The combination of multiple plant growth promotion and hydrolytic enzyme producing rhizobacteria and their effect on Jerusalem artichoke growth improvement.

Rhizobacteria are well recognized for their beneficial multifunctions as key promoters of plant development, suppressing pathogens, and improving soil health. In this study, experiments focused on characterizing the plant growth promotion (PGP) and extracellular hydrolase production traits of rhizobacteria, and their impact on Jerusalem artichoke growth. A total of 50 isolates proved capable of either direct PGP or hydrolase-producing traits. Two promising strains (Enterobacter cloacae S81 and Pseudomonas azotoformans C2-114) showed potential on phosphate and potassium solubilization, IAA production, and 1-aminocyclopropane-1-carboxylic acid deaminase activity and hydrolase production. A hydrolase-producing strain (Bacillus subtilis S42) was able to generate cellulase, protease, amylase, ß-glucosidase, and phosphatase. These three selected strains also gave positive results for indirect PGP traits such as siderophore, ammonia, oxalate oxidase, polyamine, exopolysaccharide, biofilm, motility, and tolerance to salinity and drought stress. Colonization was observed using a scanning electron microscope and rhizobacteria appeared at the root surface. Interestingly, inoculation with consortia strains (S42, S81, and C2-114) significantly increased all plant parameters, including height, biomass, root (length, surface, diameter, and volume), and tuber fresh weight. Therefore, we recommend that potential consortia of PGP and hydrolase-producing rhizobacteria be employed as a biofertilizer to improve soil and boost crop productivity.

The effect of salinity on soil chemical characteristics, enzyme activity and bacterial community composition in rice rhizospheres in Northeastern Thailand.

Saline soil is one of the major problems limiting rice productivity in the Northeastern area of Thailand. Thus, the aims of this study were to determine soil physicochemical analysis and soil enzyme activities, and bacterial communities in the rhizosphere of 'RD 6' rice grown in salt-affected rice fields. The Ban Thum sample showed the highest electrical conductivity (EC; greater than 6 dS m-1) and total Na, while the EC in other fields were at non- or slightly saline levels. The principal component analysis revealed that soil chemical characteristics and soil enzymes activities explained 73.4% of total variation. Soil enzyme activities including dehydrogenase and fluorescein diacetate (FDA) hydrolysis, and soil characteristics including organic matter (OM) and organic carbon (OC) were significantly negatively correlated to EC. This indicated that these soil properties were adversely impacted by salts. Interestingly, activities of all hydrolytic enzymes were not affected by soil salinity. Bacteria that were able to colonize the rhizosphere soils were Achromobacter cholinophagum, Rhizobium tarimense, and unculturable bacteria. In this regard, study on the relationship of soil chemical characteristics and soil enzyme activities together with bacterial communities provided promising data for assessing rice field soil quality in the future.