Agronomic Diversity Among Cultivars in the U.S. Cotton Germplasm Collection.

A valuable collection of diverse cotton (Gossypium hirsutum L.) genetic resources is available in the U.S. Cotton Germplasm Collection.  Within this collection is a group of improved cultivars, collected from other countries, that represent the most accessible and immediately useful germplasm to breeders, but whose diversity has not been adequately characterized.  The overall objective of this research is to determine the genetic diversity and relationships among cultivars available in the U.S. Cotton Germplasm Collection, specifically those collected from several cotton-growing regions of the world, including Africa, China, and the United States.  As a preliminary step, we have evaluated these accessions in replicated trials.  Sixty cultivars from the U.S. Cotton Germplasm Collection (twelve from northern Africa, twelve from southern Africa, twelve from China, and twenty-four from the United States including 12 recent and 12 obsolete cultivars) along with the G. hirsutum genetic standard, TM-1, and the G. barbadense genetic standard, 3-79, were grown in replicated trials at College Station and Lubbock, TX, in 2009.  Agronomic traits measured include lint yield, lint percent, and seed index.  The group of recent cultivars from the U.S. had the highest average lint yield (1,102 kg ha^-1) with the lowest seed index values (9.99 g).  The cultivars from northern and southern Africa had the lowest lint yields (584 kg ha^-1) while the cultivars from southern Africa had the highest seed index values (11.484 g).  Fiber properties reported include fiber length, strength, uniformity, elongation, micronaire, and short fiber content.  The group of recent cultivars from the U.S. had the highest estimated micronaire (4.41 units) while the group from northern Africa had the lowest micronaire (3.65 units).  The cultivars from southern Africa had the lowest short fiber content (8.45 %) while the Chinese cultivars had the highest short fiber content (9.64 %).  This group of Chinese cultivars had the weakest (268.8 kN m kg^-1) and shortest (27.3 mm) fibers.  The cultivars from southern Africa had the strongest (310.7 kN m kg^-1) and most uniform (82.8 %) fibers while the group from northern Africa had the longest fibers (29.3 mm).  The results of these agronomic evaluations combined with results from molecular characterization efforts in progress will provide cotton breeders with more information for the selection of unique and desirable parental germplasm to introduce genetic diversity, reduce genetic vulnerability, and provide genetic improvements for agronomic and fiber quality traits.