Genetic progress in soybean of the US midsouth

Yield increase in crops has occurred due to plant breeding and improved pro duction and management techniques. The amount of increase due to plant bree ding in soybean in the southern USA has not been determined. The objective of this study was to evaluate the genetic improvements in soybean yield and other important agronomic traits. 'CNS' and 'S-100' were chosen as represe ntative ancestral lines from the 1940s. 'Ogden' and 'Lee', 'Hill' and 'Esse x', and 'TN 5-85', and 'Hutcheson' were released in early 1950s, late 1950s and early 1970s, and late 1980s, respectively. The experiments were conduc ted in Knoxville Experiment Station in Knoxville, TN and at the Ames Planta tion near Grand Junction, TN, for 3 yr, and at the Milan Experiment Station in Milan, TN, and at the Highland Rim Station in Springfield, TN, for 2 yr . Results showed that cultivar improvement increased soybean yield 14 kg ha (-1) per year. Yield increase over time was linear. This linear increase de monstrates that a yield plateau in the U.S. Midsouth has not been reached i n soybean [Glycine max (L.) Merr.]. Most of the increase has come via genet ically related elite by elite parent crosses. However, infusion of exotic g ermplasm into elite germplasm can often promote increases in yield, as in t he development of Hutcheson. Current cultivars showed better yield stabilit y and more response to favorable growing conditions than ancestral lines. G enetic improvement resulted in shorter plant height and decreased lodging. Oil content was increased until the 1980s, but then started to decrease. Ho wever, because of correlated effects, protein content started to increase a fter the 1980s.