(KI) (0.2%), at 8–10 days after R 5 plus 8–10 days stage and (2) unsprayed control
(Bhatia et al. 2014) and ~10% of the accessions (six accessions) were selected for the
trait. These promising six accessions were evaluated in the third tier for a number of
above-ground plant traits at soil drying plant stress of 70% RWC at pod filling
stage in the rainout shelter test and below-ground traits by morphologically measuring root system architecture traits, adopting standard lysimetric procedure under
well-watered condition using PVC pipes (Vadez 2014) and WinRhizo Arabidopsis
(Regents, Canada) root image analysis. The approach of lysimetric system for root
studies is a set of long and large PVC tubes, in which plants are grown individually
and have plant spacing and soil volume available for soil exploration close to what is
practiced under field conditions (Vadez et al. 2008, 2013). Root growth is known to
stop its downward movement around anthesis (Robertson et al. 1993), although
maintenance of growth can be found (e.g., Hafner et al. 1993), a trait worthy of
screening, provided water is available at depth. The importance of deep-water
extraction would be more if its timing coincided with the time of most critical
water demand, i.e. reproduction and grain filling. Water extraction after anthesis
with restricted vegetative growth completely contributes to grain development
leading to high water use efficiency (kg grain mm
À1 ).
In breeding populations, the three-tier selection scheme is applicable in advance
generations where approximately half of the seeds from selected F 4 generation single
plants are used for screening lines for delayed senescence trait in F 5 generation
during summer field trial in the first tier. The remaining half of the seeds from those
F 4 single plants, of which lines were selected for delayed senescence trait, serves as a
population for selecting lines for SRM trait during rainy season in the second tier.
Thus, the scheme offers selection for delayed senescence trait followed by SRM trait
in consecutive summer and rainy seasons, respectively, in the same year and
selection can be practiced effectively for both the traits at 10% intensity in each
selection cycle. Selected lines are evaluated for above-ground plant traits in rainout
shelter-induced water stress condition vis-à-vis root architecture traits in the PVC
pipes. Multiplexing drought tolerance related traits, using principal component
analysis for correlation matrix in SAS (Version 3.0), provides a powerful multitrait index which helps in identifying a set of drought-tolerant accessions or elite
breeding lines (Satpute et al. 2020) for developing climate-smart drought resilient
soybean varieties, understanding the role of surrogate traits and discovering unique
drought tolerance related genes/QTLs.
4.3.2 Genetic and Genomic Resources
In crops such as soybean, drought resistance is translated to several related traits
enhancing yield stability rather than that increasing survivability under drought
(Blum 2009; Passioura 2010; Sinclair 2011; Valliyodan et al. 2016). These related
traits are correlated with yield under drought and have no yield penalty under
non-stress conditions. The success of soybean improvement through molecular
approaches under drought stress depends on the discovery of genetic variations for
92
G. K. Satpute et al.
(Bhatia et al. 2014) and ~10% of the accessions (six accessions) were selected for the
trait. These promising six accessions were evaluated in the third tier for a number of
above-ground plant traits at soil drying plant stress of 70% RWC at pod filling
stage in the rainout shelter test and below-ground traits by morphologically measuring root system architecture traits, adopting standard lysimetric procedure under
well-watered condition using PVC pipes (Vadez 2014) and WinRhizo Arabidopsis
(Regents, Canada) root image analysis. The approach of lysimetric system for root
studies is a set of long and large PVC tubes, in which plants are grown individually
and have plant spacing and soil volume available for soil exploration close to what is
practiced under field conditions (Vadez et al. 2008, 2013). Root growth is known to
stop its downward movement around anthesis (Robertson et al. 1993), although
maintenance of growth can be found (e.g., Hafner et al. 1993), a trait worthy of
screening, provided water is available at depth. The importance of deep-water
extraction would be more if its timing coincided with the time of most critical
water demand, i.e. reproduction and grain filling. Water extraction after anthesis
with restricted vegetative growth completely contributes to grain development
leading to high water use efficiency (kg grain mm
À1 ).
In breeding populations, the three-tier selection scheme is applicable in advance
generations where approximately half of the seeds from selected F 4 generation single
plants are used for screening lines for delayed senescence trait in F 5 generation
during summer field trial in the first tier. The remaining half of the seeds from those
F 4 single plants, of which lines were selected for delayed senescence trait, serves as a
population for selecting lines for SRM trait during rainy season in the second tier.
Thus, the scheme offers selection for delayed senescence trait followed by SRM trait
in consecutive summer and rainy seasons, respectively, in the same year and
selection can be practiced effectively for both the traits at 10% intensity in each
selection cycle. Selected lines are evaluated for above-ground plant traits in rainout
shelter-induced water stress condition vis-à-vis root architecture traits in the PVC
pipes. Multiplexing drought tolerance related traits, using principal component
analysis for correlation matrix in SAS (Version 3.0), provides a powerful multitrait index which helps in identifying a set of drought-tolerant accessions or elite
breeding lines (Satpute et al. 2020) for developing climate-smart drought resilient
soybean varieties, understanding the role of surrogate traits and discovering unique
drought tolerance related genes/QTLs.
4.3.2 Genetic and Genomic Resources
In crops such as soybean, drought resistance is translated to several related traits
enhancing yield stability rather than that increasing survivability under drought
(Blum 2009; Passioura 2010; Sinclair 2011; Valliyodan et al. 2016). These related
traits are correlated with yield under drought and have no yield penalty under
non-stress conditions. The success of soybean improvement through molecular
approaches under drought stress depends on the discovery of genetic variations for
92
G. K. Satpute et al.