Identification of soybean plant characteristics that indicate the timing of drought stress

Low-cost, phenotype-based techniques are needed to help crop breeders interpret genotype X environment interactions. Our objective was to determine how drought stress imposed on soybean [Glycine max (L.) Merr.] at various growth stages affected selected plant characteristics. Determinate (Spot) and indeterminate (Weber) soybean cultivars were grown under greenhouse conditions and subjected to two levels of drought stress (30 and 50% plant-available water) during vegetative (V4-R1), flowering (R1-R3), pod lengthening (R3-R5), or seed-filling (R5) stages. Mean internode length was the most drought sensitive factor during the vegetative and flowering stages. Significant height differences for the determinate cultivar accurately differentiated between stress periods, with shorter plants being associated with vegetative stress. The number of pods per vegetative dry matter unit was significantly affected by stress during pod lengthening. Early stress during seed fill reduced the number of seeds per pod, whereas late stress (after the abortion limit stage) decreased seed weight. These results suggest that precise periods of drought stress can be determined by measuring a posteriori several morphological factors and yield components of determinate and indeterminate soybean genotypes at physiological maturity.