The phenylpropanoid pathway inhibitor piperonylic acid induces broad-spectrum pest and disease resistance in plants.

Although many phenylpropanoid pathway-derived molecules act as physical and chemical barriers to pests and pathogens, comparatively little is known about their role in regulating plant immunity. To explore this research field, we transiently perturbed the phenylpropanoid pathway through application of the CINNAMIC ACID-4-HYDROXYLASE (C4H) inhibitor piperonylic acid (PA). Using bioassays involving diverse pests and pathogens, we show that transient C4H inhibition triggers systemic, broad-spectrum resistance in higher plants without affecting growth. PA treatment enhances tomato (Solanum lycopersicum) resistance in field and laboratory conditions, thereby illustrating the potential of phenylpropanoid pathway perturbation in crop protection. At the molecular level, transcriptome and metabolome analyses reveal that transient C4H inhibition in tomato reprograms phenylpropanoid and flavonoid metabolism, systemically induces immune signalling and pathogenesis-related genes, and locally affects reactive oxygen species metabolism. Furthermore, C4H inhibition primes cell wall modification and phenolic compound accumulation in response to root-knot nematode infection. Although PA treatment induces local accumulation of the phytohormone salicylic acid, the PA resistance phenotype is preserved in tomato plants expressing the salicylic acid-degrading NahG construct. Together, our results demonstrate that transient phenylpropanoid pathway perturbation is a conserved inducer of plant resistance and thus highlight the crucial regulatory role of this pathway in plant immunity.

Acidification of composts versus woody management residues: Optimizing biological and chemical characteristics for a better fit in growing media.

Previous research has demonstrated that composts (COM) and woody residues from nature management (MR) are potential peat replacers for growing media, but their compositions are highly variable. Our goal is to make growing media more sustainable by optimizing the selection of local and sustainable alternatives for peat. Different batches of COM and MR were incubated to assess the microbial activity based on (1) the N drawdown risk, (2) the C mineralization and (3) the inoculation efficiency of a commercially available biocontrol fungus. The various batches were characterized based on biochemical, chemical (pH, available and total nutrients) and microbiological biomass analysis. COM and MR were scored based on chemical or stability characteristics to assess their suitability to replace peat, lime and fertilizers in growing media. This score allowed for a clear differentiation between the materials; MR received higher scores on average than COM. Five composts were further tested for the effect of storage after blending with an acidic MR, acidification with elemental S, or removal of the finer fraction. One batch of chopped soft rush was acidified with elemental S. Blending and acidification were the most effective treatments as they resulted in a clear increase of the suitability score.

Daring to be differential: metabarcoding analysis of soil and plant-related microbial communities using amplicon sequence variants and operational taxonomical units.

BACKGROUND: Microorganisms are not only indispensable to ecosystem functioning, they are also keystones for emerging technologies. In the last 15 years, the number of studies on environmental microbial communities has increased exponentially due to advances in sequencing technologies, but the large amount of data generated remains difficult to analyze and interpret. Recently, metabarcoding analysis has shifted from clustering reads using Operational Taxonomical Units (OTUs) to Amplicon Sequence Variants (ASVs). Differences between these methods can seriously affect the biological interpretation of metabarcoding data, especially in ecosystems with high microbial diversity, as the methods are benchmarked based on low diversity datasets. RESULTS: In this work we have thoroughly examined the differences in community diversity, structure, and complexity between the OTU and ASV methods. We have examined culture-based mock and simulated datasets as well as soil- and plant-associated bacterial and fungal environmental communities. Four key findings were revealed. First, analysis of microbial datasets at family level guaranteed both consistency and adequate coverage when using either method. Second, the performance of both methods used are related to community diversity and sample sequencing depth. Third, differences in the method used affected sample diversity and number of detected differentially abundant families upon treatment; this may lead researchers to draw different biological conclusions. Fourth, the observed differences can mostly be attributed to low abundant (relative abundance < 0.1%) families, thus extra care is recommended when studying rare species using metabarcoding. The ASV method used outperformed the adopted OTU method concerning community diversity, especially for fungus-related sequences, but only when the sequencing depth was sufficient to capture the community complexity. CONCLUSIONS: Investigation of metabarcoding data should be done with care. Correct biological interpretation depends on several factors, including in-depth sequencing of the samples, choice of the most appropriate filtering strategy for the specific research goal, and use of family level for data clustering.

