Genetic Gains for Physiological Traits Associated With Yield in Soft Red Winter Wheat in the Eastern United States From 1919 to 2009.

Breeding strategies can benefit from periodic evaluation of genetic gains for physiological traits and their contribution to yield progress over time in a particular environment. The objective of this research was to determine the magnitude of progress for several physiological traits in 50 soft red winter (SRW) wheat (Triticum aestivum L.) cultivars released from 1950 to 2009. A historical cultivar Red May (1919) was also included in the study. Physiological traits evaluated included canopy temperature differential (CTD), leaf width, flag leaf area (LA), leaf dry weight, specific leaf area (SLA), SPAD chlorophyll reading, and carbon-13 isotope discrimination (Δ).  Replicated experiments were performed at Warsaw and Holland, VA, in 2010 and 2011. Traits that consistently increased in magnitude over time and, at the same time, were significantly (p < 0.01) related to yield were LA, smaller leaf area-higher yields; leaf dry weight, lighter leaves-higher yields; and Δ, higher Δ-higher yields. Traits that did not significantly increased in magnitude over time but were significantly (p < 0.01) related to yield were CTD evaluated from boot to approximately 2 wk after flowering, cooler leaves-higher yields; leaf width, narrower leaves-higher yields; SLA, smaller SLA-higher yields; and SPAD chlorophyll reading, greener leaves-higher yields. It is emphasized that further yield increase in the SRW wheat grown in Eastern Unites States can be achieved through selection of cultivars with cooler, greener leaves, and reduced SLA.