A Novel Bio-Fertilizer Produced by Prickly Ash Seeds with Biochar Addition Induces Soil Suppressiveness against Black Shank Disease on Tobacco

A novel bio-fertilizer, produced from prickly ash seeds (PAS), Bacillus subtilis and biochar, was evaluated for its disease-preventing potential on tobacco black shank caused by Phytophthora nicotianae. The results showed that biochar promoted the growth of Tpb55 in PAS and increased the pH of the organic fertilizer. The final concentration of B. subtilis could reach 1.7 × 1010 cfu g−1 in the biological organic fertilizer (PBB) under the optimal medium under conditions of solid-state fermentation. PBB exhibited a strong fumigation effect on P. nicotianae, including inhibiting mycelium growth, reducing the disease severity and decreasing the pathogen population in rhizospheric soil. PBB treatment also could significantly increase the pH of acidified soil and improve soil nutrition content such as available K, alkali hydrolysable N and organic carbon. High-throughput pyrosequencing of 16S and 18S rRNA genes revealed that 4% PBB addition in soil had significant effects on the diversity and richness of fungi but not on that of bacteria. The microbial community structure was also shifted after PBB treatment. Some potentially beneficial microbes such as Bacillus, Mucor, Cunninghamella, Chitinophaga and Phenylobacterium were enriched, while potential pathogen Fusarium was significantly decreased. In conclusion, the agricultural waste PAS combined with biochar can replace soybean as a source for the production of biocontrol B. subtilis Tpb55, and the novel bio-fertilizer could effectively control tobacco black shank by pathogen inhibition, soil nutrient improvement and shifting the rhizomicrobial community.

Phloroglucinol Derivatives in Plant-Beneficial Pseudomonas spp.: Biosynthesis, Regulation, and Functions

Plant-beneficial Pseudomonas spp. aggressively colonize the rhizosphere and produce numerous secondary metabolites, such as 2,4-diacetylphloroglucinol (DAPG). DAPG is a phloroglucinol derivative that contributes to disease suppression, thanks to its broad-spectrum antimicrobial activity. A famous example of this biocontrol activity has been previously described in the context of wheat monoculture where a decline in take-all disease (caused by the ascomycete Gaeumannomyces tritici) has been shown to be associated with rhizosphere colonization by DAPG-producing Pseudomonas spp. In this review, we discuss the biosynthesis and regulation of phloroglucinol derivatives in the genus Pseudomonas, as well as investigate the role played by DAPG-producing Pseudomonas spp. in natural soil suppressiveness. We also tackle the mode of action of phloroglucinol derivatives, which can act as antibiotics, signalling molecules and, in some cases, even as pathogenicity factors. Finally, we discuss the genetic and genomic diversity of DAPG-producing Pseudomonas spp. as well as its importance for improving the biocontrol of plant pathogens.

Physico-Chemical Characterization and Biological Activities of a Digestate and a More Stabilized Digestate-Derived Compost from Agro-Waste

The excessive use of agricultural soils and the reduction in their organic matter, following circular economy and environmental sustainability concepts, determined a strong attention in considering composting as a preferred method for municipalities and industries to recycle organic by-products. Microorganisms degrade organic matter for producing CO2, water and energy, originating stable humus named compost. The current study analyzed the chemical composition of a cow slurry on-farm digestate and a more stabilized digestate-derived compost (DdC), along with their phytotoxic, genotoxic and antifungal activities. The chemical analysis showed that digestate cannot be an ideal amendment due to some non-acceptable characteristics. Biological assays showed that the digestate had phytotoxicity on the tested plants, whereas DdC did not induce a phytotoxic effect in both plants at the lowest dilution; hence, the latter was considered in subsequent analyses. The digestate and DdC induced significant antifungal activity against some tested fungi. DdC did not show genotoxic effect on Vicia faba using a micronuclei test. Soil treated with DdC (5 and 10%) induced damping-off suppression caused by Fusarium solani in tomato plants. The eco-physiological data indicated that DdC at 5–10% could increase the growth of tomato plants. In conclusion, DdC is eligible as a soil amendment and to strengthen the natural soil suppressiveness against F. solani.

