Fusarium Oxysporum F. Sp. Melonis Research Articles

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.

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.

Validity Determination of Some Molecular Markers Used in Melon Breeding

The present work aimed to validate some molecular markers (AM, FM, Fom2-R408, Fom2-S342, SCAPB051046, SCOPE14541, T1, T1ex, M3A and M3a SCAR markers and Fom1R-Fom1S, CAPS-Dde I, CAPS2, CAPS3 and EX1-C170T CAPS markers) developed for melon breeding in the literature on some melon cultivars and genotypes in Turkey with the aid of marker-assisted selection. For this purpose, these molecular markers developed for resistance to Fusarium oxysporum f. sp. melonis (FOM), Cucumber mosaic virus (CMV) and powdery mildew or sex determination have been tested. AM, FM, Fom2-R408 and Fom2-S342, (SCAR) and Fom1R-Fom1S, CAPS2, and CAPS3 (CAPS) markers for FOM; SCAPB051046 and SCOPE14541, (SCAR) for CMV; CAPS-Dde I for powdery mildew; T1, T1ex, CAPS EX1-C170T, M3a and M3A markers for sex determination were employed. These selected markers were examined in 24 melon genotypes, 11 of which were commercial F1 cultivars. The results were obtained from FM, Fom2-R408 and Fom2-S342 SCAR markers and Fom1R-Fom1S CAPS marker for Fusarium wilt disease and SCAR SCOPE14541 for CMV. In this context, it is seen that the resultant SCAR and CAPS markers could be used effectively in MAS studies.

Multiple fungal diseases resistance induction in Cucumis melo through co-transformation of different pathogenesis related (PR) protein genes

Achieving multiple resistance to fungal diseases, major threat in cucurbits production, is challenging due to the quick rate of variation of fungi species and races, the lack in the knowledge of resistance genes or their complexity, and dragging undesired genesin traditional breeding. Here, we generate polygenic resistance to fusarium and powdery mildew by introducing a transgene cassette of three antifungal pathogenesis related (PR) protein genes (chitinase, glucanase and PR1) into melon (Cucumis melo L.) as a single locus. The presence of three PRs was confirmed by PCR in eight transgenic plantlets among 130 regenerants grown in selective medium. Southern blot hybridization confirmed integration of the transgene cassette in the genome of three lines. Enzyme activity assay demonstrated that chitinase and b-1,3-glucanase activity were higher in transgenic lines than in wild type plants. In-vitro and in-vivo bioassay tests showed that transgenic lines were also more resistant to fungal diseases. Finally, to evaluate the stability and heritability of the acquired resistance, selected transgenic lines were self-pollinated and T1 generation was further evaluated for disease resistance. After artificial inoculation by Fusarium oxysporum f. sp. melonis (FOM), more than 80% of wild types seedlings were infected. By contrast, on avarage 87% of T1 transgenic seedlings did not show disease signs. Moreover, powdery mildew infection was strongly delayed in transgenic plants.

Total Phenolic, Total Flavonoids, Antioxidant and Antifungal Activity of Inula viscosaExtracts from Turkey

This study was conducted to investigate antioxidant, total phenolic, and total flavonoid of ethyl acetate, methanol and hexane extracts of Inula viscosa and the antifungal activity of methanol extract. In the antioxidant study, Free Radical Scavenging Activity (DPPH), ABTS (2,2-azinobis- (3-ethylbenzothiazoline- 6-sulphonic acid), Ferric Reducing Antioxidant Power Activity (FRAP), Cupric Reducing Antioxidant Capacity Activity (CUPRAC), Total phenolic and Flavonoid analyses of each extract were performed. The antioxidant results were calculated at rates ranging between lC50 10.53-157.07 (gg/mL) for DPPH, lC50 4.7020.38 (gg/mL) for ABTS, 0.59-4.28 (gmol TE/mg extracts) for FRAP, and 0.23-7.40 (gmol TE/mg extracts) for CUPRAC. The total phenolic and total flavonoid contents of the extracts were determined to be between 11.38-136.18 (mg GAE/g extract) and 14.38-28.83 (mg QE/g Extract). The antifungal activity of the methanol extract of Inula viscosa against Rhizoctonia solani (R.S), Sclerotinia sclerotiorum (S.S), Fusarium oxysporum f sp. melonis (FOM), and Fusarium. oxysporum f sp. cucumerinum (FOC). Agar diffusion method was used in the activity studies. The activity levels of the 1000, 2000 and 4000 ppm doses of the extract against pathogens were determined. Also, it inhibited the FOC, FOM, SS and RS mycelial growths at the rates of 68.23%, 72.04%, 83.51% and 100% at a high dose, 400 ppm. It is considered that the results obtained in this study are important as they guide the development of new natural antifungal substances.

