Abstract
Limited information is available that seed biopriming with plant growth-promoting Enterobacter spp. play a prominent role to enhance vegetative growth of plants. Contrary to Enterobacter cloacae, Enterobacter hormaechei is a less-studied counterpart despite its vast potential in plant growth-promotion mainly through the inorganic phosphorus (P) and potassium (K) solubilization abilities. To this end, 18 locally isolated bacterial pure cultures were screened and three strains showed high P- and K-solubilizing capabilities. Light microscopy, biochemical tests and 16S rRNA gene sequencing revealed that strains 15a1 and 40a were closely related to Enterobacter hormaechei while strain 38 was closely related to Enterobacter cloacae (Accession number: MN294583; MN294585; MN294584). All Enterobacter spp. shared common plant growth-promoting traits, namely nitrogen (N2) fixation, indole-3-acetic acid production and siderophore production. The strains 38 and 40a were able to produce gibberellic acid, while only strain 38 was able to secrete exopolysaccharide on agar. Under in vitro germination assay of okra (Abelmoschus esculentus) seeds, Enterobacter spp. significantly improved overall germination parameters and vigor index (19.6%) of seedlings. The efficacy of root colonization of Enterobacter spp. on the pre-treated seedling root tips was confirmed using Scanning Electron Microscopy (SEM). The pot experiment of bioprimed seeds of okra seedling showed significant improvement of the plant growth (> 28%) which corresponded to the increase of P and K uptakes (> 89%) as compared to the uninoculated control plants. The leaf surface area and the SPAD chlorophyll index of bioprimed plants were increased by up to 29% and 9% respectively. This report revealed that the under-explored species of P- and K-solubilizing Enterobacter hormaechei sp. with multiple plant beneficial traits presents a great potential sustainable approach for enhancement of soil fertility and P and K uptakes of plants.
Highlights
The application of sizable inputs of synthetic chemical fertilizer such as those containing inorganic phosphorus (P) and potassium (K) has long been employed in conventional agriculture practices
All bacterial cultures were retrieved from glycerol stocks of our previous bacterial isolation works from several sources, such as from agricultural soil, oil palm empty fruit bunch (OPEFB) and chicken manure co-composting process
To the best of our knowledge, this is the first report to simultaneously focus on both P and K solubilization by Enterobacter hormaechei sp., highlight the plant beneficial traits and apply to pot experiment to measure the plant nutrient uptake on okra seedlings using seed biopriming technique
Summary
The application of sizable inputs of synthetic chemical fertilizer such as those containing inorganic phosphorus (P) and potassium (K) has long been employed in conventional agriculture practices. There have been several reported cases of groundwater and waterways contamination due to nutrient leaching of P, K and Nitrogen (N), especially in the areas which received high rainfalls and near streams or drains [2,3,4,5]. Such environmental issues have been extensively discussed as to mitigate the loss of nutrients added to the soil and the risk of eutrophication occurring in the adjacent water bodies. The exploration of alternative strategies that can promote competitive crop growth while maintaining environmental safety is a timely measure
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