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India is the only country in the world where all the four cultivated species are grown on commercial scale. In India, cotton is planted in about 122.38 lakh hectares of land and it occupies second position in production with 361.00 lakh bales (each of 170 kg) among all cotton producing countries in the world i.e. next to China.

Average productivity of India is 501 kg/ha which is low as compared to world average of 779 kg/ha. Gujarat is the second largest growing state with acreage of 27.09 lakh hectares and the highest cotton producing state of India with production of 92 lakh bales. The average productivity of cotton in state (577 kg/ha) is higher than the national average (Anon, 2018). There are four cultivated species of cotton viz., Gossypium arboreum, G. herbaceum, G. hirsutum and G. barbadense. The first two species are diploid (2n = 26) and are native to old world. They are also known as Asiatic cottons because they are grown in Asia. The last two species are tetraploid (2n = 52) and are also known as New world cottons. G. arboreum is also known as desi cotton or lowland cotton.

MATERIALS AND METHODS

Plant material
The present investigation carried out at Cotton Research Station, Junagadh Agricultural University, Junagadh during kharif 2019. The experimental material consisted of fifty diverse genotypes of cotton (Gossypium arboreum L.). The pure seeds of these genotypes were obtained from the Cotton Research Station, Junagadh Agricultural University,    Junagadh.
Field trial
Fifty genotypes of cotton were sown on 26th June, 2019 in a Randomized Block Design (RBD) with three replications at Cotton Research Station, Junagadh Agricultural University, Junagadh. Each line was sown in a single row plot of 6.3 × 1.2 m length with each row spaced 120 cm apart and plant to plant distance within row was 45 cm. The genotypes were randomly allotted to the plots in each replication. Fertilizers at recommended doses were applied and other cultural practices were carried out at regular intervals during the course of experimentation. Application of N was split into two equal installments i.e., basal and top dressing. All the recommended agronomical practices along with necessary plant protection measures were followed timely for the successful raising of the crop. The observations were recorded on five randomly selected plants from each genotype in each replication for days to first flowering, days to boll opening, plant height (cm), number of monopodia per plant, number of sympodia per plant, number of bolls per plant, boll weight (g), seed cotton yield per plant (g), ginning percentage (%), seed index (g), lint index (g) and oil content (%).
Statistical analysis
The analysis of variance for randomized block design (RBD) was done for each character as per Panse and Sukhatme (1985). The genotypic and phenotypic coefficient variations were calculated as per the formula given by Burton (1952). Heritability and expected genetic advance as per cent of mean (GA as % of mean) was calculated for each character by adopting the procedure as suggested by Allard (1960).

