Fusarium Wilt Of Melon Research Articles

Comparative transcriptomics and bioinformatics profiling provide insights into resistance to Fusarium wilt in melon

Comparative transcriptomics and bioinformatics profiling provide insights into resistance to Fusarium wilt in melon

Oriental melon roots metabolites changing response to the pathogen of Fusarium oxysporum f. sp. melonis mediated by Trichoderma harzianum

IntroductionTrichoderma spp. is a recognized bio-control agent that promotes plant growth and enhances resistance against soil-borne diseases, especially Fusarium wilt. It is frequently suggested that there is a relationship between resistance to melon wilt and changes in soil microbiome structures in the rhizosphere with plant metabolites. However, the exact mechanism remains unclear.MethodThis study aims to investigate the effects of Trichoderma application on the metabolic pathway of oriental melon roots in response to Fusarium oxysporum f. sp. melonis in a pot experiment. The experiment consisted of three treatments, namely water-treated (CK), FOM-inoculated (KW), and Trichoderma-applied (MM) treatments, that lasted for 25 days. Ultra-performance liquid chromatography-electron spray ionization-mass spectrometry (UPLC-ESI-MS) was used to analyze the compounds in melon roots.ResultsThe results show that Trichoderma harzianum application resulted in a reduction in the severity of oriental melon Fusarium wilt. A total of 416 distinct metabolites, categorized into four groups, were detected among the 886 metabolites analyzed. Additionally, seven differential metabolites were identified as key compounds being accumulated after inoculation with Fusarium oxysporum f. sp. melonis (FOM) and Trichoderma. The mechanism by which Trichoderma enhanced melon's resistance to Fusarium wilt was primarily associated with glycolysis/gluconeogenesis, phenylpropanoid biosynthesis, flavone and flavonol biosynthesis, and the biosynthesis of cofactors pathway. In comparison with the treatments of CK and MM, the KW treatment increased the metabolites of flavone and flavonol biosynthesis, suggesting that oriental melon defended against pathogen infection by increasing flavonol biosynthesis in the KW treatment, whereas the application of Trichoderma harzianum decreased pathogen infection while also increasing the biosynthesis of glycolysis/gluconeogenesis and biosynthesis of cofactors pathway, which were related to growth. This study also aims to enhance our understanding of how melon responds to FOM infection and the mechanisms by which Trichoderma harzianum treatment improves melon resistance at the metabolic level.

The effect of environmental factors on the genetic differentiation of Cucurbita ficifolia populations based on whole-genome resequencing

BackgroundCucurbita ficifolia is one of the squash species most resistant to fungal pathogens, and has especially high resistance to melon Fusarium wilt. This species is therefore an important germplasm resource for the breeding of squash and melon cultivars.ResultsWhole-genome resequencing of 223 individuals from 32 populations in Yunnan Province, the main cucurbit production area in China, was performed and 3,855,120 single-nucleotide polymorphisms (SNPs) and 1,361,000 InDels were obtained. SNP analysis suggested that levels of genetic diversity in C. ficifolia were high, but that different populations showed no significant genetic differentiation or geographical structure, and that individual C. ficifolia plants with fruit rinds of a similar color did not form independent clusters. A Mantel test conducted in combination with geographical distance and environmental factors suggested that genetic distance was not correlated with geographical distance, but had a significant correlation with environmental distance. Further associations between the genetic data and five environmental factors were analyzed using whole-genome association analysis. SNPs associated with each environmental factor were investigated and genes 250 kb upstream and downstream from associated SNPs were annotated. Overall, 15 marker-trait-associated SNPs (MTAs) and 293 genes under environmental selection were identified. The identified genes were involved in cell membrane lipid metabolism, macromolecular complexes, catalytic activity and other related aspects. Ecological niche modeling was used to simulate the distribution of C. ficifolia across time, from the present and into the future. We found that the area suitable for C. ficifolia changed with the changing climate in different periods.ConclusionsResequencing of the C. ficifolia accessions has allowed identification of genetic markers, such as SNPs and InDels. The SNPs identified in this study suggest that environmental factors mediated the formation of the population structure of C. ficifolia in China. These SNPs and Indels might also contribute to the variation in important pathways of genes for important agronomic traits such as yield, disease resistance and stress tolerance. Moreover, the genome resequencing data and the genetic markers identified from 223 accessions provide insight into the genetic variation of the C. ficifolia germplasm and will facilitate a broad range of genetic studies.