Quantification of Extracellular Proteases and Chitinases from Marine Bacteria.

A total of 92 marine bacteria belonging to Pseudomonas, Pseudoalteromonas, Psychrobacter, and Shewanella were first screened for their proteolytic activity. In total, four Pseudomonas strains belonging to Ps. fluorescens, Ps. fragi, Ps. gessardii, and Ps. marginalis; 14 Pseudoalteromonas strains belonging to Psa. arctica, Psa. carrageenovora, Psa. elyakovii, Psa. issachenkonii, Psa. rubra, Psa. translucida, and Psa. tunicata; and two Shewanella strains belonging to S. baltica and S. putrefaciens were identified to have a weak to high proteolytic activity (from 478 to 4445 mU/mg trypsin equivalent) against skim milk casein as protein source. Further chitinolytic activity screening based on these 20 proteolytic strains using colloidal chitin yielded five positive strains which were tested against three different chitin substrates in order to determine the various types of chitinases. Among the strains that can produce both proteases and chitinases, Psa. rubra DSM 6842T expressed not only the highest proteolytic activity (2558 mU/mg trypsin equivalent) but also the highest activity of exochitinases, specifically, ß-N-acetylglucosaminidase (6.33 mU/107 cfu) as well. We anticipate that this strain can be innovatively applied to the valorization of marine crustaceans side streams.

Plant Growth Promotion Driven by a Novel Caulobacter Strain.

Soil microbial communities hold great potential for sustainable and ecologically compatible agriculture. Although numerous plant-beneficial bacterial strains from a wide range of taxonomic groups have been reported, very little evidence is available on the plant-beneficial role of bacteria from the genus Caulobacter. Here, the mode of action of a Caulobacter strain, designated RHG1, which had originally been identified through a microbial screen for plant growth-promoting (PGP) bacteria in maize (Zea mays), is investigated in Arabidopsis thaliana. RHG1 colonized both roots and shoots of Arabidopsis, promoted lateral root formation in the root, and increased leaf number and leaf size in the shoot. The genome of RHG1 was sequenced and was utilized to look for PGP factors. Our data revealed that the bacterial production of nitric oxide, auxins, cytokinins, or 1-aminocyclopropane-1-carboxylate deaminase as PGP factors could be excluded. However, the analysis of brassinosteroid mutants suggests that an unknown PGP mechanism is involved that impinges directly or indirectly on the pathway of this growth hormone.

Biochar-amended potting medium reduces the susceptibility of rice to root-knot nematode infections.

BACKGROUND: Biochar is a solid coproduct of biomass pyrolysis, and soil amended with biochar has been shown to enhance the productivity of various crops and induce systemic plant resistance to fungal pathogens. The aim of this study was to explore the ability of wood biochar to induce resistance to the root-knot nematode (RKN) Meloidogyne graminicola in rice (Oryza sativa cv. Nipponbare) and examine its histochemical and molecular impact on plant defense mechanisms. RESULTS: A 1.2 % concentration of biochar added to the potting medium of rice was found to be the most effective at reducing nematode development in rice roots, whereas direct toxic effects of biochar exudates on nematode viability, infectivity or development were not observed. The increased plant resistance was associated with biochar-primed H2O2 accumulation as well as with the transcriptional enhancement of genes involved in the ethylene (ET) signaling pathway. The increased susceptibility of the Ein2b-RNAi line, which is deficient in ET signaling, further confirmed that biochar-induced priming acts at least partly through ET signaling. CONCLUSION: These results suggest that biochar amendments protect rice plants challenged by nematodes. This priming effect partially depends on the ET signaling pathway and enhanced H2O2 accumulation.

Commodity risk assessment of Petunia spp. and Calibrachoa spp. unrooted cuttings from Kenya.

