Enhanced tomato plant growth in soil under reduced P supply through microbial inoculants and microbiome shifts.

Soil microbial communities interact with roots, affecting plant growth and nutrient acquisition. In the present study, we aimed to decipher the effects of the inoculants Trichoderma harzianum T-22, Pseudomonas sp. DSMZ 13134, Bacillus amyloliquefaciens FZB42 or Pseudomonas sp. RU47 on the rhizosphere microbial community and their beneficial effects on tomato plants grown in moderately low phosphorous soil under greenhouse conditions. We analyzed the plant mass, inoculant colony forming units and rhizosphere communities on 15, 22, 29 and 43 days after sowing. Selective plating showed that the bacterial inoculants had a good rhizocompetence and accelerated shoot and root growth and nutrient accumulation. 16S rRNA gene fingerprints indicated changes in the rhizosphere bacterial community composition. Amplicon sequencing revealed that rhizosphere bacterial communities from plants treated with bacterial inoculants were more similar to each other and distinct from those of the control and the Trichoderma inoculated plants at harvest time, and numerous dynamic taxa were identified. In conclusion, likely both, inoculants and the rhizosphere microbiome shifts, stimulated early plant growth mainly by improved spatial acquisition of available nutrients via root growth promotion. At harvest, all tomato plants were P-deficient, suggesting a limited contribution of inoculants and the microbiome shifts to the solubilization of sparingly soluble soil P.

Analysis of the genome sequence of plant beneficial strain Pseudomonas sp. RU47.

Pseudomonas sp. RU47 (RU47) is a rhizosphere-competent strain showing plant growth-promoting and biocontrol activities. In this study, the genome sequence of strain RU47 was obtained and phylogenetic and comparative genome analyses were performed. Multilocus sequence analysis (MLSA) coupled with the calculation of average nucleotide identity (ANI) and in silico DNA-DNA hybridization (DDH) values suggested that strain RU47 belongs to the P. koreensis group of the P. fluorescens complex, but cannot be assigned to any known Pseudomonas species. Multiple genes and operons encoding functions that likely contribute to its previously reported high rhizosphere competence, biocontrol of Rhizoctonia solani and plant growth promotion in soils with reduced fertilization were identified. Putative genes and gene clusters for the production of hydrogen cyanide, cyclic lipopeptides, bacteriocins, siderophores, indole-3-acetic acid, spermidine, alkaline protease A, chitinase and ß-1,3-glucanase were identified, as well as loci associated with solubilization of inorganic phosphate. Several of these functions were also confirmed by in vitro testing. Distribution of putative genes and gene clusters that may contribute to the plant growth-promoting and biocontrol activities was largely similar among strains belonging to P. koreensis group, as revealed by comparative genome analysis. Data presented in this study further support the potential of RU47 for its application in agriculture and may be a valuable resource for further studies.

A new bacterial disease on Mandevilla sanderi, caused by Pseudomonas savastanoi: lessons learned for bacterial diversity studies.

Leaf lesions of Mandevilla sanderi were shown to be caused by Pseudomonas savastanoi. While BOX fingerprints were similar for P. savastanoi isolates from different host plants, plasmid restriction patterns and sequencing of plasmid-located pathogenicity determinants revealed that Mandevilla isolates contained similar plasmids distinct from those of other isolates. A repA-based detection method was established.