<i>Corrigendum to</i>: Assessing genetic diversity and population structure of Iranian melons (<i>Cucumis melo</i>) collection using primer pair markers in association with resistance to Fusarium wilt

We evaluated genetic diversity and population structure of Iranian melons (Cucumis melo L.) using combinations of 35 primer pairs: 15 Simple-Sequence-Repeats (SSR); 10 Inter-Simple-Sequence-Repeats (ISSR); and 10 Sequence-related amplified polymorphism (SRAP) markers in association with resistance to melon Fusarium wilt, caused by Fusarium oxysporum f. sp. melonis (FOM ). Genetic similarity was determined by simple matching coefficient (SSM) and dendrogram by clustering-analysis with unweighted pair groups using arithmetic averages (UPGMA). By combining ISSR-SSR-SRAP markers, a high degree of variation among the melons was detected. The mean polymorphism information content (PIC), marker index (MI), effective-number of alleles (I), expected heterozygosity (H), and Nei's gene diversity parameters were 0.392, 0.979, 1.350, 0.551 and 0.225, respectively. According to MI, PIC, I, H, and Nei indices evaluation, ISSR6, ISSR9, SRAP3, SRAP5, SSR3 and SSR6 had the best performance in genetic diversity of the related melons population. The 35 primers yielded a total of 264 bands, of which 142 showed polymorphism. Clustering of genotypes based on resistance to Fusarium wilt, and comparison with grouping on SSR, SRAP and ISSR marker revealed a significant compliance between disease severity and molecular marker dendrograms. Thus, increasing the number of molecular markers for genetic diversity provides a powerful tool for future agricultural and conservation tasks.

Molecular Variability of the Fusarium solani Species Complex Associated with Fusarium Wilt of Melon in Iran.

Species of the Fusarium solani species complex (FSSC) are responsible for the Fusarium wilt disease of melon (Cucumis melo), a major disease of this crop in Iran. According to a recent taxonomic revision of Fusarium based primarily on multilocus phylogenetic analysis, Neocosmospora, a genus distinct from Fusarium sensu stricto, has been proposed to accommodate the FSSC. This study characterized 25 representative FSSC isolates from melon collected in 2009-2011 during a field survey carried out in five provinces of Iran. Pathogenicity assays showed the isolates were pathogenic on different varieties of melon and other cucurbits, including cucumber, watermelon, zucchini, pumpkin, and bottle gourd. Based on morphological characteristics and phylogenetic analysis of three genetic regions, including nrDNA internal transcribed spacer (ITS), 28S nrDNA large subunit (LSU) and translation elongation factor 1-alpha (tef1), Neocosmospora falciformis (syn. F. falciforme), N. keratoplastica (syn. F. keratoplasticum), N. pisi (syn. F. vanettenii), and Neocosmospora sp. were identified among the Iranian FSSC isolates. The N. falciformis isolates were the most numerous. This is the first report of N. pisi causing wilt and root rot disease in melon. Iranian FSSC isolates from different regions in the country shared the same multilocus haplotypes suggesting a long-distance dispersal of FSSC, probably through seeds.

