relation to per
se performance involved for different characters in rice
The minimum amount of heterosis -16.99% (IR 58025AxNDR6054) and -19.62% (NMS4AxIR42686-2-118-6-2R)
was recorded over better parent and standard variety, respectively. However,
the maximum significant heterosis observed over the better parent was 8.29%
(PMS10AxIR46R), while in case of standard heterosis, it was 0.18% (IR58025AxIR
48749-53-2-2-2R) and mean heterosis over better parent and standard variety
was 5.98 and -9.26% respectively. Five crosses namely NMS4AxIET 201102, NMS4AxNDR
358, PMS10AxIET201108, PMS10AxIR 42686-2-118-6-2R and PMS10AxIR46R exhibited
significant positive heterobeltiosis, whereas forty three and fifty three crosses
expressed dwarf stature in comparison to both better parent and standard variety,
it was obvious from the data (Table 2) that the hybrid combinations
have a tendency of dwarfness of trait in most of the cases. In respect of the
most promising cross combinations for dwarfness were IR58025AxNDR 6054, NMS4AxIR42686-2-118-6-2R,
IR58025AxNDR 3008, IR58025AxIR 58110-114-2-2-2R and IR 58025AxIET201108. None
of the desirable combinations were common for both the heterosis, suggesting
that heterosis for plant height is cross specific. Present observations are
in close agreement with earlier report of several workers (Pillai,
1961; Sivasubranian and Menon, 1973.; Khalique
et al., 1977; Mallick et al., 1978;
Singh et al., 1996; Arnirthadeverathinam,
1983; Tseng and Huang, 1987; Sharma
and Mani, 1989; Peng and Virmani, 1991; Lokaprakash
et al., 1992; Nuruzzaman et al., 2002;
Alam et al., 2004).
Pollen fertility percent: Pollen fertility is one of the constraints in hybrid rice breeding programme, which affects the yield considerably. Among 60 crosses studied for pollen fertility percent, only three and four hybrids showed significant positive heterosis over pollen parent and standard variety respectively. The overall range of heterobeltiosis and standard heterosis varied from -15.12 to 9.49%, respectively. However, pollen fertility in hybrids should be required as in pollen parent and or standard variety this indicates that the pollen parent in hybrid expressed full restoring capacity over a particular CMS line. Therefore, hybrids having non-significant differences over both the parents (BP and SV) either in positive or negative direction would be beneficial for this trait. The seven crosses and twenty eight cross combinations had positive but non-significant differences for both heterobeltiosis and standard heterosis; of these, PMS10AxIR35454-18-1-1-2R, IR58025AxIR53480-8-39-3-1-2R, PMS10AxIR58110-114-2-2-2R, NMS4AxIR 46R and NMS4AxIR 53480-8-39-3-1-2R were most useful crosses for this trait.
Panicle bearing tillers (Effective tillers) per plant: More panicle
bearing tillers per plant is believed to be closely associated with high grain
yield per plant resulting high productivity. Therefore, the cross combinations
with more panicle bearing tillers per plant were to be identified. The significant
positive heterosis for this trait was exhibited by 9 and 41 hybrids over better
parent and standard variety, respectively. The mean heterosis was observed-6.88%
over better parent and 24.44% over standard variety. Further the heterobeltiosis
varied from -34.00% (NMS4AxIR 48749-53-2-2-2R) to 39.53% (PMS 10xIR 35454-18-1-1-2R)
and standard heterosis from -8.33 (NMS4AxIR 48749-53-2-2-2R) to 66.67% (PMS10AxIR
35454-18-1-1-2R). As regards the expression of heterobeltiosis, the most promising
crosses were PMS 10AxIR 35454-18-1-1-2R, PMS10AxIR60966-29-4-2-2-2R, PMS10 AxIR
52256-9-2-2-1R, NMS4AxIR 53480-8-39-3-1-2R and PMS10AxIR 48749-53-2-2-2R. Considering
standard heterosis, the five superior cross combinations were NMS4AxIR 53480-8-39-3-1-2R,
NMS4AxIR35454-18-1-1-2R, IR58025AxIET201102, PMS10AxIR60966-29-4-2-2-2R and
NMS4AxIR 62030-81-1-3-2R. Results for significantly high number of productive
tillers per plant are in comformity with those obtained, by Srivastava
and Seshu (1982); Govindraj (1983); Sahai
et al. (1987); Viraktamath (1987); Manual and
Palanisamy, 1989). However these findings are in disagreement with the findings
of Virmani et al. (1981) who reported hybrids
posses significantly lower tillers than mid parent, better parent and check
