Stepwise regression analyses provided an estimate of the net effect of yield components on lint yield of Upland cotton. Data from strain tests in the Pee Dee, South Carolina, cotton breeding program for crop years 1968 and 1969 were used in these analyses. Lint yield/m2 was the dependent variable. Independent variables were: bolls/m*, lint/seed, and seeds/boll.Correlation analyses indicated the relationships among yield components. Partial correlation coefficients were utilized to show the order of variable addition in the regression equations. We found that bolls/m2 assumes the major role in determining yield. The lint/seed component assumes the secondary role in the development of lint yield. Seeds/boll made a relatively larger total contribution only after lint/seed had made its contribution.These data indicate that selection pressure should be placed on prolificacy (bolls/m2) and seeds/boll, concommitantly with selection to maintain or increase lint/seed. Although the lint/seed component makes a relatively smaller total contribution to lint yield, it is necessary to maintain or increase this component to secure the increased contributions of seeds/boll.

A model of cotton (Góssypium sp) lint yield that equated yield to the volume of a parallelepiped with three dimensions was developed by Kerr. The model is extended to basic units by dividing the axes of the parallelepiped and the seed is recognized as the basic unit of yield. Yield per seed, per boll, and per unit area of land can be stated in equation form by using the divisions of the axes. The relative contributions of the primary lint yield components decrease as the complexity of the model increases from yield/seed to yield/unit area of land. The summation of each model has an upper R3 limit of 1.0. Therefore by the inclusion of additional components, the relative contribution of yield components from the previous models must decrease. Data are presented that illustrate a use of the model to define the component of yield more susceptible to alteration to increase yield.

Fiber tenacity, elongation, length, fineness, and color were measured for 5 Gossypium barbadense L. and 37 G. hirsutum L. fiber samples. These samples were spun into 12- and 27-tex yarns on a ring system and into 27-tex yarns on an open-end system; yarn tenacity was determined. Fiber tenacity and length were positively correlated with yarn tenacity. No correlations of fiber fineness with tenacity of 27-tex yarns were detected. A substantial portion of the variation in 27-tex yarn tenacity was attributable to variations in fiber tenacity and length.