Phenotypic Evaluation
To determine optimum PEG 6000 concentration for drought stress
treatment, all the four soybean genotypes viz., DTP, DSP, DTL & DSL
were subjected to different concentrations of PEG treatments viz.,
10%,15% & 20% (w/v) in three biological replicates at germination
stage, and the results revealed that 15% PEG is the optimum
concentration for the evaluation of drought stress tolerance(Fig 1A). In the present study, GR and RL were used to evaluate
drought tolerance of DTP, DSP, DTL & DSL genotypes under 15 % PEG and
control conditions (Fig 1B & C) . The results revealed that all
four genotypes showed normal germination under control conditions
(Fig 1B ); however, under stress conditions tolerant genotypes
viz., DTP & DTL showed normal germination (GR=100%) at the
4th day of stress treatment, whereas sensitive
genotypes (DSP & DSL) revealed only 20% GR at the same time interval(Fig. 1C). Under control conditions, all genotypes showed
normal RL, whereas the RL of all genotypes were reduced under stress
relative to control condition (Fig. 1D ). Furthermore, the RL of
sensitive genotypes (DSP & DSL) were significantly
(P<0.01 ) reduced under stress compared to tolerant
genotypes viz., DTP & DTS (Fig. 1D) , and transgression effect
has been identified in DTL for RL. Hence, our results revealed
that DTP and DTL are tolerant to drought stress, whereas DSP and DSL are
drought-sensitive, and suggested that these contrasting genotypes can be
effectively used for the analysis of drought tolerance.