Suppression Of Fusarium Wilt Disease Research Articles

Comparative Effect of Seed Coating and Biopriming of Bacillus aryabhattai Z-48 on Seedling Growth, Growth Promotion, and Suppression of Fusarium Wilt Disease of Tomato Plants.

Beneficial plant microbes can enhance the growth and quality of field crops. However, the benefits of microbes using cheap and efficient inoculation methods are still uncommon. Seed coating with biocontrol agents can reduce the amount of inocula along with having the potential for large-scale application. Hence, in this research work, the comparative potential of tomato seed coating and biopriming with Bacillus aryabhattai Z-48, harboring multiple plant-beneficial traits, to suppress Fusarium wilt disease along with its beneficial effect on seedling and plant growth promotion was analyzed. Among two bacterial strains, B. aryabhattai Z-48 was able to antagonize the mycelial growth of Fusarium oxysporum f.sp. lycopersici in vitro and its application as a seed coating superiorly benefited seedling traits like the germination percentage, vigor index, and seedling growth index along with a reduced germination time. The seed coating with B. aryabhattai Z-48 resulted in significant increases in the shoot length, root length, dry biomass, and total chlorophyll contents when compared with the bioprimed seeds with the same bacterial strain and non-inoculated control plants. The seed coating with B. aryabhattai Z-48 significantly reduced the disease index (>60%) compared with the pathogen control during pot trials. Additionally, the seed coating with B. aryabhattai Z-48 resulted in a significantly higher production of total phenolics, peroxidase, polyphenol oxidase, and phenylalanine ammonia lyase enzyme in tomato plants. The GC/MS-based non-targeted metabolic profiling indicated that the seed coating with B. aryabhattai Z-48 could cause large-scale metabolite perturbations in sugars, sugar alcohols, amino acids, and organic acids to increase the fitness of tomato plants against biotic stress. Our study indicates that a tomato seed coating with B. aryabhattai Z-48 can improve tomato growth and suppress Fusarium wilt disease effectively under conventional agricultural systems.

Exploring Microbial Rhizosphere Communities in Asymptomatic and Symptomatic Apple Trees Using Amplicon Sequencing and Shotgun Metagenomics

The rhizosphere is a dynamic and highly interactive habitat where diverse microbial communities are established, and it plays crucial roles in plant health and disease dynamics. In this study, microbial communities and functional profiles in the rhizosphere of both asymptomatic and symptomatic apple trees were investigated through amplicon sequencing and shotgun metagenomics. The research was conducted at a location in the municipality of Cuauhtemoc, Chihuahua State, Mexico, and a total of 22 samples were collected, comprising 12 for amplicon sequencing and 10 for shotgun metagenomic sequencing. Symptomatic trees were identified based on reddish branches and internal necrosis in the trunk and root, while asymptomatic trees exhibited a healthy physiology. The findings showed that the dominant bacterial phyla included Proteobacteria, Actinobacteria, and Bacteroidetes, with prevalent genera such as Streptomyces, Pseudomonas, and Rhodanobacter. The fungal communities featured Ascomycota, Mortierellomycota, and Basidiomycota, which were dominated by Fusarium, Penicillium, and Mortierella. In the fungal communities, Mortierellomycota, notably abundant in asymptomatic trees, holds potential as a biocontrol agent, as seen in other studies on the suppression of Fusarium wilt disease. The application of shotgun metagenomic sequencing revealed significant differences in alpha and beta diversities in bacterial communities, suggesting a health-dependent change in species composition and abundance. Functional profile analysis highlighted enzymatic activities associated with lipid synthesis/degradation, amino acid biosynthesis, carbohydrate metabolism, and nucleotide synthesis, which have been documented to participate in symbiotic relationships between plants. These insights not only contribute to understanding the dynamics of rhizosphere microbial activity but also provide valuable perspectives on the potential application of microbial communities for tree health and implications for the management of apple orchards.

