Cotton is the most important fibre crop. Cotton production in Pakistan is declining every year so there is need to develop new high yielding varieties of cotton to boost country's economy. This research study was directed to assess heterotic potential of nine F1 hybrids for different morphological and within boll yield components. For this purpose, the nine F1 hybrids along with their parent were sown in two replications in the field area of Department of Plant Breeding and Genetics, University of Agriculture Faisalabad during the normal growing season. The analysis of variance showed highly significant difference among genotypes for all the traits except seed index and fiber length which showed significant difference. The cross VH-329×CRS-2 showed maximum significant heterosis (80.05%) and heterobeltiosis (65.18%) for seed cotton yield with positive heterosis in bolls per plant (45.68%), seed volume (22.58%), fiber length (9.20%) and negative heterosis in node number of first fruiting branch (-23.64%), number of monopodial branches (-0.73%) and fiber fineness (-15.74%) followed by the cross VH-329×CIM-595 which showed 41.06% heterosis and 15.72% heterobeltiosis with positive heterosis in sympodial branches (23.76%), bolls per plant (56.83%), seeds per boll (7.76%), lint index (12.56%), lint percentage (13.39%) and negative heterosis in node number for first fruiting branch (-23.64%), monopodial branches (-20.0%) and fiber fineness (-19.07%). The cross combinations i.e., VH-329×CRS-2 and VH-329×CIM-595 may be used for commercial exploitation of heterosis in cotton.

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*Corresponding author: jazibjaved.uaf@gmail.com

Copyright 2023 TBPS

1. INTRODUCTION

Cotton is the main fibre crop utilized in the textile industry, as well as a source of edible oil, is grown in over 80 countries throughout the world (Shahzad et al. 2019).

The requirement for fiber in textile industry is rising. To meet this problem, hybridization can be used to boost the production potential of modern cotton genotypes. In this aspect, hybrids are produced by the use of heterosis. Heterosis is the phenomenon in which the offspring of two genetically distinct parents outperform the mid-parent (relative heterosis) or better parent (heterobeltiosis) for different traits. Primary aim is to make varieties or hybrids that are resistant to major pests, diseases and abiotic stresses in addition to higher yield and fibre quality. The heterosis research is useful in crop breeding programmes to generate a significant degree of heterotic response by parents with desirable traits (Adsare et al. 2017).

Heterosis is the essential genetic tool for improving the yield in both self-pollinated and cross-pollinated crops (Chakholoma et al. 2021). Due to the ease of manual emasculation and pollination, commercial exploitation of heterosis in cotton has become possible and cost-effective. Using heterosis in crops has provided major economic benefits during the last century. Various workers have observed heterosis and heterobeltiosis in cotton. Cotton heterosis has proven to be a successful technique to boost yields, enhance fibre quality, and improve disease resistance in cotton (Zhou et al. 2021). Within-boll yield components have a significant impact on yield estimation. Within-boll yield components have received minimal selection pressure due to the difficulties of measuring them (Tang and Xiao, 2013).

Cotton experts have long aimed to use heterosis breeding to increase production and fibre quality attributes. Several studies have found considerable heterosis for a variety of features, such as favorable heterotic effects on fibre elongation (Solongi et al. 2019). Depending on the characters involved, both positive and negative heterosis can be beneficial. Basal et al. (2011) proposed that the best new F1 hybrids may be identified and selected based on their specific combining ability and heterotic estimations.

The demand for natural fibre products with superior quality features necessitates the improvement of superior and high yielding hybrids in cotton. The purpose of this study is to determine the extent of heterosis and heterobeltiosis of cotton germplasm for several morphological and within boll yield traits. Breeders can utilize this information to select the top performing crosses for their future breeding programme based on these traits.

1. MATERIALS AND METHODS

The experiment was carried out in the Department of Plant Breeding and Genetics, University of Agriculture, Faisalabad. The plant material studied in this genetic study was generated by crossing three cotton lines, Tarzan-05, FH-342, and VH-329, as well as three testers, CRS-2, CIM-595, and BS-80. In October 2020, the parent genotypes were grown in pots in a glasshouse to produce F1 seeds. The temperature in the glasshouse was kept at 35 degrees Celsius. Crosses were made at the time of flowering, and all preventive precautions were taken to avoid genetic contamination. On May 2021, hybrids and their parents were planted in a field. The experiment was designed in a randomized complete block design with two replications, with randomization of parents and hybrids. Maximum ten plants were planted in each row. The space between rows and plants was fixed at 75cm and 30cm, respectively. Every genotype received all of recommended agronomic cultural practices. The following parents and hybrids were used in the experiment.

