Soil Suppressiveness Research Articles

Approaches for the discrimination of suppressive soils for Pythium irregulare disease

The study of soil suppressiveness is of great interest in the field of sustainable agriculture. In the current study, eight soils located in the Region of Murcia (Spain) were sampled, evaluated and categorized according to their suppressiveness against Pythium irregulare in baby-leaf lettuce plants. We analyzed the chemical and biological properties as well as the bacterial and fungal community by sequencing 16S rRNA and ITS genes. We also attempted a non-targeted metabolomics analysis of the soil. The differences between the suppressive and non-suppressive soils were mainly associated with abiotic properties, such as pH, electrical conductivity (CE) and total organic carbon. Yet we also found links to biotic properties: several bacteria and fungi were found in suppressive soils (S) that were less abundant in the medium- (MS) or non-suppressive soils (NS). The differences observed in this study could play a decisive role against P. irregulare, and the data found could contribute significantly to the eventual control of this lettuce pathogen.

Deciphering Underlying Drivers of Disease Suppressiveness Against Pathogenic Fusarium oxysporum.

Soil-borne diseases, especially those caused by fungal pathogens, lead to profound annual yield losses. One key example for such a disease is Fusarium wilt disease in banana. In some soils, plants do not show disease symptoms, even if the disease-causing pathogens are present. However, the underlying agents that make soils suppressive against Fusarium wilt remain elusive. In this study, we aimed to determine the underlying microbial agents governing soil disease-suppressiveness. We traced the shift of microbiomes during the invasion of disease-causing Fusarium oxysporum f. sp. cubense in disease-suppressive and disease-conducive soils. We found distinct microbiome structures in the suppressive and conducive soils after pathogen invasion. The alpha diversity indices increased (or did not significantly change) and decreased, respectively, in the suppressive and conducive soils, indicating that the shift pattern of the microbiome with pathogen invasion was notably different between the suppressive and conductive soils. Microbiome networks were more complex with higher numbers of links and revealed more negative links, especially between bacterial taxa and the disease-causing Fusarium, in suppressive soils than in conducive soils. We identified the bacterial genera Chryseolinea, Terrimonas, and Ohtaekwangia as key groups that likely confer suppressiveness against disease-causing Fusarium. Overall, our study provides the first insights into agents potentially underlying the disease suppressiveness of soils against Fusarium wilt pathogen invasion. The results of this study may help to guide efforts for targeted cultivation and application of these potential biocontrol agents, which might lead to the development of effective biocontrol agents against Fusarium wilt disease.

Sandy soils amended with bentonite induced changes in soil microbiota and fungistasis in maize fields

The addition of bentonite, used as soil conditioner, can promote sandy soil macro-aggregate formation, moisture content retention and increase soil nutrient concentrations. However, there is limited knowledge about how bentonite influences soil microbial communities and interconnections among community members associated with crops, such as maize in continuous production on sandy soils. Metabarcoding analysis of the fungal internal transcribed spacer 1 (ITS1) region and the bacterial 16S rRNA gene V4 region revealed that the fungal communities in sandy maize fields (dominated by Guehomyces, Alternaria and Mortierella) were more diverse and abundant in soils amended with bentonite than those without bentonite amendment. By contrast, the bacterial communities (dominated by Proteobacteria and Actinobacteria) had similar alpha-diversity under both conditions but many functional guilds, including those affiliated with fermentation and N-cycling, differed significantly in community compositional structure between soils with and without bentonite amendment. The increase in soil nutrient concentrations due to the addition of bentonite was a key factor associated with changes in the bacterial communities. However, the fungal communities were more strongly influenced by the capacity of bentonite to increase soil moisture retention and enhance macro-aggregate development. Molecular ecological network analysis revealed more competitive (62.1% of total significant associations) than cooperative (37.9%) associations among microbial community members across all soils studied. The observation that fungal phytopathogens recovered from bentonite-amended soils had more negative correlations (75.6%) with naturally occurring beneficial bacteria and/or fungi than those in non-bentonite soils (65.2%), perhaps suggests, although speculation, that the addition of bentonite promoted soil fungistasis. In summary, our study showed that the addition of bentonite increased maize productivity and reshaped the microbial functional guilds in sandy soils, a consequence of improved soil structure as well as water and nutrient retention; however, the amendment’s long-term impact on soil suppressiveness to fungal phytopathogens is worth further investigation.