Development and Evaluation of a New Source of Tolerance to Fusarium Wilt Race 1.2 in Melon

Melon Fusarium wilt, caused by Fusarium oxysporum f. sp. melonis (Fom), is one of the most prevalent fungal diseases affecting melon (Cucumis melo L.). We aimed at finding an effective resource for breeding cultivars tolerant to Fom race 1.2, which includes pathotypes that cause yellowing (race 1.2y) and wilting (race 1.2w). We screened 294 melon accessions that originated mainly in Africa and Asia for tolerance to race 1.2y. The highest level of tolerance was observed in the Indian accession PI124550; one of the five PI124550 plants tested showed no disease symptoms. From this plant, a tolerant inbred line, YR01, was developed after seven rounds of selfing combined with selection for tolerance to race 1.2y. YR01 had a high level of tolerance not only to race 1.2y, but also to race 1.2w. It was more tolerant to race 1.2y than the tolerant reference control ‘Isabelle’ and was equally tolerant to race 1.2w. Analysis of F1 hybrids and an F2 population developed by crossing YR01 with susceptible ‘Earl’s Favorite Harukei 3’ suggested that YR01 had multiple recessive and dominant (or codominant) genes for tolerance to race 1.2y and one dominant gene for tolerance to race 1.2w. These results indicate that PI124550 and its derivative YR01 are a promising breeding material with novel genes conferring practically useful tolerance to both pathotypes of race 1.2.

Assessing genetic diversity and population structure of Iranian melons (Cucumis melo) collection using primer pair markers in association with resistance to Fusarium wilt.

We evaluated genetic diversity and population structure of Iranian melons (Cucumis melo L.) using combinations of 35 primer pairs: 15 Simple-Sequence-Repeats (SSR); 10 Inter-Simple-Sequence-Repeats (ISSR); and 10 Sequence-related amplified polymorphism (SRAP) markers in association with resistance to melon Fusarium wilt, caused by Fusarium oxysporum f. sp. melonis (FOM). Genetic similarity was determined by simple matching coefficient (SSM) and dendrogram by clustering-analysis with unweighted pair groups using arithmetic averages (UPGMA). By combining ISSR-SSR-SRAP markers, a high degree of variation among the melons was detected. The mean polymorphism information content (PIC), marker index (MI), effective-number of alleles (I), expected heterozygosity (H), and Nei's gene diversity parameters were 0.392, 0.979, 1.350, 0.551 and 0.225, respectively. According to MI, PIC, I, H, and Nei indices evaluation, ISSR6, ISSR9, SRAP3, SRAP5, SSR3 and SSR6 had the best performance in genetic diversity of the related melons population. The 35 primers yielded a total of 264 bands, of which 142 showed polymorphism. Clustering of genotypes based on resistance to Fusarium wilt, and comparison with grouping on SSR, SRAP and ISSR marker revealed a significant compliance between disease severity and molecular marker dendrograms. Thus, increasing the number of molecular markers for genetic diversity provides a powerful tool for future agricultural and conservation tasks.

Exploring Potential Mechanisms of Fludioxonil Resistance in Fusarium oxysporum f. sp. melonis.

Melon Fusarium wilt (MFW), which is caused by Fusarium oxysporum f. sp. melonis (FOM), is a soil-borne disease that commonly impacts melon cultivation worldwide. In the absence of any disease-resistant melon cultivars, the control of MFW relies heavily on the application of chemical fungicides. Fludioxonil, a phenylpyrrole fungicide, has been shown to have broad-spectrum activity against many crop pathogens. Sensitivity analysis experiments suggest that fludioxonil has a strong inhibitory effect on the mycelial growth of FOM isolates. Five fludioxonil-resistant FOM mutants were successfully generated by repeated exposure to fludioxonil under laboratory conditions. Although the mutants exhibited significantly reduced mycelial growth in the presence of the fungicide, there initially appeared to be little fitness cost, with no significant difference (p < 0.05) in the growth rates of the mutants and wild-type isolates. However, further investigation revealed that the sporulation of the fludioxonil-resistant mutants was affected, and mutants exhibited significantly (p < 0.05) reduced growth rates in response to KCl, NaCl, glucose, and mannitol. Meanwhile, molecular analysis of the mutants strongly suggested that the observed fludioxonil resistance was related to changes in the sequence and expression of the FoOs1 gene. In addition, the current study found no evidence of cross-resistance between fludioxonil and any of the other fungicides tested. These results indicate that fludioxonil has great potential as an alternative method of control for FOM in melon crops.