Five plants from each genotype and replication were randomly selected and data for the following traits were recorded.

2.3. Number of Sympodial Branches

Direct fruit bearing branches are sympodial branches. Sympodial branches were counted from five plants in a row and then average was calculated for analysis.

2.4. Mature Bolls per Plant

For each cultivar in every replication, the total number of bolls from both picking was counted, and the average was calculated.

2.5. Node Number of 1st Fruiting Branch

The number of nodes above the cotyledonary node along the main stem until the one that gave rise to the first fruiting branch on the plants was used to calculate the node number for the first fruiting branch. In each replication, the data were averaged for each family.

2.6. Plant Height (cm)

The height of the plant was measured after it had stopped growing. Then average was calculated for further investigation.

2.7. Number of Monopodial Branches

The average number of monopodial branches was estimated for analysis after counting monopodial branches from selected five plants in a row.

2.8. Boll Weight (g)

Boll weight is measured in grams. It is calculated by dividing the seed cotton yield by total number of picked bolls on that plant. Mean values were calculated for each genotype and replication.

Boll weight =

2.9. Seed Index (g)

Seed index is the weight of 100 seeds in grams. After ginning, the weight of hundred seeds was measured in grams using an electric balance for each plant. These 100 seeds were taken randomly. Mean values were calculated.

2.10. Number of Seeds Per Boll

After the ginning of cotton bolls from each plant, the seedsfrom five selected bolls were counted separately for each plant and then divided by the number of bolls. For each genotype, the average data was computed.

2.11. Seed Volume Per 100 Seeds (cm3)

Ethanol was used to determine seed volume. Firstly, ethanol was poured into a flask and the volume was measured. Then, pour 100 cotton seeds into the ethanol-filled flask and measured the increased volume of ethanol.

2.12. Seed Density (g/cm3)

Seed density is the ratio of seed weight and seed volume. Seed density was calculated by using following formula:

Seed density=

2.13. Lint Index (g)

Lint index is calculated as the weight of lint generated by 100 seeds in grams. The following formula was used to compute it:

Lint Index =

2.14. Lint Percentage

After weighing the seed cotton, a single rolling electrical ginner was used to gin it. The weight of the lint was measured using an electronic balance. The following formula was used to compute the lint percentage:

Lint percentage = x 100

2.15. Seed Cotton Yield (g)

From each plant, mature bolls were picked. The picking was done twice to obtain total seed cotton. The electrical balance was used to weigh the harvest in grams. The average seed cotton yield of each genotype was obtained.

2.16. Fibre Fineness (µg/inch)

The HVI system was used to measure fibre fineness by placing a 10 g sample of lint in a micronaire compartment. When the sample weight was within the range, the Micronaire test began immediately and was shown on the testing screen. By opening the chamber's cover, a compilation sample was released. For statistical analysis, average fibre fineness was recorded in this manner for all samples of each genotype.

2.17. Fibre Length (mm)

Uster HVI-900 is used to measure fibre length in millimeters. The mean values were computed for each of the genotype.

2.18. Fibre Strength (g/tex)

Uster HVI-900 is also used to measure fibre strength in g/tex. The mean values were computed for each of the genotype.

2.19. Statistical Analysis

The data of the research was analyzed for genotypic variations at the genetic level of each trait under study. Significant traits were further investigated to estimate the heterosis and heterobeltiosis by following Falconer and Mackay (1996).

Heterosis= ×100

Heterobeltiosis= ×100

T-test was used to test the significance of heterosis and heterobeltiosis. T-value was calculated by the formula explained by Wynne et al. (1970).

t-test for heterosis

t= [ ]0.5

t-test for heterobeltiosis

t= [ ]0.5

Where, F1= mean of F1 cross; MP= mid parent value; EMS= error mean square.

1. RESULTS

To check the genotypic difference for traits the data was subjected to analysis of variance. Heterosis and heterobeltiosis were determined by calculating the percent increase or decrease in F1 hybrids and their significance was determined using the T-test.

