Genetic Variations for Terminal Heat Tolerance in Southeastern Soft Wheat Germplasm.

Stress due to high temperature at grain filling has emerged as a common limiting factor for most of the wheat growing regions in the USA. Thus developing heat tolerant cultivars has become one of the precedence breeding objectives. Information on genetic variation for heat tolerance in US south eastern soft wheat germplasm is really limited though temperature above optimum with intermittent extreme high temperature is a common phenomenon during grain filling.  To identify unique sources of heat tolerance, a panel of 140 southeastern soft wheat were evaluated under field conditions in the experimental site of North Florida Research and Education Center (NFREC), Quincy  where temperature during grain filling rages between 29  to 35^oC. The panel was characterized for chlorophyll content, spike and canopy temperatures, spike fertility and other yield contributing traits.  Our preliminary data analysis exhibited significant genetic differences in spike fertility, individual grain weight, grains/spike, canopy temperatures and SPAD chlorophyll content.  Spike fertility demonstrated strongest correlation with grain yield and selecting high yielding lines based on spike fertility were more efficient under post-anthesis high temperature stress conditions compare to other physiological and yield contributing traits. Our results produce new information on soft what germplasm as possible sources of heat tolerance in wheat breeding programs.