The present study was conducted in central cotton research Institute Sakrand to analyze the genetic variability, phenotypic, genotypic and environmental coefficient of variation, heritability and genetic advance during summer 2014. In this experiment analysis of variance indicated that significant variation present among the accessions of the upland cotton for all the traits under study. The highest genotypic (GCV) and phenotypic coefficient of variation (PCV) were exhibited by the number of bolls per plant, lint index and seed cotton yield per plant. GCV had similar trend as PCV. High heritability and high genetic advance was observed in the lint index, number of bolls per plant and seed cotton yield per plant. The combination of the high heritability and high genetic advance provide the clear image of the trait in the selection process.
Gene overlap between the sporophytic and gametophytic phases and successful in vitro germination of cotton pollen grains have motivated plant breeders that if more reliable and consistent protocols of in vitro pollen germination become available, they could impose certain stresses like heat, salinity and others and selection could be made accordingly in controlled laboratory conditions instead of time consuming and expensive field conditions. Our studies were aimed to utilize two methods of in vitro germination in an artificial medium. One was a droplet method and another was cellophane paper method. The difference in percent of pollen germination and pollen tube length were obvious where droplet method gave higher % of pollen tubes also longer tube length as compared to cellophane paper method. The pollen busting in droplet was also very high and very uncommon on cellophane paper. These results thus suggest that when both the methods are made consistent and reliable, the percent of pollen germination and tube length may be used as criterion of selection for different stress conditions.
It was suspected that differences in style length and other reproductive structures of tetraploid and diploid cottons may contribute towards failure of crossing between two ploidies. Style length, stigma depth and pollen grain size of tetraploid were 20.5, 60.0 and 10.0 mm against 8.5, 2.0 and 7.0 mm of G. harknessii and 9.0, 2.5 and 7.0 mm of G. arboreum respectively. In vitro germinated pollen tubes of both the ploidy levels also varied significantly where tetraploid produced pollen tubes upto 20.5 mm long against 8 to 9.0 mm pollen tubes of both diploid species. It was therefore confirmed that style length is highly correlated with pollen tube length. Thus, shorter pollen tubes of diploid species are not expected to grow long enough in the longer styles of tetraploids and reach the ovary to fertilize it. Since, pollen grain size and stigma depth are also considered as food reserves for pollen tubes to grow into the styles and the differences in these structures can also be accountable to the failure of fertilization between the ploidy levels. Based on these results, it can be predicted that differential reproductive structure could at least be partially responsible for crossing failure and reciprocal crosses may be tried for successful fertilization.
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