3.1. Number of Sympodial Branches

Analysis of variance showed highly significant genotypic differences for number of sympodial branches among genotypes (Table 1). Mean performance of parents and crosses as well as heterosis are given in Table 2. Among hybrids, maximum value fornumber of sympodial branches (33.54) was observed in crossVH-329×BS-80 while minimum value for number of sympodial branches (16.33) was observed in the cross Tarzan-05×BS-80. Among parents, VH-329 exhibited maximum value for number of sympodial branches (22.60) and BS-80 showed minimum value (18.70).

Table 1: Mean square values for different traits in cotton

Table 2: Heterosis and heterobeltiosis (%) of nine crosses for number of sympodial branches in cotton

The heterosis and heterobeltiosis (%) for number of sympodial branchesis shown in Table 1.2. Five crosses showed positive heterosis and four crosses showed negative heterosis. The heterosis ranged from -15.06% (Tarzan-05×BS-80) to 64.89% (VH-329×BS-80). Only two crosses VH-329×CIM-595 and VH-329×BS-80 showed highly significant positive heterosis.

Five crosses showed positive heterobeltiosis and four crosses showed negative heterobeltiosis. Theheterobeltiosis ranged from -17.32% (Tarzan-05×BS-80) to 50.66% (VH-329×BS-80). One cross VH-329×BS-80 showed highly significant positive heterobeltiosis for number of sympodial branches.

3.2. Mature Bolls Per Plant

Analysis of variance showed highly significant genotypic differences for mature boll per plant among genotypes (Table 1). Mean performance of parents and crosses as well as heterosis are given in Table 3. Among hybrids, maximum value for mature boll per plant (42.50) was observed incross VH-329×CIM-595 while minimum value (21.40) was observed incross Tarzan-05×CRS-2. Among parents, CIM-595 showed maximum valuefor mature boll per plant (29.10) whilst Tarzan-05 exhibited minimum value (20.88). The results showed positive heterosis in six crosses and other three crosses exhibited negative heterosis. The heterosis ranged from -10.17% (FH-342×CIM-595) to 56.83% (VH-329×CIM-595). Tarzan-05×BS-80 and FH-342×CRS-2 showed significant positive heterosis whilst the crossesTarzan-05×CIM-595, VH-329×CRS-2 and VH-329×CIM-595 showed highly significant positive heterosis.

The results showed that six crosses revealed positive heterobeltiosis and three crosses showed negative heterobeltiosis. Theheterobeltiosis ranged from -19.59% (FH-342×CIM-595) to 46.05% (VH-342×CIM-595). FH-342×CIM-595 showed significant negative heterobeltiosis. Two crossesVH-329×CRS-2 and VH-329×CIM-595 exhibited highly significant positive heterobeltiosis for number of bolls per plant.

3.3. Node Number of 1st Fruiting Branch

Analysis of variance showed highly significant genotypic differences for node number for first fruiting branch among genotypes (Table 1). Mean performance of parents and crosses as well as heterosis are given in Table 4. Among hybrids, maximum valuefor node number for first fruiting branch (9.00) was observed incross FH-342×CIM-595while minimum value (4.90) was observed incross VH-329×CRS-2. Among parents, FH-342 exhibited maximum valuefor node number for first fruiting branch (10.40) and CRS-2 showed minimum value (7.70).

The heterosis and heterobeltiosis (%) for node number for first fruiting branch is shown in Table 3.2. Negative heterosis had been observed in all the crosses expect the cross Tarzan-05×CRS-2. The heterosis ranged from -41.14% (Tarzan-05×CIM-595) to 2.35% (Tarzan-05×CRS-2). Only one cross combinationTarzan-05×BS-80 showed significant negative heterosis. The cross Tarzan-05×CIM-595 revealed maximum negative heterosis (-41.14%) followed by VH-329×CRS-2 (-38.75%) and VH-329×CIM-595 (-23.64%).

The results showed negative heterobeltiosis in all crosses for node number of first fruiting branch. The heterobeltiosis ranged from -44.62% (Tarzan-05×CIM-595) to -6.45% (Tarzan-05×CRS-2). Two crossesTarzan-05×BS-80 and FH-342×BS-80 showed significant negative heterobeltiosis. The cross combination Tarzan-05×CIM-595 exhibited maximum significant negative heterobeltiosis (-44.62%) followed byVH-329×CRS-2 (-40.96%), VH-329×CIM-595 (-24.01%) and FH-342×CRS-2 (-19.23%) for node number of first fruiting branch.

