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

Low-cost, phenotype-based techniques are needed to help crop breeders inter pret genotype X environment interactions. Our objective was to determine ho w drought stress imposed on soybean [Glycine max (L.) Merr.] at various gro wth stages affected selected plant characteristics. Determinate (Spot) and indeterminate (Weber) soybean cultivars were grown under greenhouse conditi ons and subjected to two levels of drought stress (30 and 50% plant-availab le water) during vegetative (V4-R1), flowering (R1-R3), pod lengthening (R3 -R5), or seed-filling (R5) stages. Mean internode length was the most droug ht 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 vegetativ e stress. The number of pods per vegetative dry matter unit was significant ly affected by stress during pod lengthening. Early stress during seed fill reduced the number of seeds per pod, whereas late stress (after the aborti on limit stage) decreased seed weight. These results suggest that precise p eriods of drought stress can be determined by measuring a posteriori severa l morphological factors and yield components of determinate and indetermina te soybean genotypes at physiological maturity.