Development of Short and Coarse‐Fibered American Pima Cotton for Use as Parents of Interspecific Hybrids

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Short, coarse‐fibered Pima (Gossypium barbadense L.) cotton strains may be desirable as parents of interspecific F1 hybrid cottons. This study was conducted to determine if selective advance toward short, coarse‐fiber types could be accomplished within a subset of Pima strains while maintaining adequate fiber strength, uniformity, and lint percentage. The fiber selection criteria of extralong length and fineness used for American Pima cotton were reversed within the subset. Two diallel tests were conducted at Maricopa and Marana, AZ in 1985. Significant (0.01 level) genotype mean squares and general combining ability (GCA) estimates indicated useful variability for shorter, coarser fiber. Comparisons of GCA and specific combining ability (SCA) sums of squares (SS) with the total sums of squares indicated that greater additive genetic variability was available for fiber micronaire (x̄GCA SS/total SS = 0.70) than for fiber length (x̄ GCA SS/total SS = 0.34). A single best parent could not be identified based upon GCA effects due to the necessity of simultaneous selection for several traits. Population variances and ranges, estimated from individual plant data from F1 and F2 generations grown in 1985 and 1986, were consistent with genetic segregation in the F2 generation for fiber length and micronaire. Broadsense heritability estimates ranged from 0.20 to 0.52 for 2.5% span length and from 0.51 to 0.69 for micronaire in the F2 populations. Transgressive segregation was observed in F2 populations for shorter and coarser fiber. Selective advance toward Pima cotton with short, coarse fiber appears possible, but progress is expected to be slow.