PHYSIOLOGICAL AND AGRONOMIC RESPONSES OF DIVERS PUBESCENT SOYBEAN ISOLINES TO DROUGHT STRESS (NEBRASKA)

Near-isogenic lines of Clark and Harosoy soybean {Glycine max (L.) Merr.} cultivars with dense and normal pubescence density characteristics were observed during 1980 and 1981 at a site in Eastern Nebraska under dryland conditions. Sparse, normal, and dense pubescent isolines of the Harosoy cultivar were grown in Western Nebraska during 1982 under several supplemental irrigation levels. Soil water content was monitored each year and a water budget was calculated from the data. Growth measurements consisting of aerial phytomass dry weight (W), leaflet dry weight (LW), leaf area index (LAI), and plant height were recorded every year at each location. In two of the years, intensive plant sampling in 200 mm vertical segments and at each node was conducted. Traditional growth analysis techniques were applied to the plant sampling data in order to quantify pubescence density differences. Water relations of the various isolines were observed in 1982. Dense pubescence in the Clark cultivar effected no significant change in nearly all of the variables measured. Dense pubescence in the Harosoy cultivar at the site in Eastern Nebraska increased W, LW, LAI, plant height and seed growth. Photosynthesis per unit ground area was also increased while photosynthesis per unit leaf area, as determined by growth analysis techniques, was unaffected by the dense pubescent Harosoy isoline. Water use efficiency per unit leaf area and per unit ground area was increased in the Harosoy dense pubescent isoline. When grown under fully irrigated conditions in Western Nebraska, dense pubescence in the Harosoy decreased W, LW, LAI and plant height. Photosynthesis per unit ground area was also decreased. Under dryland conditions when stress was eliminated at midseason, the Harosoy dense pubescent isoline exhibited a growth and water use response similar to that observed in Eastern Nebraska. Under severe stress, dense pubescence in the Harosoy decreased stomatal resistance which resulted in increased transpirational cooling and decreased canopy temperature