Progress From 80 Years of Breeding Soybean in the USA.

Soybean improvement efforts have been ongoing in the USA since the 1920’s. During the period from 1924 to 2011, average on-farm soybean yields in the USA have increased at a rate of 24 kg hectare^-1 year^-1. Our objective was to determine the degree of genetic improvement in that same time frame. A historic set of soybean cultivars with release dates from 1923 to 2008 were performance tested in replicated trials conducted in 2010 and 2011 in 17 states and one Canadian province. The number of cultivars in each separate maturity group (MG) trial was 60 in MG II, 59 in MG III, and 49 in MG IV. Averaged over ca. 27 site-year combinations, the estimated rate of genetic yield improvement was 23 kg hectare^-1 year^-1 for both MG II and III, and 20 kg hectare^-1 year^-1 for MG IV. A segmental regression model fit the data better than the simple linear model, and indicated that the current rate of genetic gain across all three MGs is 30 kg hectare^-1 year^-1. In addition to greater yield, new cultivars matured later, had greater lodging resistance, are shorter, and generally exhibited greater disease resistance than old cultivars. Composition analysis of seed harvested from these trials revealed that over generations of breeding for greater yield, seed protein concentration had decreased from 0.27 to 0.15 g kg^-1 year^-1, depending on MG, and oil concentration increased from 0.14 to 0.06 g kg^-1 year^-1. These data support other research which suggests that most of the soybean yield advances on the average USA farm have resulted from continuous genetic improvement, and by comparison, agronomic improvements have had a smaller impact.