Resistance risk assessment of Fusarium oxysporum f. sp. melonis against phenamacril, a myosin inhibitor

Fusarium wilt caused by Fusarium oxysporum f. sp. melonis (FOM) is one of the most notorious seed-borne diseases worldwide. Phenamacril is a cyanoacrylate fungicide with novel chemical structure and strong inhibitive activity against FOM. To evaluate the risk of FOM developing phenamacril resistance, five phenamacril-resistant mutants with >800μgml−1 minimum inhibitory concentration were obtained by repeated exposure to the fungicide in the laboratory. Compared with the parental isolate, four of the five phenamacril-resistant mutants showed enhanced biological fitness in sporulation and virulence, but not in sensitivity to various stresses (oxidative and osmotic pressure, cell membrane and wall inhibitor). No positive cross-resistance was observed among phenamacril and the other five fungicides, including azoxystrobin, carbendazim, boscalid, fluazinam and tebuconazole. Sequencing alignment results of the myosin 5 from the five resistant mutants and the parental strain indicated that the three resistant mutants fo-2, fo-3 and fo-4 had a single point mutation (S175L), which may confer the resistance of FOM against phenamacril. Interestingly, the resistant mutant fo-4 harbored not only one mutation (S175L) at myosin 5, but also the other mutation (A52G) at β2-tublin. Our data supported that resistance risk of Fusarium oxysporum f. sp. melonis against phenamacril was between the moderate to high level.

Fusarium oxysporum f. Sp. melonis-melon interaction: Effect of grafting combination on pathogen gene expression

This work is part of a comprehensive study addressed to gain new insights into Fusarium oxysporum f. sp. melonis (FOM)-melon interaction and understand molecular mechanisms of disease control by grafting. Grafting vegetable is primarily used to provide resistance to soilborne diseases. In this study, the effect on FOM race 1 and race 1,2 gene expression was investigated by quantitative PCR (qPCR), during infection of both resistant and susceptible grafted melon scion-rootstock combinations. Eleven fungal genes related to pathogenicity were considered. The expression of the selected genes varied according to race, susceptible or resistant interaction, and time clustering into six profiles. Classical infection related genes, including Zn-Cys transcription factor FOW2, xylanase, and its relative transcriptional activator were highly induced particularly in the resistant combination when infected by race 1,2 at any time point. In turn, ROS degrading catalase/peroxidase enzyme and actin binding protein were upregulated only at the early stage of infection, in both resistant and susceptible combinations. Genes such as E3 ubiquitin-protein ligase and UTP-glucose-1-phosphate uridylyl transferase showed significant differences between both FOM races in both grafting combinations. Whereas MADS-box transcription factor and acyl-CoA synthetase were essentially unmodulated in race 1, but induced in race 1,2. The only gene significantly dependent on fungal race, resistant/susceptible interaction, and time, was a histidine kinase. Temporal transcription profiles were consistent with the capacity of race 1,2 to grow in the resistant host without inducing wilting symptoms being race 1,2 host colonization independent from virulence. In general, single FOM gene transcription profiles showed no evident differences between rootstock and scion confirming at a molecular level that a melon grafted plant reacts to the pathogen as a single genotype ruled by the rootstock.

