HIGH-TEMPERATURE EFFECTS ON PHOTOSYNTHESIS AND WATER RELATIONS OF GRAIN LEGUMES

Effects of high temperature on photosynthesis, and its interaction wit h water relations in common bean (Phaseolus vulgaris), cowpea (Vigna u nguiculata), faba bean (Vicia faba), and five cultivars of field pea ( Pisum sativum) were investigated. Responses of all species were compar ed at 20/15, 30/15, or 30/25 degrees C day/night, and cowpea and pea w ere compared at 20/15 and 30/25 degrees C under well-watered and limit ed-water conditions. Response of pea to 20/15 and 30/25 degrees C duri ng flowering was ascertained, and sensitivity of the photosystem of pe a and faba bean to 40 degrees C was determined. High temperature decre ased chlorophyll variable fluorescence (F-v), a measure of injury to p hotosynthesis, in all species except cowpea, which was highly tolerant . Leaf chlorophyll and most measures of growth were favored by high da y temperature but not by high night temperature, and photosynthetic ra tes were enhanced by high temperatures that increased leaf chlorophyll and nitrogen (N) contents. High temperature diminished growth less th an water deficiency and increased water use of all three species but o nly lowered the water potential in faba bean. Water deficiency general ly decreased growth, water use, and water potential more at 30/25 degr ees C than at 20/15 degrees C. Stress from high temperature during flo wering of pea decreased all components of yield at maturity, particula rly at nodes that flowered latest. Whole-chain photosynthetic activity in thylakoids of pea, faba bean, and wheat (Triticum aestivum) were e qually sensitive to high temperature, suggesting that Photosystem Il w as the most labile component. The results show that high temperature a ffects photosynthesis, growth, and water relations of grain legumes, a nd sensitivity to the stress differs among species and genotypes.