Seed coating with the synthetic consortium of beneficial Bacillus microbes improves seedling growth and manages Fusarium wilt disease

Fusarium wilt disease of the pea crop caused by the infection of Fusarium oxysporum f. sp. pisi (FOP) is a serious soilborne disease. In this study, we developed a seed coating containing a synthetic consortium of beneficial Bacillus microbes to manage the fusarium wilt disease. Three bacterial strains IS1, IS6, and IS7 isolated from the rhizosphere of different healthy-looking crop plants, were selected for the seed coating based on antagonism against the FOP shown during in-vitro studies, and suppression of fusarium wilt disease when applied as seed priming in preliminary pot trials. The strains were identified as B. subtilis (IS1), B. amyloliquificiens (IS6), and B. fortis (IS7) by 16 s rRNA gene sequencing. The seed coating with the consortium of all three bacterial strains showed a significant positive effect on seed germination, seedling height, and biomass accumulation of pea seedlings. Upon exposure to FOP, a > 50 % reduction in disease index was seen in pea plants raised from coated seeds than the pathogen control along with the ameliorative effect on plant growth attributes. Besides, the coating of consortium induced significant up-regulation of total phenolic compounds and enzymes of phenylpropanoid pathways. Additionally, the non-targeted metabolomic analysis indicated a large number of perturbations in amino acids, sugars, carbohydrates, and phenylpropanoids in pea plants raised from consortium-coated seeds and subsequently challenged with FOP. Based on the findings, consortium coating of Bacillus spp. on pea seeds may have the potential to develop a bio-based remedy for the management of wilt diseases in pea plants and improvement in growth attributes.

Effects of Rhizosphere Microbial Communities on Cucumber Fusarium wilt Disease Suppression.

Cucumber Fusarium wilt is a worldwide soil-borne disease that seriously restricts the yield and quality of cucumber. The rhizosphere soil microbiome, as the first line of defense against pathogens invading plant roots, plays a key role in rhizosphere immune formation and function. The purpose of this study was to reveal the key microecological factors and dominant microbial flora affecting cucumber resistance and susceptibility to Fusarium wilt by analyzing the physical and chemical properties and microbial flora of rhizosphere soil with different degrees of susceptibility and resistance to cucumber Fusarium wilt, thereby laying a foundation to establish cucumber resistance to the Fusarium wilt rhizosphere core microbiome. Firstly, Illumina Miseq sequencing technology was used to evaluate the physical and chemical properties and microbial groups of cucumber rhizosphere soil at different health levels, and the key environmental factors and microbial factors related to cucumber Fusarium wilt were screened out. Subsequently, PICRUSt2 and FUNGuild were used to predict the functions of rhizosphere bacteria and fungi. Combined with functional analysis, the possible interactions among soil physical and chemical properties, cucumber rhizosphere microorganisms, and Fusarium wilt were summarized. The results showed that the available potassium content in the rhizosphere soil of healthy cucumber decreased by 10.37% and 0.56%, respectively, compared with the rhizosphere soil of severely susceptible cucumber and mildly susceptible cucumber. Exchangeable calcium content increased by 25.55% and 5.39%; the α diversity Chao1 index of bacteria and fungi in the rhizosphere soil of healthy cucumber was significantly lower than that in the rhizosphere soil of seriously infected cucumber, and the MBC content of its physical and chemical properties was also significantly lower than that in the rhizosphere soil of seriously infected cucumber. There was no significant difference in the Shannon and Simpson diversity indexes between healthy cucumber rhizosphere soil and seriously infected cucumber rhizosphere soil. The results of the β diversity analysis showed that the bacterial and fungal community structure of healthy cucumber rhizosphere soil was significantly different from that of severely and mildly infected cucumber rhizosphere soil. At the genus level, through statistical analysis, LEfSe analysis, and RDA analysis, the key bacterial and fungal genera with potential biomarker values were screened out as SHA_26, Subgroup_22, MND1, Aeromicrobium, TM7a, Pseudorhodoplanes, Kocuria, Chaetomium, Fusarium, Olpidium, and Scopulariopsis, respectively. The bacteria SHA_26, Subgroup_22, and MND1 related to cucumber Fusarium wilt inhibition belong to Chloroflexi, Acidobacteriota, and Proteobacteria, respectively. Chaetomiacea belongs to Sordariomycates. The results of functional prediction showed that changes to the KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway in the bacterial microbiota were concentrated in tetracycline biosynthesis, selenocompound metabolism, lipopolysaccharide biosynthesis, etc., which were mainly involved in the metabolism of terpenoids and polyketides, energy metabolism, metabolism of other amino acids, glycan biosynthesis and metabolism, lipid metabolism, cell growth and death, transcription, metabolism of cofactors and vitamins, and biosynthesis of other secondary metabolites. The difference in fungi was mainly dung saprotroph-ectomycorrhizal-soil saprotroph-wood saprotroph. Through the correlation analysis and functional predictions of the key environmental factors, microbial flora, and cucumber health index in cucumber rhizosphere soil, we determined that the inhibition of cucumber Fusarium wilt was a synergistic effect of environmental factors and microbial flora, and a model diagram was drawn to briefly explain its mechanism. This work will provide a basis for the biological control of cucumber Fusarium wilt in the future.

