Conducive Soil Research Articles

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.

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.

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.

Bacteria from four phylogroups of the Pseudomonas syringae complex can cause bacterial canker of apricot

Pseudomonas syringae is described as a species complex, containing P. syringae‐related species classified into 13 phylogroups and 23 clades. Pseudomonas syringae is one of the main pathogens of fruit trees, affecting nut trees, hazelnut and kiwi, pome and stone fruits. Bacterial canker of apricots is an important disease in regions of production with cold winters and conducive soils. This work characterizes the bacteria able to induce canker in apricots isolated in different French orchards. Bacteria from four phylogroups were able to induce canker. The pathogenicity to apricot was not linked to the pathogenicity to the three herbaceous species and cherry fruits tested, and was not always related to hypersensitive reaction on tobacco and ice nucleation activity. Bacteria pathogenic to apricot belong to phylogroups 01, 02, 03 and 07. The bacteria of phylogroups 01a and 07a (Pseudomonas viridiflava) characterized in this work have not previously been described as pathogenic to apricot.

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.

Biocontrol Prospects of Pseudomonas fluorescens AS15 Against Banded Leaf and Sheath Blight Disease of Maize Under Field Condition in Conducive Soil

Banded leaf and sheath blight (BL&SB) disease of maize caused by Rhizoctonia solani is widespread in humid Terai region of Western Himalayas and leads to 11–40% yield loss in maize. Pseudomonas fluorescens AS15 is an ideal antagonist against BL&SB pathogen. Disease severity is reduced when population of AS15 reaches threshold level 5.3 × 105 CFU g−1 in soil at 45 days after inoculation. It is metabolically versatile and utilizes various carbohydrates and nitrogen sources of plants root exudates. Application of P. fluorescens AS15 in conducive soil reduced disease incidence and disease severity and increased grain yield to 33.4%, 46.8% and 8.4%, respectively, during June 2014 field trial. The reduction in disease incidence (18.1%) and disease severity (35.6%) along with the increase in yield (8.1%) was also observed in June 2015 trial carried out in the same fields without further application of antagonistic bacteria. The results clearly demonstrate biocontrol efficacy and successful rhizospheric colonization of P. fluorescens AS15 in natural conditions.

Microbial Community Composition in Take-All Suppressive Soils.

Gaeumannomyces graminis var. tritici (Ggt) is the main soilborne factor that affects wheat production around the world. Recently we reported the occurrence of six suppressive soils in monoculture areas from indigenous “Mapuche” communities, and evidenced that the suppression relied on the biotic component of those soils. Here, we compare the rhizosphere and endosphere microbial community structure (total bacteria, actinomycetes, total fungi, and ascomycetes) of wheat plants grown in suppressive and conducive soils. Our results suggested that Ggt suppression could be mediated mostly by bacterial endophytes, rather than rhizosphere microorganisms, since the community structure was similar in all suppressive soils as compared with conducive. Interestingly, we found that despite the lower incidence of take-all disease in suppressive soils, the Ggt concentration in roots was not significantly reduced in all suppressive soils compared to those growing in conducive soil. Therefore, the disease suppression is not always related to a reduction of the pathogen biomass. Furthermore, we isolated endophytic bacteria from wheat roots growing in suppressive soils. Among them we identified Serratia spp. and Enterobacter spp. able to inhibit Ggt growth in vitro. Since the disease, but not always pathogen amount, was reduced in the suppressive soils, we propose that take all disease suppressiveness is not only related to direct antagonism to the pathogen.

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.

Bacterial community assemblages in the rhizosphere soil, root endosphere and cyst of soybean cyst nematode-suppressive soil challenged with nematodes.

