Introduction
Cotton is an important fiber yielding crop of global importance, which is grown in tropical and subtropical regions of more than 80 countries the world over. It provides livelihood to about sixty million people and is an important agricultural commodity providing remunerative income to million of farmers both in developed and developing countries. In India, inspite of severe competition from synthetic fibers in recent years, it is occupying the premiere position with 70 per cent share in the textile industry.

Gossypium hirsutum L. provides 90% of world fiber and is major cash and industrial crop. Cotton is grown on almost 32.4 million hectares in more than 90 countries of temperate, sub-tropical, and tropical regions of the world. The four main producing countries are China, India, USA and Pakistan and accounted for approximately three quarters of world output. If Uzbekistan and Brazil are added, six countries would account for 83% of world cotton production. Cotton is long day and often cross-pollinated crop, and usually requires little heavy soil, moderate rainfall and mostly sunshine. Intra- hirsutum hybrids have been released for commercial cultivation in all nine major cotton growing states. These hybrids cover maximum area, among cotton hybrids, under cultivation and can be grown both under irrigated and rainfed conditions. Intra- hirsutum hybrids are more tolerant to sucking pests than inter specific hybrids between G. hirsutum and G. barbadense.

Heterosis works as a basic tool for improvement of crops in form of F₁ and F₂ populations, and economic heterosis (over standard cultivar). It also contributes to choose genotypes with desired genetic variance, vigor and maternal effects. Therefore, it is essential to have detailed information about desirable parental combiners in any breeding program, which can reflect a high degree heterotic response. In intra- and inter-specific heterosis, yield increase over better parent or greater than best commercial cultivar (useful heterosis) has been documented (Baloch et al., 1993b; Galanopoulou-Sendouca and Roupakias, 1999; Wei et al., 2002; Yuan et al., 2001 & 2002; Khan et al., 2007; Khan, 2011). Both positive and negative heterotic values have been detected, demonstrating potential of hybrid combinations for traits improvement in breeding programs (Hassan et al., 1999; Khan et al., 2009). F₁ hybrids with high heterosis were also associated with higher inbreeding depression; therefore, moderate type of heterosis has some stability in segregating populations (Tang et al., 1993; Soomro, 2000; Soomro and Kalhoro, 2000). Therefore, heterotic studies can provide basis for exploitation of valuable hybrid combinations in future breeding program.

The main objective of this study to study the heterosis and per se performance of new cotton intra hirsutum hybrids in respect of kapas yield and its attributing characters.

1 Results and Discussion
1.1 Analysis of variance
The mean sum of squares for kapas yield and its attributing characters in 51 hybrids of cotton are presented in Table 1. Mean sum of squares for hybrids was highly significant for all the characters except number of monopodia per plant, mean boll weight and seed index indicating presence of significant differences among the hybrids evaluated in respect of these traits. The mean sum of squares for hybrids vs checks was highly significant for plant height number of sympodia per plant, number of bolls per plant, kapas yield per plant and ginning outturn revealing superiority of hybrids over checks and presence of heterosis in respect of these traits.

Table 1 Analysis of variance for kapas yield per plant and its attributing characters in checks and experimental hybrids of cotton (G. hirsutum L.)

 
1.2 Mean per se performance of hybrids
The mean per se performance of hybrids in respect of kapas yield and its attributing characters (Table 2) are briefly presented below.

Table 2 Mean per se performance of experimental hybrids and checks of cotton (G. hirsutum L.) in respect of kapas yield per plant and its attributing characters