Root-Associated Antagonistic Pseudomonas spp. Contribute to Soil Suppressiveness against Banana Fusarium Wilt Disease of Banana.

Members of the microbiotas colonizing the plant endophytic compartments and the surrounding bulk and rhizosphere soil play an important role in determining plant health. However, the relative contributions of the soil and endophytic microbiomes and their mechanistic roles in achieving disease suppression remain elusive. To disentangle the relative importance of the different microbiomes in the various plant compartments in inhibiting pathogen infection, we conducted a field experiment to track changes in the composition of microbial communities in bulk and rhizosphere soil and of root endophytes and leaf endosphere collected from bananas planted on Fusarium-infested orchards in disease-suppressive and disease-conducive soils. We found that the rhizosphere and roots were the two dominant plant parts whose bacterial communities contributed to pathogen suppression. We further observed that Pseudomonas was potentially a key organism acting as a pathogen antagonist, as illustrated by microbial community composition and network analysis. Subsequently, culturable pathogen-antagonistic Pseudomonas strains were isolated, and their potential suppressive functions or possible antibiosis in terms of auxin or siderophore synthesis and phosphate solubilization were screened to analyze the mode of action of candidate disease-suppressive Pseudomonas strains. In a follow-up in vivo and greenhouse experiment, we revealed that microbial consortia of culturable Pseudomonas strains P8 and S25 (or S36), isolated from banana plantlet rhizosphere and roots, respectively, significantly suppressed the survival of pathogens in the soil, manipulated the soil microbiome, and stimulated indigenous beneficial microbes. Overall, our study demonstrated that root-associated microbiomes, especially the antagonistic Pseudomonas sp. components, contribute markedly to soil suppression of banana Fusarium wilt. IMPORTANCE Soil suppression of Fusarium wilt disease has been proven to be linked with the local microbial community. However, the contribution of endophytic microbes to disease suppression in wilt-suppressive soils remains unclear. Moreover, the key microbes involving in Fusarium wilt-suppressive soils and in the endophytic populations have not been fully characterized. In this study, we demonstrate that root-associated microbes play vitally important roles in disease suppression. Root-associated Pseudomonas consortia were recognized as a key component in inhibiting pathogen abundance associated with the host banana plants. This finding is crucial to developing alternate strategies for soilborne disease management by harnessing the plant microbiome.

Cross-kingdom synthetic microbiota supports tomato suppression of Fusarium wilt disease

The role of rhizosphere microbiota in the resistance of tomato plant against soil-borne Fusarium wilt disease (FWD) remains unclear. Here, we showed that the FWD incidence was significantly negatively correlated with the diversity of both rhizosphere bacterial and fungal communities. Using the microbiological culturomic approach, we selected 205 unique strains to construct different synthetic communities (SynComs), which were inoculated into germ-free tomato seedlings, and their roles in suppressing FWD were monitored using omics approach. Cross-kingdom (fungi and bacteria) SynComs were most effective in suppressing FWD than those of Fungal or Bacterial SynComs alone. This effect was underpinned by a combination of molecular mechanisms related to plant immunity and microbial interactions contributed by the bacterial and fungal communities. This study provides new insight into the dynamics of microbiota in pathogen suppression and host immunity interactions. Also, the formulation and manipulation of SynComs for functional complementation constitute a beneficial strategy in controlling soil-borne disease.

Inducing banana Fusarium wilt disease suppression through soil microbiome reshaping by pineapple–banana rotation combined with biofertilizer application

Abstract. Crop rotation and biofertilizer application have historically been employed as efficient management strategies for soil-borne disease suppression through soil microbiome manipulation. However, how this occurs and to what extent the combination of methods affects the microbiota reconstruction of diseased soil is unknown. In this study, pineapple–banana rotation combined with biofertilizer application was used to suppress banana Fusarium wilt disease, and the effects on both bacterial and fungal communities were investigated using the MiSeq Illumina sequencing platform. Our results showed that pineapple–banana rotation significantly reduced Fusarium wilt disease incidence and the application of biofertilizer caused additional suppression. Bacterial and fungal communities thrived using rotation combined with biofertilizer application: taxonomic and phylogenetic α diversity of both bacteria and fungi increased along with disease suppression. Between the two strategies, biofertilizer application predominantly affected both bacterial and fungal community composition compared to rotation. Burkholderia genus may have been attributed to the general wilt suppression for its change in network structure and high relative importance in linear models. Our results indicated that pineapple–banana rotation combined with biofertilizer application has strong potential for the sustainable management of banana Fusarium wilt disease.