Antioxidant enzymes associated with resistance to Fusarium oxysporum f. sp. melonis race 1.2 in melon

Fusarium wilt of melon, Cucumis melo L. (Cucurbitaceae) caused by Fusarium oxysporum f. sp. melonis (FOM), induces severe symptoms, thus dramatically limiting the yield in melons globally. Incorporating genetic resistance in cultivated crops is considered the most efficient and sustainable solution to control root rot diseases. However, resistance to FOM in melon is quantitative in nature, and the mechanism is poorly understood, and the information about melon-FOM race interactions is still limited. This study explored the changes in the eight antioxidant enzyme activities; catalase (CAT), chitinase (CHI), β-1,3-glucanase (GLU), peroxidase (POX), phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), superoxide dismutase (SOD), and as well as total phenol contents (TPCs) in roots of two resistant ‘Shante-F1’ and ‘Khatooni’ and two susceptible ‘Shante-T’ and ‘Shahabadi’ melon accessions, over the time courses of 7, 14 and 21 days (dpi) following inoculation with an isolate of FOM race-1.2.The results revealed that the up-regulated of this set of defense-related enzymes was a key factor against FOM race-1.2 infection, with levels being elevated up to 3-fold in the resistant accessions. In addition, biomass growth parameters (BMPs), roots and shoots (fresh and dry weights, heights, diameters and roots volume) following inoculation displayed almost similar trends observed for the enzyme activity in resistant melon accessions in comparison to susceptible ones. Thus, studying the physiological metabolic pathways of the related enzymes appears to be an important biochemical marker for breeding programs aiming to elucidate the FOM race 1.2 resistance mechanisms in melon. A better insight in melon defense responses can help to establish biochemical characteristics for the selection of resistant melon sources and provide a theoretical basis for disease control and breeding of melon plants with higher levels of resistance to FOM race 1.2 isolates.

Identification of Fusarium wilt resistance sources in melon (Cucumis melo L.) landraces of Iran using marker-assisted selection technique

Melon (Cucumis melo L.) is an important popular high-consumption product in the world. Melon Fusarium wilt (Fusarium oxysporum f.sp. melonis: FOM) is a global destructive disease. In this research, 88 melon landraces from different geographical regions of Iran together with reference genotypes as control genotypes were screened for resistance to 0 and 1 races of Fusarium wilt disease agent using artificial inoculation and two functional markers for the presence or absence of Fom-2 gene. The landraces in multiple replicates were examined in a greenhouse experiment. Thirty-five out of the 88 landraces were selected to determine the disease incidence percentage (DIP), disease severity percentage (DSP) and area under disease progress curve (AUDPC). Based on the results of marker-assisted selection, 83 genotypes had at least one susceptible allele, while 43 heterozygote genotypes had at least one resistance allele. Among genotypes evaluated in artificial inoculation test, three landraces including Shahd-e-Shiraz Gosht Narenji, Korki and Alam Gorgor indicated the highest level of resistance. It seems that these landraces can be considered as the most useful sources of resistance in breeding programs for introducing Fusarium resistant melons. In contrast, Jalali, Petra falat and Habib-Abad landraces were the most sensitive genotypes, which can be used to produce sensitive standard check lines.

