Differential wilting among soybean genotypes in response to water deficit

Genotypic differences for canopy wilting have been reported for soybean [Glycine max (L.) Merr.], but no wilting data have been published, and mechanisms for differences remain unresolved. In field studies in 2002 and 2003, differences for wilting among 19 genotypes were consistent across years. Plant introductions (PI 416937 and PI 471938) were among the slowest wilting genotypes, and breeding lines (93705-34 and 93705-95) were among the fastest wilting. Row spacing (18 vs. 80 cm wide) did not affect wilting, indicating that lateral rooting did not contribute to genotypic differences. In a separate field study, volumetric soil water content at 15- and 50-cm depths was generally greater for slow-wilting PI 416937 than for fast-wilting 93705-95. Wilting for both genotypes responded similarly to soil water content ([r.sup.2] = 0.63-0.74). In a growth chamber study, transpiration declined similarly for fast- and slow-wilting genotypes in response to soil water deficit. Wilting response to soil water was the same for slow-wilting P1416937 and fast-wilting genotypes 93705-34 and A5959. Slow-wilting 93705-36 began wilting at a lower soil water content than did PI416937, 93705-34, and A5959, indicating that more than one mechanism may be responsible for slow wilting.