Characterization and chemical management of Cashew Fusarium Wilt Disease caused by Fusarium oxysporum in Tanzania

Cashew (Anacardium occidentale L.) is the present leading currency earning crop in Tanzania, generating income to over 2.5 million farmers. Despite of its importance, cashew is threatened by a new serious destructive disease called Cashew Fusarium Wilt (CFWD), which is caused by Fusarium oxysporum. The impact of the disease has reduced income at both household and national levels. The current study was conducted to characterize CFWD and investigate chemical management options for the disease. The study was conducted during the rainy and off-rainy season(s) at Tuungane-Liwale and Kitangari-Newala in Lindi and Mtwara regions respectively. Disease characterization involved field observation of the infected cashew trees, laboratory isolation and characterization of the causative agent. Chemical management involved application of azoxystrobin, carbendazim and thiophanate methyl each at a concentration of 5, 10 and 15 g of formulated product/L. Laboratory findings revealed that the causative agent of the cashew wilting symptoms is Fusarium oxysporum characterized by whitish mycelia growth, chlamydospores, macroconidia and microconidia. The tested chemical fungicides revealed significant effects on the suppression of Fusarium wilt disease and thus enhancing cashew recovery after 120 days of application. Azoxystrobin and carbendazim reduced severity and enhanced recovery. Application of azoxystrobin (15 g/L) promoted 65.2 percent recovery of cashew from 50.0 percent of disease severity and 10 g/L of carbendazim enhanced 49.4 percent of cashew recovery from 50.0 percent severity. Thiophanate methyl exhibited significant effect (P ≤ 0.05) on reducing the severity of the disease and enhancing cashew recovery whereby 15 g/L of thiophanate methyl enhanced 21.6 percent recovery from 45.0 percent severity. These findings advocate the administration of these chemicals, especially carbendazim and azoxystrobin in proper concentration for timely disease management in the affected areas. Studies to establish the effect of the applied chemicals to other biota for betterment and continued applications to combat the disease are underway.

Phenolic Acid-Degrading Consortia Increase Fusarium Wilt Disease Resistance of Chrysanthemum

Soil microbial community changes imposed by the cumulative effects of root-secreted phenolic acids (PAs) promote soil-borne pathogen establishment and invasion under monoculture systems, but the disease-suppressive soil often exhibits less soil-borne pathogens compared with the conducive soil. So far, it remains poorly understood whether soil disease suppressiveness is associated with the alleviated negative effects of PAs, involving microbial degradation. Here, the long-term monoculture particularly shaped the rhizosphere microbial community, for example by the enrichment of beneficial Pseudomonas species in the suppressive soil and thus enhanced disease-suppressive capacity, however this was not observed for the conducive soil. In vitro PA-degradation assays revealed that the antagonistic Pseudomonas species, together with the Xanthomonas and Rhizobium species, significantly increased the efficiency of PA degradation compared to single species, at least partially explaining how the suppressive soil accumulated lower PA levels than the conducive soil. Pot experiments further showed that this consortium harboring the antagonistic Pseudomonas species can not only lower PA accumulation in the 15-year conducive soils, but also confer stronger Fusarium wilt disease suppression compared with a single inoculum with the antagonistic bacteria. Our findings demonstrated that understanding microbial community functions, beyond the single direct antagonism, facilitated the construction of active consortia for preventing soil-borne pathogens under intensive monoculture.

Combination of Trichoderma viride and Pseudomonas fluorescens for the enhanced control of Fusarium wilt disease caused by Fusarium oxysporum infecting Arachis hypogaea L.