Use of omic approaches for characterizing microbiota from suppressive compost to control soil-borne plant pathogens

Microbiomes composition, diversity, and variability into a collection of suppressive composts were investigated for effective biological control of soil-borne phytopathogens. Pyrosequencing resulted be a reliable and faster method for characterizing fungal and bacterial microbiomes into composts derived from a varied feedstock of different composition, origin and provenience. Differences in taxonomic structure assessed by bioinformatics analyses were related to feedstock origin. Green composts derived from agro-waste and agroindustrial co/byproducts provided the most varied microbiomes either related to suppression of Rhizoctonia damping-off in bean and Verticillium wilt in eggplant, either to control of Phytium damping-off in cucumber and Phytophthora root rot in tomato. On the other hand, composted municipal solid wastes and co-composted cow manure with household waste prevalently given a most specific microbiota related to suppression of Fusarium wilt in melon.

Development of a Colorimetric Loop-mediated Isothermal Amplification Assay for the Visual Detection of Fusarium oxysporum f.sp. melonis

Fusarium wilt of melon, Fusarium oxysporum f.sp. melonis is one of the most important diseases, causing tremendous losses in melon growing areas in Iran. There is a real need for a rapid and inexpensive assay to facilitate accurate disease diagnosis and surveillance for better management of Fusarium wilt outbreaks. One of the procedures designed for detection of this disease is loop-mediated isothermal amplification (LAMP) assay; its efficiency has been contrasted with polymerase chain reaction (PCR). The translation elongation factor 1-alpha gene is basically used for designing the LAMP (i.e. F3, B3, FIP, and BIP) together with PCR (F and B). Using hydroxynaphthol blue (HNB) dye, LAMP was placed in a water bath after the optimization was done. The results show LAMP is an advantageous method because it is highly sensitive (100-fold), quite cheap, user-friendly, and safe; in addition, it is performed quickly by visual detection and does not require DNA extraction (in direct-LAMP). The LAMP is believed to be a simple and reliable tool for laboratory purposes because it needs only very basic instruments and the results can be observed and contrasted visually.

Control of Fusarium wilt of melon by combined treatment with biocontrol, plant-activating, and soil-alkalizing agents

Fusarium wilt of melon is one of the destructive diseases of melon worldwide. To develop a method to control the soilborne disease Fusarium wilt of melon, we applied various combinations of a crop-protective microbe, a plant activator, and a soil pH increaser during seedling cultivation in preliminary greenhouse tests and chose the crop-protective Fusarium oxysporum strain SL0037, plant activator probenazole (PBZ), and soil-alkalizer slag fertilizer (SFR) for further tests in the field. From 2012 to 2014, the effects of treatment combinations with SL0037, PBZ, and SFR were tested in a field that was amended with the melon wilt pathogen F. oxysporum f. sp. melonis. Although disease incidence varied among the 3 years of the study, the main stem of melon plants was longer than that of the untreated control plants or those treated with one or two of the three agents. Results suggest a combination of SL0037, PBZ, and SFR treatments can be used to control Fusarium wilt of melon and improve growth of melon plants.

Evaluation of biocontrol potential of Achromobacter xylosoxidans against Fusarium wilt of melon

To investigate the potential of biological control measures against soil-borne plant pathogens, this study evaluated the in vitro and in vivo antifungal activity of endophytic bacteria, Achromobacter xyloxidans, against isolates of Fusarium oxysporum and Fusarium solani responsible of Fusarium wilt of melon (Cucumis melo) in Tunisia. Twenty-one Fusarium isolates were recovered and identified from diseased tissues of different melongrowing regions. The bacterial isolate was recovered and identified from contaminated Petri plates of the Fusarium phytopathogenic isolate. In vitro assay, the results showed positive effects of A. xylosoxidans by reducing significantly 80% of pathogen mycelial growth compared to the control. Furthermore, under greenhouse conditions, A. xylosoxidans significantly reduced 60% of disease severity on melon plants inoculated with Fusarium isolates. According to our results, A. xylosoxidans could be used as a promising and potentially Fusarium disease bio-control agent.

Comparative genomics of Fusarium oxysporum f. sp.melonis reveals the secreted protein recognized by the Fom-2 resistance gene in melon.