3.4. Plant Height (cm)

Analysis of variance showed highly significant genotypic differences for plant height among genotypes (Table 1). Mean performance of parents and crosses as well as heterosis are given in Table 5. Among hybrids, maximum value for plant height (125.73) was observed incross VH-329×CIM-595while minimum value (83.40) was observed inthe cross Tarzan-05×BS-80. Among parents, CIM-595 showed maximum value for plant height (123.44) whilstCRS-2 exhibited minimum value (100.33).

The heterosis and heterobeltiosis (%) for plant height is shown in Table 5. The results revealed positive heterosis in two crosses and all other crosses showed negative heterosis. The heterosis ranged from -21.96% (Tarzan-05×BS-80) to 6.76% (FH-342×BS-80). Only two cross combinations Tarzan-05×CIM-595 and FH-342×CIM-595 showed significant negative heterosis and two crosses FH-342×BS-80 and VH-329×CIM-595 showed significant positive heterosis. Only one cross Tarzan-05×BS-80 showed highly significant negative heterosis.

Only two crosses showed positive heterobeltiosis and all other crosses exhibited negative heterobeltiosis. Theheterobeltiosis ranged from -24.00% (Tarzan-05×BS-80) to 6.02% (FH-342×BS-80). One hybrid (FH-342×BS-80) showed significant positive heterobeltiosis. The cross Tarzan-05×BS-80 showed maximum highly significant negative heterobeltiosis (-24.00%)followed by the cross Tarzan-05×CIM-595 (-14.31%), FH-342×CIM-595 (-11.73%) and VH-329×CRS-2(-7.70%) for plant height.

3.5. Number of Monopodial Branches

Analysis of variance showed highly significant genotypic differences for number of monopodial branches among genotypes (Table 1). Mean performance of parents and crosses as well as heterosis are given in Table 6. Among hybrids, maximum value for number of monopodial branches (2.20) was observed in the cross FH-342×CRS-2while minimum value (0.80) was observed in cross FH-342×BS-80. Among parents, CRS-2 showed maximum value for number of monopodial branches (1.70) and BS-80 exhibited minimum value (0.70).

The heterosis and heterobeltiosis (%) for number of monopodial branches is shown in Table 5.2. The results revealed positive heterosis in six crosses and three crosses showed negative heterosis. The heterosis ranged from -20.0% (VH-329×CIM-595) to 122.22% (Tarzan-05×BS-80). Only one crossFH-342×CIM-595 showed significant positive heterosis. The crossTarzan-05×BS-80 showed highly significant positive heterosis (122.22%) followed by the crosses VH-329×BS-80 (82.35%), FH-342×CRS-2 (66.04%) and FH-342×BS-80 (62.50%) for number of monopodial branches.

The results showed positive heterobeltiosis in six crosses and three crosses exhibited negative heterobeltiosis. The heterobeltiosis ranged from -34.29% (Tarzan-05×CRS-2) to 81.82% (Tarzan-05×BS-80). One crossTarzan-05×CRS-2 showed highly significant negative heterobeltiosis, two crosses FH-342×CRS-2 and FH-342×BS-80 showed significant positive heterobeltiosis and two crosses Tarzan-05×BS-80 and VH-329×BS-80 showed highly significant positive heterobeltiosis for monopodial branches.

3.6. Boll Weight (g)

Analysis of variance showed highly significant genotypic differences for boll weight among genotypes (Table 1). Mean performance of parents and crosses as well as heterosis are given in Table 7. Among hybrids, maximum value for boll weight (3.82) was observed inFH-342×CRS-2followed by the crosses FH-342×BS-80 (3.79), VH-329×CRS-2 (3.72) and FH-342×CIM-595 (3.71) while minimum value (2.93) was observed inVH-329×CIM-595. Among parents, CIM-595 exhibited maximum value for boll weight (4.06) whilstVH-329 showed minimum value (3.13).

Table 3: Heterosis and heterobeltiosis (%) of nine crosses for number of bolls per plant in cotton

Table 4: Heterosis and heterobeltiosis (%) of nine crosses fornode number of 1st fruiting branchin cotton

Table 5: Heterosis and heterobeltiosis (%) of nine crosses for plant height in cotton

Table 6: Heterosis and heterobeltiosis (%) of nine crosses for number of monopodial branches in cotton

The heterosis and heterobeltiosis (%) for boll weight is shown in Table 6.2. Only four crosses exhibited positive heterosis and five crosses showed negative heterosis. The heterosis ranged from -18.34% (VH-329×CIM-595) to 8.26% (VH-329×CRS-2). Only one crossVH-329×CRS-2 showed significant positive heterosis and three crossesVH-329×CIM-595, Tarzan-05×CIM-595 and VH-329×BS-80 showed highly significant negative heterosis.