Bacterial, archaeal and micro-eukaryotic communities characterize a disease-suppressive or conducive soil and a cultivar resistant or susceptible to common scab

Control of common scab disease can be reached by resistant cultivars or suppressive soils. Both mechanisms are likely to translate into particular potato microbiome profiles, but the relative importance of each is not known. Here, microbiomes of bulk and tuberosphere soil and of potato periderm were studied in one resistant and one susceptible cultivar grown in a conducive and a suppressive field. Disease severity was suppressed similarly by both means yet, the copy numbers of txtB gene (coding for a pathogenicity determinant) were similar in both soils but higher in periderms of the susceptible cultivar from conducive soil. Illumina sequencing of 16S rRNA genes for bacteria (completed by 16S rRNA microarray approach) and archaea, and of 18S rRNA genes for micro-eukarytes showed that in bacteria, the more important was the effect of cultivar and diversity decreased from resistant cultivar to bulk soil to susceptible cultivar. The major changes occurred in proportions of Actinobacteria, Chloroflexi, and Proteobacteria. In archaea and micro-eukaryotes, differences were primarily due to the suppressive and conducive soil. The effect of soil suppressiveness × cultivar resistance depended on the microbial community considered, but differed also with respect to soil and plant nutrient contents particularly in N, S and Fe.

Analysis of the structure of bacterial and fungal communities in disease suppressive and disease conducive tobacco-planting soils in China

To clarify the differences between microbial communities resident in disease suppressive soil (DSS) and disease conducive soil (DCS) in tobacco cultivation, representative soil samples were collected from tobacco plantations in Shengjiaba, China, and the structure and diversity of the resident bacterial and fungal communities were analysed using high-throughput sequencing technology. Our results showed a greater number of operational taxonomic units associated with bacteria and fungi in DSS than in DCS. At the phylum level, abundances of Chloroflexi, Saccharibacteria, Firmicutes, and Planctomycetes in DSS were lower than in DCS, but abundance of Gemmatimonadetes was significantly higher. Abundances of Zygomycota and Chytridiomycota were higher in DSS than DCS, but abundance of Rozellomycota was significantly lower. At the genus level, abundances of 18 bacterial and nine fungal genera varied significantly between DSS and DCS. Relative abundances of Acidothermus, Microbacterium, Curtobacterium, and Colletotrichum were higher in DCS than DSS. The Shannon and Chao1 indices of DSS microbial communities were higher than those of DCS communities. High microbial diversity reduces the incidence of soil-borne diseases in tobacco plantations and promotes the formation of DSSs.

Physicochemical and biological properties of the coffee (Coffea arabica) rhizosphere suppress the root-knot nematode Meloidogyne exigua

ABSTRACTWe investigated the properties of rhizospheric soils infested with root-knot nematode (RKN) Meloidogyne exigua in 17 coffee (Coffea arabica) farms from the Southern region of Minas Gerais, Brazil. Physicochemical (pH, clay and organic matter) and biological properties (RKN parasites and microbiota volatile toxicity on M. exigua) were correlated with the number of second-stage juveniles (J2) and the egg hatching of M. exigua extracted from those rhizospheres. In the five most suppressive farms, the number of J2 was less than 50/100 g of soil and the egg hatching was significantly low. The bacterium Pasteuria penetrans was found in four of the most suppressive farms with an average of 30% of J2 infected with endospores. By using in vitro experiments the microbiota volatiles emitted from the most suppressive soils killed more than 83% of the J2. Additionally, volatiles produced by Fusarium oxysporum, Cladosporium sp. and Syncephalastrum sp. isolated from M. exigua eggs, significantly killed the J2. Identification of nematicidal compounds from the soils by GC-MS supported the strong involvement of the microbiota volatile toward RKN suppressiveness. Clay percentage and pH were similar in farms with the most suppressive soils (42.5% and 6.6%, respectively). Finally, the most suppressive soils came from farms with the highest coffee bean yields. Collectively, these results suggest the strong involvement of parasitic microorganisms, clay percentage and the pH suppressing RKN in soils from the major coffee production region in Brazil, and that volatiles emitted from total microbiota and exclusively from egg-isolated fungi are toxic to M. exigua.

