Basis of Slow‐Wilting Phenotype in Soybean PI 471938

Abstract

To increase soybean [Glycine max (L.) Merr.] productivity, it will be necessary to improve yields in water‐deficit regions. Genotype PI 471938, which exhibits a slow‐wilting phenotype under water‐deficit conditions, has proven to be a good genetic resource in developing drought‐resistant progeny even though the physiological basis for this advantage is not known. The objective of this study was to investigate the involvement of four water‐saving, physiological mechanisms as candidates contributing to drought tolerance of PI 471938. (i) In response to soil drying, the soil water content at which leaf gas exchange began to decrease in PI 471938 was not different from the other tested genotypes. (ii) Measurement of leaf photosynthetic capacity failed to show that PI 471938 had a high capacity allowing high CO2 assimilations even with partial stomata closure. (iii) Plant Introduction 471938 failed to exhibit a limited transpiration rate with increasing vapor pressure deficit (VPD), which would have allowed this genotype to conserve soil water during midday periods of high VPD. (iv) Finally, PI 471938 did not show an ability to maintain high leaf water potential (ΨLeaf) when VPD was increasing. In fact, there was a dramatic decrease in ΨLeaf with increasing VPD, which usually implies a decrease in leaf turgor pressure. Overall this study resulted in the rejection of four major hypotheses to explain the slow‐wilting phenotype exhibited by PI 471938, and the basis for its drought resistance remains unknown.

Expression of Drought‐Tolerant N2 Fixation in Heterogeneous Inbred Families derived from PI471938 and Hutcheson Soybean

“…In any case, within experiments, there was little indication of genetic variation in the FTSW transpiration threshold for NTR (Table 2). This is consistent with previous reports of little genetic variation in the transpiration threshold among soybean lines (Devi and Sinclair, 2013; Sadok et al, 2012). However, an interesting exception to the small level of variation among genotypes was the very high NTR threshold (0.51) found for ‘N05‐UGA‐889’.…”

Identification of Shoot Traits Related to Drought Tolerance in Common Bean Seedlings

“…In soybeans, slow wilting has been identified as a beneficial trait under drought. This condition involves a restricted transpiration rate under increasing vapor pressure deficit levels (Fletcher et al, 2007;Sadok et al, 2012). This phenotype was initially identified in soybean PIs (PI471938 and PI416937) (Hufstetler et al, 2007;King et al, 2009;Sloane et al, 1990).…”

“…In legumes, different shoots traits are used to select drought-tolerant genotypes. For instance, maintenance of green stem was shown to be an important criterion for seedling stage drought tolerance in cowpea (Muchero et al, 2008), whereas a slow wilting trait is associated with drought tolerance in soybean (Sadok et al, 2012). In cowpea, the ''wooden box'' seedling screening method was developed for phenotyping cowpea for drought tolerance (Singh et al, 1999).…”

Genome‐wide Association Analysis for Drought Tolerance and Associated Traits in Common Bean

“…Slow wilting is a water conservation trait that permits transpiration rates to continue increasing despite atmospheric vapor pressure deficits of ~2.1 kPa or 2.00 † Wilting was scored on a scale of 0 to 5, with 0 being no sign of wilting and 5 being completely wilted (Mukeshimana et al, 2014b). ‡ DAP, d after planting higher (Sadok et al, 2012). Since limited work has been conducted to survey wilting across the common bean germplasm, a comparative mapping study between the two species would provide the opportunity to exploit synteny (McClean et al, 2010) among the two genomes and to further exploit the present sizeable disparity between genomic resources in soybean and common bean.…”