Evaluation of genetic divergence , character associations and path analysis in upland cotton genotypes

The present experiment was laid out in randomized complete block design with three replications in order to estimate the genetic divergence, correlation and path analysis in ten upland cotton genotypes. The mean squares revealed highly significant differences (P<0.05) for all the investigated traits among the tested genotypes, proving that used genetic resources showed a great potential for further breeding experiments. On the basis of mean performance, the variety NB-111 displayed desirable performance for variety of traits, unveiling its importance in cotton breeding programs. The results also exhibited that plant height, bolls plant, boll weight and seed index developed positive and significant (P<0.05) associations with seed cotton yield plant. Pertaining to path analysis, maximum positive direct effects to seed cotton yield palnt was contributed by bolls plant, followed by boll weight, GOT% and seed index. This demonstrates that genotypes possessing higher extent of these traits may be chosen in selection for developing high yielding cotton genotypes. Considering genetic distance, diverse parents with broad genetic distance were also identified, signifying their importance for upcoming hybridization programs in cotton crop.


Introduction
Crop improvement primarily refers to the evolution and development of resistant and high yielding crop varieties.The breeding programs are executed generally with the intension to develop varieties with superior qualitative and quantitative traits.However, selection is the most powerful tool for considering a particular trait, which entirely depends on the extent of correlation between yield traits related and seed yield [1]. Crop genetic diversity is a critical component in crop improvement, which helps to identify conservation oriented breeding programs.Hence, it is essential to know the relationships among crop varieties and genetic diversity in order to recognize complexity of gene pool and also to identify the gaps in the genotype collections [2].It has become necessary to exploit the germplasm properly and also to add new germplasm in the existing genetic pool.These practices have enough potential to create sufficient variations to evolve superior genotypes [3].The variability in the germplasm is responsible to induce resistance against abiotic and biotic stresses.To attain desirable genetic variability, various strategies such as hybridization, exotic germplasm and the polyploidy have been practiced in plant breeding [4].Correlation is a statistical technique that can show whether and how strongly pairs of variables are related to each other.The correlation coefficient is the extent of linear relationships generally exists among the variables.In breeding, genotypic and phenotypic correlations are applied to determine extent of relationship between yield and yield contributing traits

