Identifying additional variation in soybean water-use phenotypes-screening of exotic germplasm

Twenty-three soybean genotypes were screened in greenhouse studies for vegetative-phase variation in three potential drought resistance traits: Water use efficiency (WUE), response of whole plant transpiration defined as normalized transpiration ratio (NTR) to soil water deficits, and epidermal conductance (ge). A computer-automated lysimeter was used to impose distinct levels of water stress on potted soybean plants in the first experiment; significant variation was found between genotypes for both WUE and response of NTR to soil water content. In a second experiment, significant variation was found between soybean genotypes under well-watered conditions for ge measured by leaf gas exchange, and a strong negative correlation was found between WUE (measured in the first experiment) and ge. Results from the two experiments demonstrated that genetic variability exists in the twenty-three genotypes for all three traits examined.