Drought Tolerance in Cultivated and "Wild" Soybean Species.

Soybean farmers in the Southeast do not irrigate because of cost. Droughts can be devastating. Improvements in soybean drought tolerance stem from utilizing more genetically diverse germplasm. Drought tolerance was observed in the exotic soybean line PI_416937 nearly 20 years ago. The mechanism attributed to drought tolerance in this line is early stomata closure, which may occur in response to high atmospheric vapor pressure deficit (VPD) or to soil drying.  Early stomata closure allows temporary avoidance or delay of the progression into severe drought stress and conservation of soil water reserves. Many other soybean genotypes have been tested for early stomata closure, and some genetic variation has been reported. The undomesticated soybean species, Glycine soja, is more diverse than cultivated soybean and may provide additional genetic resources for drought tolerance. Accessions have been collected from dry regions of China. The focus of this research was to characterize G. soja (PI_468917) water use efficiency and early stomata closure in response to drought as compared to soybean (cultivar Hutcheson). Plants were grown in pots sealed with a plastic cover to eliminate evaporation. Water use and stomata closure were measured by weighing plants in water-replete and water-deficit soil. Daily weight loss was used to estimate transpiration. Glycine soja used more water per unit dry mass produced under control conditions, and therefore, had lower water use efficiency than soybean. Glycine soja closed stomata sooner, however, when exposed to drying conditions. These results suggest that G. soja may possess a favorable physiological trait that could be used for improving drought tolerance of modern soybean cultivars.