RESULTS AND DISCUSSION

Variability is the prerequisite for organization of breeding programmes and its estimates helps in realization of response to selection as the progress in breeding depends upon its amount, nature and magnitude of variability (Singh & Narayanan, 2013).
Analysis of variance
The analysis of variance revealed that mean squares due to genotypes were highly significant for all the characters indicating the presence of sufficient amount of variability in the experimental used (Table-1). Similar results were obtained by Dhivya et al. 2014; Dahiphale et al. 2015; Handi et al. 2016 and Sunayana et al. 2017.
Genotypic and phenotypic coefficients of variation
Close relationship between genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV) was observed for all the characters (Figure-I & Table-2). The magnitude of PCV was slightly greater than GCV revealed a very little influence of environmental variation for their expression. This indicated that phenotypic variability may be considered as reliable measure of genotypic variability. Similar results have also been reported by Dhamayanathi et al. 2010; Dahiphale et al. 2015; Abdullah et al. 2016 and Sunayana et al. 2017.
The high GCV and PCV were observed for number of monopodia per plant followed by number of bolls per plant and boll weight. The high genotypic coefficient of variation indicated the presence of wide variation for the characters under study to allow selection for individual traits. High value of GCV and PCV for number of bolls per plant was also reported by Dahiphale et al. 2015 and Sunayana et al. 2017.
In the present study moderate value for phenotypic and genotypic coefficient of variation was observed for number of monopodia per plant were reported by Araujo et al. 2012 and Deshmukh et al. 2019; seed cotton yield per plant by Sunayana et al. 2017 and Deshmukh et al. 2019; lint index and in addition to this, two characters viz., number of sympodia per plant and boll weight. This finding is in accordance with Dhivya et al. 2014; Vinodhana et al. 2013 and Latif et al. 2015.
Days to first flowering, days to boll opening, plant height, ginning percentage, seed index, oil content, 2.5 % span length, fibre strength and fibre fineness exhibited low magnitude of both genotypic and phenotypic coefficient of variation. This finding is in accordance with Sunayana et al. 2017 for days to first flowering; Dhivya et al. 2014 for days to boll opening and plant height; Vinodhana et al. 2013 and Sunayana et al. 2017 for ginning percentage; Shahzad et al. 2015 for seed index and Dhamayanathi et al. 2010 for oil content, while, for 2.5 % span length, fibre strength and fibre fineness by Erande et al. 2014 and Chinchane et al. 2018.
Heritability
In present study, very high heritability in broad sense estimates were observed for days to boll opening (95.31 %), number of bolls per plant (95.05 %), days to first flowering (94.03 %), fibre strength (91.68 %), number of monopodia per plant (90.52 %), ginning percentage (90.25 %), lint index (88.23 %), seed cotton yield per plant (87.72 %), number of sympodia per plant (86.20 %), fibre fineness (84.69 %) and 2.5 % span length (80.09 %). High estimate of heritability was observed for boll weight (78.24 %), plant height (72.63 %) and seed index (72.25 %). Very high heritability estimates for days to boll opening also recorded by Erande et al. 2014; Haritha et al. 2014 and Handi et al. 2016; for number of bolls per plant by Sunayana et al. 2017 and Deshmukh et al. 2019; for days to first flowering by Dahiphale et al. 2015; Patil et al. 2014 and Deshmukh et al. 2019; for fibre strength by Sunayana et al. 2017; for number of monopodia per plant and ginning percentage by Dhamayanathi et al. 2010 and Handi et al. 2016; for lint index by Rajeev et al. 2014; Erande et al. 2014 and Sunayana et al. 2017; for seed cotton yield per plant by Haritha et al. 2014 and Deshmukh et al. 2019; for number of sympodia per plant by Vinodhana et al. 2013 and Sunayana et al. 2017; for fibre fineness by Vinodhana et al. 2013 and Deshmukh et al. 2019; for 2.5 % span length by Dhivya et al. 2014 and Latif  et al. 2015; for boll weight by Haritha et al. 2014 and Vinodhana et al. 2013; for plant height by Dhivya et al. 2014 and Patil et al. 2014; and for seed index by Shahzad et al. 2015 and Sunayana et al. 2017.
Genetic advance expressed as per cent of mean
The genetic advance expressed as per cent of mean was highest for number of bolls per plant (42.41 %), number of monopodia per plant (35.04 %), seed cotton yield per plant (32.91 %), lint index (27.04 %) and number of sympodia per plant (22.83). The highest values of genetic advance expressed as per cent of mean have been reported in cotton for number of bolls per plant by Dahiphale et al. 2015; Patil et al. 2014 and Deshmukh et al. 2019; for number of monopodia per plant by Sunayana et al. 2017 and Deshmukh et al. 2019; for seed cotton yield per plant by Vinodhana et al. 2013 and Deshmukh et al. 2019; for number of sympodia per plant by Dhivya et al. 2014 and Latif et al. 2015 and for lint index by Vinodhana et al. 2013.
The moderate estimate of genetic advance as per cent of mean was observed for the boll weight (19.77 %), plant height (12.16 %), days to first flowering (12.12 %), fibre strength (11.88 %) and seed index (11.71 %). The similar finding was also obtained by for boll weight by Sunayana et al. 2017; for plant height by Dhivya et al. 2014; for days to first flowering by Dahiphale et al. 2015; for fibre strength by Rajeev et al. 2014; for fibre fineness by Haritha et al. 2014 and for seed index by Shahzad et al. 2015.
The lower genetic advance as per cent of mean was observed for the ginning percentage (9.48 %), days to boll opening (9.29 %), fibre fineness (7.56 %), 2.5 % span length (6.95 %) and oil content (2.35 %). The similar finding was also obtained by Dhamayanathi et al. 2010; Vinodhana et al. 2013 and Sunayana et al. 2017.
In the present investigation, the estimates of high heritability coupled with genetic advance expressed as per cent of mean was observed for number of bolls per plant, number of monopodia per plant, seed cotton yield per plant, lint index and number of sympodia per plant. These characters may have contributed to preponderance of additive gene action and selection pressure could profitably be applied on these characters for their rationale improvement (Panse, 1957).

The very high heritability associated with moderate genetic advance expressed as per cent of mean was observed for days to first flowering. While, high heritability along with moderate genetic advance (% of mean) was expressed by boll weight, plant height and seed index. The very high heritability associated with low genetic advance (% of mean) was found for ginning percentage, days to boll opening and oil content. It may be inferred that these traits were regulated by non additive gene action and presence of high genotype × environment interaction. The heritability is being exhibited due to favourable influence of environmental factors rather than the genotypes alone and simple selection will not be rewarding. As such, progeny testing is to be practiced for amelioration of these traits. However, they can be improved either by development of hybrid varieties if commercially feasible or by utilization of transgressive segregants in segregating generations.

Table 1: Analysis of variance for all the characters in 50 genotypes of cotton

*, ** Significant at 5 and 1% levels, respectively

Table 2: Mean, phenotypic range, σ2g, σ2p, σ2e, GCV %, PCV %, heritability, genetic advance, genetic advance per cent of mean for all the characters of cotton