Control Verticillium Wilt Research Articles

CGTase, a novel antimicrobial protein from Bacillus cereus YUPP-10, suppresses Verticillium dahliae and mediates plant defence responses.

Verticillium wilt is a plant vascular disease caused by the soilborne fungus Verticillium dahliae that severely limits cotton production. In a previous study, we screened Bacillus cereus YUPP‐10, an efficient antagonistic bacterium, to uncover mechanisms for controlling verticillium wilt. Here, we report a novel antimicrobial cyclodextrin glycosyltransferase (CGTase) from YUPP‐10. Compared to other CGTases, six different conserved domains were identified, and six mutants were constructed by gene splicing with overlap extension PCR. Functional analysis showed that domain D was important for hydrolysis activity and domains A1 and C were important for inducing disease resistance. Direct effects of recombinant CGTase on V. dahliae included reduced mycelial growth, spore germination, spore production, and microsclerotia germination. In addition, CGTase also elicited cotton's innate defence reactions. Transgenic Arabidopsis thaliana lines that overexpress CGTase showed higher resistance to verticillium wilt. Transgenic CGTase A. thaliana plants grew faster and resisted disease better. CGTase overexpression enabled a burst of reactive oxygen species production and activated pathogenesis‐related gene expression, indicating that the transgenic cotton was better prepared to protect itself from infection. Our work revealed that CGTase could inhibit the growth of V. dahliae, activate innate immunity, and play a major role in the biocontrol of fungal pathogens.

Verticillium Wilt of Mint in the United States of America.

Verticillium wilt, caused by the fungus Verticillium dahliae, is the most important and destructive disease of mint (Mentha spp.) in the United States (U.S.). The disease was first observed in commercial mint fields in the Midwestern U.S. in the 1920s and, by the 1950s, was present in mint producing regions of the U.S. Pacific Northwest. Verticillium wilt continues to be a major limiting factor in commercial peppermint (Mentha x piperita) and Scotch spearmint (Mentha x gracilis) production, two of the most important sources of mint oil in the U.S. The perennial aspect of U.S. mint production, coupled with the soilborne, polyetic nature of V. dahliae, makes controlling Verticillium wilt in mint a challenge. Studies investigating the biology and genetics of the fungus, the molecular mechanisms of virulence and resistance, and the role of soil microbiota in modulating host-pathogen interactions are needed to improve our understanding of Verticillium wilt epidemiology and inform novel disease management strategies. This review will discuss the history and importance of Verticillium wilt in commercial U.S. mint production, as well as provide a format to highlight past and recent research advances in an effort to better understand and manage the disease.

Pectin lyase enhances cotton resistance to Verticillium wilt by inducing cell apoptosis of Verticillium dahliae

Verticillium wilt caused by Verticillium dahliae Kleb. is a major disease in cotton. We found that pectin lyase can enhance cotton resistance to Verticillium wilt and induce cell apoptosis of V. dahliae strain Vd080. The biocontrol effect of pectin lyase on Vd080 reached 61.9%. Pectin lyase increased ERG4 (Delta (24 (24 (1)))-sterol reductase) expression, the ergosterol content of the cell membrane, the collapse of mitochondrial membrane potential, hydrogen peroxide content, metacaspase activity, and Ca2+ content in the cytoplasm in the Vd080 strain and induced endoplasmic reticulum (ER) stress. Pectin lyase also increased the expression levels of the ER molecular chaperone glucose regulating protein Grp78 (BiP), protein disulfide isomerase (PDI) and calnexin (CNX), reduced the expression levels of the protein Hsp40. When the PDI and BiP genes of Vd080 were knocked out, the mutants △BiP and △PDI had reduced sensitivity to pectin lyase. In the absence of external stress, ER stress appeared in mutant △BiP cells. Pectin lyase affects the ergosterol content of the Vd080 cell membrane, which causes ER stress and increases the level of BiP to induce Vd080 cell apoptosis. These results demonstrate that pectin lyase can be used to control Verticillium wilt in cotton.

