Abstract
Soybean (Glycine max (L.) Merr) is the most important commercial grain legume
and oil seed crop which represent the most important plant source of vegetable oil
and protein in the world. A set of experiments were conducted to analyze the
genetic diversity, identify the drought stress tolerant soybean genotypes and
assess the physiological and biochemical responses of selected soybean genotypes
against drought stress. Finally, molecular characterization of selected soybean
genotypes with GmLEA DII and GmDREB2 genes were carried out and their field
performances were also assessed. Genetic diversity analysis of fifty (50) soybean
genotypes were performed using twenty simple sequence repeat (SSR) markers
and grouped into four (4) major clusters. The most diverse genotypes were SBG-1,
PM-78-6-3-13, BS-3 and AGS-31, which suggest that the SSR markers are very
efficient for genetic diversity analysis and it may be utilized in the future breeding
program. The fifty soybean genotypes were screened in a glasshouse for drought
stress tolerance and categorized into four groups on the basis of yield reduction
under drought stress condition. Five genotypes YESOY-4, PK-416, Shohag, SBM-09
and Binasoybean-6 were categorized as tolerant (<35% yield reduction), fourteen
genotypes were categorized as moderately tolerant (35%-60% yield reduction),
twenty five genotypes were categorized as moderately susceptible (61%-80% yield
reduction) and rest six genotypes were categorized as susceptible (>80% yield
reduction). Different physio-biochemical properties of selected soybean genotypes
were analyzed under drought stress conditions and the number of leaves, leaf
area, shoot dry weight, root dry weight, root: shoot ratio, chlorophyll content,
relative water content, proline content, MDA content were significantly affected by
the drought stress. The tolerant genotypes SBM-09, PK-416, YESOY-4 and Shohag
performed better under drought stress condition. To confirm the drought tolerance
of selected soybean genotypes at molecular level, the amplification and sequencing
of GmLEA DII and GmDREB2 genes were performed. The selected soybean
genotypes SBM-09, PK-416 and YESOY-4 were amplified with GmLEA DII and
GmDREB2 genes at the fragments of 700 bp and 1000 bp, respectively but absent in
susceptible genotypes. The phylogenetic analysis of GmDREB2 gene sequence
showed very high similarity to the DREB2 nucleotide sequence of other 16 tested
materials obtained from NCBI. Finally, the field performance of selected soybean
genotypes was evaluated and the drought tolerant genotypes SBM-09, PK-416 and
YESOY-4 performed better in seed yield under field condition. From the result of
the series of experiment, it could be concluded that the genotypes SBM-09, PK-416
and YESOY-4 are drought stress tolerant genotypes with better field performance.
Further research of drought tolerance in soybean may help the researchers for
better understanding the mechanisms of drought tolerance which may be helpful
for quality oil seed production.