Cell Membrane Stability as a Measure of Drought and Heat Tolerance in Wheat1

Drought and heat tolerance tests that were developed for sorghum ( Sorghum bicolor L. Moench) were adapted to and evaluated in field grown wheat ( Triticum aestivum L. and T. durum Desf.) during 1977/1978 and 1978/1979. The drought tolerance test is based on the measurement of the electroconductivity of aqueous media containing leaf discs that were previously water stressed in vitro by exposure to a solution of polyethylene glycol‐6,000 (PEG). The heat tolerance test is similarly based on exposure of leaf discs to heating, in vitro, to 44 C. Drought tolerance of wheat leaves decreased with plant age. For a given plant growth stage, some variation was revealed in drought tolerance, according to leaf position. Maximal separation of wheat cultivars in drought tolerance was obtained with 40% (w/v) solution of PEG, when plants were grown under conditions of favorable moisture regime and sampled during the late jointing growth stage. Wheat was more drought tolerant than maize, sorghum or millet, based on published data. When plants were sampled during a period of water stress, they were more drought tolerant than well‐watered plants, indicating adjustment of cell membrane stability to drought stress. Wheat cultivars varied in their ability to adjust, in this respect. Unlike in sorghum, drought and heat tolerance were not correlated in wheat. The inclusion of a limited number of barley ( Hordeum vulgare ) and triticale (X Triticosecale Wittmark ) genotypes in this study indicated that the methods discussed work equally well with these crop plants.