The European Commission requested the EFSA Panel on Plant Health to evaluate the probability of entry of pests (likelihood of pest freedom at entry), including both regulated and non-regulated pests, associated with unrooted cuttings of the genera Petunia and Calibrachoa produced under physical isolation in Kenya. The relevance of any pest for this opinion was based on evidence following defined criteria, based on the methodology used for High-Risk Plants adapted for the specificity of this assessment. Fourteen EU-regulated pests (Bemisia tabaci, cowpea mild mottle virus, Liriomyza huidobrensis, Liriomyza sativae, Liriomyza trifolii, potato leafroll virus, potato spindle tuber viroid, Ralstonia pseudosolanacearum, R. solanacearum, Scirtothrips dorsalis, tomato mild mottle virus, tomato spotted wilt virus, tomato yellow leaf curl virus and Xanthomonas vesicatoria) and six EU non-regulated pests (Aleurodicus dispersus, pepper veinal mottle virus, Nipaecoccus viridis, Phenacoccus solenopsis, Tetranychus neocaledonicus and tomato yellow ring virus) fulfilled all relevant criteria and were selected for further evaluation. For these pests, the risk mitigation measures proposed in the technical dossier from Kenya were evaluated, taking into account the possible limiting factors. Additionally, an expert judgement is given on the likelihood of pest freedom, taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. The estimated degree of pest freedom varies among the pests evaluated, with T. neocaledonicus being the pest most frequently expected on the imported cuttings. The Expert Knowledge Elicitation indicated, with 95% certainty, that between 9942 and 10,000 bags containing unrooted cuttings of Petunia spp. and Calibrachoa spp. per 10,000 would be free of T. neocaledonicus.

Commodity risk assessment of Sorbus aucuparia plants from the UK.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as 'high risk plants, plant products and other objects'. Taking into account the available scientific information, including the technical information provided by the applicant country, this Scientific Opinion covers the plant health risks posed by the following commodities: Sorbus aucuparia bare-root plants and rooted plants in pots up to 7 years old and specimen trees in pots up to 15 years old imported into the EU from the UK. A list of pests potentially associated with the commodities was compiled. The relevance of any pest was assessed based on evidence following defined criteria. Three EU quarantine pests (Entoleuca mammata and Phytophthora ramorum (non-EU isolates), Erwinia amylovora), were selected for further evaluation. For two of the selected pests (E. mammata and P. ramorum), the risk mitigation measures implemented in the UK and specified in the technical dossier were evaluated taking into account the possible limiting factors. For these pests, an expert judgement is given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. The degree of pest freedom varies between the pests evaluated, with P. ramorum being the pest most frequently expected on the imported S. aucuparia plants. The Expert Knowledge Elicitation indicated, with 95% certainty, that between 9812 and 10,000 bare-root S. aucuparia plants per 10,000 will be free from P. ramorum.

Commodity risk assessment of Petunia spp. and Calibrachoa spp. unrooted cuttings from Guatemala.

The European Commission requested the EFSA Panel on Plant Health to evaluate the probability of entry of pests (likelihood of pest freedom at entry), including both, regulated and non-regulated pests, associated with unrooted cuttings of the genera Petunia and Calibrachoa produced under physical isolation in Guatemala. The relevance of any pest for this opinion was based on evidence following defined criteria, based on the methodology used for high-risk plants adapted for the specificity of this assessment. Nineteen EU regulated pests (Bemisia tabaci, pepper golden mosaic virus, pepper huasteco yellow vein virus, tomato severe leaf curl virus, tomato yellow leaf curl virus, tomato spotted wilt virus, Liriomyza huidobrensis, Liriomyza sativae, Liriomyza trifolii, Bactericera cockerelli, Eotetranichus lewisi, Epitrix subcrinita, Epitrix cucumeris, Helicoverpa zea, Chloridea virescens, Spodoptera ornithogalli, Ralstonia solanacearum, Ralstonia pseudosolanacearum, Xanthomonas vesicatoria) and one EU non-regulated (Phenacoccus solenopsis) pest fulfilled all relevant criteria and were selected for further evaluation. For these pests, the risk mitigation measures proposed in the technical dossier from Guatemala were evaluated taking into account the possible limiting factors, and an expert judgement is given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. The limited and partially conflicting information provided in the dossier contributes to the wide estimates of pest freedom. The estimated degree of pest freedom varies among the pests evaluated, with Ralstonia spp. (R. solanacearum and R. pseudosolanacearum) being the pest most frequently expected on the imported cuttings. The expert knowledge elicitation indicated, with 95% certainty, that between 9916 and 10,000 bags containing unrooted cuttings per 10,000 would be free of Ralstonia spp.