 
1.2.1 Days to 50 per cent flowering
Among 51 hybrids evaluated, the hybrid RAH 97 x SC 68 took minimum number of days for 50 per cent flowering (66.50 days) followed by the hybrids RAH 318 x RGR 58, RAH 243 x RGR 32 and RAH128 x RGR 24 (67.00 days), RAH 318 x SC 68, RAH 243 x SC7 and BUNNY Bt (67.50 days), RAH128 x RGR 32 (68.00 days), RAH 318 x SC 7, RAH128 x SC 68 and RAH 97 x RGR 58 (68.50 days), RAH 243 x SC 14 and RAH 97 x RGR 24 (69.00 days) and RAH 318 x RGR 24, RCH2 Bt, RAH 243 x RGR 24, RAH146 x SC 7, RAH 97 x SC 7, RAH 97 x RGR 32, RAH 124 x SC 18 and RAH 124 x SC 7 (69.50 days) which are statistically on par with one another. Contrary to this, the hybrid RAH128 x SC 14 took maximum number of days (72.50) followed by the hybrids RAH 243 x SC 18, RAH128 x RGR 37, RAH146 x RGR 32, RAH146 x RGR 37, RAH 97 x SC 14, RAH 97 x SC 18 and RAH 124 x RGR 37 (72.00 days).

1.2.2 Plant height (cm)
The hybrid RAH146 x RGR 24 recorded maximum plant height (138.70 cm) followed by the hybrid RAH128 x SC 14 (134.30 cm), while the hybrid RAH 318 x RGR 37 recorded minimum plant height of (84.30 cm).

1.2.3 Number of monopodia per plant
Among the 51 hybrids, the hybrid RAH146 x RGR 37 recorded maximum number of monopodia per plant (2.50) followed by RAH 318 x RGR 58 and RAH 97 x RGR 32 (2.40), RAH 243 x SC 68 and RAH 243 x RGR 24 (2.30) and RAH 243 x SC 14 and RAH 124 x RGR 32 (2.25) which are on par with each other. On the other hand, the hybrid RAH 124 x SC 7 (1.20) recorded minimum number of monopodia per plant.

1.2.4 Number of sympodia per plant
Maximum number of sympodia per plant were observed in the hybrid RAH 124 x SC 18 (28.85) followed by the hybrid RAH128 x SC 14 (28.40) and RAH 243 x SC 68 (28.30) which are on par with one another. On the other hand, the hybrid RAH 318 x SC 18 recorded lowest number of sympodia per plant (16.30) followed by RAH 318 x RGR 37 (17.50).

1.2.5 Number of bolls per plant
The hybrid RAH146 x RGR 58 produced maximum number of bolls per plant (33.80) followed by the hybrid RAH128 x SC 68 (33.30), RAH 318 x RGR 24 (33.20), RCH2 Bt (31.60) and RAH 243 x SC 7 (3140). On the other hand, the hybrid RAH 97 x SC 68 produced minimum number bolls per plant (13.10) followed by RAH 97 x RGR 24 (13.20).

1.2.6 Mean boll weight (g)
The hybrid RAH 97 x SC 7 exhibited maximum mean boll weight (3.76 g) followed by the hybrid RAH 97 x RGR 32 (3.74 g), RAH 97 x SC 14 (3.58 g) and RAH 97 x SC 18 (3.52 g), while the hybrid RAHH 95 had minimum mean boll weight (2.31g) followed by the hybrid RAH 243 x RGR 58 (2.48 g).

1.2.7 Kapas yield per plant (g/plant)
Maximum kapas yield per plant was observed in the hybrid RAH 97 x SC 18 (139.96 g), while the hybrid RAH 97 x SC 68 recorded minimum kapas yield per plant (36.93 g) followed by RAH 124 x RGR 24 (38.05 g).

1.2.8 Ginning percentage (%)
The hybrid RAH146 x RGR 32 possessed maximum ginning out turn (42.23%) followed by the hybrid RAH 97 x RGR 24 (41.47%), RAH146 x RGR 58 (41.37%), RAH146 x SC 68 (40.38%) and RAH 97 x RGR 32 (39.38%), while the hybrid RAH 243 x SC 18 recorded minimum (28.74%) ginning out turn.

