Comparison of Surface Temperatures of Barley Varieties under High Temperature Conditions

Regional specialities of world wide barley cultivars under high temperature conditions were studied, using surface temperatures of plant canopy measured by an infrared thermometer. A total of 274 barley cultivars consisting of 5 north American cvs, 11 north African cvs, 19 Chinese cvs, 37 Ethiopian cvs, 35 south west Asiatic cvs, 30 Japanese cvs, 30 Korean cvs, 21 Nepalese cvs, 18 Turkish cvs, and 68 European cvs were randomly taken from the stocks preserved in the Barley Germplasm Center of Okayama University. Under nearly zero stress conditions on cloudy days, differences (Ts-Ta) between canopy surface temperatures (Ts) of barley cultivars and ambient air temperatures (Ta) decrease with increasing air temperatures and water vapor pressure deficits, having very high correlation coefficients. On the other hand, under higher air temperature and dry conditions on clear afternoons, Japanese cvs, south west Asiatic cvs, and Nepalese cvs maintained low surface temperatures, but barley cultivars from higher latitudes such as European cvs had the tendency to increase surface temperatures. These imply that the former cvs have the ability to change energy dissipation rates in response to changes in energy absorption but the latter cvs have a limited ability to change the rates of some energy loss mechanisms such as transpiration. Barley cultivars in the habitats with higher annual air temperature and more annual precipitation generally tended to have greater ability to moderate leaf temperatures.