Fusarium wilt caused by Fusarium oxysporum is a devastating disease of peanut. The fungus causes severe yield loss in groundnut. Combinations of biocontrol agents that are compatible with each other is a viable approach to control the plant disease. The study was conducted to determine the beneficiary aspects of combining different species of Trichoderma and Pseudomonasfluorescens i.e Trichoderma viride+Pseudomonas fluorescens (Tv+Pf), Trichoderma harzianum+Pseudomonas fluorescens (Th+Pf) and Trichoderma viride +Trichoderma harzianum (Tv+Th) to control the Fusarium wilt in biochemicalparameters such as DNA, RNA, Amino nitrogen, phenols, dihydroxy and proline contents of Arachis hypogaea.L. Among the three combinations tested, Trichoderma viride + Pseudomonas fluorescens (1+2%) sprayed leaves provided greater suppression of Fusariumoxysporum by increasing the levels of DNA,RNA,Amino nitrogen contents resulting in the suppression of Fusarium wilt disease of Arachis hypogaea L.Maximum reduction of DNA, RNA, Amino nitrogen was observed in the infected Fusariumoxysporumleaves Phenol, Dihydroxy phenols and proline contents increase sharply in the treated plants treated with (Tv+Pf) as compared to the control plants. At the same time the other two combinations resulted in enhanced control in comparison with individual ones. This present study indicates that specific combination of Trichoderma viride and Pseudomonas fluorescens could have the greater efficacy in the inhibition of pathogen in the biocontrol of Fusarium wilt disease as compared with individual strains.

Microflora that harbor the NRPS gene are responsible for Fusarium wilt disease-suppressive soil

Non-ribosomal peptides (NRPs) are one of the largest groups of natural microbial secondary metabolites, which include peptides such as the antibiotics vancomycin and gramicidin, as well as lipopeptides (surfactin, iturin A and bacillomycin). In this study, banana Fusarium wilt disease suppressive and conducive soils were chosen to investigate the role of microbes that harbor the NRPS gene in disease suppression based on the 454-pyrosequencing platform and real-time PCR technique. The results showed that higher abundances and diversity of microbes that harbor the NRPS gene were observed in the suppressive soil samples than in the conducive soil. According to the results of the DNA sequences blastx of NRPS, the main microbial taxa harboring the NRPS gene were identified, and Pseudomonas in Proteobacteria and Streptomyces in Actinobacteria might be remarkably related to Fusarium wilt disease suppression. Furthermore, the Mantel test showed that compared with bacteria community and chemical properties, the microbial community harboring the NRPS gene had a more significant impact on the disease incidences of Fusarium wilt. This study provided non-specific relationships between groups of microbes harboring NRPS genes and Fusarium wilt disease suppression suggesting potential interaction based on correlation evidence, and pointed out a potential mechanism of suppressive soil.

Soil pre-fumigation could effectively improve the disease suppressiveness of biofertilizer to banana Fusarium wilt disease by reshaping the soil microbiome

Two seasonal pot experiments were conducted to investigate the effect of biofertilizer application after mixture of lime and ammonium bicarbonate (LA) fumigation, on banana Fusarium wilt disease suppression and soil microbial community composition. Biofertilizer application after LA fumigation decreased 80% of disease incidence compared to control of biofertilizer application to non-fumigated soil. Biofertilizer application after fumigation clearly manipulated soil microbial community composition as revealed by non-metric multidimensional scaling and Venn diagram. LA fumigation significantly reduced the abundance of F. oxysporum while biofertilizer application after fumigation could further decrease it. Furthermore, indigenous microbes, e.g., Bacillus, Pseudomonas, and Mortierella, were associated with disease suppression. Biofertilizer application after fumigation significantly (p < 0.05) increased the soil pH and content of soil total C and available P and K, and this probably reshaped soil microbial community as revealed by redundancy analysis and variance partitioning analysis. The observed disease suppression due to biofertilizer application after soil fumigation can be attributed to the reduced abundance of F. oxysporum by general suppression resulting from manipulated soil properties and recovered soil microbiome.

