Cytoplasmic and Combining Ability Effects on Agro-Morphological Characters in Intra and Inter Crosses of Pima and Upland Cottons ( G . Hirsutum and G . Barbadense )

Combining ability and heterosis were determined in a population obtained from the full diallel crossing of four different cotton genotypes (G. hirsutum and G. barbadense) for agro morphological traits and yield. High variation was observed for characteristics among parents and the F1 combinations. So, selection could be done for improved yield, yield components and agro morphological traits. Barbadense 5539 and Termeze14 (G. barbadense) had positive GCA for height, bolls/plant and sympodia branch/plant, Inverse, Sahel and Sepid (G. hirsutum) had negative GCA for these characteristics. G. barbadense genotypes showed negative GCA for monopodia branch/plant, sympodia branch length and boll weight, Inverse, G. hirsutm genotypes was observed positive GCA for this traits. The GCA: SCA ratios for the studied traits were higher than one indicating the presence of additive genetic effects for most of the characteristics studied, except for sympodia branch length.

Upland cotton, G. hirsutum, dominates the worlds' cotton fiber production, representing 90% of the production.Compared with the upland cotton, the second most cultivated species, G. barbadense, has superior fiber length, strength, and fineness.G. hirsutum varieties, however, are usually early-maturing and higher yielding (Lacape et al.2005).
Upland cotton (Gossypium hirsutum L) is the most extensively cultivated of the four cultivated Gossypium species, and, as such, it has been the target of numerous genetic studies and breeding efforts.The level of genetic diversity is low in G. hirsutum, especially among agriculturally elite types, as revealed by all means of assessment (Gutiefrrez et al. 2002;Ulloa and Meredith 2000;wendel et al. 1989).
Gossypium barbadense (L.) is the only 52-chromosome relative of upland cotton (G.hirsutum, 2n=52) that is cultivated.It is valued for its fiber length and quality, whereas upland cotton is more valuated for its high yield (Saha et al. 2006).
Most genetic traits useful for cotton improvement are influenced by several genes.These are called quantitatively inherited traits (Shappley et al., 1998).The identification and characterization of genes controlling traits of use in plant improvement has long been a focus of scientists in the agricultural community.Cotton is the most important textile fiber crop and the worlds' second-most important oil-seed crop after soybean (Poehlman and Sleper, 1995).It is grown commercially in the temperate and tropical region of more than 50 countries, including the United States, India, China, central and South America, The Middle East, and Australia (Fryxell, 1979;Smith, 1999).
Increasing diversity is therefore essential to genetic improvement efforts.Each of the three major approaches to increasing genetic diversity (mutagenesis, germplasm introgression, and transformation) has advantages and disadvantages.Interspecific germplasm introgression is particularly attractive in that it utilizes abroad germplasm base, can be targeted to one or more specific traits or genes or modulated to include thousands of genes or even entire genomes.However, the biological and technical challenges of introgression increase as the phyletic distance between the donor and recipient genome increases (Saha et al. 2006).
Diallel crossing technique in cotton has been used by cotton breeders.Baloch et al. (1995) revealed the importance of specific combining ability for yield, 100-seed weight and lint percentage, and general combining ability for boll number per plant and lint percentage.Wilson (1991): Tang et al.(1993) and Nadeem et al. (1998) reported significant general and specific combining ability effects for lint yield, lint percentage, seed cotton weight per boll and boll number per plant.
Hybrid vigor in cotton has been observed in interspecific crosses as well as in crosses between varieties within the species.Fryxell et al. (1958), Hutchinson et al. (1938), Marani (1967), Stroman (1961), andWare (1931) in particular showed that crosses between G. barbadense and G. hirsutum were much more productive than either parent.Because of the differences in the characteristics of the lint of the two species, it frequently has objectionable qualities in the hybrid.This problem is less likely to arise in intraspecific hybrids where considerable hybrid vigor has also been shown.
In a molecular analysis of G. hirsutum introgression into Pima (G.barbadense) cotton, 7.3% of the alleles of Pima cultivars were found to be derived from G. hirsutum (Wang et al., 1995).These alleles were not randomly distributed within the G. barbadense genome, since nearly 60% of the total introgression was found within five specific chromosomal regions accounting for less than 10% of the genome.
Transfer of reniform nematode resistance from G. Longicalyx into G. hirsutum requires introgression of genes from the unique diploid F genome of G. Longicalyx into either the A or D sub genome of allotetraploid G. hirsutum.As bridges, two synthetic tetraploid triple species hybrids, referred to as HLA and HHL, were developed (Bell and Robinson, 2004).Robinson et al. (2007) was studied two trispecies hybrids of G. hirsutum, G. longicalyx and either G. armourianum Kearney or G. herbaceum L. to introgress high resistance to the nematode from G. Longicalyx into G. hirsutum.Introgression was pursued from 28 resistant BC1 plants, each of which was backcrossed four to seven times to G. hirsutum to derive agronomically suitable types.
The objective of this study was to estimate parental general combining ability effects, to compare performance among F1 hybrids, and to identify those superior for yield and agro morphological traits.