Development of resistant crops is the most effective way to control plant diseases to safeguard food and feed production. Disease resistance is commonly based on resistance genes, which generally mediate the recognition of small proteins secreted by invading pathogens. These proteins secreted by pathogens are called 'avirulence' proteins. Their identification is important for being able to assess the usefulness and durability of resistance genes in agricultural settings. We have used genome sequencing of a set of strains of the melon wilt fungus Fusarium oxysporum f. sp.melonis (Fom), bioinformatics-based genome comparison and genetic transformation of the fungus to identify AVRFOM2, the gene that encodes the avirulence protein recognized by the melon Fom-2 gene. Both an unbiased and a candidate gene approach identified a single candidate for the AVRFOM2 gene. Genetic complementation of AVRFOM2 in three different race 2 isolates resulted in resistance of Fom-2-harbouring melon cultivars. AvrFom2 is a small, secreted protein with two cysteine residues and weak similarity to secreted proteins of other fungi. The identification of AVRFOM2 will not only be helpful to select melon cultivars to avoid melon Fusarium wilt, but also to monitor how quickly a Fom population can adapt to deployment of Fom-2-containing cultivars in the field.

Studies on the mechanisms of pathogenicity in soil-borne plant pathogens

Numerous soil-borne plant pathogens cause wilt diseases by invading host roots. Therefore, the control of wilt diseases using chemical sprays on host leaves is difficult, and the management of soil-borne plant pathogens depends on the fumigation of soil and the breeding of disease resistant cultivars. However, because these methods require time and effort and may have temporary effects, novel methods that can be used in combination with these existing methods are required. Thus, to facilitate the development of methods to control wilt diseases, we examined the pathogenicity of the causal agents of Fusarium wilt of melon, Fusarium oxysporum f. sp. melonis, and bacterial wilt of tomato, Ralstonia solanacearum.

Molecular characterization of Fom-1 gene and development of functional markers for molecular breeding of resistance to Fusarium race 2 in melon

Melon Fusarium wilt disease caused by the soil-borne pathogen Fusarium oxysporum f. sp. melonis (Fom) is one of the most devastating melon diseases worldwide. Recently, the Fom-1 gene responsible for resistance against Fom races 0 and 2 was cloned. In this study we amplified, cloned and sequenced full genomic DNA and cDNA of Fom-1 from several melon resistant and susceptible accessions using three pairs of primers designed within this gene. Sequence analyses showed that this gene contains four exons interrupted by three introns. The comparative sequence analysis of the cloned cDNA amplicons from resistant and susceptible genotypes revealed eight nucleotide substitutions, within Fom-1 coding regions, among which four were non-synonymous. RT-PCR revealed that the Fom-1 expression is induced by Fom race 2 inoculation. The Fom-1 predicted protein (FOM-1) exhibits a tripartite modular structure composed of an N-terminal TIR domain, a central NB–ARC domain and a C-terminal LRR domain. FOM-1 from resistant melon accessions share four amino acid differences relative to the FOM-1 protein in susceptible ones. Two amino acid substitutions N56K and R103H were located at the FOM-1 TIR domain and the substitution E385K in the NB–ARC domain. Based on single nucleotide polymorphisms within the coding region of the Fom-1 locus, we have generated two CAPS markers, Fom-1R and Fom-1S. Results from screening various melon accessions clearly demonstrated the usefulness of both functional CAPS markers in the marker-assisted selection for melon breeding programs.

Control of Fusarium wilt in melon by the fungal endophyte, Cadophora sp.