Verticillium Wilt in Oilseed Rape-the Microbiome is Crucial for Disease Outbreaks as Well as for Efficient Suppression.

Microbiome management is a promising way to suppress verticillium wilt, a severe disease in Brassica caused by Verticillium longisporum. In order to improve current biocontrol strategies, we compared bacterial Verticillium antagonists in different assays using a hierarchical selection and evaluation scheme, and we integrated outcomes of our previous studies. The result was strongly dependent on the assessment method chosen (in vitro, in vivo, in situ), on the growth conditions of the plants and their genotype. The most promising biocontrol candidate identified was a Brassica endophyte Serratia plymuthica F20. Positive results were confirmed in field trials and by microscopically visualizing the three-way interaction. Applying antagonists in seed treatment contributes to an exceptionally low ecological footprint, supporting efficient economic and ecological solutions to controlling verticillium wilt. Indigenous microbiome, especially soil and seed microbiome, has been identified as key to understanding disease outbreaks and suppression. We suggest that verticillium wilt is a microbiome-driven disease caused by a reduction in microbial diversity within seeds and in the soil surrounding them. We strongly recommend integrating microbiome data in the development of new biocontrol and breeding strategies and combining both strategies with the aim of designing healthy microbiomes, thus making plants more resilient toward soil-borne pathogens.

A non-pathogenic strain of Fusarium oxysporum and grape marc compost control Verticillium wilt of olive

Verticillium wilt of olive (VWO), caused by the widespread soil-borne fungus Verticillium dahliae Kleb., is currently the most serious disease affecting olive trees (Olea europaea L.) in all production areas. An integrated management strategy using eco-friendly approaches such as genetic resistance and biological control is considered the most advisable approach for controlling the disease in commercial olive orchards. This study evaluated a non-pathogenic strain of F. oxysporum (FO12) and the grape marc compost CGR03 for reducing inoculum density of V. dahliae and the disease progress in two olive cultivars with different VWO resistance levels. The experiment was conducted under semi-controlled conditions, using a naturally infested soil with two inoculum densities of V. dahliae. The biocontrol treatments (FO12 and CGR03) were previously selected out of 220 natural products as two of the most effective treatments against the pathogen. FO12 and CGR03 treatments significantly reduced pathogen inoculum density in comparison with that of the control (P = 0.05), with minimum microsclerotium amounts of 0.13 g-1 for FO12 and 0.53 g-1 for CGR03, during the experimental period. CGR03 reduced the progression of the disease compared with that in the control (P = 0.05), and FO12 achieved complete control of VWO, since no plants treated with this biological control strain developed VWO symptoms. This study highlights the effectiveness of these biocontrol treatments, and the potential use of eco-friendly approaches for control of VWO.

Transcriptome analysis reveals the defense mechanism of cotton against Verticillium dahliae in the presence of the biocontrol fungus Chaetomium globosum CEF-082

BackgroundVerticillium wilt of cotton is a serious soil-borne disease that causes a substantial reduction in cotton yields. A previous study showed that the endophytic fungus Chaetomium globosum CEF-082 could control Verticillium wilt of cotton, and induce a defense response in cotton plants. However, the comprehensive molecular mechanism governing this response is not yet clear.ResultsTo study the signalling mechanism induced by CEF-082, the transcriptome of cotton seedlings pretreated with CEF-082 was sequenced. The results revealed 5638 DEGs at 24 h post inoculation with CEF-082, and 2921 and 2153 DEGs at 12 and 48 h post inoculation with Verticillium dahliae, respectively. At 24 h post inoculation with CEF-082, KEGG enrichment analysis indicated that the DEGs were enriched mainly in the plant-pathogen interaction, MAPK signalling pathway-plant, flavonoid biosynthesis, and phenylpropanoid biosynthesis pathways. There were 1209 DEGs specifically induced only in cotton plants inoculated with V. dahliae in the presence of the biocontrol fungus CEF-082, and not when cotton plants were only inoculated with V. dahliae. GO analysis revealed that these DEGs were enriched mainly in the following terms: ROS metabolic process, H2O2 metabolic process, defense response, superoxide dismutase activity, and antioxidant activity. Moreover, many genes, such as ERF, CNGC, FLS2, MYB, GST and CML, that regulate crucial points in defense-related pathways were identified and may contribute to V. dahliae resistance in cotton. These results provide a basis for understanding the molecular mechanism by which the biocontrol fungus CEF-082 increases the resistance of cotton to Verticillium wilt.ConclusionsThe results of this study showed that CEF-082 could regulate multiple metabolic pathways in cotton. After treatment with V. dahliae, the defense response of cotton plants preinoculated with CEF-082 was strengthened.

