CANOPY TEMPERATURE AS AN INDICATOR OF DIFFERENTIAL WATER-USE AND YIELD PERFORMANCE AMONG WHEAT CULTIVARS

Field experiments were conducted at Phoenix, Arizona to investigate the usefulness of canopy temperatures in screening wheat genotypes for water use and yield characteristics. Six spring wheat (Triticum aestivum L.) cultivars were grown under well-watered conditions and two deficit irrigation regimes. Canopy temperatures (Tc) were measured daily at 1045 h, 1345 h and 1545 h (MST) using hand-held infrared thermometers. Leaf stomatal conductances were obtained between 1245 h and 1400 h. Seasonal water use was estimated via a soil water budget approach. There were small but consistent differences in Tc among cultivars in the well-watered treatments. "Yecora", the warmest cultivar, had a mean midday Tc of 25.1°C over the growth period from stem elongation until the hard dough stage of growth; "Siete Cerros" the coolest, was 23.3°C. Tc values were lower earlier and later in the day but all cultivars maintained the same ranking relative to each other. Cultivars with higher midday canopy temperatures under well-watered conditions used less water (r2 = 0.90; p < 0.01) and had lower stomatal conductances (r2 = 0.86; p < 0.01) than those with cooler temperatures. Grain yields for all cultivars were similar under well-watered conditions but varied considerably under water stress. Cultivars that were warmest when well-watered maintained the highest relative yields when exposed to deficit irrigation regimes (r2 = 0.78; p < 0.05). Results indicate that routine Tc comparisons between new cultivars and genotypes having well-known water use and yield characteristics will provide additional selection criteria for maximizing performance under water stress conditions. © 1990.