Comparative Growth of Obsolete and Modern Cotton Cultivars. III. Relationship of Yield to Observed Growth Characteristics1

Yield differences among cotton (Gossypium hirsutum L.) lines have been used as the measure of cultivar suitability in this century. The result has been a steady increase in yields as progressively newer cultivars have been developed, while little or no information pertaining to the alterations in growth responsible for the enhanced performance has been collected. To assess the association of growth response to lint yield, 12 cotton cultivars representing release years since 1900 were examined for yield, yield components, and their relationship to seasonal vegetative and reproductive growth patterns resulting from two planting dates during 1982. The observed yield of lint exhibited a linear increase in association with the increased year of cultivar release. The largest contributor to yield variation was the number of bolls produced. The modern cultivars (since 1950) produced a greater proportion of their total lint and boll number before 135 days after planting. The early lint production of these cultivars is associated with smaller vegetative plant canopies and an earlier transition to reproductive growth. The modern cultivars exhibited smaller boll weights and a greater lint percentage. Fiber quality, with the exception of micronaire, showed little improvement due to plant breeding. Micronaire tended to increase in the newer cultivars. The data indicate that breeding efforts have altered the number of harvestable bolls to a greater extent than any other characteristic.