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Rice sheath blight caused by Rhizoctonia solani Kühnis increasingly threatening rice production in China. DNA fingerprints of 220 R. solani strains isolated in 11 provinces of China were established by random amplified polymorphic DNA (RAPD)-PCR. Cluster analysis of strains isolated from the same region showed high similarity, indicating that the genetic diversity of R. solani strains is significantly related to geographical origin. We assessed potential bio-control abilities of bio-control agents (BCAs) by values according to inhibition zones against R. solani , extracellular hydrolytic enzymes activity and siderophores production in vitro. Fourteen strains with diverse expected bio-control potential were tested for their bio-control efficacy against rice sheath blight caused by 11 pathogenic exemplars and for growth promoting ability, separately. Bio-control efficacy of single bacterium against various R. solani strains differed significantly (−36.23% ∼ 88.24%), while Pseudomonas fluorescens 4aYN11 achieved a relatively stable control efficacy of 32.26%–78.79% and growth promotion of 18.43%. Pearson correlation coefficient between bio-control efficacy of each BCAs and their assessment is 0.717. In the present study, we established an improved strategy for screening stable bio-control agents based on an assessment system, their growth promotion potential and phylogenetic diversity of pathogen R. solani , and the result provides us not only one promising bio-control strain 4aYN11 with an average bio-control efficacy of 56.50%, but also a practical way for future screen of novel BCAs. [ABSTRACT FROM AUTHOR]

Bacterial fruit blotch (BFB) was a serious threat to cucurbitaceae crops. It was caused by the gram-negative bacterium Acidovorax avenae subsp. citrulli . Two hundred strains, which have the potential in controlling plant diseases in our laboratory's biocontrol strain library, were employed to this research to screen some antagonistic bacteria, which can efficiently control bacterial fruit blotch disease. Based on the results of antagonistic activity experiments, greenhouse tests and field trials, 5 of the test strains have high abilities to control BFB. One of the 5 bacteria strains has the highest potential to control BFB named 54. The biocontrol efficacy of 54 was up to 60%. To characterize the strain, we used series of methods to evaluate the bacterium, including morphology analysis, physiological biochemical test and biomolecular assay. We found that the bacterium 54 belongs to the species Bacillus amyloliquefaciens. The colonization test results showed that 54 had the highest colonization levels, and the density of the strain on leaves was up 10 5 colony forming units (CFU) per gram of leaf tissue. Our recent results show that B. amyloliquefaciens 54 can promote the plant growth due to raised the contents of available N, P, K and the leaf chlorophyll. The antagonistic bacterium 54 can significantly control the BF B by increasing the expression level of defense-related gene PR1 and the accumulation the hydrogen peroxide in the plant. The results of trail experiment was also verified this efficient results of bacterium. This is also the first report of B. amyloliquefaciens strain that is able to control BFB. [ABSTRACT FROM AUTHOR]

The beneficial effects of plant growth-promoting rhizobacteria (PGPR) on crop growth and yield have been widely recognized. However, the application of PGPR in traditional planting systems is often restricted due to the concerns about the incompatibility between PGPR and chemical agricultural inputs. The aim of this study is to test whether the application of PGPR has a beneficial effect on the productivity and sustainability of the green planting system, where the use of low-toxic chemical pesticides and proper amount of chemical fertilizer is allowed. In the current study, field trials of four agriculture systems: green agriculture system, green agriculture system supplemented with beneficial microorganism consortium, organic agriculture system supplemented with the consortium and the control system, were carried out with white, yellow and purple flesh sweet potato varieties. The application of PGPR increased the plant growth and suppressed the stem nematode disease in green system. As a consequence, PGPR increased the yield by 26.44% and raised the farmers' projected returns in green system on an average of the two-year assessment. Moreover, PGPR promoted the product nutritive quality by 7.51% in soluble sugar and 14.30% in vitamin C content, and also increased the anthocyanin content of the purple sweet potato by 10.73%. Exogenous PGPR significantly retarded the depletion of soil fertility during the crop cultivation, promoted the soil bacterial diversity and altered the bacteria community structure. PGPR treatment increased the relative abundances of Pseudomonas and Lysobacter in the rhizosphere soil, while reduced the amounts of Erwinia and Ralstonia. The changes of soil nutrient and microbes were correlated with the application of exogenous beneficial bacteria regardless of in organic or green agriculture system. Here, we showed the ability of PGPR to efficiently improve the productivity in green agriculture system under the tested condition, and provided evidence for the feasibility of using exogenous PGPR to achieve agricultural sustainability by constructing a positive feedback in crop-soil-microbe interactions. [Display omitted] • PGPR increased soil micro ecological diversity and remodeled population structure. • PGPR in green agriculture system improved the sustainability of agricultural soil. • Proposed the virtuous cycle of plant-soil-microbe driven by PGPR. • PGPR help to develop a balance between productivity, environment and economics. [ABSTRACT FROM AUTHOR]