Developing a high-throughput method to screen soybean germplasm for hypoxia tolerance in a hydroponic system

Current field screening methods for soybean [Glycine max L. (Merr.)] flood tolerance are time- and labor-intensive. The purpose of this research was to develop a method of screening soybean in a low-O-2 and CO2-rich treatment using hydroponic culture in a greenhouse setting. Growth media, solution, and plant response were evaluated at various days after termination of gas treatment (DAT). Initially, a flood-susceptible genotype at early vegetative stage was subjected to a hypoxic treatment, displacing O-2 by bubbling CO2 into the system for 5 d. The methodology was tested with 33 soybean genotypes, and normalized difference vegetation index (NDVI), soil-plant analysis development (SPAD), and foliar damage score (FDS) were measured. Then, the reaction of 17 genotypes was compared between hydroponic and field conditions. Expanded clay pebbles were identified as the best substrate for the screening method, as germination rate was not different from control. Gas treatment was shown to affect the level of dissolved O-2 in solution and to elicit phenotypic responses, of which NDVI was the most effective for differentiating germplasm, with an average of 0.29 and 0.69 for the CO2 treatment and ambient air control, respectively (p < .0001). Also, repeatability of NDVI response across genotypes was 94.5%. Finally, preliminary field validation supported the ability of this new hydroponic methodology to separate susceptible and tolerant genotypes under hypoxia and water-logged conditions.