Evaluation of Plant Growth-Promoting Rhizobacteria in Bahrain and their Effects on Abiotically Stressed Plants.

Abstract

Abstract : To the best of our knowledge, this is the first study of its kind performed in Bahrain, investigating native and exotic plant growth-promoting rhizobacteria for plant growth promotion abilities. Water stress tolerance represented by different osmotic pressures (-0.15, -0.49, -0.73, -1.2 MPa) was assessed for each of the 13 morphologically distinct isolates found. The isolates obtained varied slightly in their colony characteristics (color, morphology, texture), Gram's staining and catalase testing. Screening for positive ammonia production, phosphate solubilization and salinity tolerance was then performed to assess the isolates' plant growth promotion abilities. Among the 13 isolates obtained, Isolate J demonstrated the highest PGPR potential reflected in the highest PSI (6.80±0.66), high ammonia production and salinity tolerance (up to 3 M) followed by isolate B (PSI of (6.44±0.47), moderate ammonia production and salinity tolerance up to 3M) and isolate CC (PSI of 5.66 0.38 and moderate results for ammonia production and salinity tolerance up to 3M). All of the isolates were then used to prime maize seeds placed under the same varying water stresses established by PEG6000. Improvements in the germination, morphological parameters, photosynthetic pigments, and total soluble protein concentration were observed for plants raised from isolate-primed maize seeds compared to non-primed counterparts. Germination analysis highlighted the potential of isolates E, C, J respectively through the observed improved germination index and mean germination time although not significant. In the green-house experimentation, and under drought stress, the best and most significant plant morphological parameter supporting isolates found was PF followed by CC and PF2. Improvements in the growth parameters due to PGPRs were attributed to phytohormone production. Photosynthetic pigment concentration was highest for maize primed with isolate PF highlighting its potential in supporting maize growth during increasing water stress levels. The total soluble protein concentration was superior under water stress for isolate F primed maize. This study documented several observed benefits of PGPRs isolated from plants growing in Bahrain. Consequently, these isolates can be used by farmers as biofertilizers in arid and semi-arid regions with the intention of alleviating the effects of water stress. However, to achieve that, additional identification and testing of the isolates which showed the best potential is required.