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Earliness Factors in Three Pima Cotton Genotypes¹

Pima cotton cultivars (Gossypium barbadense L.) were characteristically tall and late maturing, but newly developed Pima genotypes are shorter and earlier. The objective of this study was to ascertain phenotypic differences between the early and late Pima genotypes and relate them to earliness characters in upland genotypes (G. hirsutum L.). Among three Pima genotypes, characters studied were plant height, stem and branch weight, number of mainstem nodes, mainstem internodal length, node of first sympodium, cut-out node, axillary bolls on mainstem, early bolls set and shed, and late green and mature bolls. Data from dried plants collected at end-of-season were obtained for 1980, 1981, and 1982 at Phoenix, AZ. Early season genotypes, when compared to late season genotypes, had i) shorter mainstem and sympodial internodalength, ii) less stem weight, iii) lower first sympodium node, iv) lower cut-out node, and more bolls on the mainstem that developed in the axils of the sympodia. On the first 30 fruiting sites per plant that flowered, the early genotypes set more bolls and shed fewer bolls on a smaller number of sympodia. The early genotypeshowed a larger fruiting-efficiency ratio of mature fruit numbers to stem weight, and a larger proportion of all the fruits per plant in the group of first 30 fruiting sites. Many of the earliness characters were similar to those in upland cotton. Fruiting-efficiency ratio may be the most useful selection parameter.

Key Words: Gossypium barbadense L. • G. hirsutum L. • Phenotypic characters • Plant height • Plant weight • First sympodial node • Cut-out • Axillary fruit

² Plant physiologist, USDA-ARS, Univ. of Arizona Cotton Res. Center, 4207 E. Broadway Rd., Phoenix, AZ 85040.

Received for publication October 22, 1984.