High-Oil Soybean for More Efficient Energy Conversion to Soy-Based Biodiesel

Protein and oil are the most important components of soybean Glycine max (L.) Merr.], and they have been shown to have an inverse relationship. As there is a growing demand for soybean oil-based diesel as an alternative fuel source, a better understanding of the protein–oil inverse relationship in conjunction with seed yield could be useful in determining the potential of soybean as a source of biodiesel. We retrospectively examined advanced soybean breeding lines from multiple breeding programs across the southern USA to determine associations between protein and oil and seed yield. The data analyzed were a subset of the Uniform Soybean Tests and consisted of 31 different soybean breeding lines and four checks grown at 10 locations in 2000, six locations in 2001, and eight locations in 2002. A progressive multiple regression analysis was used to develop a single equation describing seed yield over all entries, locations, and years as a function of five traits: oil content, protein content, maturity, lodging, and plant height. From this equation, the optimum plant type for maximum seed yield in the southern USA had either high oil (225 g kg⁻¹) and low protein (385 g kg⁻¹), or high protein (437 g kg⁻¹) and low oil (190 g kg⁻¹). Seed yield continues to be the dominant trait of selection in soybean breeding programs. This study demonstrates that high yield can be achieved with either high protein or high oil. Hence, there is potential for maintaining yield while improving soybean cultivars for oil production. Given the energy balance between fossil-derived and soy-derived diesel, if soy-based biodiesel is to be a significant option, an increased focus on developing high-oil/high-yield soybean needs to occur.