In an investigation of the genetic diversity and structure of Gossvpium barbadense L. it was determined that northwestern South America was the species' center of variability and probably the species' center of origin. Cultivars of the species were found to possess as much genetic variability as the center of variability. Cultivar variability was due in large part to introgression with G. hirsutum. Studies of interspecific hybrid performance revealed that development of G. barbadense parents could significantly affect the plant height, earliness, and yield of the resulting hybrids. Environment significantly affected hybrid performance and could enhance or obscure any beneficial effects of hybrid parent selection. A conversion program to convert photoperiodic short-day flowering tropical accessions to day neutrality continues. Preliminary results from inheritance and linkage studies of a male sterility factor and a foliar mutant indicate that both are single gene, recessive traits. No linkages between the male sterility factor and 21 marker traits were found.

Pima experimental strains P67, P69, P71, P73, P74, and Pima S -6 were grown in Regional tests at 11 locations across the Pima belt in 1990. P73 averaged highest in mean yield across locations followed by P74, P69, P67, Pima S-4 and P71. The experimental strains, in comparison with Pima S-6, had longer, stronger, finer, and more whitish fiber. Experimental strains P45, PSI, P53, P62, P66, and EIS were released jointly by the USDA ARS and the Arizona Agricultural Experimental Station, and registered in Crop Science.

An isozyme study of the diversity and structure of Goss_vpium nii revealed levels of genetic variation within the species which were high for an island endemic. Infraspecific diversity of G. darwinii was observed among populations of the various Galapagos Islands. Evidence of introgression of other Gossypium species into darwinii was noted. An investigation into the effects of altered Pima (G. barbadense) fiber genotypes on interspecific hybrid fiber characteristics indicated that parent genotype could significantly affect hybrid fiber length, strength, uniformity, and micronaire. However, hybrid heterosis for fiber length and micronaire greatly exceeded the influence of parent genotype. Hybrid fiber characteristics were unique, fitting within neither the extra -long staple nor long staple classifications. A conversion program to convert photoperiodic short-day accessions of a Gossvpium barbadense germplasm collection to day neutrality continues.

Pima experimental strains P73, P74, P75, P76, P77, and P78 and the varieties Pima S-6 (PS-6) and Pima S-7 (PS-7) were grown in Regional tests at seven locations across the Pima belt in 1991. When yields were averaged across five test locations below 2,500 feet, the strains P73, P74, P75, and P76 ranked higher than PS-6, but lower than PS-7. At two test locations above 2,500 feet the strains P76 and P73 ranked higher in yield than PS-6 and PS-7. There was a trend across all locations for the strains P73, P74, P75 and P76 to be shorter in height than PS-6. The strain P76, which was the highest yielding strain across all locations, was the shortest strain at five of the seven locations. Strains included in all tests tended to have whiter, stronger fiber than PS-6. The above was not the case for P77 and P78, which were present in only two tests.

An investigation was conducted to determine the inheritance, allelism, and linkage associations of a spontaneous, male- sterile mutant found in plants of American Pima (Gossypium barbadense L.) cotton. Analyses of F₁, F₂, and BC populations of the mutant indicated that it was inherited as a single, recessive gene. T ests for allelism of the new gene with three previously described recessive male - sterility genes (ms₁, ms₂ and ms₃) were negative. Analyses of F₂ population segregation from crosses to 23 mutant marker stocks produced no evidence of linkage associations. We have proposed that the male sterility mutant be designated male-sterile-13 and be given the gene symbol ms₁₃. A conversion program to convert photoperiodic short-day accessions of a Gossypium barbadense germplasm collection to day neutrality continues.

Pima experimental strains P73, P74, P75, P76, P77, P79 and the varieties Pima S-6 (PS-6) and Pima S-7 (PS-7) were grown in replicated Regional tests at ten locations across the Pima belt in 1992. Tests were machine harvested for yield determination, plant heights were measured, and fiber samples were collected for fiber analysis. Considerable genotype by environment interaction for yield potential occurred across tests in 1992. Across all locations, the cultivar PS-7 ranked first in yield followed by the strains P79 and P75. The cultivar PS-6 was the tallest entry in the tests, followed by P75. The strains P76, P77, and P79 were uniformly shorter. Considering yield and fiber properties concurrently, strain P75 was the superior strain entry of the 1992 tests.

Two investigations, one of the inheritance of stomatal regulation and its relation to heat tolerance and the other of seed gossypol content in Gossvpium barbadense, began yielding results in 1992. Mode of gene action conferring stomatal conductance varied with the parentage of crosses. Selective advance for high conductance appeared to be feasible in wide crosses, but limited in crosses of elite Pima strains. Variability for seed gossypol content in G. barbadense was surprisingly high. There was evidence of geographic and taxonomic structure to the variability observed. A conversion program to convert photoperiodic short-day flowering accession's of the G. barbadense germplasm collection to day neutrality continued.

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