Bio-fertilizer application induces soil suppressiveness against Fusarium wilt disease by reshaping the soil microbiome

Fusarium wilt disease is a growing problem in agriculture systems. Application of bio-fertilizers containing beneficial microbes represents a promising disease control strategy. However, the mechanisms underlying disease suppression remain elusive. Here, in order to assess the importance of direct antagonism and modified soil microbiota on suppression of Fusarium wilt disease, we conducted a pot experiment with chemical, organic and biologically enhanced fertilizers, we tracked the impact of those fertilizer amendments on disease incidence, and measured the pathogen density and changes in soil microbiota. Alterations in bacterial abundance and community structure after bio-fertilizers application were determined to be key factors in constraining the pathogen, Fusarium oxysporum. In particular, bio-fertilizer application increased the abundance of indigenous microbial groups with reported antifungal activity, such as Lysobacter spp., which could play a keystone role in controlling this pathogen. The microbes introduced in the bio-fertilizer treatments (e.g. Bacillus and Trichoderma spp.) induced suppressiveness via alteration of the soil microbiome rather than direct pathogen inhibition. These results contrast with the commonly held paradigm of disease suppression using beneficial microbes and open up new perspectives for the promotion of soil health. In addition to seeking antagonistic microbes based on their direct inhibitory activity, disease suppression may also be achieved by introducing keystone species that reshape soil microbiome structure and function.

The influence of different concentrations of bio-organic fertilizer on cucumber Fusarium wilt and soil microflora alterations

Fusarium wilt is one of the main diseases of cucumber, and bio-organic fertilizer has been used to control Fusarium wilt. In this study, a pot experiment was conducted to evaluate the effects of bio-organic fertilizer applied at four levels on the suppression of Fusarium wilt disease in cucumber, the soil physico-chemical properties and the microbial communities. In comparison with the control (CK), low concentrations of bio-organic fertilizer (BIO2.5 and BIO5) did not effectively reduce the disease incidence and had little effect on soil microorganisms. High concentrations of bio-organic fertilizer (BIO10 and BIO20) significantly reduced the disease incidence by 33.3%-66.7% and the production was significantly improved by 83.8%-100.3%. The soil population of F. oxysporum f. sp. cucumerinum was significantly lower in bio-organic fertilizer treatments, especially in BIO10 and BIO20. The microorganism activity increased with the bio-organic fertilizer concentration. High-throughput sequencing demonstrated that, at the order level, Sphingomonadales, Bacillales, Solibacterales and Xylariales were significantly abundant in BIO10 and BIO20 soils. At the genus level, the abundance and composition of bacterial and fungal communities in BIO10 and BIO20 were similar, illustrating that high concentrations of bio-organic fertilizer activated diverse groups of microorganisms. Redundancy analysis (RDA) showed that Xanthomonadales, Sphingomonadales, Bacillales, Orbiliales, Sordariales, and Mucorales occurred predominantly in the BIO10 and BIO20. These microorganisms were related to the organic matter, available potassium and available phosphorus contents. In conclusion, a high concentration of bio-organic fertilizer application suppressed the Fusarium wilt disease and increased cucumber production after continuous cropping might through improving soil chemical condition and manipulating the composition of soil microbial community.

Distinct roles for soil fungal and bacterial communities associated with the suppression of vanilla Fusarium wilt disease

Characterizing microbial communities associated with disease-suppressive soil is an important first step toward understanding the potential of microbiota to protect crops against plant pathogens. In the present study, we compared microbial communities in suppressive- and conducive-soils associated with Fusarium wilt disease in a vanilla long-term continuous cropping system. Suppressive soil was associated with higher fungal diversity and lower bacterial diversity. The fungal phyla Zygomycota and Basidiomycota, and the bacterial phyla Acidobacteria, Verrucomicrobia, Actinobacteria and Firmicutes were strongly enriched in the suppressive soil. Notably, suppressive soil was dominated by the fungal genus Mortierella, accounting for 37% of the total fungal sequences. The hyper-dominance of Mortierella spp. in suppressive soil suggests that this taxon may serve as an indicator and enhancer of Fusarium wilt disease suppression in vanilla. In addition, Molecular Ecological Network analysis revealed that fungal communities were more connected and showed more co-occurrence relationships in the suppressive versus conducive soils. Our results indicate that fungal communities may be important in the development of soil suppressiveness against vanilla Fusarium wilt disease.