Material and Method
During the summer of 2005, four different cotton genotypes, Thermez 14 (line 2) and barbadense 5539 (line 18) of G. barbadense species, Sepid (line 22) and Sahel (line 13) of G. hirsutum species, were crossed to produce F1 seeds.These genotypes display a continuous spectrum of morphological traits between the two parental species (Ulloa et al., 2000).Parents and F1 seed was planted in the spring of 2006.Four parents and 12 hybrids were planted in randomized complete blocks.Plots consisted of four, 10m-long row with 80 cm apart.Soil was a silt-loam.Plant density was about 33000 plants ha-1.Weed control, irrigation, and insect control were standard practices for production of cotton in the Hashemabad cotton research station, Gorgan, Iran.Boll weight was determined from 20 hand-harvested bolls, just prior to first harvest from each plot.Seed cotton yield was determined by hand harvest.Plant height was measured from ground level to the top of the plant at harvest time.Monopodia and sympodia branch length, monopodia and sympodia branches/plant was measured prior to first harvest.
The data for each measurement was tabulated and analyzed by Fisher's analysis of variance.The diallel analysis was used to evaluate traits that had significant variation among the parents.Griffing-type diallel analysis was applied to estimate the GCA and SCA effects.

Results
Preliminary analysis of variance indicated that parents and their hybrids were significantly different from each other for all investigated traits in the study, which enable the diallel analysis to be run (Table 1).

Female parents different
The four parents used in this study varied significantly for each components and agro morphological traits except for sympodia and monopodia branch length (Table 2).Termeze 14 had the highest values in height characters.About boll/plant, barbadense 5539 and Termeze 14 had the highest value.The maximum monopodia branch number/plant was for Sahel and Sepid cultivars.Termeze 14 and barbadense 5539 had the highest values in sympodia branch/plant.The monopodia and sympodia branch length were not significantly difference in female parents.Sahel and Sepid (G.hirsutum spesies) had the weightiest boll.These, also, had the highest values for yield.

Male parent's difference
The genotypes used for male parents were significantly different for each yield components and agro morphological traits except for boll/plant and boll weight characters.Barbadense 5539 had the highest value for height.G. hirsutum species, Sahel and Sepid, had the maximum monopodia branch/ plant and minimum sympodia branch/plant.The highest sympodia branch length was for Sahel cultivar.Barbadense 5539 had the lowest monopodia branch length.Sepid had the highest value for seed cotton yield.

Agro morphological GCA and SCA
Analysis of variance for genotypes indicated the presence of significant differences among genotypes (Table 4).Combining ability mean squares for the characteristics are presented in Table 4. Significant GCA mean squares for yield components, height, bolls/plant, monopodia branches/plant, sympodia branches/plant, monopodia and sympodia branch length, boll weight and seed cotton yield indicated that additive genes controlled most of the characteristics.GCA mean square values were higher compared to the mean squares for SCA except for sympodia branch length (Table 4).
Results for GCA effects are given in Table 6.Sahel had negative GCA effects for height, bolls/plant, sympodia branches/plant and yield.Sahel, known to have big bolls, had positive and significant GCA effects for boll weight, monopodia branches/plant, sympodia and monopodia branch length.GCA effects for barbadense 5539 on height, bolls/plant and sympodia branches/plant were positive.GCA effects for sympodia branches/plant, sympodia and monopodia branch length, boll weight and yield were negative at Hashemabad research station (Table 6).The GCA effect for Sepid cultivar was positive for monopodia branches/plant, sympodia and monopodia branch length, boll weight and yield.Negative GCA effects were observed for bolls/plant, height, sympodia branches/plant.Positive GCA effects were shown by Termeze 14 genotype for height, bolls/plant, sympodia branches/plant and monopodia branch length while the values for monopodia branches/plant, sympodia branch length, boll weight and yield were negative.

Cytoplasmic effects
Results for cytoplasmic effects are given in Table 8.Sahel×barbadense 5539 and barbadense 5539×Sepid combinations had positive effect.For height, positive maternal effect was showed at barbadense5539×Sepid crosses.Barbadense5539×Termeze 14 combinations had positive maternal effect for bolls/plant.Maternal effect was positive for monopodia branches/plant at barbadense5539×Termeze14 crosses.About sympodia branches/plant Sahel×barbadense5539, barbadense5539×Sepid and Sepid×Termeze14 had positive maternal effects.Positive cytoplasmic effects were observed for sympodia branch length at barbadense5539×Sepid crosses.The observed maternal effect for boll weight, Sahel×Termeze14 and barbadense5539×Termeze14 combinations were positive.For seed cotton yield, Sahel×barbadense5539 and Sahel×Termeze14 had the positive cytoplasmic effect (Table 8).