Only two crosses showed positive heterobeltiosis and six crosses exhibited negative heterobeltiosis. The heterobeltiosis ranged from -28.03% (VH-329×CIM-595) to 2.49% (FH-342×BS-80). The cross Tarzan-05×CRS-2 showed significant negative heterobeltiosis. Four cross combinations VH-329×CIM-595, Tarzan-05×CIM-595, and VH-329 × BS-80 and FH-342 × CIM-595 showed highly significant negative heterobeltiosis for boll weight.

3.7. Seed Index (g)

Analysis of variance showed significant genotypic differences for seed index among genotypes (Table 1). Mean performance of parents and crosses as well as heterosis are given in Table 8. Among hybrids, maximum value for seed index (8.30) was observed in the cross Tarzan-05×BS-80 followed by the crosses FH-342×BS-80 (8.1), Tarzan-05×CRS-2 (8.0) and FH-342×CRS-2 (7.9) while minimum value (6.66) was observed inVH-329×CRS-2. Among parents, CIM-595 exhibited maximum value for seed index (8.60) and VH-329 showed minimum value (6.85).

The heterosis and heterobeltiosis (%) for seed index is shown in Table 6. Only three crosses exhibited positive heterosis and six crosses showed negative heterosis. The heterosis ranged from -10.70% (Tarzan-05×CIM-595) to 8.01% (Tarzan-05×CRS-2). The cross Tarzan-05×CIM-595exhibited significant negative heterosis (-10.70%) followed by the cross FH-342×CIM-595 (-10.59%) for seed index.

Two crosses showed positive heterobeltiosis and other cross combinations showed negative heterobeltiosis. The heterobeltiosis ranged from -17.44% (VH-329×CIM-595) to 4.80% (Tarzan-05×BS-80). Two cross combinationsVH-329×BS-80 andFH-342×CIM-595 exhibited significant negative heterobeltiosis. Two crosses Tarzan-05×CIM-595 and VH-329×CIM-595 showed highly significant negative heterobeltiosis for seed index.

3.8. Number of Seeds Per Boll

Analysis of variance showed highly significant genotypic differences for number of seeds per boll among genotypes (Table 1). Mean performance of parents and crosses as well as heterosis are given in Table 9. Among hybrids, maximum value for number of seeds per boll (35.40) was observed incross FH-342×CRS-2 while minimum value (30.90) was observed in the cross Tarzan-05×CRS-2. Among parents, CRS-2 exhibited maximum value for number of seeds per boll (35.10) and FH-342 showed minimum value (28.85).

The heterosis and heterobeltiosis (%) for number of seeds per boll is shown in Table 8.2. Only one cross showed negative heterosis and all other crosses showed positive heterosis. The heterosis ranged from -4.11% (Tarzan-05×CRS-2) to 13.88% (FH-342×CIM-595). All the hybrids showed highly significant positive heterosis expect two cross combinations Tarzan-05×CRS-2 and VH-329×CRS-2.

Two cross combinations showed negative heterobeltiosis and seven crosses showed positive heterobeltiosis. The heterobeltiosis ranged from -11.97% (Tarzan-05×CRS-2) to 11.47% (Tarzan-05×BS-80). Three crossesTarzan-05×CIM-595, FH-342×BS-80 and VH-329×CIM-595 displayed significant positive heterobeltiosis and three crosses Tarzan-05×BS-80, FH-342×CIM-595 and VH-329×BS-80 showed highly significant positive heterobeltiosis. One cross Tarzan-05×CRS-2 showed highly significant negative heterobeltiosis for number of seeds.

3.9. Seed Volume Per 100 Seeds (cm3)

Analysis of variance showed highly significant genotypic differences for seed volume among genotypes (Table 1). Mean performance of parents and crosses as well as heterosis are given in Table 10. Among hybrids, maximum value for seed volume (10.0) was observed in cross Tarzan-05×BS-80 and FH-342×BS-80while minimum value (7.0) was observed inTarzan-05×CIM-595. Among parents, BS-80 exhibited maximum value for seed volume (10.0) and CRS-2 showed minimum value (7.5).

Table 7: Heterosis and heterobeltiosis (%) of nine crosses for boll weight in cotton

Table 8: Heterosis and heterobeltiosis (%) of nine crosses for seed index in cotton