Inoculation of Cucumber (Cucumis sativus L.) Seedlings with Salt-Tolerant Plant Growth Promoting Bacteria Improves Nutrient Uptake, Plant Attributes and Physiological Profiles

Abstract

Salinity is one of the major abiotic stresses that cause retarded plant growth and crop production. It has been reported that harmful effects of salinity could be managed by application of salt-tolerant plant growth-promoting (PGP) bacteria. In this study, eight salt-tolerant bacteria were selected from an array of 150 cultures, based on salt-tolerant properties. All the isolates were identified based on 16S rRNA gene sequencing and subjected to different PGP properties. The results showed the production of indole acetic acid (28.83–62.35 µg/ml), ammonia (35.49–67.48 µg/ml), phosphate solubilization (1.45–3.42 µg/ml), and siderophores. Further, these isolates were evaluated in pot studies on their response in Cucumis sativus plants against 100 mM salinity stress and without salinity stress (normal water) along with uninoculated controls. The results revealed that bacterized seeds had enhanced plant growth parameters and there was a corresponding increase in biomass in both conditions compared to control plants. The maximum enhancement in root and shoot length under normal condition was 54.6% (SBR-4) and 69.3% (SBS-19), whereas under saline conditions it was 42.3% (SBR-5) and 100.4% (SBS-18), respectively. Further, the inoculated seedlings maximum enhanced chlorophyll a (SBS-3; 50.6% and SBR-4; 45.4%) and chlorophyll b (SBR-1; 83.6% and SBS-3; 209.6%), proline (SBS-18; 62.0% and SBR-1; 32.8%), total phenol (SBR-1; 48.2% and SBR-5; 67.8%), ascorbic acid (SBS-2; 118.6% and SBR-1; 22.4%), and shoot and root N and P contents (twofold to threefold) under both normal and saline conditions. Among the eight isolates, isolates SBS-19, SRB-5, SBS-18, and SBR-4 improved plant growth and other parameters under both conditions in C. sativus plants. Therefore, it is suggested that these salt-tolerant PGP bacteria may be used for cultivation of C. sativus in salinized agricultural lands.