Commodity risk assessment of Cornus alba and Cornus sanguinea plants from the UK.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as 'high risk plants, plant products and other objects'. Taking into account the available scientific information, including the technical information provided by the applicant country, this Scientific Opinion covers the plant health risks posed by the following commodities: Cornus alba and Cornus sanguinea bare-root plants and rooted plants in pots up to 7 years old imported into the EU from the UK. A list of pests potentially associated with the commodities was compiled. The relevance of any pest was assessed based on evidence following defined criteria. Four EU quarantine pests (Meloidogyne fallax, Phytophthora ramorum (non-EU isolates), tobacco ringspot virus, and tomato ringspot virus) and one EU non-regulated pest (Discula destructiva), were selected for further evaluation. For the selected pests, the risk mitigation measures implemented in the technical dossier from the UK were evaluated taking into account the possible limiting factors. For these pests, an expert judgement is given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. The degree of pest freedom varies among the pests evaluated, with P. ramorum being the pest most frequently expected on the imported C. alba and C. sanguinea plants. The Expert Knowledge Elicitation indicated, with 95% certainty, that between 9823 and 10,000 bare-root C. alba and C. sanguinea plants per 10,000 will be free from P. ramorum.

Elucidating the microbiome of the sustainable peat replacers composts and nature management residues.

Sustainable peat alternatives, such as composts and management residues, are considered to have beneficial microbiological characteristics compared to peat-based substrates. Studies comparing microbiological characteristics of these three types of biomass are, however, lacking. This study examined if and how microbiological characteristics of subtypes of composts and management residues differ from peat-based substrates, and how feedstock and (bio)chemical characteristics drive these characteristics. In addition, microbiome characteristics were evaluated that may contribute to plant growth and health. These characteristics include: genera associated with known beneficial or harmful microorganisms, microbial diversity, functional diversity/activity, microbial biomass, fungal to bacterial ratio and inoculation efficiency with the biocontrol fungus Trichoderma harzianum. Bacterial and fungal communities were studied using 16S rRNA and ITS2 gene metabarcoding, community-level physiological profiling (Biolog EcoPlates) and PLFA analysis. Inoculation with T. harzianum was assessed using qPCR. Samples of feedstock-based subtypes of composts and peat-based substrates showed similar microbial community compositions, while subtypes based on management residues were more variable in their microbial community composition. For management residues, a classification based on pH and hemicellulose content may be relevant for bacterial and fungal communities, respectively. Green composts, vegetable, fruit and garden composts and woody composts show the most potential to enhance plant growth or to suppress pathogens for non-acidophilic plants, while grass clippings, chopped heath and woody fractions of compost show the most potential for blends for calcifuge plants. Fungal biomass was a suitable predictor for inoculation efficiency of composts and management residues.

Can multi-cropping affect soil microbial stoichiometry and functional diversity, decreasing potential soil-borne pathogens? A study on European organic vegetable cropping systems.

