Monday, November 13, 2006

Heat Tolerance as Related to Leaf Morphology, Spike Traits, and Canopy Temperature in Winter Wheat.

James Heitholt1, Russell L. Sutton1, Maricela Garcia-Martinez1, and Gaylon Morgan2. (1) Texas Agric. Exp. Stn., 17360 Coit Rd., Dallas, TX 75252-6599, (2) Rm 349B Heep Center, Texas A&M University - Rangeland Ecology & Management, Texas A&M University, Soil & Crop Science Department, College Station, TX 77843-2474

Limitations to yield of winter wheat in north Texas include water stress, temperature stress (both cold and hot), fertility, and disease.  The objectives of this research were to characterize leaf morphology, spike characteristics, and canopy temperature of selected genotypes and relate these traits to grain yield.  Twenty-five (2005) and 30 (2006) cultivars of red winter wheat were grown in north Texas.  Cultivars were selected for diversity and included six awnless and five soft red winter cultivars.  Soil type was a Houston Black clay.  Seed were sown in mid-October and mid-December.  Flag leaf morphology, relative water content (RWC), spike traits, canopy temperature depression (CTD), and grain yield were determined.  Only 2005 results are available in this abstract.  Leaf RWC was higher in Coker 9663, Mason, and Fannin whereas Scout 66, Crawford and Mit were among the lowest.  Spikes of Mason and P25R47 were consistently wide whereas spikes of Lockett and Scout 66 were among the narrowest.   Traits that were associated with yield, especially in the late planting, were taller plants, early maturity, wide spikes, and a relatively disease-free canopy.  Traits that were associated with greater CTD included narrow spikes, later maturity, tall plants, and healthy leaves (low chlorosis rating).  Grain yield was not associated with CTD.  Heat-tolerant entries were Jagalene, TAM 200, and 2174 whereas heat-susceptible types were Deliver, 2145, and OK 102.  Delayed planting reduced yield and this yield decline was strongly and positively associated with the difference in average ambient temperature during grain filling (between early and late planting for each variety).  These results provide new information on physiological and morphological traits that might prove valuable as selection criteria in future wheat breeding efforts for yield stability.