Results and discussion
The current study was carried out to assess the genetic divergence, character associations and path analysis in ten elite upland cotton genotypes.The analysis of variance was carried out for eight parameters recorded for seed cotton yield and its related traits.Mean squares displayed that all the characters, including plant height, sympodial branches plant -1 , bolls plant -1 , boll weight , seed cotton yield plant -1 , seed index (100-seed weight, g), staple length and ginning outturn (%) were highly significant differences (P≤0.01%)among the tested genotypes (Table 2).This demonstrates that used genetic resources tend to have useful genetic variations, which may be exploited for further breeding programs so as upland cotton genotypes may be improved for variety of traits.Similar to our findings, other researchers, including Baloch et al. [11], Jatoi ([12] and Mugheri [13] also found the significant genetic variance for the number of traits.Mean performance for various traits of genotypes is given in (Table 2).Results revealed that maximum plant height (151.80 cm) was attained by NB-111, followed by BH-180 (146.30cm), while minimum plant height was recorded in IR-1524 (82.83 cm).For sympodial branches plant -1 , maximum sympodial branches were recorded in Lalazar (28.62), followed by CRIS-342 (27.62) and minimum sympodial branches plant -1 were recorded in BT-905 (16.46).The major trait in seed cotton yield contributing character is the bolls plant -1 .It has been generally observed that an increase in number of bolls in cotton plant will in due course increase the seed cotton yield.Regarding bolls plant -1 , the maximum bolls plant -1 (48.21) was set in NB-111; next in rank was the genotype BH-180 (41.16); however, minimum bolls plant -1 was set in BT-905 (26.66).Boll weight incorporates a major contribution on seed cotton yield because as the boll weight increases, the yield may also increases simultaneously.Concerning parameter boll weight, the maximum boll weight was weighed in CIM-602 (4.01 g), while minimum boll weight was weighed in BT-905 (3.12 g).Makhdoom et al. [14] suggested that boll mean weight is the key independent yield component and play a prime role in improving seed cotton yield.Yield is the most important character, which plays a vital role in strengthening the socio-economic conditions of the growers and ultimately the country yield production to its maximum level.For seed cotton yield plant -1 , maximum seed cotton yield plant -1 was produced by the genotype NB-111 (188.01 g), followed by CIM-602 (162.00 g), whereas minimum was produced by the cultivar BT-905 (83.17 g).Fiber length has secured a unique importance among the quality parameters of cotton crop because it is more useful for textile mills in yarn manufacturing.With regard to staple length, longer fiber length was measured in NB-111 (30.08 mm), while minimum was measured in the genotype VH-282 (24.83 mm).As far as seed index is concerned, higher seed index was obtained in NB-111 (7.93 g); nonetheless, lower seed index was achieved in VH-282 (6.20 g).Taking ginning outturn percentage, the maximum ginning outturn was recorded in CIM-602 (39.66%), while minimum was reported in Lalazar (31.93%).All in all, the variety NB-111 displayed better performance in terms of plant height, bolls plant -1 , seed cotton yield plant -1 , staple length and seed index.Hence, this identified cotton genotype could be used in upcoming breeding projects so as number of traits can be improved in order to develop desirable cotton varieties.The estimates of correlation coefficients was worked out among seven yield and fibre quality related characters with seed cotton yield plant 1 (Table 3).Of the total traits, four traits namely plant height (r=0.778** ), bolls plant -1 (r=0.873** ), boll weight (r=0.759* ) and seed index (r=0.691* ) developed significant and positive associations with seed cotton yield plant -1 .Hence, selection for these traits will help in selecting genotypes with higher seed cotton yield plant -1 .Similar results of positive association between seed cotton yield and its related traits were reported by Baloch et al. ([11], Ashokkumar and Ravikesavan [15] and Kaleri [16].The inter correlation among the important component traits is also important in order to decide which trait to be given due weightage in exercising selection.The positive and significant inter correlation among the traits was only observed for plant height with bolls plant -1 (r=0.666* ) and boll weight (r=0.633* ).Similar results were reported by Baloch et al. [11] and Kalpande et al. [17].However, among the yield contributing traits, it is interesting to note that sympodial branches plant -1 developed significant but negative inter correlation with ginning outturn percentage (r=-0.771** ).It suggests that great care should be taken while selection is being carried out for sympodial branches plant -1 .Path coefficient analysis of seed cotton yield plant -1 showed that traits like bolls plant -1 , boll weight, seed index and ginning outturn percentage depicted highest positive direct effect towards seed cotton yield (Table 4).This is in agreement with the findings of Altaher and Singh [18], An et al. [19] and Magadum et al. [20] for number of bolls plant -1 and boll weight, and lint index; Ahuja and Dhayal [21] for number of sympodial branches plant -1 .The high indirect positive effect on seed cotton yield plant -1 was perceived for plant height via bolls plant and boll weight; staple length and seed index through only bolls plant -1 .Hence, the direct and indirect effects of yield characters such as bolls plant -1 , boll weight and number of sympodial branches plant -1 displayed that these are the major yield contributing characters under intraspecific crosses and may be considered for improving yield in cotton breeding programs.Considering the genetic distance, it ranged between 10.382 and 134.837.Out of 45 pair of comparisons from genetic distance (Table 5), quite a few numbers of pairs revealed wide genetic distance, such as NB-111 and BT-905, followed by NB-111 and CRIS-134, NB-111 and Lalazar, NB-111 and CRIS-342), NB-111 and IR-524, BH-180 and BT-905, NB-111 and AA-919 and BH-180 and CRIS-134.Of the special note, these pairs can better be utilized in heterosis breeding programs in cotton crop since these pairs contain variety of genes for various traits.However, the narrow genetic distance was found between CIM-602 and BT-905, followed by BT-905 and CRIS-134, Lalazar and CRIS-134 and VH-282 and AA-919.Hence, these pairs of genotypes could be proved reliable breeding materials for backcross breeding.

Conclusions
The mean squares indicate that used materials can be evaluated for further experiments.Based on mean performance, the genotype NB-111 exhibited desirable performance for a range of traits, exhibiting its importance in cotton breeding programs.
The results also showed that plant height, bolls plant -1 , boll weight and seed index developed positive and significant (P<0.05)associations with seed cotton yield plant -1 .
Referring to path analysis, maximum positive direct effects to seed cotton yield palnt -1 was added by bolls plant, followed by boll weight, GOT% and seed index.This reveals that genotypes having higher extent of these traits may be preferred in selection for evolving high yielding cotton genotypes.Considering genetic distance, diverse parents have also been identified, signifying their importance for upcoming hybridization programs in cotton crop.