Tracking of the gene Fom2 and study on the genetic diversity of NB-ARC domain in the number of resistant and sensitive melon cultivars against Fusarium oxysporum f. sp. melonis (race 1)

Vascular wilt caused by Fusarium oxysporum f. sp. melonis (FOM) is one of the most important diseases in melon. Four pathogenic races named: 0, 1, 2, and 1.2 have been identified in population of this fungus based on the pathogenicity pattern on differential varieties. The gene Fom2 has been reported as a key gene for conferring resistance to the fungus race 1. The majority of Iranian melon cultivars are susceptible to race 1. Clarifying the occurrence pattern of Fom2 in the fungus race 1 in sensitive and resistant Iranian melon cultivars in comparison with two standard melon lines could be helpful for the investigation on the role of Fom2 in the cultivars reaction. Since, the full sequence of Fom2 from Melon and I2 from Tomato resistance sources were cloned; it has been shown that the LRR and NB-ARC domains in the coded proteins play critical roles in detection of Avr proteins and R proteins activation as well. Considering to the importance of NB-ARC domain and the lack of functional information in this region of the gene Fom2, this domain was selected for sequencing, identifying possible mutations and to study their possible relationship of mutations with the type of cultivars reaction against fungal races. Six melon cultivars including four Iranian local melon cultivars (Mashhadi, Shahde Shiraz, Khatooni and Khaghani) and two standard melon cultivars (Charentais Fom1 and Charentais Fom2) were used in this study. Two specific primer pairs (PSh20-F/R and PSh20.2-F/R) were designed and used for the tracking of partial and full-length sequence of Fom2. More investigation was performed on the diversity occurrence pattern among cultivars and its conformity with cultivars resistive pattern against the fungus race 1. Our results showed that the partial and the full length sequence of Fom2 had this potential to be tracked in sensitive as well as resistant cultivars. On the other hand, the cultivars reactions were not predictable based on the gene occurrence pattern. However, some studies have already been reported that the linked markers of Fom2 were not useful for the prediction of reaction pattern in Iranian melon cultivars. The partial segments of Fom2 amplified by PSh20-F/R primers were bi-directionally sequenced and the results were submitted in gene bank. Sequence analysis of NB-ARC domain in the six varieties led to detection of 16 polymorphic nucleotide positions, which nine of them appeared in protein levels. Six out of the nine mutations placed in AAA-ATPase subdomain. Although the polymorphic pattern of mutations in nucleotide and amino acid positions were not in accordance with the cultivars resistive pattern but the cultivars could be discriminated based on some other mutations. Due to the switching function of AAA-ATPase sub domain in ATP hydrolysis and activation of R proteins, variation in this region between the resistant and susceptible cultivars could be considerable. It seems the presence of identified mutations at AAA-ATPase subdomain of Fom2 could be considered in cultivars resistive pattern unconformity and it needs to be followed in future studies to clarify the action of detected mutations in this subdomain.

Identification of predictor parameters to determine agro-industrial compost suppressiveness against Fusarium oxysporum and Phytophthora capsici diseases in muskmelon and pepper seedlings.

The lack of reliable prediction tools for evaluation of the level and specificity of compost suppressiveness limits its application. In our study, different chemical, biological and microbiological parameters were used to evaluate their potential use as a predictor parameter for the suppressive effect of composts against Fusarium oxysporum f. sp. melonis (FOM) and Phytophthora capsici (P. capsici) in muskmelon and pepper seedlings respectively. Composts were obtained from artichoke sludge, chopped vineyard pruning waste and various agro-industrial wastes (C1: blanched artichokes; C2: garlic waste; C3: dry olive cake). Compost C3 proved to offer the highest level of resistance against FOM, and compost C2 the highest level of resistance against P. capsici. Analysis of phospholipid fatty acids isolated from compost revealed that the three composts showed different microbial community structures. Protease, NAGase and chitinase activities were significantly higher in compost C3, as was dehydrogenase activity in compost C2. The use of specific parameters such as general (dehydrogenase activity) and specific enzymatic activities (protease, NAGase and chitinase activities) may be useful to predict compost suppressiveness against both pathogens. The selection of raw materials for agro-industrial composts is important in controlling Fusarium wilt and Phytophthora root rot.

