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1.
Verticillium wilt is a devastating disease caused by the soil-borne fungus Verticillium dahliae that causes severe wilt symptoms in more than 400 plant species, including economically important cotton. However, the molecular mechanism of plant resistance to Verticillium remains unclear. In this study, we identified an Arabidopsis mutant, vsad1 (verticillium sensitive and anthocyanin deficient 1), which showed more serious disease symptoms such as discoloration and chlorosis than wild-type Arabidopsis. vsad1 is a previously identified allele of the transparent testa 4 gene (tt4), which encodes chalcone synthase (CHS), a key enzyme involved in the biosynthesis of flavonoids. Our results showed that VSAD1 expression was induced in response to Verticillium dahliae infection. Overexpression of VSAD1 partially recovered the anthocyanin accumulation phenotype of the vsad1–1 mutant. The concentration of V. dahliae increased and ROS accumulation decreased in the vsad1 mutant after infection with V. dahliae. Knockdown of the homologous gene GhCHS in cotton plants increased their susceptibility to V. dahliae infection. Thus, we conclude that VSAD1 is involved in the regulation of plant resistance to Verticillium wilt.  相似文献   

2.
Effects simultaneous and sequential inoculations of Meloidogyne incognita, Ralstonia solanacearum and Phomopsis vexans were studied on the growth, chlorophyll and carotenoid contents of eggplants grown in 25% fly ash and 25% sand mix soil. Plants grown in 25% fly ash mix soil had lesser plant growth than grown in 25% sand ash mix soil. Inoculation of M. incognita / R. solanacearum or P. vexans caused reduction in plant growth, chlorophyll and carotenoid contents in both types of soils but these pathogens in combination caused a greater reduction in than individual inoculation. Inoculation of M. incognita 20 days prior to R. solanacearum caused a greater reduction in plant growth than inoculation of M. incognita prior to P. vexans. Inoculation of P. vexans prior to R. solanacearum caused a lesser reduction in plant growth, chlorophyll and carotenoid contents than inoculation of P. vexans prior to M. incognita. Inoculation of R. solanacearum 20 days prior to M. incognita caused a greater reduction in plant growth, chlorophyll and carotenoid contents than inoculation of R. solanacearum prior to P. vexans. Galling and multiplication of M. incognita was higher in plants grown in 25% sand amended soil than with 25% fly ash soil. R. solanacearum and P. vexans had adverse effects on galling and nematode multiplication. Wilt and blight indices caused by R. solanacearum and P. vexans were 3 respectively. Wilt and blight indices were 4 when two pathogens were inoculated together.  相似文献   

3.
Verticillium wilt, caused by Verticillium dahliae, is the most serious disease in olive cultivation areas in western Turkey. Two hundred and eight isolates of V. dahliae from olive (Olea europea var. sativa) trees were taken for vegetative compatibility analysis using nitrate non-utilizing (nit) mutants. One isolate did not produce a nit mutant. Nit mutants of 207 isolates were tested against tester strains of internationally known vegetative compatibility groups (VCGs) 1A, 2A, 2B, 3, 4A and 4B, and also paired in many combinations among themselves. One hundred and eighty nine of the isolates (90.9%) were strongly compatible with T9, the tester strain of VCG1A, and thus were assigned to VCG1A. Eight isolates were assigned to VCG2A and four isolates to VCG4B. One isolate was heterokaryon self-incompatible (HSI) and five isolates could not be grouped to any of the VCGs tested. Pathogenicity assays were conducted on a susceptible olive cultivar (O. europea cv. Manzanilla) and a susceptible local cotton cultivar (Gossypium hirsutum cv. Çukurova 1518). Both cotton and olive inoculated with all VCG1A isolates showed defoliating symptoms in greenhouse tests. This is the first report on VCGs in V. dahliae from olive trees in Turkey which demonstrates that VCG1A of the cotton-defoliating type is the most commonly detected form from olive plants in the western part of Turkey.  相似文献   

