Identification of drought tolerance in early-maturing indeterminate soybeans (Glycine max (L.) Merr.)

Abstract

Drought escape through earliness is a potential strategy for the expansion of soybean (Glycine max (L.) Merr.) production into marginal rainfall areas that has not been fully evaluated. In this study, early-maturing (Maturity Groups II to IV), indeterminate inbred lines of soybeans were developed from six single cross populations and evaluated under naturally occurring terminal drought stress at a latitude normally associated with maturity adaptation corresponding to Groups V to VII. Parallel evaluation under a high yield irrigation regime provided the basis for evaluation of genotypic response to moisture stress. All lines were early enough to exhibit drought escape, but there was an additional response in some genotypes. While all genotypes showed premature senescence under drought stress some genotypes, in the WilliamsxCalland population, continued growth for significantly longer than the parents or the population average under the terminal drought stress. A stress index for maturity was devised to describe the degree of premature senescence, and this index was shown to be a heritable trait not correlated with maturity per se. It is concluded that these lines represent a previously unreported source of tolerance to drought stress and, when used in conjunction with early maturity drought escape, they provide an additional trait for improving soybean tolerance to moisture stress.