Two soil-borne fungal endophytes almost completely suppressed the effects of a post-inoculated and virulent strain of Fusarium oxysporum f. sp. melonis when inoculated to axenically reared melon seedlings in Petri dishes. They were identified as Cadophora sp. on the basis of ITS 1–5.8S rDNA–ITS 2 sequences and morphological characters and obtained from the roots of Chinese cabbage grown as bait plants in a mixed soil made up of samples from different forest soils from Alberta and British Columbia, Canada. Hyphae of Cadophora sp. grew along the surface of the root and colonized root cells of the cortex and reduced the ingress of the Fusarium pathogen into adjacent cells. Melon seedlings pre-inoculated with Cadophora sp. were also grown in soil amended with the different N sources, nitrate or the amino acids leucine and valine, and glucose (final C:N ratio = 10:1). After 4 weeks, these seedlings were transplanted into the field and disease symptoms were assessed. Only the endophyte-inoculated seedlings treated with valine could effectively inhibit the development of Fusarium wilt in two plots and reduced disease symptom development by 43 and 62 %.

Development of a New Melon Cultivar ‘Ibaraking’ with High Fruit Growth Ability under Low Temperature Conditions, High Total Soluble Solid Content, and Resistance to Fusarium Wilt

‘Ibaraking’ is a new F1 melon (Cucumis melo L.) cultivar with green-fleshed fruit, high fruit growth ability under low-temperature conditions, high total soluble solid (TSS) content, and a long shelf life. It was developed from a cross between 2 parental lines P2 and P32 at the Plant Biotechnology Institute, Ibaraki Agricultural Center, Ibaraki, Japan. The parental line, P2, was fixed by self-pollination of a line selected from somaclonal variants of a cultivar ‘Andes,’ while another line, P32, was fixed by self-pollination of a cultivar ‘Earl’s Seine Natsu 2.’ The fruit characteristics of ‘Ibaraking’ were compared with those of the common melon semi-forcing culture cultivars ‘Andes-5’ and ‘Otome,’ from 2005 to 2007, in semi-forcing culture by creeping cultivation. In ‘Ibaraking,’ low-temperature fruit growth ability and external appearance were equal to those of ‘Otome’ and exceeded those of ‘Andes-5,’ while the TSS content was similar to that of ‘Andes-5’ and exceeded that of ‘Otome.’ With regard to shelf life, ‘Ibaraking’ was superior to ‘Otome’ and equal to ‘Andes-5.’ In response to Fusarium wilt of melon, the most severe melon disease, ‘Ibaraking’ demonstrated resistance to races 0 and 2. These responses were identical to those of ‘Andes-5’ and ‘Otome.’ Therefore, we conclude that ‘Ibaraking’ appears a more suitable cultivar in semi-forcing culture by creeping cultivation in Ibaraki prefecture, Japan.

Biological control of plant pathogens by microorganisms isolated from agro-industrial composts

Plant diseases caused by pathogenic bacteria and fungi are a severe problem for Mediterranean agriculture and some composts have shown a suppressive capacity due to the antagonistic action of microbial communities inhabiting those substrates. The purpose of this work was to isolate and identify those microorganisms from agro-industrial waste-based compost able to antagonize Xanthomonas campestris and Fusarium oxysporum f.sp. melonis, two devastating phytopathogens in the Southeast of Spain. To this end, a collection of 135 strains comprising bacteria, actinobacteria and fungi was isolated and their suppressiveness tested in vitro. Those strains with the best inhibition indexes were selected for in vivo tests.While performing in vitro assays, half of the tested strains were effective only against F. oxysporum f.sp. melonis, less than a 4% of the tested strains only antagonized X. campestris and eight strains were noticed to be antagonists against both phytopathogens. In vivo assays were performed using five strains selected because of their higher inhibition indexes and identified by molecular methods as Acetobacter indonesiensis, Bacillus pumilus, Paecilomyces variotii, Streptomyces griseus and Acremonium chrysogenum. Additional assays were carried out to check the plants health status in the absence of pathogens so as to discard possible damaged caused by those five biocontrol agents. The in vivo tests succeeded in pointing out P. variotii as a broad spectrum biocontrol agent effective against both bacterial spot of tomato and fusarium wilt of melon.