IN VITRO CONTROL OF FUSARIUM WILT USING AGROINDUSTRIAL SUBPRODUCT-BASED COMPOSTS

Some kinds of compost suppress soil-borne plant pathogens and although their exact mode of action is not yet clear, several mechanisms seem to be involved in the supressive effect. The abiotic component of compost is an important factor for its suppressive effect in soils, however it must be kept in mind that compost is considered a source of biocontrol agents against several serious plant pathogens. The main aim of this work was to discriminate the biotic and abiotic components in agroindustrial subproduct-based composts that could be potentially used as suppressive soil amendments. Results have shown that the compost’s suppressive effect on mycelial development of Fusarium oxysporum f. sp. melonis (FOM), the causal agent of Fusarium wilt of melon, was due to a combination of biotic and abiotic factors. Similar results were observed when compost extracts were used against the pathogenic fungus. In this case, compost extracts with a concentration between 0.1 and 50% inhibited FOM growth. However, sterilized compost extracts inhibited fungal development when applied at a dose lower than 10%, while higher concentrations (>10%) were not effective, probably due to the toxic substances and nutrient content ratio in the culture media. This can be indicative of a masking of the inhibitory effect at high nutritional levels. Based on these results, we conclude that the suppressive effect of compost is due to a combination of biotic and abiotic factors, though the former are mainly responsible for the biocontrol activity against FOM.

Does organic farming increase soil suppression against Fusarium wilt of melon?

Under Israeli organic farming conditions, compost (mostly made of animal manure) is annually applied as a source of plant nutrients, to enhance soil microbial activity and nutrient cycling and to improve soil structure. Composts are also known for their suppressive properties against soil-borne diseases. The objective of the present study was to assess the level of suppressiveness against Fusarium oxysporum f. sp. melonis (FOM) that may develop in soils with a history of organic farming as compared with conventional farming. Pairs of organic vs. conventional taxonomically identical soil samples were collected from adjacent plots, at various sites throughout the main agricultural areas in Israel. Out of 15 pairs, four of the organically managed soils were significantly more suppressive than their corresponding conventional plots. On the average, the area under the disease progress curve and the final disease incidence of the inoculated plants grown in conventionally managed soils were higher at 12% and 21%, respectively, than those of the plants grown in the organically managed soils. Both differences were significant when examined using two-factor ANOVA test (site and farming system). Microbial activity of the organic soils, as expressed by heat production rate, was positively correlated with soil suppressiveness and was significantly higher by a factor of 2.2 as compared with the conventionally managed paired soils. It is suggested that organic farming practices and especially compost application may lead, with time, to some reduction of the problems caused by FOM. This beneficial effect of organic farming seems non-specific to soil type or climatic region in Israel.

The transcription factor SNT2 is involved in fungal respiration and reactive oxidative stress in Fusarium oxysporum and Neurospora crassa

The Fusarium oxysporum f. sp. melonis (FOM) Snt2 transcription factor is related to pathogenesis. In FOM and Neurospora crassa Δsnt2 strains, hydrogen peroxide-induced SOD activity was impaired. The expression of fe,mn sod genes in the Δsnt2 mutants, was up-regulated following hydrogen peroxide induction, indicative of a mitochondrial function defect. Furthermore, cytochrome-dependent oxidation in FOM and N. crassa was affected, leading to reduced oxygen consumption in the mutants, linking snt2 to regulation of fungal aerobic respiration. This was accompanied by increased expression of an alternative oxidase gene, suggesting the presence of a compensatory mechanism or the potential presence of a direct link between snt2 and regulation of alternative oxidation.

Horticultural Characteristics Of Licorice Waste Compost

Licorice (Glycyrrhiza glabra L.) is a leguminous herbaceous perennial. Its root extracts are commonly used for medicinal uses and as a flavoring agent in the food and tobacco industries. After extraction, about 10,000 tones of licorice root residues are accumulated in Israel annually with no recycling outlet. The objectives of the current research were to develop a reliable protocol for licorice root wastes composting, to test the use of licorice compost as a peat substitute in growing media and to study its suppressiveness against Fusarium oxysporum f. sp. melonis (FOM) – the causal agent of Fusarium wilt of melon (Cucumis melo L.). Licorice root wastes were cocomposted using temperature controlled forced aeration with the coarse fraction of separated cow manure, in order to enrich both its nutrients content and microbial population. Thermophilic conditions prevailed in the pile for 90 days and the compost stabilized and reached ambient temperature 110 days from start. The physical characteristics of the resulted compost were comparable to that of peat. Nutrient content was high and salinity was relatively low. No phytotoxicity was found in the compost extract, based on the cress germination test. Tomato plants grown in compost showed enhanced development as compared to peat. The number of surviving FOM spores incubated in the compost declined faster then in peat. Fusarium infested melon plants survived much better if planted in the licorice compost, as compared to peat. It is concluded that licorice compost can serve as a peat substitute with preferable qualities.

