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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