1.2.9 Seed index (g)
Among all the hybrids, the hybrid RAH 97 x RGR 24 recorded maximum seed index (11.50 g) followed by the hybrids RAH 97 x SC 7, RAH 97 x RGR 58 and RAH 97 x RGR 37 (10.75 g) , RAH 97 x SC 18 (10.50 g), RAH128 x RGR 37, RAH 97 x SC 14, RAH 97 x RGR 32, RAH 124 x SC 18, and RAH 124 x SC 7 (10.25 g) and the hybrids RAH128 x RGR 24 and RAH146 x RGR 24 (10.00 g). On the other hand, the hybrids RAH 318 x RGR 37 and BUNNY Bt recorded minimum seed index (8.00 g) followed by RAH 243 x SC 14 and RAH128 x SC 7 (8.25 g).

1.2.10 Lint index (g)
The hybrid RAH 97 x RGR 24 had maximum lint index (8.15 g) followed by the hybrid RAH146 x RGR 32 (6.76 g), RAH146 x RGR 58 (6.70 g) which are on par with one another, while the hybrid RAH 243 x SC 18 recorded minimum lint index (3.53 g) followed by RAH 243 x SC 14 (3.90 g).

1.3 Heterosis studies
Kapas yield is the most important character determining the worth of hybrid from the point of view of recommendation for general cultivation. Heterosis is the superiority of the F₁ over the mid parental value or over the better parent or over the standard check (Hayes et al., 1955). The magnitude of standard heterosis for seed cotton yield had been studied widely by Kalsy and Garg, (1995). Heterosis for yield is expressed in the form of increased yield which in turn is dependent on the contribution of many component characters. All the component characters of yield were studied for heterosis manifestation in order to assess the worth of cross for a character.

In the present study, 48 hybrids were evaluated for standard heterosis over commercial check hybrids viz., BUNNY Bt, RCH2 Bt and RAHH 95. The results are presented in Table 3~12. 

Table 3 Performance of hybrids and heterosis over commercial check (RAHH 95) and best Bt hybrid check (RCH2 Bt) with respect to days to 50% flowering in cotton (G. hirsutum L.)

Table 4 Performance of hybrids and heterosis over commercial check (RAHH 95) and best Bt hybrid check (RCH2 Bt) with respect to plant height in cotton (G. hirsutum L.)

Table 5 Performance of hybrids and heterosis over commercial check (RAHH 95) and best Bt hybrid check (RCH2 Bt) with respect to number of monopodia per plant in cotton (G. hirsutum L.)

Table 6 Performance of hybrids and heterosis over commercial check (RAHH 95) and best Bt hybrid check (BUNNY Bt) with respect to number of sympodia per plant in cotton (G. hirsutum L.)

Table 7 Performance of hybrids and heterosis over commercial check (RAHH 95) and best Bt hybrid check (RCH2 Bt) with respect to number of bolls per plant in cotton (G. hirsutum L.)

Table 8 Performance of hybrids and heterosis over commercial check (RAHH 95) and best Bt hybrid check (RCH2 Bt) with respect to mean boll weight in cotton (G. hirsutum L.)

Table 9 Performance of hybrids and heterosis over commercial check (RAHH 95) and best Bt hybrid check (RCH2 Bt) with respect to kapas yield per plant in cotton (G. hirsutum L.)

Table 10 Performance of hybrids and heterosis over commercial check (RAHH 95) and best Bt hybrid check (BUNNY Bt) with respect to ginning outturn in cotton (G. hirsutum L.)

Table 11 Performance of hybrids and heterosis over commercial check (RAHH 95) and best Bt hybrid check (RCH2 Bt) with respect to seed index in cotton (G .hirsutum L.)

Table 12 Performance of hybrids and heterosis over commercial check (RAHH 95) and best Bt hybrid check (RCH2 Bt) with respect to lint index in cotton (G. hirsutum L.)

