Comparison of Past and Recently Developed Soybean Cultivars in Maturity Groups VI, VII, and VIII1

Abstract

In the southeastern U.S., soybean [Glycine max (L.) Merr.] seed yields have increased due to improved cultivars, cultural practices, and general management. To determine the contribution of improved genotypes to this increase, 18 cultivars in maturity groups VI, VII, and VIII ranging in introduction or release date from 1914 to 1973 were evaluated in a common environment for 3 years. Other plant traits were evaluated to determine if differences existed among cultivars and if these differences were associated with year of release and seed yield. The regression of seed yield on year of release indicated significant genetic improvement in seed yield had occurred. Averagedo ver all maturity groups for the period 1942 to 1973, this increase was 0.7%/year. For cultivars in maturity group VIII, pods/m, plant height, and number of nodes were related to year of release. The differences in plant height and nodes/plant for cultivars in maturity group VIII were primarily due to the indeterminate growth habit of ‘Yelnanda’ and ‘Improved Pelican.’ The other cultivars in this experiment have the determinate growth habit. The differences for traits other than yield in cultivars within maturity groups VI and VII were not associated with year of release. The yield increase of recently developed cultivars was not consistently associated with any of the traits measured.