Panicle length: Generally, larger panicle is associated with high number
of grains panicle resulting into higher productivity; therefore, hybrids with
positive heterosis for panicle length are desirable. The present study revealed
that heterosis for panicle length was relatively low as indicated by mean heterosis
of 0.37% over better parent and -3.65% over standard variety. Out of 60 crosses
20 and 16 crosses showed higher panicle length over the better parent and standard
variety, respectively, whereas 19 crosses possessed significant negative heterobeltiosis
and 22 crosses exhibited negative standard heterosis with shorter panicle. The
observed heterobeltiosis values ranged between -39.26 (NMS4AxNDR3008) to 48.30%
(PMS10AxIET201108) with a mean of 0.37% and standard heterosis between -40.63
(PMS10AxIR 53480-8-39-3-1-2R) to 23.20% (PMS10AxIR 35454-18-1-1-2R) in case
of standard heterosis with mean of -3.65 per cent. The five superior cross combinations
having heterobeltiosis for panicle length were PMS 10AxIET 201108, PMS10AxIR
47310-94-4-3-1R, IR58025AxIR 32419-28-3-1-3R, IR58025AxIET201102 and PMS10 AxIR54853-43-1-3R.
As regards standard heterosis the most promising crosses for panicle length
were NMS4AxIR35454-18-1-1-2R, IR58025AxIR62030-81-1-3-2R, NMS4AxIR60966-29-4-2-2-2R,
NMS4AxIR52256-9-2-2-1R and IR58025AxIET201102. Similar findings were also reported
by Rao (1965), Karunakaran (1968);
Chang et al. (1973); Anandakumar
and Sreerangasamy (1984); Rangaswami and Natarajamoorthy,
1988); Vivekanandan (1991); Lokaprakash
et al. (1992) and Singh et al. (1992)
who observed positive as well as negative heterosis for panicle length.
Number of spikelets per panicle: For number of spikelets per panicle,
the hybrids with positive heterosis are desirable. The lowest estimates of heterosis
(-40.44%) over better parent and (-33.58%) standard variety were recorded in
the cross PMS10AxIR 53480-8-39-3-1-2R, while, maximum heterosis over better
parent and standard variety was observed in case of cross NMS4AxIR47310-94-4-3-1R
(8.65%) and NMS4AxIET201102 (12.08%). Out of 60 crosses studied 3 crosses over
better parent and 29 crosses over standard variety exhibited significant higher
number of spikelets per panicle. Significantly poor spikelets per panicle over
the better parent and standard, variety was observed in 48 and 22 crosses, respectively.
The five superior crosses were considering standard heterosis, the superior
cross combinations were NMS4AxIET 201102, PMS 10AxIET 9352, IR58025AxNOR 6054,
IR58025AxIET 202202 and NMS4AxIR 47310-94-4-3-1R. Results revealed that three
hybrids expressed heterosis in desired direction with significant value when
tested against better parent and almost 48 hybrids showed heterobeltiosis negative
direction over standard variety. Positive heterosis over better parent and standard,
variety was reported by Virmani et al. (1981,
1982) they concluded that heterosis in yield was primarily
due to increased number of spikelets per panicle.
Number of fertile spikelets per panicle: The number of fertile spikelets directly contributes to the seed yield hence positive heterotic effect would be highly desirable. The successful utilization of CMS in development of hybrids is not possible unless the effective restorer lines are identified. In the present study, more number of fertile spikelets is closely associated with high yield per plant resulting in high productivity. Therefore, the main interest is to find out the cross combinations with more number of long and heavy panicle bearing tillers. In the present study, the significant and positive heterosis for this trait was exhibited by 47 and 35 hybrids over better parent and standard variety, respectively. Significant negative heterosis was observed in case of 17 crosses over better parent and in 12 crosses over standard variety with mean heterosis was observed in positive direction for both better parent (10.61%) and standard variety (3.99%). The range of heterosis observed over better parent and standard variety was -20.66% (IR58025AxNDR 3008) to 46.61% (NMS4AxIR 47310-94-4-3-1R) and -16.86% (NMS4AxNDR358) to 21.02% (PMS10AxNDR6054), respectively. The five superior crosses were considering heterobeltiosis were NMS4AxIR 47310-94-4-3-1R, PMS10AxIET201108, NMS4AxIR633-76-1R, PMS 10 AxNDR 6054 and PMS 10 AxIET9352.