 
1.3.1 Days to 50 per cent flowering
Among 48 hybrids, none of the hybrids showed significant heterosis over the check RCH2 Bt, but the hybrid RAH 97 x SC 68 (-4.32%) followed by RAH128 x RGR 24, RAH 243 x RGR 32 and RAH 318 x RGR 58 (-3.60%), RAH 243 x SC 7 and RAH 318 x SC 68 (-2.88%), RAH128 x RGR 32 (-2.16%), RAH 318 x SC 7 and RAH 97 x RGR 58 (-1.44%) exhibited heterosis in desirable direction over RCH2 Bt (Table 3). However, the hybrid RAH 97 x SC 68 (-6.99%) followed by RAH128 x RGR 24, RAH 243 x RGR 32 and RAH 318 x RGR 58 (-6.29%) exhibited low heterosis in desirable direction over RAHH 95 check. This is in confirmity with the results of Marani (1964), Police Patil (1975), Vijendradas (1982) and Taware et al. (1987).

1.3.2 Plant height (cm)
Three out of 48 hybrids showed significant heterosis over the check RAHH 95. Of these, the hybrid RAH 318 x RGR 37 (-24.93%) and the hybrid RAH128 x RGR 37 (-23.33%) (Table 4) exhibited negative significant heterosis, but the hybrid RAH146 x RGR 24 (23.51%) showed positive significant heterosis. Although 3 hybrids expressed significant heterosis over RCH2 Bt, only one hybrid RAH146 x RGR 24 (24.06%) expressed significant positive heterosis and two hybrids viz, RAH 318 x RGR 37 (-24.60%) and RAH128 x RGR 37 (-22.99%) exhibited significant negative heterosis. Similar results were reported by Marani (1963), Young and Murray (1966), Quisenberry (1977), Vijendradas (1982) and Singh and Bhat (1984).

1.3.3 Number of monopodia per plant
Positive heterosis over RCH2 Bt with respect to this trait was observed in the hybrid RAH146 x RGR 37 (19.05%) followed by RAH 318 x RGR 58 and RAH 97 x RGR 32 (14.29%), RAH 243 x SC 68 and RAH 243 x RGR 24 (9.52%), RAH 124 x RGR 32 (7.14%) and RAH 318 x SC 14 and RAH146 x RGR 58 (4.76%). Whereas, nine hybrids RAH 318 x SC 14 and RAH146 x RGR 58 (57.14 %), RAH 318 x RGR 58 and RAH 97 x RGR 32 (71.43%), RAH 243 x SC 14 and RAH 124 x RGR 32 (60.71%), RAH 243 x SC 68 and RAH 243 x RGR 24 (64.29%) and RAH146 x RGR 37 (78.57%) exhibited highest significant positive heterosis over RAHH 95 (Table 5). Heterosis for number of monopodia per plant was earlier reported by Gill and Singh (1982), Duhoon et al. (1983), Kaushik et al. (1984) and Kolte and Thombre (1984).

1.3.4 Number of sympodia per plant
Thirty four out of 48 hybrids exhibited non significant positive heterosis over RAHH 95 check, of which the hybrid RAH 124 x SC 18 (20.71%) recorded highest heterosis followed by the hybrid RAH128 x SC 14 (18.83%), RAH 243 x SC 68 (18.41%), RAH146 x RGR 58 (17.15%), RAH146 x SC 18 (16.74%) and RAH128 x SC 68 (15.48%). On the other hand, 20 hybrids exhibited non significant positive heterosis over BUNNY Bt (Table 6), of which the hybrid RAH 124 x SC 18 recorded higher heterosis (12.26%) followed by RAH128 x SC 14 (10.51%), RAH 243 x SC 68 (10.12%), RAH146 x RGR 58 (8.95%) and RAH146 x SC 18 (8.56%). Heterosis for number of sympodia per plant was earlier reported by Gill and Singh (1982), Duhoon et al. (1983), Kaushik et al. (1984) and Kolte and Thombre (1984).

1.3.5 Number of bolls per plant
Only three of 48 hybrids exhibited non significant positive heterosis over RCH2 Bt check, of which RAH146 x RGR 58 (6.96%) recorded highest heterosis (Table 7) followed by the hybrid RAH128 x SC 68 (5.38%) and RAH 318 x RGR 24 (5.06%). On the other hand, 8 hybrids expressed positive heterosis over RAHH 95 check, of which the hybrid RAH146 x RGR 58 (10.46%) followed by the hybrid RAH128 x SC 68 (8.82%) and the hybrid RAH 318 x RGR 24 (8.50%). This is in accordance with the report of Marani (1963).