Crop diversification in spatial and temporal patterns can optimize the synchronization of nutrients plant demand and availability in soils, as plant diversity and soil microbial communities are the main drivers of biogeochemical C and nutrient cycling. The introduction of multi-cropping in organic vegetable production can represent a key strategy to ensure efficient complementation mediated by soil microbiota, including beneficial mycorrhizal fungi. This study shows the effect of the introduction of multi-cropping in five European organic vegetable systems (South-West: Italy; North-West: Denmark and Belgium; North-East: Finland and Latvia) on: (i) soil physicochemical parameters; (ii) soil microbial biomass stoichiometry; (iii) crop root mycorrhization; (iv) bacterial and fungal diversity and composition in crop rhizosphere; (v) relative abundance of selected fungal pathogens species. In each site, three cropping systems were considered: (1) crop 1-monocropping; (2) crop 2-monocropping; (3) crop 1-crop 2-intercropping or strip cropping. Results showed that, just before harvest, multi-cropping can increase soil microbial biomass amount and shape microbial community toward a predominance of some bacteria or fungi phyla, in the function of soil nutrient availability. We mainly observed a selection effect of crop type on rhizosphere microbiota. Particularly, Bacteroidetes and Mortierellomycota relative abundances in rhizosphere soil resulted in suitable ecological indicators of the positive effect of plant diversity in field, the first ones attesting an improved C and P cycles in soil and the second ones a reduced soil pathogens' pressure. Plant diversity also increased the root mycorrhizal colonization between the intercropped crops that, when properly selected, can also reduce the relative abundance of potential soil-borne pathogens, with a positive effect on crop productivity in long term.

Commodity risk assessment of Jasminum polyanthum unrooted cuttings from Uganda.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation EU/2018/2019 as 'High risk plants, plant products and other objects'. This Scientific Opinion covers plant health risks posed by unrooted cuttings of Jasminum polyanthum that are imported from Uganda, taking into account the available scientific information, including the technical information provided by the NPPO of Uganda. The relevance of any pest for this opinion was based on evidence following defined criteria. Six species, two EU-regulated pests (Bemisia tabaci, non-European populations and Scirtothrips dorsalis) and four EU non-regulated pests (Coccus viridis, Diaphania indica, Pulvinaria psidii and Selenaspidus articulatus), fulfilled all relevant criteria and were selected for further evaluation. For these pests, the risk mitigation measures proposed in the technical dossier from Uganda were evaluated taking into account the possible limiting factors. For these pests, an expert judgement is given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. The estimated degree of pest freedom varies among the pests evaluated, with B. tabaci and S. dorsalis being the pests most frequently expected on the imported plants. The Expert Knowledge Elicitation indicated, with 95% certainty, that between 9,950 and 10,000 plants per 10,000 would be free of B. tabaci.

Commodity risk assessment of specified species of Lonicera potted plants from Turkey.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in the Commission Implementing Regulation (EU) 2018/2019 as 'High-risk plants, plant products and other objects'. This Scientific Opinion covers plant health risks posed by potted plants (2-4 years old) of specified Lonicera species produced in nurseries and that are imported from Turkey, taking into account the available scientific information, including the technical information provided by the NPPO of Turkey. The relevance of any pest for this Opinion was based on evidence following defined criteria listed in Section 4.1. Three species, the EU-quarantine pests Lopholeucaspis japonica and Meloidogyne chitwoodi and the protected zone quarantine pest Bemisia tabaci, fulfilled these criteria and were selected for further evaluation. For these pests, the risk mitigation measures proposed in the technical dossier from Turkey were evaluated taking into account the possible limiting factors. For these pests, an expert judgement is given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. The estimated degree of pest freedom varies among the pests evaluated, with B. tabaci on evergreen species of Lonicera spp. being the pest most frequently expected on the imported plants. The Expert Knowledge Elicitation indicated, with 95% certainty, that between 9,293 and 10,000 plants per 10,000 would be free of B. tabaci.

Commodity risk assessment of Berberis thunbergii potted plants from Turkey.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in the Commission Implementing Regulation (EU) 2018/2019 as 'High-risk plants, plant products and other objects'. This Scientific Opinion covers plant health risks posed by potted plants (2-3 years old) of Berberis thunbergii produced in nurseries and imported into the EU from Turkey, taking into account the available scientific information, including the technical information provided by the NPPO of Turkey. The relevance of any pest for this Opinion was based on evidence following defined criteria. Two species, the EU-quarantine pest Bemisia tabaci and the non-regulated pest Malacosoma parallela, fulfilled the relevant criteria and were selected for further evaluation. For these pests, the risk mitigation measures proposed in the technical dossier from Turkey were evaluated taking into account the possible limiting factors. For these pests, an expert judgement is given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. The estimated degree of pest freedom varies among the pests evaluated, with B. tabaci being the pest most frequently expected on the imported plants. The Expert Knowledge Elicitation indicated, with 95% certainty, that between 9,928 and 10,000 plants per 10,000 would be free of B. tabaci. The role of Berberis thunbergii as possible host of Puccinia spp. is discussed in the body of the opinion.