Antagonistic role of the microbiome from a Meloidogyne hapla-suppressive soil against species of plant-parasitic nematodes with different life strategies

Summary In certain soils populations of plant-parasitic nematodes (PPN) decline. Understanding this effect may open up environmentally friendly management options. We identified such a suppressive soil containing virtually no PPN. Inoculated Meloidogyne hapla declined in this soil more than in a control soil and reproduction on tomato was reduced. The extracted soil microbiome alone decreased root invasion of second-stage juveniles (J2) and progeny as well as the native soil. We tested the antagonistic potential against PPN that differ in life strategies. The microbiome was most suppressive against two populations of M. hapla and one population of Pratylenchus neglectus, and least suppressive against M. incognita and the ectoparasite Hemicycliophora conida. In a split-root system with M. hapla, plant-mediated but not direct effects of the microbiome significantly reduced root invasion of J2, while direct exposure of M. hapla to the microbiome significantly affected reproduction. Overall, both plant-mediated and direct effects of the microbiome were responsible for the soil suppressiveness against M. hapla.

Bacteria isolated from the cuticle of plant-parasitic nematodes attached to and antagonized the root-knot nematode Meloidogyne hapla

Plant-parasitic nematodes are associated with specifically attached soil bacteria. To investigate these bacteria, we employed culture-dependent methods to isolate a representative set of strains from the cuticle of the infective stage (J2) of the root-knot nematode Meloidogyne hapla in different soils. The bacteria with the highest affinity to attach to J2 belonged to the genera Microbacterium, Sphingopyxis, Brevundimonas, Acinetobacter, and Micrococcus as revealed by 16S rRNA gene sequencing. Dynamics of the attachment of two strains showed fast adhesion in less than two hours, and interspecific competition for attachment sites. Isolates from the cuticle of M. hapla J2 attached to the lesion nematode Pratylenchus penetrans, and vice versa, suggesting similar attachment sites on both species. Removal of the surface coat by treatment of J2 with the cationic detergent CTAB reduced bacterial attachment, but did not prevent it. Some of the best attaching bacteria impaired M. hapla performance in vitro by significantly affecting J2 mortality, J2 motility and egg hatch. Most of the tested bacterial attachers significantly reduced the invasion of J2 into tomato roots, suggesting their beneficial role in soil suppressiveness against M. hapla.

Wheat yield as a measure of the residual fertility after 20 years of forage cropping systems with different manure management in Northern Italy