The effectiveness of rhizosphere microorganisms to control Verticillium wilt disease caused by Verticillium dahliae Kleb. in olives

Soil is an important natural resource for the existence of plants, animals, and microorganisms. In this study, the effectiveness of some biological preparations from soil-derived microorganisms against Verticillium wilt caused by Verticillium dahliae, which is a very important disease in olive, was investigated. Harpin protein (Messenger Gold), Mycorrhiza (ERS)-Trichoderma harzianum strain (T22 Planter Box), and different combinations of these treatments were used as biological preparations against V. dahliae. Additionally, the effectiveness of Bordeaux mixture, which is an important component in sustainable agriculture and is widely used by the farmers, was added to this study in order to compare soil microorganisms. Plants have been observed every month for a year, and after 12 months, the plants were evaluated according to the scale of 0–4. As a result, high efficacy results have been obtained in Messenger Gold, Messenger Gold + ERS-T22 Planter Box + Bordeaux mixture, and Messenger Gold + Bordeaux mixture applications (P ≤ 0.05). Application of Messenger Gold and in combination with Messenger Gold suppressed the Verticillium wilt disease in the parts of the trees where the symptoms occurred, and these trees showed regeneration by new shoot development. The application of ERS-T22 Planter Box and Bordeaux mixture suppressed the Verticillium wilt, and the disease symptoms have not spread to the other parts of plants. However, no shoot formation occurred in these diseased parts. According to our results, it is considered that Harpin protein may have a positive effect on the activation of xylem in olive and induces the pathogen host defenses. In addition, the presence of some beneficial microorganisms can restrict the fungal sporulation and growth of V. dahliae. Therefore the Harpin protein can be used as a biological control agent in combination with other antagonism microorganisms.

Biological control of Verticillium wilt of olive in the field

Verticillium wilt of olive (VWO) caused by Verticillium dahliae is considered one of the most serious diseases in olives. Effective control of this disease requires an integrated management strategy in which implementing biological control is a potential tool. Thus, the aim of this study was to evaluate the effect of 16 natural biological compounds, including biological control agents, organic amendments and one essential oil, under field conditions. The compounds were selected out of 220 treatments previously evaluated against V. dahliae under controlled conditions in both in vitro and in planta experiments. Three experiments were conducted under three different scenarios for the natural infection of V. dahliae in the Andalusian Region (southern Spain): under semi-controlled conditions on potted plants grown with naturally infested soil (Experiment I); new plantation in a field with high inoculum density (ID) of V. dahliae in the soil (Experiment II); replanting a commercial olive orchard affected by Verticillium wilt with 1 or 30 year-old trees (Experiment III). In the Experiment I, the non-pathogenic strain of Fusarium oxysporum (FO12) and a commercial essential oil from Thymus sp. were the most effective treatments, achieving a total reduction of the ID two months after planting. In Experiment II, the grape marc compost (CGR03) was the most effective treatment in reducing the ID of the pathogen in soil up to 100%. In Experiment III, both FO12 and CGR03 treatments reduced significantly the disease incidence in both 1 or 30 year-old olive plants in comparison with the untreated control plants (P = 0.05). This work provides a practical basis for the use of these selected treatments and a useful methodology for the establishment of future field experiments for research on the biological control of VWO.