Outlook: a vision of the future of integrated nematode management.

Integrated nematode management (INM) employs a diversity of management practices and focuses on key concepts such as targeted rotations, intercropping, advanced genetics for resistance breeding, remote sensing to monitor nematode distribution and densities, precision agriculture to target control treatments and molecular tools to measure soil suppressiveness. This chapter further discusses new building blocks of INM that could improve the future of nematode management. Outlooks on chemical control in the future; the growth of biological control; the need for resistance breeding; suppressive soil and its antagonistic potential for nematode management; climate change adaption; regional and site-specific approach in nematode management; loss of applied nematology positions at universities and plant protection agencies; and recommended INM programmes are described. For INM to become a reality, applied nematology needs to be at the forefront of the science of nematology again, and funded accordingly.

Can repeated soil amendment with biogas digestates increase soil suppressiveness toward non-specific soil-borne pathogens in agricultural lands?

Soil suppressiveness which is the natural ability of soil to support optimal plant growth and health is the resultant of multiple soil microbial components; which implies many difficulties when estimating this soil condition. Microbial benefits for plant health from repeated digestate applications were assessed in three experimental sites surrounding anaerobic biogas plants in an intensively cultivated area of northern Italy. A 2-yr trial was performed in 2017 and 2018 by performing an in-pot plant growth assay, using soil samples taken from two fields for each experimental site, of which one had been repeatedly amended with anaerobic biogas digestate and the other had not. These fields were similar in management and crop sequences (maize was the recurrent crop) for the last 10 yr. Plant growth response in the bioassay was expressed as plant biomass production, root colonization frequency by soil-borne fungi were estimated to evaluate the impact of soil-borne pathogens on plant growth, abundance of Pseudomonas and actinomycetes populations in rhizosphere were estimated as beneficial soil microbial indicators. Repeated soil amendment with digestate increased significantly soil capacity to support plant biomass production as compared to unamended control in both the years. Findings supported evidence that this increase was principally attributable to a higher natural ability of digestate-amended soils to reduce root infection by saprophytic soil-borne pathogens whose inoculum was increased by the recurrent maize cultivation. Pseudomonas and actinomycetes were always more abundant in digestate-amended soils suggesting that both these large bacterial groups were involved in the increase of their natural capacity to control soil-borne pathogens (soil suppressiveness).

Microplastics in agroecosystem – effects of plastic mulch film residues on soil-plant system

<p>In the last decades, the use of plastic mulch film in (semi-) arid agricultural regions has strongly increased. Plastic residues from mulching remain and accumulate in soil that can lead to serious environment problems. Biodegradable plastic mulch films were produced as environmentally friendly alternative for solving plastic pollution in agricultural land. However, the effects of polyethylene and biodegradable mulch film residues on soil-plant system are largely unknown.</p><p>In this PhD project, we performed a series of experiments to assess the effects of low density polyethylene (LDPE) and biodegradable plastic (Bio, made of polyethylene terephthalate, polybutylene terephthalate, pullulan) with macro- (5 mm<sup>2</sup>, Ma) and micro- (50 µm-1 mm, Mi) sizes on wheat growth, rhizosphere microbiome, soil physicochemical and hydrological properties and soil suppressiveness. The results showed that plastic residues presented negative effects on both above- and below-ground  parts for both vegetative and reproductive development of wheat. We also identified significant effects of Bio and LDPE plastic residues on the rhizosphere bacterial communities and on the blend of volatiles emitted in the rhizosphere. Tested with a gradient in concentration of plastic residues (0, 0.5%, 1% and 2% w/w), soil physicochemical and hydrological properties nonmonotonically responded to residual amount of plastic debris in the soil. Lastly, although we did not observe effects of plastic residues on disease infection in our experiment, we anticipated that soil suppressiveness and other soil functions would be affected with the presence of plastics in soil.</p><p>Overall, our study provides evidence for impacts of plastic residues on the soil-plant system, suggesting urgent need for more research examining their environmental impacts on agroecosystems.</p>