4.
Pinewood nematode (PWN), Bursaphelenchus xylophilus, the causal agent of pine wilt disease (PWD), was detected in Spain in 2008. This gives rise to serious concern, as the disease has caused severe environmental and economic losses in Portugal and in Asian countries. We studied interspecific variation in susceptibility to pine wilt disease and differences in constitutive chemical compounds in the xylem tissue of the seven pine species -P. canariensis, P. halepensis, P. pinaster, P. pinea, P. sylvestris, P. radiata and P. taeda. Two-year-old trees were inoculated with B. xylophilus. Water potential and nematode densities were measured for each species on specific dates; whereas, wilting symptoms were recorded weekly until the end of the assay. Chemical compounds in the xylem were determined prior to inoculation. Three different resistance groups can be established in terms of the pine species susceptibility to PWN: non- to slightly-susceptible (P. canariensis, P. halepensis, P. taeda and P. pinea), susceptible (P. pinaster and P. radiata), and highly-susceptible (P. sylvestris). Nematodes migrated downward to the roots in all seven species. Constitutive xylem nitrogen, total polyphenols, and marginally phosphorus were negatively correlated with mortality caused by PWN. The most susceptible species, Pinus sylvestris, presented high levels of constitutive lipid-soluble substances and low levels of manganese, pointing to a possible relation between these components and PWN susceptibility. The results suggest P. sylvestris, P. pinaster and P. radiata forests could be severely damaged by PWN in Spain and highlight how constitutive chemical compounds such as nitrogen might play a role in resistance mechanisms against PWN.  相似文献   

5.
Cucurbit bacterial wilt, caused by Erwinia tracheiphila, is a devastating disease of cucurbit crops in the Midwest and Northeast U.S. Current management of bacterial wilt relies primarily on insecticide applications to control striped and spotted cucumber beetles (Acalymma vittatum and Diabrotica undecimpunctata howardi, respectively), which vector E. tracheiphila. Development of alternative management strategies is constrained by a lack of understanding of bacterial wilt etiology. The impact of host age on rate on symptom development and extent of bacterial movement in the xylem of muskmelon (Cucumis melo cv. Athena) was evaluated following wound inoculation of 2- to 8-week-old plants in growth chamber experiments. Wilting occurred more rapidly in plants after inoculating E. tracheiphila into 2- or 4-week-old plants than 6- or 8-week-old plants. Recovery of viable cells from stem segments revealed that vascular spread of E. tracheiphila was more extensive below than above the inoculation point. These findings provide experimental evidence that host age impacts the rate of symptom development in cucurbit bacterial wilt and that movement of the xylem-inhabiting pathogen E. tracheiphila within muskmelon plants occurs primarily in the downward direction.  相似文献   

6.
Wilt disease of lentil caused by Fusarium oxysporum f.sp. lentis (Fol) is one of the most important diseases affecting lentil worldwide. Differential response of six lentil accessions with reported differences in the level of resistance to Fol was studied micro and macroscopically. Penetration took place through root epidermal cells without formation of any specific structure. Hyphae reached the stele within two days after inoculation (dai) and subsequently invaded xylem bundles having colonised the endodermis, vascular system and even vascular parenchyma phloem already by 4 dai. Resistance was observed as a quantitative trait in all studied accessions resulting from varying levels of xylem occlusion with gum-like substances and of degree of colonization observed only after 4 dai. An indication of a qualitative resistance was detected in accession BGE019696 inoculated with pathotype 1 as a fast secretion of phenolic compounds at 4 dai. Plasmolysis of cytoplasm, lignification and accumulation of phenolic compounds, gum-like substances and/or tyloses were observed from 15 to 30 dai. As a result of the various operative mechanisms, significantly lower numbers of propagules were recovered from roots by 15 dai, and a retardation of disease was measured as lower disease index by 30 dai in plants inoculated with pathotype 1, but not in those inoculated with pathotype 7.  相似文献   

7.
Eucalyptus globulus, a non-native species, is currently the most abundant forest species in Portugal. This economically important forest tree is exploited mainly for the production of pulp for the paper industry. The community of Botryosphaeriaceae species occurring on diseased and healthy E. globulus trees was studied on plantations throughout the country. Nine species from three different genera were identified, namely Botryosphaeria (B. dothidea), Diplodia (D. corticola and D. seriata) and Neofusicoccum (N. australe, N. algeriense, N. eucalyptorum, N. kwambonambiense, N. parvum and Neofusicoccum sp.). Of these, N. algeriense, D. corticola and D. seriata are reported for the first time on E. globulus, while N. algeriense, N. eucalyptorum and N. kwambonambiense correspond to first reports in Portugal. The genus Neofusicoccum was clearly dominant with N. australe and N. eucalyptorum being the most abundant species on both diseased and healthy trees. In artificial inoculation trials representative isolates from all nine species were shown to be pathogenic to E. globulus but there were marked differences in aggressiveness between them. Thus, D. corticola and N. kwambonambiense were the most aggressive while B. dothidea and D. seriata were the least aggressive of the species studied.  相似文献   