Soil chemical and microbial responses to biogas slurry amendment and its effect on Fusarium wilt suppression

The rapid development of biogas production will result in increased use of biogas slurry (BS) as organic fertilizer. However, side effects such as suppression of soilborne diseases are not yet well investigated and understood. Therefore, the objectives of the study were to evaluate the effects of biogas slurry application on suppression of Fusarium wilt disease of watermelon and its relationship with soil chemical and microbiological properties. Pot and field experiments were conducted to compare effects of biogas slurry application on Fusarium wilt disease suppression of watermelon in soil with a moisture content of 60% water holding capacity (WHC) or flooded continuously. Fusarium wilt was significantly suppressed in soil from biogas slurry amended plots. Biogas slurry flooding enhanced the degree of suppression in the pot experiment. Moreover, the biogas slurry treatment also significantly suppressed Fusarium wilt in the field with a disease index of 33.2% compared with 69.6% in water treatment. Biogas slurry strongly reduced the pathogen population in rhizosphere soil. The populations were decreased by 43.1% and 95.9% in the biogas slurry moist and flooding treatments, respectively. Biolog data indicated that average well color development (AWCD) and Shannon-weaver index were increased significantly in biogas flooding treatment. Principal component analysis showed that Fusarium wilt was negatively correlated with NH4+-N, available K (AK), water-soluble carbon (DOC), water soluble nitrogen (DON) and phenolic acid (PA) contents in soil and positively correlated to soil pH and soil redox potential (Eh). Microbial communities, in general, did not significantly correlate with disease suppression.

Rhizosphere Inhibition of Cucumber Fusarium Wilt by Different Surfactin- excreting Strains of Bacillus subtilis.

Bacillus subtilis B006 strain effectively suppresses the cucumber fusarium wilt caused by Fusarium oxysporum f. sp. cucumerinum (Foc). The population dynamics of Foc, strain B006 and its surfactin over-producing mutant B841 and surfactin-deficient mutant B1020, in the rhizosphere were determined under greenhouse conditions to elucidate the importance of the lipopeptides excreted by these strains in suppressing Foc. Results showed that B. subtilis strain B006 effectively suppressed the disease in natural soil by 42.9%, five weeks after transplanting, whereas B841 and B1020 suppressed the disease by only 22.6% and 7.1%, respectively. Quantitative PCR assays showed that effective colonization of strain B006 in the rhizosphere suppressed Foc propagation by more than 10 times both in nursery substrate and in field-infected soil. Reduction of Foc population at the cucumber stems in a range of 0.96 log10 ng/g to 2.39 log10 ng/g was attained at the third and the fifth weeks of B006 treatment in nursery substrate. In field-infected soil, all three treatments with B. subtilis suppressed Foc infection, indicated by the reduction of Foc population at a range of 2.91 log10 ng/g to 3.36 log10 ng/g at the stem base, one week after transplanting. This study reveals that the suppression of fusarium wilt disease is affected by the effective colonization of the surfactin-producing B. subtilis strain in the rhizosphere. These results improved our understanding of the biocontrol mechanism of the B. subtilis strain B006 in the natural soil and facilitate its application as biocontrol agent in the field.

Combined application of native Trichoderma isolates possessing multiple functions for the control of Fusarium wilt disease in banana cv. Grand Naine

Fusarium wilt caused by Fusarium oxysporum f. sp. cubense (Foc) is considered as a lethal disease of bananas worldwide. To manage the disease effectively, 20 rhizospheric and 43 endophytic Trichoderma isolates obtained from 12 different Foc resistant banana accessions were evaluated against Foc in vitro and in vivo. In vitro screening among Trichoderma isolates for their multiple functions (mycelial and spore germination inhibition, hydrogen cyanide, chitinolytic enzymes, non-volatile and volatile metabolites production) in suppressing Foc and promoting plant growth (IAA production and phosphate solubilisation) indicated that the multiple biocontrol actions were significantly higher in 6 isolates of rhizospheric Trichoderma and 10 isolates of endophytic Trichoderma compared to other isolates. The greenhouse evaluation of individual application of these rhizospheric and endophytic Trichoderma isolates against Fusarium wilt pathogen in cv. Grand Naine (AAA) indicated significant suppression of Fusarium wilt disease and increased plant growth characters as compared to Foc pathogen inoculated plants. However, none of these individual Trichoderma isolates recorded complete suppression of Fusarium wilt disease. Therefore, the greenhouse evaluation involving combination of rhizospheric Trichoderma sp. NRCB3 + endophytic Trichoderma asperellum Prr2 recorded 100% reduction of Fusarium wilt disease and increased plant growth parameters up to 250% when compared to individual isolates application and Foc alone-inoculated plants. Further, the field evaluation of this combination of Trichoderma isolates applied for three times: (1) at 15 days before planting, (2) second month after planting and (3) fourth month after planting resulting in significant reduction of Fusarium wilt disease and also increase in bunch weight as compared to untreated control plants. Therefore, these Trichoderma isolates may be used in combination for the effective suppression of Fusarium wilt disease in banana.