In disease-suppressive soil, plants rely upon mutualistic associations between roots and specific microbes for nutrient acquisition and disease suppression. Notably, the transmission of suppressiveness by the cysts of sugar beet cyst nematode from suppressive to conducive soils has been previously observed in greenhouse trials. However, our current understanding of the bacterial assemblages in the cyst, root endosphere and rhizosphere soil is still limited. To obtain insights into these bacterial microbiota assemblages, the bacterial communities inhabiting the plant-associated microhabitats and cysts in soybean cyst nematode (SCN)-suppressive soil were characterized by deep sequencing, using soybean grown under growth room conditions with additional SCN challenge. Clustering analysis revealed that the cyst bacterial community was closer to the root endosphere community than to the rhizosphere and bulk soil communities. Interestingly, the cyst bacterial community was initially established by the consecutive selection of bacterial taxa from the soybean root endosphere. We found a set of potential microbial consortia, such as Pasteuria, Pseudomonas, Rhizobium, and other taxa, that were consistently enriched in the rhizocompartments under SCN challenge, and more abundant in the cysts than in the bulk soil. Our results suggest that the soybean root-associated and cyst microbiota may cause the suppressiveness of SCN in suppressive soil.

Watermelon planting is capable to restructure the soil microbiome that regulated by reductive soil disinfestation

Reductive soil disinfestation (RSD) is an effective method to suppress many types of soil-borne diseases in various crops. However, the changes of soil-borne pathogens and microbial communities after crop cultivation in the RSD-treated soils are poorly understood. In the present study, pot experiment was conducted to evaluate the impacts of RSD treatment, with the incorporation of sugar fermentation liquor, on soil Fusarium oxysporum populations, microbial activities, and microbial communities at both after RSD treatment and watermelon planting. The results showed that RSD treatment could considerably inhibit the F. oxysporum and Fusarium wilt disease, promote the growth of watermelon, and enhance microbial activity. However, the pathogen of F. oxysporum resurged quickly after the watermelon cultivation. Although RSD treatment could significantly alter soil microbial communities, the watermelon cultivation also had the capacity to restructure the soil microbial communities to a similar status with control. Collectively, RSD treatment could considerably reduce soil conduciveness to Fusarium wilt and this conduciveness was quickly resurged after watermelon planting. Thus, the changes of F. oxysporum and soil microbial community after watermelon cultivation were likely due to the root exudates released by watermelon that had enough powerful driving force to select similar taxa by filtering the microbial seed bank.

Comparative Microbiome Analysis of a Fusarium Wilt Suppressive Soil and a Fusarium Wilt Conducive Soil From the Châteaurenard Region.

Disease-suppressive soils are soils in which specific soil-borne plant pathogens cause only limited disease although the pathogen and susceptible host plants are both present. Suppressiveness is in most cases of microbial origin. We conducted a comparative metabarcoding analysis of the taxonomic diversity of fungal and bacterial communities from suppressive and non-suppressive (conducive) soils as regards Fusarium wilts sampled from the Châteaurenard region (France). Bioassays based on Fusarium wilt of flax confirmed that disease incidence was significantly lower in the suppressive soil than in the conducive soil. Furthermore, we succeeded in partly transferring Fusarium wilt-suppressiveness to the conducive soil by mixing 10% (w/w) of the suppressive soil into the conducive soil. Fungal diversity differed significantly between the suppressive and conducive soils. Among dominant fungal operational taxonomic units (OTUs) affiliated to known genera, 17 OTUs were detected exclusively in the suppressive soil. These OTUs were assigned to the Acremonium, Chaetomium, Cladosporium, Clonostachys, Fusarium, Ceratobasidium, Mortierella, Penicillium, Scytalidium, and Verticillium genera. Additionally, the relative abundance of specific members of the bacterial community was significantly higher in the suppressive and mixed soils than in the conducive soil. OTUs found more abundant in Fusarium wilt-suppressive soils were affiliated to the bacterial genera Adhaeribacter, Massilia, Microvirga, Rhizobium, Rhizobacter, Arthrobacter, Amycolatopsis, Rubrobacter, Paenibacillus, Stenotrophomonas, and Geobacter. Several of the fungal and bacterial genera detected exclusively or more abundantly in the Fusarium wilt-suppressive soil included genera known for their activity against F. oxysporum. Overall, this study supports the potential role of known fungal and bacterial genera in Fusarium wilt suppressive soils from Châteaurenard and pinpoints new bacterial and fungal genera for their putative role in Fusarium wilt suppressiveness.