The Role of Volatile Organic Compounds and Rhizosphere Competence in Mode of Action of the Non-pathogenic Fusarium oxysporum FO12 Toward Verticillium Wilt.

Verticillium wilts caused by Verticillium spp. are among the most challenging plant diseases to control and affect numerous hosts worldwide. Due to the lack of effective, conventional control methods, integrated control strategies provide a promising approach to manage these diseases. The non-pathogenic Fusarium oxysporum strain FO12 was reported in previous studies to be an effective biocontrol agent against Verticillium dahliae, however, its mode of action remains to be elucidated. In this study, complementary in vitro and in vivo experiments were conducted in order to explore the implications of inhibitory substances and rhizosphere competence in antagonistic effects of FO12 against V. dahliae and V. longisporum. Volatile organic compounds and soluble substances produced by FO12, which caused significant inhibition of mycelial growth and microsclerotia viability in the two tested Verticillium species, were identified by means of gas and liquid chromatography-mass spectrometry. We showed that the antagonistic effect of F. oxysporum FO12 is partially due to the production of bioactive compounds such as 3-methyl-1-butanol and 2-methyl-1-butanol, among others. Several metabolic pathways of FO12 were altered upon contact with V. dahliae ELV22 volatiles. The reduced production of alpha, alpha-trehalose, a metabolite used in starch and sucrose metabolism, suggests that the biocontrol agent activates its stress response in the presence of the phytopathogen. Microscopic analysis using sGFP-tagged FO12 on oil seed rape as a model plant suggests that the biocontrol strain is an efficient root colonizer, which could compete with V. dahliae in the same ecological niche. The findings obtained in this study provide new insights into the mode of action of this potential biocontrol agent, which are relevant for controlling Verticillium wilt through an ecologically friendly approach.

Overexpression of the Key Virulence Factor 1,3-1,4-β-d-Glucanase in the Endophytic Bacterium Bacillus halotolerans Y6 To Improve Verticillium Resistance in Cotton.

Verticillium wilt, caused by Verticillium dahliae, results in a dramatic loss of cotton yields in China. There is great potential for biocontrol to manage this destructive crop disease. In this study, we obtained the endophytic bacterium Bacillus halotolerans Y6 from Verticillium wilt-resistant cotton Gossypium barbadense Xinhai15; this bacterium possesses strong antagonistic abilities that inhibit V. dahliae spore germination and mycelial growth. The results of the enzyme activity assay, heterologous expression, and gene knockdown showed that the key virulence factor of Y6 for antagonizing V. dahliae was β -glucanase Bgy6. To facilitate field tests of biological control, we constructed the homologous Bgy6-overexpression strain OY6. Compared with the wild-type Y6 strain, the β-glucanase activity of OY6 was increased by 91.79%, and the inhibition rate of OY6 against V. dahliae V991 exceeded 96.7%. Moreover, the spores of V. dahliae V991 treated with OY6 showed more mucus and larger holes on the surface, as observed by scanning electron microscopy. Potting test results illustrated that both OY6 and Y6 could improve the resistance of upland cotton to Verticillium wilt. With the inoculation of V. dahliae V991 for 45 days, the disease index of G. hirsutum TM-1 treated with OY6 was only 8.33, which was significantly lower than that in plants treated with the wild-type strain Y6 (17.86) or the controls without bacteria (35.94). Our research provides a new idea for the control of Verticillium wilt in upland cotton via transforming endophytic bacteria of Verticillium wilt-resistant cotton and proposes a new solution to prevent and control Verticillium wilt.