Compost suppressiveness against Fusarium oxysporum was not reduced after one-year storage under various moisture and temperature conditions

The effect of storage conditions on compost suppressiveness against fusarium wilt of melon, caused by Fusarium oxysporum f. sp. melonis (FOM) was studied in relation to the dynamics of compost microbial activity and biodegradability. For this purpose, mature suppressive compost, prepared from tomato plants and separated cow manure, was divided into four portions and stored for one year under cool/warm (12 or 28 °C) or dry/wet (15–35 or 55–65% moisture content) conditions, in four different combinations: cool-dry, warm-dry, cool-wet and warm-wet. All composts retained and even enhanced their suppressive capacity during storage, with no significant differences among them by the end of the storage period. However, significant differences were found in the dynamics of some of the measured chemical and microbial properties. The microbial activity of composts stored under wet conditions was higher than that of those stored under dry condition, which resulted in a substantial decrease in dissolved organic matter content (expressed as dissolved organic carbon; DOC) and increase in its recalcitrance to biological degradation, decrease in basal heat emission, slower response to added glucose or citric acid, and higher NO 3 concentration, indicating increased nitrification under wet conditions. The DOC significantly correlated with several microbial properties as well as with compost suppressiveness of fusarium wilt of melon seedlings, and may be regarded as a most suitable general index for compost maturity. A best-subset multiple linear regression analysis revealed that the three best predictors, namely dissolved organic carbon (DOC), basal heat, and mesophilic bacterial counts, could explain as much as 83% of the total variance in compost suppressiveness. The generally agreed association between compost maturity and suppressiveness was verified in this case. It appears that compost microbial populations might compete and interfere with the saprophytic stage of FOM conidia, between germination and host invasion. In conclusion, it was demonstrated that compost suppressiveness against fusarium wilt of melon can be maintained for at least one year under a wide range of storage conditions, without any loss of suppressive capacity. This fact has positive logistical implications for the use of suppressive composts against FOM.

Evaluation of Compost Amendments for Control of Vascular Wilt Diseases

Vascular wilt fungal pathogens cause heavy economic losses to a wide range of crops; amongst them are Fusarium oxysporum f. sp. melonis (FOM) and Verticillium dahliae Kleb. Several strategies for controlling these pathogens have been introduced, such as soil solarization, resistant rootstocks and biological control. In this study, the suppressive ability of seven different compost amendments and the plant growth-promoting rhizobacterium Paenibacillus alvei K165 (with proven activity against V. dahliae) were tested against FOM in melon and V. dahliae in eggplant. It was shown that K165 had a suppressive effect against the pathogens in all experiments. On the contrary, the composts exhibited a narrow spectrum of effectiveness against the pathogens. Two composts were effective against V. dahliae and one against FOM. Moreover, we investigated the potential of the various compost samples and K165 to induce resistance in an Arabidopsis thaliana–V. dahliae or FOM model system. It was demonstrated that three composts and K165 were effective against V. dahliae; whereas, one compost and K165 were effective against FOM. In a naturally V.dahliae infested field, the ability of K165 to enhance the suppressive effect of one of the compost amendments, was evaluated. It was demonstrated that fortification of the compost with strain K165 significantly reduced disease severity, whereas the single application of the compost was not sufficient to significantly protect the plants.