Biochar-Enhanced Resistance to Botrytis cinerea in Strawberry Fruits (But Not Leaves) Is Associated With Changes in the Rhizosphere Microbiome.

Biochar has been reported to play a positive role in disease suppression against airborne pathogens in plants. The mechanisms behind this positive trait are not well-understood. In this study, we hypothesized that the attraction of plant growth-promoting rhizobacteria (PGPR) or fungi (PGPF) underlies the mechanism of biochar in plant protection. The attraction of PGPR and PGPF may either activate the innate immune system of plants or help the plants with nutrient uptake. We studied the effect of biochar in peat substrate (PS) on the susceptibility of strawberry, both on leaves and fruits, against the airborne fungal pathogen Botrytis cinerea. Biochar had a positive impact on the resistance of strawberry fruits but not the plant leaves. On leaves, the infection was more severe compared with plants without biochar in the PS. The different effects on fruits and plant leaves may indicate a trade-off between plant parts. Future studies should focus on monitoring gene expression and metabolites of strawberry fruits to investigate this potential trade-off effect. A change in the microbial community in the rhizosphere was also observed, with increased fungal diversity and higher abundances of amplicon sequence variants classified into Granulicella, Mucilaginibacter, and Byssochlamys surrounding the plant root, where the latter two were reported as biocontrol agents. The change in the microbial community was not correlated with a change in nutrient uptake by the plant in either the leaves or the fruits. A decrease in the defense gene expression in the leaves was observed. In conclusion, the decreased infection of B. cinerea in strawberry fruits mediated by the addition of biochar in the PS is most likely regulated by the changes in the microbial community.

Chemically versus thermally processed brown shrimp shells or Chinese mitten crab as a source of chitin, nutrients or salts and as microbial stimulant in soilless strawberry cultivation.

Brown shrimp (Crangon crangon) shells and Chinese mitten crab (Eriocheir sinensis) were chemically demineralized and deproteinized (denoted as M1 to M4 for the shrimp shells and M5 to M7 for the Chinese mitten crab), and shrimp shells were torrefied at 200 to 300 °C (denoted as R200, R255, R300), and were compared with a commercially available chitin source (denoted as reference chitin). Based on their chemical characteristics, a selection of chitin sources was tested for their N mineralization capacity. The N release was high for the chemically treated shrimp shells and Chinese mitten crab, but not for the torrefied shrimp shells with or without acid treatment, indicating that treatment at 200 °C or higher resulted in low N availability. Interaction with nutrients was tested in a leaching experiment with limed peat for three thermally and two chemically processed shrimp shells and the reference chitin source. The K concentrations in the leachate for the chemically treated shrimp shells and the reference chitin were lower than for limed peat during fertigation. Irreversible K retention was observed for one source of chemically treated shrimp shells, and the reference chitin. The thermally treated shrimp shells had a significantly higher net release of P, Na and Cl than the treatment without chitin source. Three shrimp shell based materials (M4, R200 and R300) and the reference chitin were tested in a greenhouse trial with strawberry at a dose of 2 g/L limed peat. A very positive and significant effect on Botrytis cinerea disease suppression in the leaves was found for the reference chitin, M4 and R200 compared to the unamended control. The disease suppression of the 3 chitin sources was linked with an increase of the microbial biomass in the limed peat with 24% to 28% due to chitin decomposition and a 9-44% higher N uptake in the plants.

Understanding the Shift in the Microbiome of Composts That Are Optimized for a Better Fit-for-Purpose in Growing Media.

