The Effect of Supplemental Irrigation on Canopy Temperature Depression, Chlorophyll Content, and Water Use Efficiency in Three Wheat (<i>Triticum aestivum</i> L. and <i>T. durum</i> Desf.) Varieties Grown in Dry Regions of Jordan

One critical challenge facing the world is the need to satisfy the food requirements of the dramatically growing population. Drought stress is one of the main limiting factors in the wheat-producing regions; therefore, wheat yield stability is a major objective of wheat-breeding programs in Jordan, which experience fluctuating climatic conditions in the context of global climate change. In the current study, a two-year field experiment was conducted for exploring the effect of four different water regimes on the yield, yield components, and stability of three wheat (Triticum aestivum L.; T. durum Desf.) Jordanian cultivars as related to Canopy Temperature Depression (CTD), and Chlorophyll Content (measured by Soil-Plant Analysis Development, SPAD). A split plot design was used in this experiment with four replicates. Water treatment was applied as the main factor: with and without supplemental irrigation; 0%, 50%, 75%, and 100% of field capacity were applied. Two durum wheat cultivars and one bread wheat cultivar were split over irrigation treatments as a sub factor. In both growing seasons, supplemental irrigation showed a significant increase in grain yield compared to the rain-fed conditions. This increase in grain yield was due to the significantly positive effect of water availability on yield components. Values of CTD, SPAD, harvest index, and water use efficiency (WUE) were increased significantly with an increase in soil moisture and highly correlated with grain yield. Ammon variety produced the highest grain yield across the four water regimes used in this study. This variety was characterized by the least thermal time to maturity and the highest values of CTD and SPAD. It was concluded that Ammon had the highest stability among the cultivars tested. Furthermore, CTD and SPAD can be used as important selection parameters in breeding programs in Jordan to assist in developing high-yielding genotypes under drought and heat stress conditions.