Drought stress adversely affects plant health and productivity. Recently, drought-resistant bacterial isolates
are used to combat drought resistance in crops. In this in vitro study, 20 bacterial isolates were isolated
from harsh soil; their drought tolerance was evaluated using four concentrations of polyethylene
glycol (PEG) 6000. The two most efficient isolates (DS4 and DS9) were selected and identified using
16S rRNA genetic sequencing. They were registered in the NCBI database and deposited under accession
numbers MW916285 and MW916307 for Bacillus cereus (DS4) and Bacillus albus (DS9), respectively.
These isolates were screened for plant growth-promoting properties compared to non-stressed conditions.
Biochemical parameters; Proline, salicylic acid, gibberellic acid (GA), indole acetic acid (IAA),
antioxidant activity, and antioxidant enzymes were measured under the same conditions,
and in vitro seed germination was tested under stress conditions and inoculation with selected isolates.
The results showed that under the harsh conditions of PEG6000, DS4 produced the highest amount of
IAA of 1.61 mg/ml, followed by DS9 with 0.9 mg/ml. The highest amount of GA (49.95 mg/ml) was produced
by DS9. On the other hand, the highest amount of siderophore was produced from DS4 isolate followed by
DS9. Additionally, DS4 isolate recorded the highest exopolysaccharide (EPS) content of 3.4 mg/ml under
PEG (-1.2 MPa) followed by DS9. The antioxidant activity increased in PEG concentrations depending
manner, and the activity of the antioxidant enzymes increased, as catalase (CAT) recorded the highest
activity in DS4 with an amount of 1.095 mg/ml. additionally, an increase in biofilm formation was
observed under drought conditions. The isolated mixture protected the plant from the harmful effects
of drought and showed an increase in the measured variables. Under unstressed conditions, the highest
rates of emulsification index (EI 24%) were obtained for DS4 and DS9, at 14.92 and 11.54, respectively,
and decreased under stress. The highest values of germination, total seedling length, and vigor index
were obtained upon inoculation with the combination of two strains, and were 100%, 4.10 cm, and
410, respectively. Therefore, two strains combination is an effective vaccine capable of developing and
improving drought tolerance in dryland plants. |