After 20 years of application of different manure types, cropping systems and additional nitrogen (N) levels, their residual fertility effects were compared by measuring the yield of a following unfertilised wheat crop (Experiment 1), which was sown on exactly the same plots of the previous long-term trial. All previously applied factors caused significant differences in wheat yield. Wheat yielded more on plots that had received farmyard manure (FMY) compared to those where semi-liquid manure (SLM) was previously applied. Long-term application of a semi-intensive rotation, with three years of annual double cropping of autumnsown Italian ryegrass and spring-sown silage maize followed by three years of mown lucerne (R6), resulted in higher wheat yield than application of just the annual double cropping of Italian ryegrass and silage maize (R1). Application of further mineral N fertilisation to previous cropping systems caused higher yield of the subsequent wheat crop. The difference in wheat yield between the R6 and R1 systems was greater with SLM (+28%) than FYM application (+11%) resulting in a significant manure × system interaction. A companion experiment (Experiment 2) was carried out to compute the nitrogen agronomic efficiency (NAE) from the yield of wheat plots that were sown after ploughing a nearby 20- year unfertilised grassland and received four levels of mineral N fertilisation. NAE was further used to empirically estimate the productive advantage (PA) conferred by previous manure-systemmineral nitrogen combinations in the long-term trial. PA was measured as equivalent kg of mineral N to be applied to wheat to achieve the yield level recorded after any previous combination. The estimated PA values were much higher when wheat followed FYM compared to SLM application, and when it followed R6 compared to R1 system. The SLM-R1 combination had negative PA values, indicating a productive disadvantage on wheat of this preceding combination. The enhancement of residual soil fertility by long-term application of FYM compared to SLM could be attributed to greater nutrient provision during the years by FYM than by SLM. However, further fertility advantages of FYM are discussed. Despite lower nutrient supply by organic fertilisers in R6 than in R1 system, the former had higher residual fertility. The presence of lucerne in the R6 rotation likely enriched the soil in nitrogen and increased its availability for following cropping. Possible benefits of the legume on the soil suppressiveness might have been a further asset of the R6 system.

Screening of bacterial extracellular xylanase producers with potential for cellulose pulp biobleaching

In this study, two hundred fifty-seven bacterial isolates from a suppressive soil library were screened to study their secretion of alkali-thermostable xylanases for potential use in cellulose pulp biobleaching. Xylanase activity was evaluated in solid and liquid media using xylan as the carbon source. Isolates were initially evaluated for the degradation of xylan in solid media by the congo red test. Selected strains were evaluated in liquid media for enzymatic activity and determination of total protein concentration using a crude protein extract (CPE). An isolate identified as Bacillus species TC-DT13 produced the highest amount of xylanase (1808 U mL-1). The isolate was active and stable at 70°C and pH 9.0, conditions which are necessary for the paper industry. This isolate can grow and produce xylanase in medium containing wheat fiber as a substrate. The CPE of this isolate was used in preliminary testing on cellulose pulp bleaching; enzyme treatment of the pulp resulted in a 5% increase of whiteness.

Continuous cropping of soybean alters the bulk and rhizospheric soil fungal communities in a Mollisol of Northeast PR China

AbstractContinuous cropping of soybean causes soil degradation and decreased soybean yield in Northeast PR China. However, the mechanism underlying the effect on soil fungal communities and the relationship between these effects and cropping systems have not yet been fully elucidated. In this study, we comparatively investigated the abundance, diversity, and structures of fungal communities in the bulk and rhizospheric soils of soybean grown in two cropping systems, that is, continuous cropping (CC) of soybean and cropping rotation (CR) with maize using real‐time Polymerase Chain Reaction (PCR) and Illumina MiSeq sequencing methods. The results showed that the rhizospheric soil fungal abundance was significantly higher in CC than in CR, but the opposite trend was observed in bulk soils. CC decreased the fungal alpha diversity in both bulk and rhizospheric soils compared with CR. The fungal community compositions were distinctly different between CC and CR in both bulk and rhizospheric soils, and the composition and diversity in bulk soils were predominantly affected by the soil carbon to nitrigen (C/N) ratio. The soil fungal functional groups varied between the two cropping systems; CC increased the relative abundances of the potentially pathogenic fungi Fusarium oxysporum and Lectera longa and beneficial fungi Mortierella sp. and Paecilomyces lilacinus. In contrast, CR increased the relative abundance of Ustilago maydis, which is a pathogen that causes corn smut. Our findings showed that CC increased the abundances of plant pathogens, which is harmful to soybean growth; in contrast, the abundances of some beneficial fungi also increased, which suggested that suppressive soils might be developed after long‐term CC.