Comparative transcriptome analysis reveals regulatory networks and key genes of microsclerotia formation in the cotton vascular wilt pathogen

Verticillium dahliae is a soil-borne, hemibiotrophic phytopathogenic fungus that causes Verticillium wilt in a broad range of economic crops. The microsclerotia (MS), which act as the main host inoculum, can survive long-term in soil resulting in uncontrollable disease. In order to clarify the mechanism of MS formation, we sequenced the whole genome-wide expression profile of V. dahliae strain V991. Compared with M1 (no MS formation), during the process of MS formation and maturation, 1354, 1571, and 1521 unique tags were significantly regulated in M2, M3, and M4 library, respectively. During MS formation, melanin synthesis-related genes were preferentially upregulated. The process is more likely to regulated by transcription factors (TFs) including C2H2, Zn2Cys6, bZIP, and fungal-specific TF domain-containing proteins; additionally, G-protein coupled receptors, Ca2+, small GTPases, and cAMP were involved in signalling transduction. Protein kinase-encoding (VDAG_06474) and synthase-encoding (VDAG_05314) genes were demonstrated to negatively and positively influence MS production, respectively. The gene expression dynamics revealed during MS formation provide comprehensive theoretical knowledge to further understanding of the metabolism and regulation of MS development in V. dahliae, potentially providing targets to control Verticillium wilt through interfering MS formation.

Evaluation of thiophanate-methyl in controlling Verticillium wilt of potato and artichoke

Verticillium dahliae is a soil-borne vascular pathogen difficult to control, especially after the phasing out of several fumigants. Where resistant varieties are not available, Verticillium wilt (VW) is controlled through an integrated approach. Chemical control has been extensively studied, but often does not provide a satisfactory protection level. Recently, thiophanate-methyl (TM), the sole benzimidazole currently on the market, has been registered for the use in soil applications. We evaluated the efficacy of TM against V. dahliae in in vitro, greenhouse and field experiments. We confirmed that TM is one of the most effective fungicides against V. dahliae in in vitro tests (EC50 = 0.006 μg mL−1). In a greenhouse experiment, soil drenching with TM (0.073 or 0.146 mL plant−1, corresponding to 0.65 or 1.3 L ha−1) reduced the incidence of VW of artichoke, but not the symptoms severity or vascular browning. In pot-grown potato, TM (at 5.6 or 11.2 mg plant−1) completely suppressed the disease and promoted plant growth. In one field trial, a high dose of TM (2.1 L ha−1) only delayed VW progress, but did not affect yield losses. In a second field trial, with a more severe V. dahliae attack, no significant disease control was observed following TM applications, neither by foliar spray nor by chemigation.We concluded that TM is effective against V. dahliae, but it can provide only a partial VW control when the disease pressure is not too high. However, the results obtained in the field trial emphasize the need for further trials under different levels of inoculum pressure and with different application protocols.

The economic viability of suppressive crop rotations for the control of verticillium wilt in organic strawberry production

ABSTRACTSoil-borne diseases and nitrogen availability are important limits on organic strawberry production. A trial using suppressive crop rotations to combat Verticillium wilt was conducted to see its effects on strawberry yields and net returns using a split-split-plot design. An ANOVA analysis was run to understand determinants of net returns. Results show that the suppression of wilt through the planting of non-host crops such as broccoli before the planting of strawberries can have significant effects on yield and net returns, and that suppressive crop rotations are potentially commercially viable.

HyPRP1 performs a role in negatively regulating cotton resistance to V. dahliae via the thickening of cell walls and ROS accumulation

BackgroundDeveloping tolerant cultivars by incorporating resistant genes is regarded as a potential strategy for controlling Verticillium wilt that causes severe losses in the yield and fiber quality of cotton.ResultsHere, we identified the gene GbHyPRP1 in Gossypium barbadense, which encodes a protein containing both proline-rich repetitive and Pollen Ole e I domains. GbHyPRP1 is located in the cell wall. The transcription of this gene mainly occurs in cotton roots and stems, and is drastically down-regulated upon infection with Verticillium dahliae. Silencing HyPRP1 dramatically enhanced cotton resistance to V. dahliae. Over-expression of HyPRP1 significantly compromised the resistance of transgenic Arabidopsis plants to V. dahliae. The GbHyPRP1 promoter region contained several putative phytohormone-responsive elements, of which SA was associated with gene down-regulation. We compared the mRNA expression patterns of HyPRP1-silenced plants and the control at the global level by RNA-Seq. A total of 1735 unique genes exhibited significant differential expression. Of these, 79 DEGs involved in cell wall biogenesis and 43 DEGs associated with the production of ROS were identified. Further, we observed a dramatic thickening of interfascicular fibers and vessel walls and an increase in lignin in the HyPRP1-silenced cotton plants compared with the control after inoculation with V. dahliae. Additionally, silencing of HyPRP1 markedly enhanced ROS accumulation in the root tips of cotton inoculated with V. dahliae.ConclusionsTaken together, our results suggest that HyPRP1 performs a role in the negative regulation of cotton resistance to V. dahliae via the thickening of cell walls and ROS accumulation.