Common bean (Phaseolus vulgaris L.) growth promotion and biocontrol by rhizobacteria under Rhizoctonia solani suppressive and conducive soils

Rhizobacteria promote plant growth and disease control. However, in crop management practices cultivar and environmental conditions may also interfere with diseases outcome. This study aimed to evaluate the effect of common bean seed treatment with isolates ALB629 and UFLA285 of Bacillus amyloliquefaciens, combined or not with metalaxyl + fludioxonil, the control of Rhizoctonia solani damping-off and web blight (WB), plant growth parameters and common bean yield. Field and greenhouse trials were carried out in two different locations in Brazil – Lavras, MG (Southeast) with suppressive soil conditions and Boa Vista, RR (North) with a conducive WB condition, using two cultivars of common bean – Pérola and BRS Agreste. The treatments responded differently to either the locations and the cultivars regarding the disease development or plant growth parameters. In Lavras the suppressive conditions did not allow R. solani establishment and promoted higher seed germination and emergency when soils were kept in natural conditions compared to sterile soils. In Boa Vista with conducive conditions, treatments with rhizobacteria associated with fungicide reduced by up to 164% the WB incidence in both cultivars, but the treatment with only ALB629 or UFLA285 also reduced the disease severity. The combination of rhizobacteria with fungicide ensured consistency and stability of results. The common bean yield was higher than the control in 23% and about 500% in Lavras (cv. Perola) and Boa Vista (cv. BRS Agreste), respectively when seeds were treated with ALB629. The use of ALB629 is a plausible strategy for bean seed treatment to control disease and increase bean yield, and therefore an important tool to improve common bean production.

Suppression of the activity of arbuscular mycorrhizal fungi by the soil microbiota

Arbuscular mycorrhizal fungi (AMF) colonise roots of most plants; their extra-radical mycelium (ERM) extends into the soil and acquires nutrients for the plant. The ERM coexists with soil microbial communities and it is unresolved whether these communities stimulate or suppress the ERM activity. This work studied the prevalence of suppressed ERM activity and identified main components behind the suppression. ERM activity was determined by quantifying ERM-mediated P uptake from radioisotope-labelled unsterile soil into plants, and compared to soil physicochemical characteristics and soil microbiome composition. ERM activity varied considerably and was greatly suppressed in 4 of 21 soils. Suppression was mitigated by soil pasteurisation and had a dominating biotic component. AMF-suppressive soils had high abundances of Acidobacteria, and other bacterial taxa being putative fungal antagonists. Suppression was also associated with low soil pH, but this effect was likely indirect, as the relative abundance of, e.g., Acidobacteria decreased after liming. Suppression could not be transferred by adding small amounts of suppressive soil to conducive soil, and thus appeared to involve the common action of several taxa. The presence of AMF antagonists resembles the phenomenon of disease-suppressive soils and implies that ecosystem services of AMF will depend strongly on the specific soil microbiome.

SOIL FUNGAL DIVERSITY IN CABBAGE HABITATS WITH AND WITHOUT CLUBROOT SYMPTOM

Cabbage (Brassica oleracea L.) was a vegetable crops cultivated in the highlands to meet the needs of the community vegetable. The main obstacle was the cultivation of cabbage root disease outbreak mace (clubroot), which until now have not found an effective control techniques. Clubroot disease caused by organisms that resemble fungi: Plasmodiophora brassicae Wor. Which was the soil inhibitant and soil borne pathogen. Therefore, there must be a way to control environmentally friendly by using suppressive soil, find microbes antagonists related to the cabbage plant habitat in the soil. The results showed that the index of diversity both on suppressive and conducive soil of 1.2304 and 1.2811 respectively, and the index of dominance on the suppressive and conducive soil were 0.6677 and 0.6838. Prevalence micoflora of the suppressive soil amounted to 44.22 % and 43.06 % conducive soil all dominated by Fusarium spp. Microbial antagonist as a potential control of P. brassicae was Trichoderma sp . Based on the analysis in the suppressive soil as much as 171 x 103 cfu /g soil, higher than on the conducive soil to 90 x 103 cfu /g soil.