MYCOFLORA POTENTIAL IN RIZOSPHER AS BIOLOGICAL GENTSTOCONTROLWILTDISEASES ON PEPPER PLANT

The cause of wilt disease in pepperis Phytophthora capsicifungi, which attacked the pepper plantation area in Kertalangu Village, East Denpasar Sub-district, Denpasar-Bali. The results showed that the fungi on conducive soil were Phytophthora sp., Aspergillussp., and Neurosporasp. With the highest prevalence attained by Neurosporasp. of 80%, while on suppressive soil found mycellia sterillia fungus, Fusariumsp., Neurosporasp. Aspergillussp., Penicilliumsp., Mucorsp., and Trichodermasp. With the highest prevalence achieved by Penicilliumsp. By 27%. The antagonistic fungus found only in suppressive soils isthe fungus Neurosporasp., Trichodermasp., Aspergillussp., Penicillium sp., and Mucorsp. each with a percentage of resistance of 67.78 ± 1.6%, 68.52 ± 2.62%, 75.93 ± 2.62%, 68.77 ± 5.43%; and 67.59 ± 3.82%. The highest inhibition abilityis achieved byAspergillussp.

Genome-wide screening antifungal genes in Streptomyces griseus S4-7, a Fusarium wilt disease suppressive microbial agent.

Streptomyces is a widely studied bacterial genus, particularly with regard to secondary metabolites and antibiotics production. Streptomyces griseus S4-7 was isolated from a strawberry Fusarium wilt disease suppressive soil, and its biological control ability has been well established. However, the antifungal mechanism of strain S4-7 is not yet fully understood at the molecular and biochemical level. Therefore, in this study we created a random mutant library for strain S4-7 with the Tn5 transposon element to investigate antifungal traits on a genome-wide scale. In total 4646 individual mutant strains were created and 13 mutants were selected based on loss of antifungal activity. The knockout genes were identified as electron transfer oxidoreductase (eto),sigma factor-70(sig70) and nrps by Inverse PCR (I-PCR). eto regulates the geranylgeranyl reductase gene, which is involved in terpenoid-quinone biosynthesis, an important factor in cell fitness. In the △eto strain, expression of wbl, a master regulator of the production of secondary metabolites, was significantly reduced. sig70 is responsible for the cell differentiation sensing mechanism in genus Streptomyces. △nrps showed decreased production of hybrid peptide-polyketide siderophores. These results suggest that S. griseus S4-7 may have various antifungal mechanisms, and each mechanism is essential to maximal antifungal activity.

Impacts of long-term plant residue management on soil organic matter quality, Pseudomonas community structure and disease suppressiveness

The microbiome of grassland soils provides ecosystem services essential to plant health and productivity, including nutrient cycling and suppression of soil-borne diseases. Understanding how soil management practices affect soil microbial communities will provide opportunities by which indigenous soil microbes and their functions can be managed to sustain or promote plant growth and enhance disease suppressiveness. Here, we investigated the impact of 20 years of plant residue management in a long-term grassland field trial on soil chemical and (micro)biological properties, in particular the suppression of damping-off disease of kale caused by the fungal root pathogen Rhizoctonia solani AG 2–1. Plant residue management led to significant variation in the community structure of the bacterial genus Pseudomonas between treatments. Soil organic matter quality (inferred carbon recalcitrance) was responsible for 80% of the observed variation in Pseudomonas community structure. Furthermore, increased Pseudomonas species diversity (Shannon's index), microbial activity, soil organic matter content, and carbon availability distinguished suppressive (low disease) soils from conducive (high disease) soils. More specifically, Pseudomonas species diversity and richness (Margalef's) were identified as the primary parameters explaining the greatest proportion (>30%) of variation in the disease suppressive capacity of soils across treatments. Collectively, our results suggest that management-induced shifts in Pseudomonas community composition, notably species diversity and richness, provide a better indicator of disease conduciveness for a broad-host range fungal pathogen than soil chemical parameters. In conclusion, our study indicates that frequent addition of organic residues to agricultural grassland soils enhances the diversity and activity of plant-beneficial bacterial taxa.

