Enhanced Crop Productivity and Sustainability by Using Native Phosphate Solubilizing Rhizobacteria in the Agriculture of Arid Zones

The importance of phosphate solubilizing rhizobacteria (PSB) has been well-document as an option for enhancing sustainable agriculture. As a particular group of plant growth promoting rhizobacteria (PGPR), PSB play an important role in the soil phosphorus cycle, increasing the bioavailability for growth and plant development. This study analyses the plant growth promoting effects of 5 strains (BN0009, BN0013, BN0015, BN0024, and BN0035) out of 180 isolated from Jarava frigida (Phil.) F.Rojas (Poaceae), a native grass from the Andean Atacama desert from North of Chile. The five bacterial isolated (BN strains) were identified as non-pathogenic Erwinia sp. and show a high phosphate solubilization capacity for Ca(PO4) ranging from 608.9 to 781.4 mg/L. Strains IAA production varies between 23.5 and 35.9 mg/L, siderophores, phosphatase (alkaline and acid) production was also observed, but none of the five isolated presented antagonism against plant pathogens Botrytis sp. and Sclerotinia sp. All isolates enhanced seed germination in Lactuca sativa and Solanum lycopersicum (excepting BN009). Additionally, all strains stimulated the early root elongation and seedling development in lettuce and tomato. Pot experiments displayed that BN0015, BN0024, and BN0035 significantly promote plant growth regarding root and leaf area, root and leaf weight, as well as leaf number compared with non-treated plants. In a field experiment with lettuce and two fertilization treatments (50 and 100% of the recommended crop fertilization), BN0024 application improved crop productivity compared to respective control. P content in plants with bacterial inoculations increased significantly compared to control in either fertilization treatment, suggesting an improved nutrient uptake. Also, lettuce with 50% fertilization and inoculation with BN0024 equate productivity with the control 100% fertilization. Finally, we discuss these results in the context of applicability to enhance the agroecosystem productivity in arid and semiarid zones.

Screening and Molecular Identification of Phosphate-Solubilizing Rhizobacteria from Mangrove Ecosystem of the Lombok Island

Phosphate solubilizing rhizobacteria can be used as a component in biofertilizer formulations to increase local and national food production without causing adverse risks to the environment compared to the use of chemical fertilizers. In this regard, screening and identification of phosphate solubilizing bacteria from the rhizosphere of several mangrove species that grow on the coast of Lombok Island has been carried out. The method of isolation used is the Pikovskaya method. Screening and identification activities have obtained 5 isolates of mangrove rhizosphere bacteria (BRM) which are indicated by their ability to form clear zones on Pikovskaya media, namely isolates BRM1 and BRM4 (isolated from the rhizosphere of Avicennia marina), BRM2 and BRM3 (isolated from the rhizosphere of Rhizophora apicullata), BRM5 (isolated from the rhizosphere of R. stylosa). All rhizobacteria isolates were identified as Gram-positive bacteria. Molecular analysis based on the comparison of 16S rRNA gene sequences of isolates with the genome database at GenBank (NCBI) using Mega 10 software, showed that all BRM isolates occupied the same cluster as bacterial species from the Genus Paenibacillus in the dendrogram of the phylogenetic tree, namely Paenibacillus sp. JWLB1 strain, Paenibacillus sp. Strain NO13, P. cineris strain cu1-7, P. favisporus strain CHP14, with genetic distance ranging from 1.3 to 1.4. Many species of the Genus Paenibacillus are currently known to play an important roles as plant growth-promoting bacteria. The BRM isolates obtained in this study can be further developed as a biofertilizer component (inoculant) in saline and dryland agriculture.