Abstract
A diverse group of rhizobacteria persists in the rhizospheric soil, on the surface of roots, or in association with rice plants. These bacteria colonize plant root systems, enhance plant growth and crop yield. Indigenous rhizobacteria are known to promote soil health, grain production quality and serve as sustainable bioinoculant. The present study was aimed to isolate, identify and characterize indigenous plant growth promoting (PGP) diazotrophic bacteria associated with the rhizosphere of rice fields from different areas of Jammu and Kashmir, India. A total of 15 bacteria were isolated and evaluated for various PGP traits, antagonistic activity against phytopathogens, production of hydrolytic enzymes and biofilm formation under in-vitro conditions. The majority of the isolated bacteria were Gram-negative. Out of 15 bacterial isolates, nine isolates produced IAA (12.24 ± 2.86 to 250.3 ± 1.15 μg/ml), 6 isolates exhibited phosphate solubilization activity (36.69 ± 1.63 to 312.4 ± 1.15 μg/ml), 7 isolates exhibited rock phosphate solubilization while 5 isolates solubilized zinc (10–18 mm), 7 isolates showed siderophore production, 8 isolates exhibited HCN production, 6 isolates exhibited aminocyclopropane-1-carboxylate (ACC) deaminase activity, 13 isolates exhibited cellulase activity, nine isolates exhibited amylase and lipase activity and six isolates exhibited chitinase activity. In addition, 5 isolates showed amplification with the nifH gene and showed a significant amount of nitrogenase activity in a range of 0.127–4.39 μmol C2H4/mg protein/h. Five isolates viz., IHK-1, IHK-3, IHK-13, IHK-15 and IHK-25 exhibited most PGP attributes and successfully limited the mycelial growth of Rhizoctonia solani and Fusarium oxysporum in-vitro. All the five bacterial isolates were identified based on morphological, biochemical and 16S rDNA gene sequencing study, as Stenotrophomonas maltophilia, Enterobacter sp., Bacillus sp., Ochrobactrum haematophilum and Pseudomonas aeruginosa. Rice plants developed from seeds inoculated with these PGP strains individually had considerably higher germination percentage, seed vigor index and total dry biomass when compared to control. These findings strongly imply that the PGP diazotrophic bacteria identified in this work could be employed as plant growth stimulators in rice.
Highlights
Rice (Oryza sativa L.) is the world’s most significant food crop, providing a staple diet for almost 3 billion people, or roughly half of the world population
The present study aims to isolate, characterize and identify efficient PGP diazotrophic bacteria from rice rhizosphere
The isolates were labeled as IHK-1, IHK-2, IHK-3, IHK-4, IHK-5, IHK-6, IHK-7, IHK-8, IHK-9, IHK-10, IHK-11, IHK-12, IHK-13, IHK-15 and IHK-25 (Table 1)
Summary
Rice (Oryza sativa L.) is the world’s most significant food crop, providing a staple diet for almost 3 billion people, or roughly half of the world population. With the present trend of rice consumption, by 2025, it would possibly be 4.6 billion people, and to meet the demand, there must be a 20% rise in its production. Dinitrogen gas that occupies 80% of the atmosphere is not readily available to plants. The plant-available forms of nitrogen are ammonium and nitrate in the soil. Nitrogen is an important limiting factor on rice yields, and an increase in rice productivity will inevitably involve a higher demand for nitrogen-containing inorganic fertilizers [2]. Farmers worldwide use excess chemical fertilizers (especially nitrogen-containing chemical fertilizers) and pesticides to boost rice production. World nitrogen demand increased from 105.148 to 111.591 thousand tons during 2016–2022 as per FAO 2022 report (World fertilizer trends and outlook to 2022 FAO-UN)
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