1.3.6 Mean boll weight (g)
Among 48 hybrids, only nine hybrids recorded positive heterosis over RCH2 Bt check, of which the hybrid RAH 97 x SC 7 recorded highest heterosis of 13.10% (Table 8) followed by RAH 97 x RGR 32 (12.65%). On the other hand all the hybrids exhibited positive heterosis over RAHH95. This is in accordance with the report of Marani (1963).

1.3.7 Kapas yield per plant (g /plant)
Out of 48 hybrids, only one hybrid viz. the hybrid RAH 97 x SC 18 exhibited highly significant positive heterosis (30.09%) over RCH2 Bt check hybrid. Twenty four hybrids exhibited positive heterosis over RAHH 95 check, of which the hybrid RAH 97 x SC18 exhibited highly significant positive heterosis (105.36 %) (Table 9) followed by the hybrid RAH146 x RGR 37 (55.80%), RAH146 x RGR 58 (53.93%) and RAH 318 x RGR 24 (52.02%). The other six hybrids exhibited positive and significant heterosis on par with RAHH 95 check. Similar reports were made by Marani (1963), Kataraki et al. (1970), Meredith (1979), Jagtap (1986), Katageri and Kadapa (1989).

1.3.8 Ginning outturn (%)
Among 48 hybrids, eleven hybrids exhibited positive heterosis over RAHH 95 check. Of which the hybrid RAH146 x RGR 32 recorded highest heterosis (12.49%) followed by the hybrid RAH 97 x RGR 24 (10.47%) and RAH146 x RGR 58 (10.19%). On the other hand, 29 hybrids exhibited positive heterosis over BUNNY Bt check (Table 10), of which the hybrid RAH146 x RGR 32 recorded significant positive heterosis of 21.07% followed by RAH 97 x RGR 24 (18.90%) and RAH146 x RGR 58 (18.60%). For this trait, the hybrid RAH146 x RGR 32 recorded highest positive heterosis over RAHH 95 check and positive significant heterosis over BUNNY Bt was also reported by Tiwari et al. (1987), Taware and Patil (1993).

1.3.9 Seed index (g)
Of 48 hybrids, only one viz, RAH 97 x RGR 24 (24.32%) showed highest significant positive heterosis over RCH2 Bt. However, 19 hybrids exhibited positive non significant heterosis (Table 11), of which the hybrid RAH 97 x SC 7, RAH 97 x RGR 58 and RAH 97 x RGR 37 (16.22%), RAH 97 x SC 18 (13.51%) and RAH128 x RGR 37, RAH 97 x SC 14, RAH 97 x RGR 32, RAH 124 x SC 18 and RAH 124 x SC 7 (10.81) exhibited heterosis of more than 10 per cent. On the other hand, as many as nine hybrids exhibited significant positive heterosis over RAHH 95 check. The hybrid RAH 97 x RGR 24 (35.29%) recorded high heterosis. Mehta et al. (1986), Gupta and Singh (1987), Katageri and Kadapa (1989), Krishnadas and Kadambavanasundaram (1997) reported similar results.

1.3.10 Lint index (g)
Twenty six out of 48 hybrids exhibited positive heterosis over RAHH 95 check, one hybrid RAH 97 x RGR 24 (59.47%) recorded high significant positive heterosis (Table 12) over RAHH 95 check and as many as seven hybrids recorded more than 15% heterosis. On the other hand, the hybrids RAH 97 x RGR 32 (51.32 %), RAH 97 x RGR 58 (50.72%) and RAH 97 x RGR 37 (48.68%) exhibited positive significant heterosis over RCH2 Bt, but the hybrid RAH 97 x RGR 24 (85.20%) showed high positive significant heterosis over RCH2 Bt check. Marani (1963), Mehta et al. (1986), Gupta and Singh (1987) and Singh et al. (1988) also reported high heterosis for this trait.

