CROP SCIENCE, VOL. 54, SEPTEMBER– OCTOBER 2014 WWW.CROPS.ORG 2275 RESEARCH I n the U.S. Souther n High Plains (SHP), drought is one of the most important abiotic factors causing substantial crop and economic losses. This area is characterized by a semiarid climate with an average seasonal precipitation of ~250 mm, which is about one-third of the seasonal evapotranspiration requirements of wheat grown under sufcient irrigation (Lazar et al., 2004; Musick et al., 1994). In rainfed conditions, drought may cause a complete crop failure. In Texas, drought caused more than 4.1 billion dollars in economic losses in 2006 and 2011, and the loss from wheat alone was 243 million dollars in 2011 (Fanin, 2011). Previous studies showed that drought alone may decrease wheat yield by 40% under feld conditions when it occurs between tillering and maturity (Denc ˇic´ et al., 2000). A growth chamber experiment suggested that drought at anthesis may decrease yield by 69% (Pradhan et al., 2012a). Development and adoption of drought-tolerant wheat cultivars is one of the most efcient strat- egies for sustainable high yield under dryland conditions. Wheat breeding has improved drought tolerance over the years. In the Australian semiarid to arid environments, the pres- ent wheat yield (2000 kg ha 1 ) is almost two times higher than Cooler Canopy Contributes to Higher Yield and Drought Tolerance in New Wheat Cultivars Gautam P. Pradhan, Qingwu Xue,* Kirk E. Jessup, Jackie C. Rudd, Shuyu Liu, Ravindra N. Devkota, and James R. Mahan ABSTRACT Drought is an important abiotic stress limiting wheat (Triticum aestivum L.) yield in the U.S. Southern High Plains. Although wheat breeding has improved drought tolerance in the area, the physiological traits conferring drought tolerance have not been well understood. Canopy temper- ature depression (CTD), the difference between air and canopy temperatures, has been sug- gested as a trait for identifying drought-tolerant genotypes. The objective of this study was to investigate whether a higher CTD is one of the reasons for higher yield in new drought-tolerant cultivars. Field experiments were conducted in fve genotypes (TAM 111, TAM 112, TX86A5606, TX86A8072, and Dumas) under dryland condi- tions in 2009/2010, 2010/2011 and 2011/2012 seasons. The canopy temperature was mea- sured continuously from late jointing to the middle of grain flling, using wireless infrared thermometers. Although CTD varied with sky conditions, growth stage, and time of day, the genotypic variation in CTD was consistent. In general, yield was positively correlated to day- time CTD whether the CTD was used from a single clear day or a season-long mean. How- ever, including Dumas weakened the correlation under severe drought in 2012. The nighttime CTD was not correlated to yield. Two new cul- tivars (TAM 111 and TAM 112) had up to 2.7°C higher CTD and 31% more yield than other gen- otypes. Therefore, cooler daytime canopy might be the reason for higher yield in the two new and drought-tolerant cultivars under drought condi- tions. Further studies are needed to understand the physiological bases of differences in CTD among genotypes. G.P. Pradhan, Q. Xue, K.E. Jessup, J.C. Rudd, S. Liu, and R.N. Devkota, Texas A&M AgriLife Research at Amarillo, 6500 Amarillo Blvd. W., Amarillo, TX 79106; and J.R. Mahan, USDA-ARS, Plant Stress and Water Conservation Lab., 3810 4th St, Lubbock, TX 79145. Received 26 Nov. 2013. *Corresponding author (QXue@ag.tamu.edu). Abbreviations: CT, canopy temperature; CTD, canopy temperature depression; IRT, infrared thermometer; PAW, plant available soil water; SHP, Southern High Plains; SWC, soil water content; TOD, time of day. Published in Crop Sci. 54:2275–2284 (2014). doi: 10.2135/cropsci2013.11.0788 © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Published August 20, 2014