Lint yield and fiber quality in upland cotton, Gossypium hirsutum L., are interrelated through a series of individual components such as fiber length and the number of fibers produced on each seed. Numerous studies have reported the relationships among various components of yield and yield per unit land area, but none have reported on the relationships among the most basic within‐boll yield components and fiber quality parameters. The objectives of this study were (i) to determine the association of fiber quality parameters with basic within‐boll yield components for six diverse cotton genotypes and (ii) to determine if repulsion phase linkage explained the high negative correlations reported among fiber quality parameters and lint yield. The second objective was investigated by comparing the associations of fiber length, strength, and micronaire with within‐boll yield components among selected F1 populations developed by mating parents with similar direction of general combining ability (GCA) for fiber quality and within‐boll lint yield components with selected F1 populations derived by mating parents with dissimilar direction of GCA. Parents and F1s were grown at College Station, TX, in 1989 and 1992. Fiber quality parameters were determined by high volume instrumentation. Within‐boll lint yield components were determined by direct measurement or through calculations. Fiber strength and length were negatively associated with the most basic within‐boll lint yield components. Repulsion phase linkage appears to play a role in the negative association of fiber quality and within‐boll lint yield but pleiotropic effects could not be ruled out.

Lint yield and fiber quality in upland cotton, Gossypium hirsutum L., are interrelated through a series of individual components that include bolls/unit land area, mean fiber length and weight/unit length, and a series of within‐boll components. Numerous studies have investigated the relationships among various components of lint yield and yield per unit land area, but none have reported on the relationships among the most basic within‐boll yield components and fiber quality. The objective of this study was to evaluate the combining ability for within‐boll lint yield components among a group of cotton genotypes that varied by date of release, type of release, originating program, and their fiber quality parameters, especially fiber bundle strength. Four cultivars, one each released in 1905, 1943, 1979, and 1981, and two modern germplasm lines were crossed in a half diallel. Parents and F1s were grown at College Station, TX, in 1989 and 1992. Twenty‐five and 100 normal bolls were hand harvested from each plot of a randomized complete block design in 1989 and 1992, respectively. Fiber quality parameters were determined by high volume instrumentation. Within‐boll yield components were determined by direct measurement or through calculations. Genotypes having good general combining ability (GCA) estimates for fiber quality exhibited negative GCA estimates for the most basic within‐boll yield components. Among these genotypes, three‐way crosses, modified backcross, or recurrent selection procedures would be required to select for improved fiber quality and simultaneously increase the number of harvestable fibers per unit of seed surface area.

Guayule (Parthenium argentatum A. Gray) is a potential source of natural rubber, but attempts to domesticate and cultivate this perennial crop for large‐scale production in the southwestern United States have been intermittent over the past century. Genetic improvement through modern plant breeding is needed to increase its yield potential and suitability for commercialization. Natural variation for ploidy level is extensive among individuals in wild guayule populations, but less is known about the extent of ploidy level variation in guayule breeding germplasm. Because ploidy variation is among the factors that slow the rate of genetic gain in guayule breeding programs, determining the ploidy level of publicly available guayule accessions would help to accelerate the development of stable, high yielding cultivars. To that end, we adapted flow cytometry to examine the ploidy of 34 guayule accessions available from the National Plant Germplasm System. The data revealed a natural polyploid series ranging from diploid (2n = 2x = 36) to pentaploid (2n = 5x = 90), with 4x being the predominant ploidy. Interestingly, not all plants sampled from an accession had the same ploidy level (mixed ploidy). Notably, the integration of ploidy and pedigree data uncovered complex ploidy variation in guayule breeding programs. The frequency and range of ploidy variation observed in this germplasm will help to direct future breeding efforts as well as linkage analysis and genome‐wide association studies.

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