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.

Five experimental strains and Pima S-6 were grown in nine Regional Tests across the Pima belt in 1987. Experimental strain P70 averaged highest in yield both below and above 2,500 foot elevation. The difference in yield between Pima S-6 and P70 across all locations was 48 pounds of lint per acre. Sequential harvests at Phoenix and Safford, AZ, indicated that P70 was the earliest and Pima S-6 the latest entry in the 1987 Regional Test.

Seed increase of 104 accessions and data collection on 65 accessions were obtained in 1988 to further the maintenance and evaluation of the Gossypium barbadense L. germplasm collection. In a program of conversion of tropical non flowering cottons to a day-neutral flowering habit, 63 accessions were advanced 1 generation by backcross. A systematic screening of the G. barbadense collection for bacterial blight resistance involving 200 accessions from 21 countries yielded 8 accessions resistant to races 1, 2, 7, and 18 of the pathogen. Genetic inheritance and linkage investigations of a male sterile and a foliar mutant progressed. An investigation of the geographic and taxonomic distribution of the ovate leaf trait was concluded with negative results. The frequency of the 2 mutant genes ov₁ and ov₂ proved to be too rare to yield meaningful taxonomic or geographic information about the species. Preliminary results from a performance evaluation of interspecific hybrid cottons conducted at Maricopa and Safford AZ, indicated strong environmental influences on hybrids, but generally favorable yield earliness and plant height data were obtained from the higher -elevation Safford location.

A feasibility study of short season management in Pima cotton, using short season genotypes, was initiated in 1993. Four short season genotypes, a full season check, and a short season check were evaluated in replicated tests under short season and full season regimes. In this first preliminary year of data, no significant yield loss could be attributed to management regime or to earliness of genotypes. Three of the putative early maturing genotypes exceeded the full season Pima S-7 check in yield. Results were contrary to expectations. The short season test is planned for repeat in 1994. An investigation of a virescent mutant discovered in 1990 (CM-1-90) was conducted in 1991, 1992, and 1993. Crosses of the mutant to Pima S-6 to determine inheritance, and to various virescent mutants to determine allelism produced results which were anamolous to normal, nuclear inheritance. Reciprocal crosses to PS-6 and to various virescent mutants confirmed that the new mutant was cytoplasmicaly inherited.

Pima experimental strains P73, P75, P76, P77, and the cultivars Pima S-6 (PS-6) and Pima S-7 (PS-7) were grown in replicated regional tests at twelve locations across the Pima belt in 1993. Tests were machine harvested for yield determination, plant heights were measured, and lint samples were collected for fiber analysis. Considerable genotype by environment interaction for yield potential occurred across tests in 1993. Across all locations, the strain P76 ranked first in yield followed by the cultivar PS-7 and strain P75. Strains P73 and P76 produced fiber of equal or greater length, strength, and elongation than PS-7. Plant heights were greatest for the entries PS-6 and P75. Entries PS-7 and P73 were intermediate in height, while P76 and P77 were the shortest of the entries tested. Considering yield and fiber properties concurrently, P76 was the superior entry of the 1993 tests.

Twelve Pima varieties and experimental strains were grown in a replicated trial at the Maricopa Agricultural Center. Lint yield, boll size, lint %, gin turnout %, plant population and fiber property data are presented in this report.

Sixteen long staple cotton varieties (including 4 Pima experimental lines) were tested in a replicated small plot trial on the Safford Agricultural Center. Plots were machine harvested twice to determine yield and percent first pick Small hand samples were taken to determine boll size, percent lint turnout and fiber qualities. Pima S-6 was the highest yielding variety with 1110 pounds per acre of lint. Five of the sixteen varieties yielded over 2 bales per acre. A new variety OA 312 looks particularly promising with yield very close to S-6, fiber quality better than S-6 and an earliness that approaches that of S-7.