Soybean Improvements Through Plant Breeding: Physiological Traits

The goal of plant breeding programs is to improve plant performance through genetic gain, and it is widely acknowledged that breeding gains in soybean have made important contributions to increased production.

A study was conducted in Manhattan Kansas in 2010 and 2011 to identify traits that have contributed to this genetic gain in soybean production. Sixty Maturity Group (MG) III and 54 MG IV soybean varieties (including both public and private releases) that were released from the 1920's through 2010 were grown in MG-specific experiments in both nonirrigated (NI) and irrigated (IRR) environments. The NI and IRR experiments were managed similarly except for the addition of water to the IRR trials.

Measured traits on each of the varieties were canopy temperature, leaf chlorophyll content, pollen germination, electrolyte leakage, and leaf antioxidants. Seed yield, plant height, and lodging of each variety were also measured each year.

Results are presented in a Crop Science article entitled “Changes in Physiological Traits in Soybean with Breeding Advancements” by Keep, Schapaugh, Prasad, and Boyer.

A summary of the findings from this study follow.

●         Seed yield increased with year of release (YOR) in both environments in both MG’s.

●         Plant height and lodging decreased with YOR for both MG’s. Varieties with the highest lodging scores were earlier releases dating from the 1920's through most of the 1940's.

●         Canopy temperature decreased with YOR; i.e., the newer varieties in the study had cooler leaves. Previous research has identified a negative correlation between canopy temperature and seed yield.

●         Chlorophyll content increased with YOR; i.e., newer varieties had a higher chlorophyll content in leaves.

●         Newer varieties tended to be higher yielding, shorter in stature, and less prone to lodging, and had leaves that were both cooler and higher in chlorophyll content.

●         Canopy temperature and leaf chlorophyll content showed the strongest relationship with YOR and seed yield.

The relationships between canopy temperature and leaf chlorophyll content with seed yield that were found in this study indicate that selection for these traits should be included in soybean breeding programs that have the goal to improve soybean yield.

Composed by Larry G. Heatherly, Mar. 2016, larryheatherly@bellsouth.net