2 Conclusion
The enhancement of yield or economic product of any crop species is the ultimate aim of the plant breeder in the concerned crop improvement programme. The yield and its attributing characters are polygenic in nature and as such are complex in their mode of inheritance. An understanding of the genetic nature and inheritance of such complex traits and extent of their association with yield is very much essential to help and guide the plant breeder in selection experiments. It also helps in systematic handling of breeding material to achieve maximum improvement by adopting highly sophisticated statistical techniques.

The performance of three top hybrids viz., RAH 97 x SC 18, RAH 146 x RGR 37 and RAH 146 x RGR 58 in respect of kapas yield needs to be verified for their performance on large scale basis. Two hybrids RAH 97 x SC 18 and RAH 146 x RGR 37 were superior over standard commercial check hybrid RAHH 95 for kapas yield per plant, number of sympodia per plant, number of monopodia per plant, number of bolls per plant and ginning outturn and the hybrid RAH 146 x RGR 58 which exceeded best Bt check hybrid (RCH2 Bt) for kapas yield per plant.

3 Materials and Method
The plant materials used in the present study were obtained by line x tester crossing. According to this method, RAH 318, RAH 243, RAH 128, RAH 146, RAH 97 and RAH 124 were crossed as the lines with SC 14, SC 18, SC 7, SC 68, RGR 32, RGR 24, RGR 58 and RGR 37 as the testers. The six hirsutum lines representing Robust plant type classes but differing in efficiency of physiological processes like photosynthesis, were selected and crossed to a set of eight testers representing compact types and faster growth rate. The seeds of the hybrids were supplied by Dr. S.S. Patil, Senior Cotton Breeder, Agricultural Research Station, Dharwad Farm, Karnataka, India, in 2008. The experiment comprising of 48 experimental hybrids along with 3 checks (BUNNY Bt, RCH2 Bt, RAHH 95) (one repeated two times) was laid out in Randomized Complete Block Design (RCBD) with two replications. Each entry was sown in 3 row plots of 6 m length spaced at 90 cm with recommended dose of fertilizer and treatment of seeds with imidochloprid were sown on 10-7-2008, 2~3 seeds were dibbled per spot in each row and thinning was attended to retain one healthy plant per hill at 25 days after sowing. All the recommended package of practices were followed to rise healthy crop.

Samples containing 20 bolls were hand-harvested from each plot prior to picking. The days to 50 per cent flowering recorded by the number of days taken from the date of sowing to the date when the first flower opens in 50 per cent of the plants. The number of monopodia per plant are the number of branches on main stem which were lateral and axillary in position with vertical growth in acropetal succession was counted at maturity stage, avoiding small sprouts, but the number of sympodia per plant are branches which are extra-axillary in position and normally horizontal with zig -zag pattern of fruiting points were taken as sympodia. The number of such sympodia on main stem were counted at maturity stage. The boll samples were weighed to determine seed cotton weight per boll values, and ginned on a roller using laboratory gin for lint percentage (100 x lint weight/seed cotton weight) and 100-seed weight calculations (seed index). The ginned lint from each plot was weighed and divided by the number of plants within each plot to determine lint yield per plant. Five plants were selected randomly from each genotype to find the boll number per plant. The Microsoft Excel computer program was used to analyze the data. The line x tester mating design according to Singh and Chaudhary (1979) can provide information regarding the usefulness of male and female inbreds as parents for hybridization to generate segregating populations, which is expected to give prodigious selections.

Heterosis of F₁ over commercial check was calculated as per the methods of Turner (1953) and Hayes et al. (1955) as given below.

Per cent heterosis in F₁ over commercial check:

Heterosis over commercial check = (F₁-CC)/CC × 100

Where, CC = Mean value of commercial check over replication

F₁ = Mean value of hybrid over replication

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