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Comparison of Artificial and Natural Selection in American Pima Cotton under Different Environments¹

The effectiveness of artificial vs. natural selection for improving lint yield and other traits in American Pima cotton (Gossypium barbadense L.) when grown in predictable environments was evaluated at low and high elevations. A cross was made between ‘Pima S-3,’ adapted to the less fertile soils at high elevations, and ‘Pima S-4,’ adapted to low elevations and to the more fertile soils at high elevations. F₂ through F₈ populations from this cross were grown at one low-elevation and two high-elevation locations. These populations were subjected to natural selection by bulking all plants to form the next generation, or to artificial selection by bulking only selected plants to form the next generation. Phenotypic differences for lint yield, plant height, and fruiting height among plants within the succeeding generations were greatest at Phoenix, next greatest at Safford, and least at El Paso. Therefore, selection of genotypicaliy productive plants was most effective at Phoenix, somewhat less effective at Safford, and the least effective at El Paso.

Artificial- vs. natural-selection cycles 0 (F₂), 3, and from each of the three locations were evaluated at all locations. The populations developed by artificial selection at a given location tended to yield more than naturally selected populations at that location, with the greatest advantage at Phoenix, next greatest at Safford, and no advantage at El Paso. Likewise, among locations, natural selection had the most influence on yield potential at Phoenix. In some years, the artificially selected populations from one location tended to yield well at the other locations, but no population yielded well at all-three locations in both years. Selection for improvement of traits such as lint yield in the environment where the selected population will be utilized was effective. However, if the Pima improvement program were confined to one location, Phoenix appears to be the best of the three locations. At Phoenix, the magnified expression of productivity, and fruiting- and plant-height differences would permit the selection of genotypes that would be productive at each elevation of the American Pima Belt.

Key Words: Gossypium barbadense L. • Correlations • Breeding sites • Cultivar improvement • Genotype-environment interactions • Morphological traits • Fiber properties

² Research agronomist, research agronomist, and research geneticist, respectively. Univ. of Arizona Cotton Ctr., 4207 E. Broadway, Phoenix, AZ 85040.

Received for publication January 14, 1980.