2006 Annual Report 4d.Progress report. This report serves to document research conducted under a reimbursable agreement between the ARS and Cotton Incorporated entitled "Simultaneous improvement of fiber quality and heat tolerance of upland cotton germplasm." This project will be extended through 2007. Additional details of research can be found in the report for the parent CRIS 5347-21000-009-01R. In 2006 three germplasm lines possessing improved fiber and heat tolerance characteristics were distributed upon request to public and private cotton breeders for further cotton improvement efforts. The lines, released in 2005, were registered with Crop Science in 2006 and placed in the National Seed Storage Laboratory. Creation of a new germplasm pool for heat tolerance and fiber improvement breeding was initiated in 2002. In 2005, blocks of F3 progeny of four double cross populations were planted in the field at Maricopa, AZ, for individual plant selection. In 2006, 230 individual plant selections were made within the F3 progeny block and seed of each were shipped to Tecoman, Mexico, for seed increase. The 230 lines were sampled for fiber analyses as both individual plants at Maricopa, AZ, and as progeny rows at Tecoman, Mexico. Fiber samples from the 230 selections were sent to Cotton Incorporated for fiber analyses and data obtained. A subset of 70 candidate lines have been identified for further evaluation based upon these data. F3.4 seed of these 70 lines have been distributed and planted at Florence, SC; Tifton, GA; Baton Rouge, LA; Maricopa, AZ; and Shafter, CA, for evaluation as single row progeny lines in 2006. Successful progeny will be tested in replicated tests at multiple locations in 2007. A third set of crosses were initiated in 2005 to incorporate more G. barbadense derived fiber characteristics into the upland germplasm pool. Two lines from an introgressed RIL population (NM12 and NM49) and two lines from a stabilized interspecific population (DP90/S-7) have been used as high fiber quality parents. The released lines AGC 85, AGC208, and AGC375 and SG747 have been used as heat tolerant parents. Seed from the above crosses were harvested in 2005, F1 populations were planted in the greenhouse in 2005-2006 and intercrossed to produce F1 x F1 double cross populations, and the progeny of the double cross populations have been planted in the field in 2006.