Spikelet fertility percent: Spikelet fertility percent is very important
in hybrid breeding programme. Since this trait has a direct bearing on the yield,
hence manifestation of heterosis in positive direction is desirable for this
trait. Out of 60 crosses, 47 expressed positive and significant heterobeltiosis,
while 35 crosses expressed this in case of standard heterosis. The range of
heterosis over better parent and standard variety varied from -6.89% (PMS10AxNDR3008)
to 46.40% (NMS4AxIR633-76-1R) and -0.81% (NMS4AxIET9352) to 16.31% (NMS4AxIR
32419-28-3-1-3R), with mean heterosis of 11.81 and 4.17%, respectively. As regards
heterosis over better parent the best crosses were NMS4AxIR 633-76-1R, PMS10AxIR
62030-81-1-3-2R, IR58025AxIR633-76-1R, PMS10AxIR 633-76 -1R and IR58025AxIR
62030-81-1-3-2R. Results revealed that 40 hybrids expressed heterosis in desired
direction with significant value when tested against better parent and as many
as 17 hybrids showed heterosis in negative direction over standard variety.
Positive heterosis over better parent and standard variety was reported by Virmani
et al. (1981) they concluded that heterosis in yield was primarily
due to increased fertile spikelets per panicle. These results were in conformity
with the results obtained by Srivastava and Seshu (1982),
Govindraj (1983), Sahai et al.
(1987), Viraktamath (1987) and Singh
(2000) who reported hybrids posses significantly lower tiller number than
mid parent, better parent and check variety.
100 grain weight: The 100 grain weight is one of the important common traits which influence the yield. The extent of heterosis was -41.25% (PMS 10 AxIR 633-76-1R) to 71.63% (PMS10AxIET201102) over better parent with mean of 8.15% and from -43.47% (NMS4AxIR54853-43-1-3R) to 21.81% over standard variety. Significantly higher 100 grain weight was observed in case of 19 crosses when tested against their better parents and 6 crosses against the standard variety. The five best heterosis cross combinations in respect of heterobeltiosis for 100 grain weight were PMS10AxIET201102, IR58025AxIET201102, NMS4AxIET 9352, PMS10AxIR54853-43-1-3R and IR58025AxIET9352. The standard heterosis over the check for five most promising crosses were PMS10AxIR54853-43-1-3R, PMS10AxIR 35454-18-1-1-2R, PMS10AxNDR3008, PMS10AxIET201102 and NMS4AxIR47310-94-4-3-1R. Among 60 crosses, 19 and 16 hybrids showed significant heterobeltiosis over better parent in positive and negative direction, respectively, whereas 6 and 28 hybrids exhibited significant heterosis over standard variety in positive and negative direction. Heterosis with respect to 100 grain weight in positive and negative direction have also been reported by
Karunakaran (1968), Carnahan et
al. (1972), Virmani et al. (1981), Srivastava
and Seshu (1982), Viraktamath (1987), Manuel
and Palanisamy (1989), Sharma and Mani (1989) and
Lokaprakash et al. (1992).
