QUANTIFYING ACQUIRED THERMAL TOLERANCE IN WINTER-WHEAT

High temperature stress Limits productivity of winter wheat (Triticum aestivum L.) in many environments. Identification of thermal tolerant germplasm is needed to improve plant productivity under heat stress. In this study we used 2,3,5-triphenyltetrazolium chloride (TTC) reduction, an indicator of mitochondrial activity, to characterize cultivar differences for acquired thermal tolerance in winter wheat. Seven-day-old seedlings of six hard red winter wheat cultivars grown at 25 degrees C were acclimated at 37 degrees C for 24 h followed by a 50 degrees C incubation for 2 h. Leaf sections sampled after each temperature treatment were infiltrated with TTC and the resultant formazan was ethanol-extracted for optical density measurement at 530 mn. Under these test conditions, the TTC assay detected differential tolerance (expressed as percent cell viability of the 50 degrees C treated tissue compared to the 37 degrees C treated tissue) which ranged from a low of 6% for 'Siouxland', to a high of 72% for 'TAM 108'. The results of this study show that TTC reduction can be used to measure differences in acquired thermal tolerance in winter wheat.