Effect of biofertilizer for suppressing Fusarium wilt disease of banana as well as enhancing microbial and chemical properties of soil under greenhouse trial

Biofertilizer application has been proposed as a strategy for the management of banana Fusarium wilt disease, which has severely decreased banana production. In this study, a 4-season pot experiment was conducted to evaluate the effects of sustainable biofertilizer application at low and high levels on banana Fusarium wilt disease suppression, soil chemical properties and microbial communities. The results showed sustainable biofertilizer application effectively controlled the disease, especially at a high level. Next-generation sequencing of the 16S rRNA and internal transcribed spacer (ITS) genes using the MiSeq platform showed that the soil bacterial and fungal communities in the treatment amended with a high level of biofertilizer (HBIO) were significantly different from a low level biofertilizer treatment (LBIO) or chemical fertilizer control (CF). Moreover, the abundance of Firmicutes and Bacillus was significantly increased, while the abundance of Acidobacteria, Bacteroidetes and Ascomycota was significantly decreased in the HBIO treatment compared with the CF control. Furthermore, the abundance of Fusarium was significantly reduced in the HBIO treatment compared with CF control and was slightly reduced (not significant) compared with the LBIO treatment. Redundancy analysis and Spearman correlation showed that Bacillus, Spartobacteria_genera and TM7_genera dominated in the HBIO treatment and they were positively correlated with the soil pH and the contents of total nitrogen and carbon and available phosphorus, which were negatively correlated with disease incidence. In conclusion, sustainable biofertilizer application suppressed the Fusarium wilt disease might through improving soil chemical condition and manipulating the composition of soil microbial community, including specific enrichment of Firmicutes (Bacillus), Anoxybacillus, Spartobacteria_genera, TM7_genera, Cantharellus, Pateramyces and Synchytrium.

Rhizosphere microbial community manipulated by 2 years of consecutive biofertilizer application associated with banana Fusarium wilt disease suppression

In our previous work, applying biofertilizer containing Bacillus amyloliquefaciens strain NJN-6 to a banana orchard infected by a serious Fusarium wilt disease over two consecutive years effectively controlled this soil-borne disease. In this study, deep pyrosequencing of 16S ribosomal RNA (rRNA) genes and internal transcribed spacer (ITS) sequences was performed to investigate how the composition of rhizosphere microbial community responded to the application of biofertilizer (BIO), pig manure compost (PM), and chemical fertilizer (CF) and to explore the potential correlation between the microbial community composition and the Fusarium wilt disease. A total of 104,201 bacterial 16S rRNA genes and 154,953 fungal ITS sequence reads were obtained after basic quality control, and Acidobacteria, Actinobacteria, Bacteroidetes, Firmicutes, Proteobacteria, and Ascomycota were the most abundant bacterial and fungal phyla across all samples. Compared with the PM and CF control, the alpha diversity of bacteria significantly (P < 0.05) increased, whereas the value of the fungi was significantly (P < 0.05) reduced following two consecutive years of biofertilizer application. Moreover, the abundance of Acidobacteria (Gp1 and Gp3), Firmicutes, Leptosphaeria, and Phaeosphaeriopsis was significantly (P < 0.05) increased, while the abundance of Proteobacteria and Ascomycota was significantly (P < 0.05) decreased in the BIO treatment. Furthermore, the abundance of Fusarium, a causal pathogen for Fusarium wilt disease, was significantly (P < 0.05) reduced in the BIO treatment compared with the CF control and was slightly reduced (not significant) compared with the PM control. Interestingly, the disease incidence was negatively correlated with the enriched taxa of Acidobacteria (Gp1 and Gp3) and Firmicutes, Leptosphaeria, and Phaeosphaeriopsis but positively correlated with abundance of Proteobacteria, Ascomycota, Fusarium, Cylindrocarpon, Gymnascella, Monographella, Pochonia, and Sakaguchia taxa. The results from this study suggest that 2 years of biofertilizer application manipulated the composition of rhizosphere microbial community and induced the Fusarium suppression by increasing bacterial diversity and potentially stimulating microbial consortia taxa, such as Acidobacteria (Gp1 and Gp3), Firmicutes, Leptosphaeria, and Phaeosphaeriopsis.