How Cotton Varieties Have Changed over Time: A Comparison of Vegetative/Reproductive Growth, Fruiting Characteristics, and Fiber Development of Obsolete Versus Modern Varieties

Cotton lint yields have steadily increased 9 to 10 lbs/acre/year over the past 50 years across the U.S. Cotton Belt, with most of this yield increase credited to plant breeding programs selecting for increased lint production.  This increase in lint yield has resulted in changes in the reproductive growth and development of cotton varieties over time, with increases in boll numbers and lint percentages and decreases in boll size and seed size.  In a study conducted by Wells and Meredith in the early-1980’s comparing varieties from the early-1900’s to varieties from the 1930’s, 1950’s, and 1970’s, they found that more modern varieties (1970’s) made an earlier transition from vegetative growth to reproductive growth and partitioned more dry matter into reproductive organs compared to older lower yielding varieties.  Since the early 1980’s, lint yields have continued to increase approximately 9 lbs/acre/year and measured fiber quality parameters such as micronaire, fiber length and fiber strength have also increased linearly during this time.  Moreover, the introduction of transgenic traits into cotton varieties has also occurred during this time frame and little information exists on how cotton varieties have changed during this time.            

Fourteen cotton varieties representing various decades (1900’s to 2016) of release from the Stoneville and Deltapine lineage were planted in a randomized complete block design with four replications at the Pee Dee Research & Education Center in Florence, SC and at the Sandhills Research Station in Jackson Springs, NC in 2016 and 2017.  Vegetative growth was measured at various times during the season via leaf dry weights, stem dry weights, specific leaf weights, and leaf area indexes.  Reproductive growth was also monitored by both number and dry weights of squares, flowers, and bolls.  Plots were harvested with spindle type cotton pickers modified for small plot research and fiber quality was determined.