ABSTRACT
Rhizobacteria have been shown to confer beneficial effects on plants and have been shown to promote plant health in stressful environments. Studies have shown the direct and indirect influence plant growth-promoting bacteria exert on plant growth and performance. This study was carried out to assess the effect of sodium chloride on plant growth-promoting capacities of selected rhizobacteria with Amaranthus hybridus.
Heavy metal-contaminated soil was obtained from scrap yards in Benin City while seeds of Amaranthus hybridus were obtained from the Nigeria Horticultural Research Institute (NIHORI), Ibadan, Nigeria. Physicochemical properties of the soil were evaluated. Rhizobacteria from the soil were isolated and identified using standard microbiological procedure. Rhizobacteria were screened for plant growth promotion and inoculated into soil sample containing A. hybridus. A. hybridus was then analysed for morphological and physiological parameters such as plant length, diameter, chlorophyll content, number of nodes, leaf length and diameter and total number of leaves.
Heterotrophic bacterial count of soil samples ranged from 2.95±0.15x104 - 6.35±0.25x104cfu/g. Bacteria isolated from contaminated soil include Corynebacterium sp., Shigella sp, Aeromonas sp, Streptococcus sp, Providencia spandArthrobacter sp. Whole plant weight of A. hybridus inoculated with PGPR and different saline solution ranged between 0.19 – 1.74g with the highest value for weight recorded in A. hybridus treated with 5% NaCl solution inoculated with Arthrobacter sp. Shoot weight of A. hybridus inoculated with PGPRs and treated with saline solution ranged between 0.02 – 0.15g. Chlorophyll content of A. hybridus inoculated with PGPR and treated with saline solution ranged from 5.00 – 11.20g while height of A. hybridus grown on saline soil and inoculated with PGPRs ranged from 7.83 – 15g. Average number of leaves of A. hybridus inoculated with PGPRs ranged from 7.33 – 11.33g. Number of A. hybridus sprout/0.075g of seed ranged from 15.67 – 25.67, shoot height of A. hybridus ranged from 6.33 – 18.07cm and leaf area of A. hybridusranged from 4.18 – 11.55cm2. PGPRs helped improve survival levels of A. hybridus in the various saline soils. Although result variations were observed in the parameters investigated, it was generally observed that most parameters recorded higher values for A. hybridus grown in saline soils inoculated with rhizobacteria. The most effective PGPR was rhizobacterium 2 (Aeromonas sp) as it was observed to have the best ameliorative role of assisting the plant is surviving in the saline contaminated soils. This research proved the importance of rhizobacteria in ameliorating soil salinity stress on the growth of plant, hence advanced studies should be conducted on utilizing their capabilities in enhancing plant survival in saline soils.
