Changes in Physiological Traits in Soybean with Breeding Advancements

Plant breeding makes important contributions to increased production of food and fiber. The objective of this research was to characterize the changes in physiological traits in soybean [Glycine max (L.) Merr.] that have occurred with breeding advancements. Sixty maturity group (MG) III and 54 MG IV cultivars, released from the 1920s through 2010, were evaluated in MG-specific experiments in dryland and irrigated environments at Manhattan, KS, in 2010 and 2011. Genotypes were planted in four-row, 3.4-m-long plots 76 cm apart and arranged in a randomized complete block design with four replications. Genotypes were evaluated for canopy temperature (CT), leaf chlorophyll content (Chlor), pollen germination (PG), electrolyte leakage (EL) and leaf antioxidants (TAC). Genotypes differed for CT, Chlor, and PG in each of the two MGs. Among genotypes seed yield increased with year of release (YOR) in both MGs, as well as Chlor content. Canopy temperature and seed yield decreased with YOR in both MGs. This study provided evidence that CT and Chlor changed over time along with changes in maturity, plant height, lodging, and disease resistance. The changes have resulted in corresponding improvements in seed yield. The relationships between CT and Chlor with seed yield provide support to intentionally select for these traits in plant breeding programs as a possible means to improve genetic gain.