Gains from 80 years of soybean breeding
Department of Crop Sciences,
Illinois growers often ask why yield progress is slower in soybean than corn. A review of average corn and soybean yields in the US confirm that corn yields are increasing much more rapidly than soybean yields. Between 1924 and 2009, soybean yields increased 0.34 bushels/acre (b/a) annually, whereas corn yields increased 1.7 b/a annually. What is most striking is that between 1990-2009, soybean yields increased annually at a rate of 0.30 b/a, but corn yields increased 2.4 b/a. This shows that the rate of yield increase has accelerated in corn, but not in soybean.
The increases in crop yields over time are the result of both genetic and agronomic improvements. How much of the yield improvements are the result of each of these causes can be determined by growing new and old varieties in a common environment. Previous studies suggested that at least 50% of the yield increases in soybean are the result of improved genetics. Through a collaboration with soybean researchers throughout the Midwest, we are evaluating old and new varieties in yield tests to exam how much the yield improvements are the result of improved genetics. There are plots of old and new varieties at Agronomy Day so attendees can see the progress made in plant breeding over the last 80 years.
There are a number of explanations for why yield increases in soybean are not as rapid as in corn. Many of these have to do with the basic differences in the physiology of these plants. For example, photosynthesis is more efficient in corn than soybean, so corn has a greater capacity to use the sun’s energy. Another difference is that soybean seed takes more energy to produce than corn grain. This is because soybean seed has a high concentration of protein and oil, and these components take more energy to produce than starch, which is the major component of corn grain. In addition, corn is a hybrid crop and therefore can take advantage of heterosis or hybrid vigor. In contrast, economical methods of producing hybrid soybean have not been found.
All available tools are being used in soybean variety development efforts in attempt to increase the rate of yield gain. By combining traditional breeding methods with new biotechnology approaches such as marker-assisted selection and transgenic technology, breeders hope to increase these rates of gain. At the University of Illinois, researchers are attempting to increase yields through identifying new genes from exotic soybean germplasm using genetic mapping. Some genes that increase yield from exotic germplasm have been mapped and are now being bred into high yielding varieties to determine if these genes can further increase yields.