Heterosis estimates
Heterosis values for the combination varied from negative to positive (Table 5).Height heterosis was positive for all of the combinations.Sahel×Termeze14 had high positive heterosis.Heterosis values for bolls/plant were positive for most of the combinations except for Sahel×Sepid and Sahel×Termeze14, and Sahel×barbadense5539 combination had the highest heterosis (6.83).The heterosis value for monopodia branches/plant for all combinations except for Sahel×Termeze14 was negative.Heterosis estimates recorded on combinations for sympodia branches/plant varied from negative to positive.Sahel×barbadense 5539 had the highest heterosis value, Also Sahel×Termeze14 had the highest heterosis value for sympodia and monopodia branch length, When G. hirsutum and G. barbadense species were crossed, heterosis was positive.In this study, Sahel×Sepid had the maximum heterosis for boll weight.Heterosis values for seed cotton yield were positive for most of the combinations, except for Sahel×Termeze14 and Sahel×barbadense5539.The high heterosis value were obtained in Sahel×Sepid (345.83,G. hirsutum×G. hirsutum) and Sepid×Termzeze14 (758.33,G. hirsutum×G. barbadense).

Discussion
High variation was observed for characteristics among parents and the F1 combinations.So, selection could be done for improved yield, yield components and agro morphological traits.GCA values obtained for Sahel, barbadense5539, Sepid and Termeze14 indicated the possibility of good combining from these parents for the some traits.Barbadense5539 and Termzeze14 (G.barbadense) had positive GCA for height, bolls/plant and sympodia branches/plant, inverse Sahel and sepid (G.hirsutum) had negative GCA for these characteristics.G. barbadense genotypes were showed negative GCA effect for monopodia branches/plant, sympodia branch length and boll weight, inverse G. hirsutum genotypes were observed positive GCA for these traits.Positive GCA for yield was observed only in Sepid.Positive SCA effects observed for same crosses.Sahel×barbadense5539 crosses had the highest positive SCA for bolls/plant.Highest positive SCA was observed for boll weight in Sahel×Sepid.In Sahel×Sahel, highest positive SCA was showed for yield.
Significant SCA mean squares observed for boll weight was reported by Echekwu and Alaba (1995).The performance of some combinations indicated the possibility of improvement of these traits.Griffing (1956) and Machado et al. (2002) reported that crosses with high SCA values from parents with highest SCA in a population should be efficient in selection in segregation population.The high and significant positive GCA were observed in crosses for seed cotton yield, lint yield, seed/boll, bolls/plant and boll weight (Lukonge, 2005).
The GCA:SCA ratios for the studied traits were higher than one indicating the presence of additive genetic effects for most of the characteristics studied except for sympodia branch length.According to Ashraf and Ahmad (2000), high additive genetic variation for these characteristics suggested a possibility of improvement in these characteristics.Therefore normal recurrent selection would be required to accumulate the additive genes in order to increase seed cotton yield (Lukonge, 2005).
Positive heterosis for height was observed for all of combinations.Positive heterosis for boll weight was showed in Sahel×Sepid, barbadense5539×Sepid and Sepid×Termeze14.Sambamurthy et al. (1995) reported that in tetraploid cotton, boll weight and boll number for intraspecific hybrids are the major components of heterosis in yield and this usually observed in G. hirsutum crosses and not for G. barbadense.The highest positive heterosis for yield was observed in Sepid×Termeze14 and Sahel×Sepid.Xian et al. (1995) and Zhang and Zhang (1997) reported high heterosis for seed cotton and lint yield.Sahel×barbadense5539 had the highest reciprocal effects for height and yield.For bolls/plant, barbadense5539×Sepid had the high positive reciprocal effects.High positive reciprocal effects for boll weight was showed in Sahel×Termeze14.
Gossypium hirsutum and G. barbadense differ significantly in their agronomic and fiber traits (Percey et al, 2006).G. hirsutum had the higher yield potential and G. barbadense had the best fiber quality.Interspecific hybridization and introgression, G. hirsutum and G. barbadense, has led to improve lines with the higher yield and the best fiber qualities.Efforts to improve G. hirsutum or G. barbadense through introgression have been hindered by genetic breakdown in segregating interspecific breeding populations (Stephens, 1949).Genetically stable lines have been developed after

Table 1 .
Mean squares of yield components and agro morphological traits

Table 2 .
Means of yield components and agro morphological traits for female and male parents

Table 3 .
Means of yield components and agro morphological traits for hybrid combinations * Means within columns followed by the same letter(s) are not different at 0.05 probability level

Table 4 .
Mean squares for yield and agro morphological GCA, SCA and GCA: SCA ratio for cotton genotypes

Table 5 .
Mean mid-parent heterosis for yield and agro morphological traits

Table 6 .
General combining ability (GCA) effects of yield and agro morphological traits