Grain yield: The grain yield is very complex trait. It is multiplicative
end product of several basic components of yield (Grafius,
1959). A number of workers have reported wide range of variation in the
expression of heterosis for this character (Rao, 1965;
Karunakaran, 1968; Carnahan et
al., 1972; Chang et al., 1971; Murayama
et al., 1974; Parmar, 1974; Saini
and Kumar, 1973; Saini et al., 1974; Maurya
and Singh, 1978; Govindraj, 1983; Nijaguna
and Mahadevappa, 1983; Panwar et al., 1983;
Yoshida and Fujimaki, 1984; Devarathinam,
1984; Cheema and Awan, 1985; Kaushik
and Sharma, 1986; Sahai et al., 1987; Virmani
et al., 1981; Govindraj, 1983; Tseng
and Huang, 1987; Sarwagi and Srivastava, 1988; Sampath
et al., 1989; Sharma and Mani, 1989, 1990;
Peng and Virmani, 1991; Vivekanandan,
1991; Lokaprakash et al., 1992; Wilfred
and Prasad, 1992; Ali and Khan, 1995). From practical
point of view, heterosis over standard variety is more relevant. Virmani
et al. (1981) reported as high standard heterosis as 27 and 34% during
wet and dry seasons, respectively. They further suggested that a yield advantage
of 20-30% over best available standard variety should be sufficient to encourage
farmers to take-up hybrid rice cultivation. In the present investigation about
1/3 combinations exhibited standard heterosis more than 30% among these best
crosses in order of merit increased grain yield were IR58025AxIR48749-53-2-2-2R,
NMS4Ax1R633-76-1R, IR58025AxIR54853-43-1-3R, IR58025AxIR19058-107-IR and PMS10AxIR
54853-43-1-3R. These findings were in close agreement with the earlier findings
of (Watanesk, 1993; Patel et
al., 1994; Zhang et al., 1994; Rao
et al., 1996; Mishra and Pandey, 1998; Nuruzzaman
et al., 2002; Li et al., 2002; Faiz
et al., 2006; Saleem et al., 2008;
Bagheri and Jelodar, 2010; Rahimi
et al., 2010). Reddy et al. (1984). These
findings were in close agreement with the earlier findings of (Watanesk,
1993; Patel et al., 1994; Zhang
et al., 1994). In general, F1 hybrids based on a cytoplasmic
genetic male sterile system have shown as much heterosis as F1 hybrids
between conventional cultivars/lines. However, most of the data showed heterosis
ranging from about 20% over the midparent to 70% over the better parent and
heterobeltiosis ranging about 20 to 40%. China has shown 20-30% higher yield
potential for hybrids in large-scale production plots, with wider adaptability
than conventionally bred varieties (Hunan Provincial Paddy
Rice Heterosis Scientific Research Coordination and Cooperation Group, 1978;
Li, 1977; Lin and Yuan , 1980;
Wu et al., 1980).
Biological yield: The hybrid, NMS4AxIR 48749-53-2-2-2R (-35.31%) and
IR58025AxIR42686-2-118-6-2R (12.50%) had expressed heterosis for this trait
over their better parent while, NMS4AxIR48749-53-2-2-2R (-19.91%) and NMS4AxIR633-76-1R,
(35.18%) recorded heterosis in case of standard variety (Sarjoo-52). In general,
out of 60 hybrids only 16 crosses recorded significantly higher heterobeltiosis
while 45 crosses exhibited this in case of the standard heterosis. The top five
cross combinations in relation to standard heterosis for biological yield were
NMS4AxIR633-76-1R, IR58025AxIR42686-2-118-6-2R, IR58025AxIR19058-170-1R, IR58025AxIR52256-9-2-2-1R
and IR58025AxNDR 6054. Significant but negative heterosis was exhibited by 25
and 4 hybrids over better parent and standard variety, respectively. These results
are in close agreement with Virmani et al. (1993)
and Peng and Virmani (1991).
Harvest index: Harvest index which indirectly influences the grain yield
through controlling the mechanism of distribution of photosynthates to economic
and non-economic organs as such is not a yield component. Therefore, it is an
important consideration for genetic improvement. The minimum heterosis for harvest
index was -31.56 and -15.59% over better parent and standard variety, respectively
in cross IR58025AxIR53480-8-39-3-1-2R and NMS4AxIR54853-43-1-3R, however, the
maximum heterosis was 56.06% over better parent in cross IR58025AxIET201108
and 46.93% over standard variety in cross PMS10AxIR 35454-18-1-1-2R. Among 60
cross combinations 26 crosses showed significant positive and 12 showed significant
negative heterobeltiosis while 30 crosses showed significant positive heterosis
over standard variety. The five crosses having maximum positive heterobeltiosis
for harvest index in order of merit were IR58025AxIET 201108, IR58025AxIR 48749-53-2-2-2R,
NMS4AxIR 58110-114-2-2-2R, IR58025AxIR54853-43-1-3R and PMS10AxNDR 3008. The
positive heterosis was also reported by Virmani et al.
