Evaluation of PGPR in relation with drought resistance of squash was studied in vitro and pot
experiments. The activities of Azotobacter chroococcum ML1, Bacillus circulans ML2, Bacillus megaterium
ML3 and Pseudomonas fluorescence ML4 as osmoprotective agents were estimated in vitro. All tested
strains produced indole acetic acid (IAA) at range of (17.73-23.65 mg/ml), gibberellic acid (GA3) (9.38-
19.16 mg/ml), proline (4.69-15.06 g/ml), exopolysaccharides (21-467 g/ml), salicylic acid (25.98-28.35
mg/ml) and 1-aminocyclopropane-1-carboxylate (ACC-deaminase) (9.6-48.1 ml mole/ml/h). Furthermore,
values of nitrogenase activity were 35.0 and 15.0 nmol C2H4/l/h due to using A. chroococcum ML1 and Ps.
fluorescence ML4, respectively. The ability of the tested PGPR strains to enhance growth and alleviation
drought stress on squash plants compared to humic acid (HA) under different irrigation levels were tested
through a pot experiment. Results revealed that inoculation of squash with PGPR enhanced enzymes
activities in its rhizosphere. In addition, PGPR inoculants caused significant increases in osmoregulators
compounds of squash leaves and their maximum values were recorded at vegetative stage. Results also
emphasized that IAA and GA3 in squash leaves were markedly increased under drought stress when plants
were inoculated with PGPR strains. Whereas, abscisic acid decreased under the same conditions. Alongside,
photosynthetic pigments and oxidative enzymes were strongly affected under PGPR inoculation compared
to HA or chemical fertilizers applications when squash were irrigated with 75 or 50% of field capacity. Also,
growth characteristics and yield under PGPR treatments were significantly higher than those resulted from
additions of HA and chemical fertilizers. |