Crop rotation and tillage affect nematode communities more than biocides in monoculture soybean

Long-term monoculture of susceptible soybeans naturally develops suppressiveness to soybean cyst nematode (SCN) Heterodera glycines if fields are not tilled or biocides applied. Nematode community indices, that integrate the responses of different taxa and trophic groups to perturbation, provide a tool to monitor the ecological status of soil communities. We tested the hypothesis that soil suppressiveness to Heterodera glycines is correlated positively to management practices that favor both greater trophic diversity (food web complexity) and a later stage ecological succession (less disturbance) within free-living nematode communities. A factorial combination of cultivation, crop rotation, and biocide application treatments were monitored for four years in a field with a history of no-till and monoculture of susceptible soybean for 15 years. Crop rotation had the greatest impact on nematode community index values followed by descending order of cultivation and biocides. Suppressive soils did have greater food web complexity, but not necessarily ecological succession. Nematode community composition was influenced by covariables nitrogen and organic matter content (mean 6.6%), but not pH or salinity. The study is novel by using a food web approach that includes multiple trophic levels rather than simply population ecology.

Soil suppressiveness to Pythium ultimum in ten European long-term field experiments and its relation with soil parameters

Soil suppressiveness to pathogens is defined as the capacity of soil to regulate soil-borne pathogens. It can be managed by agricultural practices, but the effects reported so far remain inconsistent. Soil suppressiveness is difficult to predict and for this reason different soil properties have been linked to it with the aim to find informative indicators, but these relationships are not conclusive. The objectives of this study were i) to test if soil suppressiveness is affected by long-term agricultural management such as tillage and organic matter (OM) addition; ii) to understand the direct and indirect relationships between soil suppressiveness and labile organic carbon fractions; and iii) to understand the relationship between soil suppressiveness and other chemical, physical and biological soil quality indicators. We measured soil suppressiveness with a bioassay using Pythium ultimum - Lepidium sativum (cress) as a model system. The bioassay was performed in soils from 10 European long-term field experiments (LTEs) which had as main soil management practices tillage and/or organic matter addition. We found that the site had a stronger influence on soil suppressiveness than agricultural practices. Reduced tillage had a positive effect on the suppressive capacity of the soil across sites using an overall model. Organic farming and mineral fertilization increased soil suppressiveness in some LTEs, but no overall effect of OM was found when aggregating the LTEs. Soil suppressiveness across LTEs was linked mainly to microbial biomass and labile carbon in the soil, but not to total soil organic matter content. From structural equation modelling (SEM) we conclude that labile carbon is important for the maintenance of an abundant and active soil microbial community, which is essential for the expression of soil suppressiveness. However, soil suppressiveness could only partly (25%) be explained by the soil parameters measured, suggesting that other mechanisms contribute to soil suppressiveness such as the presence and the activity of specific bacterial and fungal taxa with high biocontrol activity.

Influence of the Potato Production System in the Soil Suppressiveness to Bacterial Wilt

The potato crop is highly affected by soil-borne diseases motivating its continuous migration to non-cultivated areas. Bacterial wilt caused by Ralstonia spp. is one of the main diseases affecting the potato crop in Brazil, since the conventional production system, used throughout the country, promotes an ideal environment for proliferation of members of this pathogen complex. Studying alternative potato production systems aiming to improve the soil biological properties is necessary in order to avoid the continuous migration of the potato crop to new areas. The objective of this work was to evaluate different potato production systems, namely, the Paces an alternative potato production system and the organic potato production systems in contrast to the conventional production system, a soil from the Paces system sterilized through autoclaving and an undisturbed Atlantic rainforest soil regarding the soil suppressiveness to bacterial wilt caused by R. solanacearum. The experimental design was randomized blocks with three replications, arranged in a 4 x 4 + 1 factorial scheme, the main factor being the production system and the secondary factor corresponding to the doses of soil contaminated with R. solanacearum added to each treatment (0, 25, 50 and 75%). The additional treatment corresponded to the soil of the conventional system with high incidence of R. solanacearum. The soil suppressiveness to bacterial wilt is a biological process inhibited by autoclaving. The Paces and the organic potato production systems have a significant potential to suppress R. solanacearum in infested soil.