Evaluation of Rootstock Resistance to Fusarium Wilt and Gummy Stem Blight and Effect on Yield and Quality of a Grafted ‘Inodorus’ Melon

Grafting represents an effective tool for controlling the race 1,2 of Fusarium oxysporum f. sp. melonis (FOM) and Didymella bryoniae in melon (Cucumis melo L.). Although not considered a soilborne pathogen, D. bryoniae survives on plant remains in the soil. The lack of effective resistant commercial hybrids and the gradual reduced use of soil fumigation with methyl bromide increase the risk of damages by both these pathogens. We determined the effectiveness of eight commercial rootstocks, ‘RS 841’, ‘P 360’, ‘ES 99-13’, ‘Elsi’ (Cucurbita maxima Duchesne × Cucurbita moschata Duchesne), and ‘Belimo’, ‘Energia’, ‘Griffin’, ‘ES liscio’ (Cucumis melo genotypes), for their resistance to FOM and D. bryoniae. During 2003 and 2004 growing seasons, the inodorus F1 hybrid Incas was grafted onto each of these commercial rootstocks and then evaluated, under greenhouse conditions, in terms of productivity and fruit quality. Cucurbita rootstocks (‘RS 841’, ‘P 360’, ‘ES 99-13’, ‘Elsi’) were highly resistant both to the race 1,2 of FOM (100% survival) and to D. bryoniae (almost absent crown lesions and low leaf disease index); this reaction clearly differed from that of both the C. melo rootstocks (‘Belimo’, ‘Energia’, ‘Griffin’, ‘ES liscio’) and the control Incas. In both years, the highest yield was recorded in the graft combination Incas/‘RS 841’ with 5.6 and 8.1 kg·m−2 during 2003 and 2004, respectively. The Cucurbita rootstock ‘RS 841’ produced yields higher than C. melo rootstocks (‘Belimo’, ‘Energia’, ‘Griffin’, ‘ES liscio’) and the control Incas. Fruit dry matter, titratable acidity, total soluble solid contents, fruit firmness, and Hunter color [L* (brightness), a* (redness), and b* (yellowness) parameters] of grafted melons were similar to those of the plants grown on their own roots.

In vitro assessment of the inhibition of humic substances on the growth of two strains of Fusarium oxysporum

The effects of four humic substance (HS) samples, a soil humic acid and two humic acids and one fulvic acid isolated from a composting substrate, were evaluated on the mycelial growth of Fusarium oxysporum f. sp. melonis (FOM) and F. oxysporum f. sp. lycopersici (FOL). In general, any HS treatment reduced significantly the radial growth of the FOM mycelium either in normal [potato dextrose agar (PDA) medium] or sub-optimal (water–agar medium) nutritional conditions. Differently, the FOL growth, which was tested only on PDA, was either inhibited or stimulated on dependence of the HS treatment used. The HS fractions isolated from the composting substrate were the most effective inhibitors of mycelial growth of both fungi. Furthermore, any HS treatment was also able to alter the germination process of FOL in aqueous medium, not only by reducing significantly the number of viable germinating conidia but also by generally decreasing the rate of conidial germ-tube elongation. Apparently, the extent of the inhibitory action was related to some chemical and functional properties of HS, such as the COOH group content and elemental composition.

Antagonistic activity of bacteria and fungi from horticultural compost against Fusarium oxysporum f. sp. melonis

The use of composts to suppress soil-borne plant pathogens has been extensively reviewed in recent decades, and several micro-organisms have been identified as biocontrol agents in compost-amended substrates. The aim of this study was to investigate the in vitro and in vivo inhibition and suppression of antagonistic bacteria and fungi from several compost classes toward Fusarium oxysporum f. sp. melonis (FOM). This fungus causes Fusarium wilt of melon which is considered a critical problem in most melon crop zones where it results in extensive economic losses. In addition, effects of the raw material, aeration conditions during composting process and compost maturity on the isolation of biocontrol agents were also analysed. Microbial strains (493) were isolated from compost samples at different maturation phases (245 bacteria, 73 actinomycetes and 175 fungi). Initial soil dilution plate screening detected 179 isolates inhibiting FOM growth. Cell-free extracts of the 179 selected strains were prepared, concentrated and then assayed for their effects on FOM growth from which 10 fungi were antagonistic. The effect of selected fungi on Fusarium wilt of melon was assayed under greenhouse conditions. Results showed that optimal aeration during the composting process was favourable for the isolation of biocontrol agents. Strains with the highest biological control activity were isolated from mature compost samples and were mostly identified as Aspergillus spp. These were consequently considered as potential biocontrol agents against FOM.