(1982) and Peng and Virmani (1991). On the other
hand, 12 and 7 hybrids exhibited significant and negative estimates for both
heterobeltiosis and standard heterosis for this trait. The significant and negative
heterosis over better parent for harvest index was also reported by Nijaguna
and Mahadevappa (1982) and over standard variety by Sarwagi
and Srivastava (1988).
Heterosis for grain yield along with heterosis of its components is very important
consideration. Forty six cross combinations out yielded the standard check variety,
Sarjoo 52, by 10.48 to 71.56%. Out of forty three crosses showing desirable
heterobeltiosis for grain yield, 3 and 40 crosses were also found to have significant
and positive heterosis for number of spikelets per panicle and number of fertile
spikelets, respectively. Similarly, the 29 crosses having standard heterosis
for number of spikelets, per panicle also exhibited significant positive standard
heterosis for both grain yield and number of fertile spikelets except in four
crosses namely PMS10AxIR 32419-28-3-1-3R for number of fertile spikelets per
panicle, PMS10AxIR 47310-94-4-3-1R, NMS4AxIR 53480-8-39-3-1-2R for grain yield
and NMS4AxIET 201102 for number of fertile spikelets and grain yield per plant.
These observations also corroborate the findings of Rao
(1965), Dhulappanavar and Mensikai (1967), Mallick
et al. (1978), Singh and Singh (1978), Mandal
(1982), Sardana and Borthakur (1985), Anandakumar
and Sreerangasamy (1984), Viraktamath (1987), Rangaswami
and Natarajamoorthy (1988), Sharma and Mani (1989,
1990), Lokaprakash et al.
(1992) and Bobby and Nadarajan, (1993) for number
of fertile spikelets per plant and finding of Pillai (1961),
Carnahan et al. (1972), Davis
and Rutgar (1976), Govindraj (1983), Kumar
and Saini (1983), Sutarya (1989), Sharma
and Mani (1990), Lokaprakash et al. (1992)
and Ali and Khan (1995) for fertile grains. Besides
above mentioned two traits, the crosses possessing significant positive heterosis
for grain yield exhibited significantly superior heterosis for harvest index,
biological yield and number of spikelets per panicle in IR58025AxIET 201108,
IR58025AxIR 60966-29-4-2-2-2R, IR58025AxNDR 6054 and NMS4AxIR 633-76-1R over
better parent and standard variety. Earlier reports on manifestation of considerable
heterosis for grain yield associated with biological yield (Virmani
et al., 1982; Rangaswami and Natarajamoorthy,
1988; Peng and Virmani, 1991), associated with harvest
index (Mohapatra and Mohanty, 1985; Peng
and Virmani, 1991; Lokaprakash et al., 1992)
and with grain weight and fertile spikelets per panicle (Sharma
and Mani, 1990) and Chakraborty et al. (1994)
for days to 50% flowering, spikelets panicle and 100 grain weight.
Heterotic combinations for commercial utilization: A hybrid with the
potential of being released for commercial cultivation should significantly
surpass the yield level of the best locally adapted variety and its CMS component
should have to ensure hybrid seed production in bulk quantities. Swaminathan
et al. (1972) and Virmani et al. (1981)
have suggested that about 20-30% standard heterosis may be considered sufficient
to offset the extra cost of hybrid seeds in self-pollinated crops. In the present
investigation, about one third of the total hybrids showed more than 20% standard
heterosis for grain yield over standard variety (Sarjoo-52). Considering the
heterosis more than 60% as well as significant sca effects for major
components, the NMS 4AxIR 633-76-1R, IR58025AxIR 19058-107-1R and IR58025AxIR
32419-28-3-1-3R were most promising combinations and need to be tested on large
scale. Besides these, some other crosses viz., NMS4AxIR52256-9-2-2-1R, NMS4AxIET9352
and IR58025AxIET201102, which expressed more than 50% heterosis along with desirable
significant sca effects for more than six important yield components,
may be considered for commercial exploitation.
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