Three characteristics are considered key for optimal use of composts in growing media: maturity, pH and organic matter content. Maturation is a critical step in the processing of composts contributing to compost quality. Blending of composts with chopped heath biomass, sieving out the larger fraction of composts and acidification of composts by adding elemental sulfur may be used either to increase organic matter content or to reduce pH for a better fit in growing media. While several studies have shown the effectiveness of these treatments to improve the use of composts in growing media, the effect of these treatments on the compost microbiome has merely been assessed before. In the present study, five immature composts were allowed to mature, and were subsequently acidified, blended or sieved. Bacterial and fungal communities of the composts were characterized and quantified using 16S rRNA and ITS2 gene metabarcoding and phospholipid fatty acid analysis. Metabolic biodiversity and activity were analyzed using Biolog EcoPlates. Compost batch was shown to be more important than maturation or optimization treatments to determine the compost microbiome. Compost maturation increased microbial diversity and favored beneficial microorganisms, which may be positive for the use of composts in growing media. Blending of composts increased microbial diversity, metabolic diversity, and metabolic activity, which may have a positive effect in growing media. Blending may be used to modify the microbiome to a certain degree in order to optimize microbiological characteristics. Acidification caused a decrease in bacterial diversity and microbial activity, which may be negative for the use in growing media, although the changes are limited. Sieving had limited effect on the microbiome of composts. Because of the limited effect on the microbiome, sieving of composts may be used flexible to improve (bio)chemical characteristics. This is the first study to assess the effects of maturation and optimization treatments to either increase organic matter content or lower pH in composts on the compost microbiome.

Shifts in the rhizobiome during consecutive in planta enrichment for phosphate-solubilizing bacteria differentially affect maize P status.

Phosphorus (P) is despite its omnipresence in soils often unavailable for plants. Rhizobacteria able to solubilize P are therefore crucial to avoid P deficiency. Selection for phosphate-solubilizing bacteria (PSB) is frequently done in vitro; however, rhizosphere competence is herein overlooked. Therefore, we developed an in planta enrichment concept enabling simultaneous microbial selection for P-solubilization and rhizosphere competence. We used an ecologically relevant combination of iron- and aluminium phosphate to select for PSB in maize (Zea mays L.). In each consecutive enrichment, plant roots were inoculated with rhizobacterial suspensions from plants that had grown in substrate with insoluble P. To assess the plants' P statuses, non-destructive multispectral imaging was used for quantifying anthocyanins, a proxy for maize's P status. After the third consecutive enrichment, plants supplied with insoluble P and inoculated with rhizobacterial suspensions showed a P status similar to plants supplied with soluble P. A parallel metabarcoding approach uncovered that the improved P status in the third enrichment coincided with a shift in the rhizobiome towards bacteria with plant growth-promoting and P-solubilizing capacities. Finally, further consecutive enrichment led to a functional relapse hallmarked by plants with a low P status and a second shift in the rhizobiome at the level of Azospirillaceae and Rhizobiaceae.

Cucurbitaceae COld Peeling Extracts (CCOPEs) Protect Plants From Root-Knot Nematode Infections Through Induced Resistance and Nematicidal Effects.

With nematicides progressively being banned due to their environmental impact, an urgent need for novel and sustainable control strategies has arisen. Stimulation of plant immunity, a phenomenon referred to as "induced resistance" (IR), is a promising option. In this study, Cucurbitaceae COld Peeling Extracts (CCOPEs) were shown to protect rice (Oryza sativa) and tomato (Solanum lycopersicum) against the root-knot nematodes Meloidogyne graminicola and Meloidogyne incognita, respectively. Focusing on CCOPE derived from peels of melon (Cucumis melo var. cantalupensis; mCOPE), we unveiled that this extract combines an IR-triggering capacity with direct nematicidal effects. Under lab conditions, the observed resistance was comparable to the protection obtained by commercially available IR stimuli or nematicides. Via mRNA sequencing and confirmatory biochemical assays, it was proven that mCOPE-IR in rice is associated with systemic effects on ethylene accumulation, reactive oxygen species (ROS) metabolism and cell wall-related modifications. While no negative trade-offs were detected with respect to plant growth or plant susceptibility to necrotrophic pests or pathogens, additional infection experiments indicated that mCOPE may have a predominant activity toward biotrophs. In summary, the presented data illustrate a propitious potential for these extracts, which can be derived from agro-industrial waste streams.