Biofertilizers with beneficial rhizobacteria improved plant growth and yield in chili (Capsicum annuum L.).

Chemical fertilizers can supply essential nutrients to crops increasing their yield, however, they can also cause serious environmental problems. Biofertilizer has received more and more attention because of its environmentally friendly and pollution-free characteristics. Haloxylon ammodendron, a desert succulent shrub, has become an important plant species for vegetation restoration in several deserts in China because of its strong drought tolerance. Its extensive root systems and unique rhizosphere bacterial community aid H. ammodendron adapt to this extreme environment. In this study, Bacillus sp. WM13-24 and Pseudomonas sp. M30-35 isolated from the rhizosphere of H. ammodendron in our previous study and Bacillus amyloliquefaciens GB03 and Sinorhizobium meliloti ACCC17578 as well-studied beneficial strains were used to prepare two types of biofertilizer, WM13-24 biofertilizer containing Bacillus sp. WM13-24 and integrated biofertilizer containing all the four strains. Results presented here showed that WM13-24 biofertilizer and the integrated biofertilizer improved chili plant growth, fruit yield and quality and the rhizosphere soil nitrogen content, enzyme activities, and the quantity and biodiversity of viable bacteria. Compared to the control, WM13-24 biofertilizer and a commercial biofertilizer, the integrated biofertilizer performed best in significantly increasing plant height, stem diameter, leaf length and width, chlorophyll content, fruit yield, soluble sugar content, ascorbic acid content, organic acid content, soil urease activity, catalase activity and the quantity and biodiversity of viable bacteria. This study provided a theoretical and practical basis for large scale development of integrated biofertilizers using beneficial rhizobacterial strains from the desert plant rhizosphere.

Induced Salt Tolerance of Perennial Ryegrass by a Novel Bacterium Strain from the Rhizosphere of a Desert Shrub Haloxylon ammodendron.

Drought and soil salinity reduce agricultural output worldwide. Plant-growth-promoting rhizobacteria (PGPR) can enhance plant growth and augment plant tolerance to biotic and abiotic stresses. Haloxylon ammodendron, a C4 perennial succulent xerohalophyte shrub with excellent drought and salt tolerance, is naturally distributed in the desert area of northwest China. In our previous work, a bacterium strain numbered as M30-35 was isolated from the rhizosphere of H. ammodendron in Tengger desert, Gansu province, northwest China. In current work, the effects of M30-35 inoculation on salt tolerance of perennial ryegrass were evaluated and its genome was sequenced to identify genes associated with plant growth promotion. Results showed that M30-35 significantly enhanced growth and salt tolerance of perennial ryegrass by increasing shoot fresh and dry weights, chlorophyll content, root volume, root activity, leaf catalase activity, soluble sugar and proline contents that contributed to reduced osmotic potential, tissue K⁺ content and K⁺/Na⁺ ratio, while decreasing malondialdehyde (MDA) content and relative electric conductivity (REC), especially under higher salinity. The genome of M30-35 contains 4421 protein encoding genes, 12 rRNA, 63 tRNA-encoding genes and four rRNA operons. M30-35 was initially classified as a new species in Pseudomonas and named as Pseudomonas sp. M30-35. Thirty-four genes showing homology to genes associated with PGPR traits and abiotic stress tolerance were identified in Pseudomonas sp. M30-35 genome, including 12 related to insoluble phosphorus solubilization, four to auxin biosynthesis, four to other process of growth promotion, seven to oxidative stress alleviation, four to salt and drought tolerance and three to cold and heat tolerance. Further study is needed to clarify the correlation between these genes from M30-35 and the salt stress alleviation of inoculated plants under salt stress. Overall, our research indicated that desert shrubs appear rich in PGPRs that can help important crops tolerate abiotic stress.