Biocontrol potential of Paenibacillus polymyxa against Verticillium dahliae infecting cotton plants

Verticillium wilt of cotton is an economically important disease caused by V. dahliae throughout the world. To control this disease, five bacterial strains from cotton-growing fields were screened for their antagonistic activity against V. dahliae. Interestingly, they were all identified as Paenibacillus polymyxa by testing morphological and ultrastructural characteristics as well as 16S rRNA sequences and fatty acid composition analysis. The observation of sporulation process revealed that the structure of the endospore coat was composed of three layers including outer, middle and inner spore coats. Among five strains, ShX301 showed highest antagonistic activity against spore germination and mycelial growth of V. dahliae. In addition, in vitro experiments showed that ShX301 had a broad-spectrum antifungal activity against other plant pathogens. The experiments for controlling Verticillium wilt of cotton in greenhouse demonstrated that inoculation by strain ShX301 reduced disease incidence and severity by 71.4% and 40.3%, respectively. Moreover, ShX301 significantly promoted the growth of cotton seedling. Assessment of plant growth promotion showed that inoculation by ShX301 promoted cotton plant growth enhancing aboveground seedling biomass by 45.5% as well as underground root length and biomass by 38.0% and 38.5%, respectively. This is the first report of P. polymyxa application to control Verticillium wilt of cotton and promoting cotton seedling growth. This study revealed that P. polymyxa ShX301 had high potential to be used as biocontrol agent and/or plant growth-promoting bacterium in agriculture.

Development of a Biological Complex Seed-Coating Agent to Control Verticillium Wilt

Development of a Biological Complex Seed-Coating Agent to Control Verticillium Wilt

Effect of Soil Temperature, Injection Depth, and Rate of Metam Sodium Efficacy in Fine-Textured Soils with High Organic Matter on the Management of Verticillium Wilt of Potato

Metam sodium is a widely used soil fumigant for Verticillium wilt management in most potato production regions of the United States. Environmental concerns regarding volatilization losses have led to restrictions on the use of metam sodium. The potato industry adapted to these restrictions by replacing metam sodium applications through sprinkler irrigation with shank injection applications of the fumigant. Previous research established parameters for effective shank application of metam sodium based on soil temperature, injection depth and rate of fumigation. However, these recommendations were based on research conducted under coarse-textured soil conditions with a low organic matter (OM) content ( 2.5%. Therefore, it is important to know whether metam sodium fumigation recommendations for coarse-textured soils can be adapted to fine-textured soils. Two field trials were conducted using a split strip-block design for studying metam sodium efficacy in managing wilt. In both years, metam sodium injection depth and soil temperature at the time of injection did not result in significant differences in any study variable evaluated. All metam sodium fumigation rates significantly (P < 0.05), lowered Verticillium microsclerotia, reduced wilt severity, and improved tuber yield compared to non-treated plots. However, significant differences among fumigation rates were not observed across any variable evaluated. A relatively low rate of 373 l/ha is as effective as higher metam sodium rates for effective control of Verticillium wilt. Results presented here suggest that current metam sodium recommendations for shank injection applications in coarse-textured soils can be implemented in field soils with a fine texture and higher OM content.

