Genotypic variation in leaf water potential of field-grown soybeans (Glycme max L. Merr.) and its association with dryland yield

Abstract

Maintenance of leaf water potential (Ψ_L) during periods of water stress may constitute an important drought-avoiding response. The identification of genotypic variation for this characteristic is, however, made difficult by the fact that comparative values for Ψ_L must be measured within an environment that changes over the period of time required for a number of measurements. In the course of two field experiments, a number of cultivars were allowed to experience water deficit during early pod fill. During this period, Ψ_L was measured for each cultivar on a number of days. The genotypic Ψ_L response was expressed on a daily basis as a residual difference from a reference value which was calculated from trends in Ψ_L observed during each daily measurement period. An average value of this residual over the entire stress period was then determined for each cultivar. The separation of variation in Ψ_L, observed over the stress period, into genotypic and non-genotypic components is discussed and the significance of the genotypic variation is examined. Significant variation in Ψ_L residuals exists among soybean cultivars under the conditions of this experiment. Such variation is not large, however, with a maximum range of about 0,075 MPa from reference values. Much of this variation was associated with cultivar maturity as earlier varieties gave lower Ψ_L values than did later ones, due possibly to their more advanced growth stage at the time of measurement. Some variation within maturity group was also apparent. Evidence of an association between Ψ_L residual and dryland yield (R ² = 0,47) was apparent among the later cultivars in these experiments.