Lime and ammonium carbonate fumigation coupled with bio-organic fertilizer application steered banana rhizosphere to assemble a unique microbiome against Panama disease.

SummaryMicrobiome plays a key role in determining soil suppressiveness against invading pathogens. Our previous study revealed that microbial community of bulk soil could be manipulated by lime and ammonium bicarbonate fumigation followed by biofertilizer application. However, the assembly of microbial community suppressive to banana Panama disease in the rhizosphere is still unclear. In this study, we used high‐throughput sequencing and quantitative PCR to explore the assembly of rhizosphere microbiome associated with banana Panama disease suppression in a two‐seasonal pot experiment. We found biofertilizer applied to lime and ammonium bicarbonate fumigated soil significantly (P < 0.05) reduced the abundance of rhizosphere Fusarium oxysporum compared to biofertilizer applied to non‐fumigated soil. Principal coordinate analysis revealed that biofertilizer applied to lime and ammonium bicarbonate fumigated soil re‐shaped the rhizosphere bacterial community composition by increasing the phylogenetic relatedness, and stimulating indigenous microbes, for example, Gemmatimonas, Sphingomonas, Pseudomonas, Lysobacter and Bacillus. Co‐occurrence analysis revealed that potential species involved in disease suppression were more interrelated in disease‐suppressive soils. Taken together, lime and ammonium bicarbonate fumigation followed by biofertilizer application could induce banana rhizosphere to assemble beneficial microbes dominated consortia to suppress banana Panama disease.

Deciphering the suppressiveness of banana Fusarium wilt with organic residues

The use of organic residues in agriculture can contribute to the management of plant diseases and improvements in soil fertility. However, their effects on banana Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense (Foc), are poorly understood. In this study, the biotic and abiotic effects on soil suppressiveness of banana Fusarium wilt were evaluated after incorporation of composted sewage sludge, biochar, shrimp peels and mussel shells into the soil. Residues were incorporated at rates of 0, 1, 2, 3, 4, and 5%, v:v in soil previously infested with Foc. Plantlets of banana cv. Maçã (AAB) were transplanted seven days after residue incorporation. Notable with respect to the other residues and concentrations studied, sewage sludge at 4% and 5% reduced plant disease (disease severity index and external severity) and increased plant growth. All concentrations of biochar and sewage sludge at 2% and 3% had intermediate effects. Disease severity and plant growth in plants grown in soil containing shrimp peels and mussel shells were similar to those of the untreated control. Negative correlations were observed between disease parameters and soil basal respiration, bacterial population, electrical conductivity, pH, V% (base saturation), CEC, P, K, Ca, Mg, Na, Zn, Mn and B.

The Structure of Bacterial and Fungal Communities in the Rhizosphere and Root-Free Loci of Gray Forest Soil

The taxonomic composition, abundance, and diversity of bacterial and fungal communities in the rhizosphere loci and bulk mass of the gray forest soil (Eutric Retisol (Loamic, Aric, Cutanic, Humic)) under potatoes, maize, and white mustard grown with the application of mineral and organic fertilizers were compared. Among bacteria, Bacillus megaterium and Paenibacillus polymyxa species predominated in all the experimental variants. The micromycete community was represented by 39 species belonging to 19 genera. Under the impact of organic fertilizers, the abundance of Trichoderma harzianum—an antagonist of many phytopathogens—increased. A decrease in the abundance of representatives of Fusarium genus was observed both in the rhizosphere and in the bulk soil. Fertilization was the most significant factor determining the structure and diversity of micromycete communities both in the soil and rhizosphere. The application of mineral fertilizers reduced the diversity of micromycetes in soil, whereas the use of organic fertilizers increased it. In general, organic fertilizers proved to be more favorable for the rhizosphere and bulk soil mycobiomes and for the total soil suppressiveness than the mineral fertilizers.