Effect of altering the steric hindrance of the nitrogen atom in 2,5-bis(pyridin-n-yl)-1,3,4 thiadiazole isomers on their ability to elicit tomato defense responses against Verticillium wilt and crown gall diseases

Three isomers of the ligand 2,5-bis(pyridinyl)-1,3,4-thiadiazole, with the N atom of pyridine group in position 2, 3 or 4, named respectively, L2, L3 and L4 were compared for their use as plant defense activators. They were examined for their ability to protect tomato plants from Verticillium dahliae and Agrobacterium tumefaciens in the greenhouse, to induce reactive oxygen species and to activate plant defenses, including antioxidant enzymes. The three ligand isomers exhibited in vitro only slight inhibition of radial growth of V. dahliae, while no significant inhibition was observed for phytopathogenic bacteria. In the greenhouse, the three ligand isomers statistically reduced the severity of Verticillium wilt and crown gall on tomato plants, and the isomers L3 and L4 were the most efficient to control Verticillium wilt. This superiority was reflected in their differential ability to activate H2O2 accumulation, antioxidant enzymes including catalase and ascorbate peroxidase and other defense-related enzymes such as guaiacol peroxidase and polyphenol oxidase. These results demonstrated that the presence of the N atom within the two pyridinyl groups in the position 3 or 4 highly enhanced the activity of plant defense and antioxidant responses as well as their ability to reduce the severity of symptoms caused by V. dahliae on tomato.

Gbvdr6, a Gene Encoding a Receptor-Like Protein of Cotton (Gossypium barbadense), Confers Resistance to Verticillium Wilt in Arabidopsis and Upland Cotton.

Verticillium wilt is a soil-borne disease that can cause devastating losses in cotton production. Because there is no effective chemical means to combat the disease, the only effective way to control Verticillium wilt is through genetic improvement. Therefore, the identification of additional disease-resistance genes will benefit efforts toward the genetic improvement of cotton resistance to Verticillium wilt. Based on screening of a BAC library with a partial Ve homologous fragment and expression analysis, a V. dahliae-induced gene, Gbvdr6, was isolated and cloned from the Verticillium wilt-resistant cotton G. barbadense cultivar Hai7124. The gene was located in the gene cluster containing Gbve1 and Gbvdr5 and adjacent to the Verticillium wilt-resistance QTL hotspot. Gbvdr6 was induced by Verticillium dahliae Kleb and by the plant hormones salicylic acid (SA), methyl jasmonate (MeJA) and ethephon (ETH) but not by abscisic acid (ABA). Gbvdr6 was localized to the plasma membrane. Overexpression of Gbvdr6 in Arabidopsis and cotton enhanced resistance to V. dahliae. Moreover, the JA/ET signaling pathway-related genes PR3, PDF 1.2, ERF1 and the SA-related genes PR1 and PR2 were constitutively expressed in transgenic plants. Gbvdr6-overexpressing Arabidopsis was less sensitive than the wild-type plant to MeJA. Furthermore, the accumulation of reactive oxygen species and callose was triggered at early time points after V. dahliae infection. These results suggest that Gbvdr6 confers resistance to V. dahliae through regulation of the JA/ET and SA signaling pathways.

Seaweed polysaccharides as bio-elicitors of natural defenses in olive trees against verticillium wilt of olive

ABSTRACTUlvan, carrageenan, alginate and laminarin were tested in olive trees’ twigs to elicit phenolic metabolism and control verticillium wilt of olive (VWO) caused by Verticillium dahliae. The elicitation effect was determined through phenylalanine ammonia-lyase activity, total polyphenol content and lignin content. VWO was assessed in twigs previously elicited (24 h) and maintained in a solution containing bio-elicitors (2 g/L) and conidial suspension (106 conidia/mL). Our results showed stimulation of the phenolic metabolism and the decline of wilt symptoms. Ulvan reduced significantly the area under the disease progress curve for severity to 39.9% and the final incidence to 28.9%. Ulvan and alginate produced significant inhibitory rates on mycelial growth of the fungus in vitro. Seaweed polysaccharides might help to overcome VWO by strengthening the host defense metabolism and restricting the pathogen’s growth.