Contrasting physical and biochemical properties of orchard soils suppressive and conducive to Fusarium wilt of banana

AbstractFusarium wilt disease is one of the most serious soil‐borne diseases in banana orchards worldwide. Some soils are suppressive to Fusarium wilt, although the mechanisms are still unclear. In this study, two typical banana‐growing soils (ultisol and inceptisol), which were either suppressive or conducive to Fusarium wilt, were collected from Hainan, China. Particle size distribution, pH values, electrical conductivity (EC), enzyme activities and microbial polymerase chain reaction amplification of the soil samples were analysed. The suppressive soils had significantly more >2 and <0.053 mm aggregates than the conducive soils. In addition, the suppressive soils had a comparatively even size distribution within the range of 0–0.25 mm. Total carbon, total nitrogen and soil enzyme activities in the aggregates of suppressive soils were also significantly higher than those in the conducive soils. For example, soil invertase activities in the >2 mm aggregates were 7.9–11.9 and 3.2–3.3 mg/g for the suppressive and conducive soils, respectively. Furthermore, in situ EC can be applied as an indicator of the integrated contrast between the suppressive and conducive soils, and could be a new tool for monitoring soil‐borne disease.

“There Is No Cultivable Land Here”: Food Security and the Politics of Coral Rag Cultivation in Jibondo Island, Tanzania

Jibondo Island is widely known as the most disadvantaged area in Mafia Island, Tanzania, where there is virtually no cultivable soil. The Island is mainly covered by coral rag, which has tended to serve as a dominant factor for explaining the seemingly absence of crop production in the area. Evidence suggests that most people in Jibondo are often food insecure than people in other villages which have conducive soils for crop production. This article employs a range of qualitative methods to analyze the narratives of various actors about food production in Jibondo. It is argued that while actors have tended to blame coral rag for constraining crop production, they must recognize and respond to other social-ecological factors to understand why crop production is problematic in the area. It is further argued that it is necessary to consider how changes in livelihood activities, land use changes, rainfall variability, soil erosion, changes in the marketing of fish and octopus as well as changes in various cultural traditions have also emerged as key constraining factors, which have often been overlooked. Furthermore, the article points out that it is necessary to show how different actors have contributed to the making and strengthening of coral rag-based explanations as a dominant narrative that continues to persist. The article concludes by pointing to the measures that are crucial for enhancing resilience of both food production and food security in changing social-ecological conditions.

粘土鉱物からのジャガイモそうか病多発地帯の予測法と病害の土壌化学的防除法(土壌伝染病害菌の防除対策-ジャガイモそうか病をめぐって-,シンポジウム)

粘土鉱物からのジャガイモそうか病多発地帯の予測法と病害の土壌化学的防除法(土壌伝染病害菌の防除対策-ジャガイモそうか病をめぐって-,シンポジウム)

KERAGAMAN MIKOFLORA TANAH SUPRESIF DALAM MENGENDALIKAN PENYAKIT AKAR GADA PADA TANAMAN KUBIS (BRASSICA OLERACEA L.)

DIVERSITY OF SUPRESSIVE LAND MICROFLORA IN CONTROL OF PALLDER DISEASE IN CUBES PLANT (BRASSICA OLERACEA L.)Cabbage (Brassica oleracea L.) was a vegetable crops cultivated in the highlands to meet the needs of the community vegetable. The main obstacle was the cultivation of cabbage root disease outbreak mace (clubroot), which until now have not found an effective control techniques. Clubroot disease caused by organisms that resemble fungi: Plasmodiophora brassicae Wor. which was the soil inhibitant and soil borne pathogen. Therefore, there must be a way to control environmentally friendly by using suppressive soil, find microbes antagonists related to the cabbage plant habitat in the soil. The results showed that the index of diversity both on suppressive and conducive soil of 1.2304 and 1.2811 respectively, and the index of dominance on the suppressive and conducive soil were 0.6677 and 0.6838. Prevalence micoflora of the suppressive soil amounted to 44.22 % and 43.06 % conducive soil all dominated by Fusarium spp. Microbial antagonist as a potential control of P. brassicae was Trichoderma sp. Based on the analysis in the suppressive soil as much as 171 x 103 cfu /g soil, higher than on the conducive soil to 90 x 103 cfu /g soil.

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.