Fruiting Height Response: A Consideration in Varietal Improvement of Pima Cotton, Gossypium barbadense L. 1

THE Pima cotton industry involves a relatively small acreage in the southwestern United States. However, the crop is grown over a wide range of environments at altitudes from approximately 100 to 4,000 feet. During the fruiting season for the crop, the lower altitudes, ranging up to 1,500 feet, are characterized by high day and night temperatures. At the higher altitudes, 2,500 feet and above, day temperatures are high and night temperatures moderate. The minimum night temperatures in the 1,500to 2,500-foot zone fluctuate between high and moderate from year to year. Observations to date indicate that minimum night temperatures near 80° F. are not conducive to efficient fruiting and should be considered as high. Historically, only one commercial variety of Pima cotton has been grown at any given time, except during the periods of transition from one variety to another. To date, only seven varieties of Pima have been grown commercially in the Southwest. The first was the 'Yuma' variety, followed by 'Old Pima,' 'SxP,' 'Amsak,' 'Pima 32,' 'Pima S-l,' and 'Pima S-2' (2). Yuma, Old Pima, SxP, Amsak, and Pima 32 were developed directly or indirectly from a few cottons introduced from Egypt. Thus, they involved a fairly narrow germplasm base and were very similar in many respects. Pima S-l was developed much differently. The parents of Pima S-l included 'Sea Island,' Pima, and 'Tanguis' from Gossypium barbadense L., and a Stoneville variety from G. hirsutum L. These parents were crossed, the resulting Fj's were crossed, and selections in later generations were subsequently recrossed over a 20to 2 5-year