8.
The ability to control soil-borne pathogens in agriculture is highly conditioned by the restricted use of synthetic pesticides. Allelopathy, the antimicrobial activity of plant extracts, is a promising option against crop pathogens. Extracts from Lycium spp. such as L. barbarum, L. chinense and L. intricatum possess biological and therapeutic properties. Individual methanolic extracts from leaves and stems of the Mediterranean medicinal species L. europaeum collected in two locations of Tunisia were each evaluated in vitro against Verticillium dahliae (Vd), Sclerotinia sclerotiorum (Ss) and Harpophora maydis (Hm). The mycelial growth of the three fungi was significantly reduced by all the extracts at doses of 10 and 30 μl mL?1 (equivalent to 1 and 3 mg plant tissue mL?1). The sporulation of Hm was almost completely inhibited in all the amendments, but that of Vd was stimulated by one of the leaf extracts when 1 and 3 mg dried plant tissue mL?1 were used. Sclerotia of Ss were formed in a smaller number, their total weight increasing at extract doses equivalent to 1 mg plant tissue mL?1 and higher. In greenhouse, the pathogenicity of Hm was confirmed as early as 6 weeks after inoculation, since it caused significant decreases of weights in both roots and aboveground parts of maize. The detrimental effect of Hm on maize root weight in greenhouse was significantly counteracted by one of the leaf extracts added by watering. In total, 11 phenolic compounds were separated in the four extracts. The hydroxycinnamic acid family, including chlorogenic acid as a major compound, represented more than 50% of the total content in all the samples. Rutin was the most abundant flavonoid. The results of this work show the detrimental effect of L. europaeum extracts against the soil-borne pathogens Hm, Ss and Vd, and highlight their potential in crop protection if adequately developed into final products and used in combination with other tools.  相似文献   

9.
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10.
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.  相似文献   

11.
In pathogen populations in Serbia, the incidence, pathogenic and morphological characters ofVerticillium spp. were studied. Biological and chemical control ofVerticillium was investigated in pepper plants (Capsicum annuum L. cv. ‘Soroksari’) with the biofungicide Polyversum® (Pythium oligandrum) and the conventional fungicides benomyl and propamocarb-hydrochloride. On the basis of macroscopic and microscopic characters of the isolates originating from eight localities in Serbia, it was established that they apparently belong to the speciesVerticillum dahliae. The isolates differed in their pathogenic characters. However, all of them caused marked wilting symptoms on pepper plants 40 days after inoculation, conducted when there were more than nine fully developed leaves on the primary stem. The fungicides were applied either before or after inoculation. Benomyl was the most efficient fungicide in wilt control (88.2% when applied after inoculation and 94.6% when applied before inoculation). Polyversum proved more efficient (66.6%) when applied before rather than after inoculation. Propamocarb-hydrochloride provided sufficient Verticillium wilt control; its efficacy and that of Polyversum were similar, and less efficient than benomyl, but still significantly different from the disease control.  相似文献   

12.
Laurel wilt is caused by Raffaelea lauricola, a nutritional symbiont of an Asian ambrosia beetle, Xyleborus glabratus. American members of the Lauraceae plant family are most susceptible and 300 million trees have been killed by the disease in the southeastern USA since 2003. Recently, commercial production of an important crop in the laurel family, avocado (Persea americana), has been affected in southern Florida. We summarize studies in which diverse measures were tested for managing the disease. In all studies, trees were treated with potential laurel wilt control measures and subsequently inoculated with R. lauricola. On potted plants in greenhouse experiments, commercial nutritional products (Greenstim and Keyplex 350) and SAR products (Agri-Fos and Nutri-Phite), when applied as soil drenches or foliar sprays, had either no impact on, or increased laurel wilt symptom development compared to non-treated control treatments. Bark applications of Tilt (a propiconazole fungicide for which emergency registration had been obtained in 2010) in a surfactant (Pentrabark) enabled significant laurel wilt protection in greenhouse studies on small potted plants, but Pentrabark and other surfactants moved little propiconazole into the xylem of fruit-bearing trees in field studies. In efficacy studies in the field, Propiconazole Pro (an injectable formulation of propiconazole), Tilt, and two experimental formulations of another triazole fungicide, tebuconazole, decreased the development of laurel wilt compared to nontreated control trees when applied as undiluted injections into branches and scaffold limbs (microinjection), or injection of dilute fungicide into tree flare roots (macroinfusion). However, symptoms developed in all treated trees by 10–11 months after inoculation with R. lauricola, indicating that trees would need to be re-treated at least on an annual basis. Regardless of how fungicides were applied, insignificant levels of different active ingredients entered fruit. Although fungicide treatment of fruit-bearing avocado trees is not a concern for food safety and several triazole and DMI fungicides can protect avocado trees from laurel wilt, cost-effective measures with which the xylem could be loaded with and protected by these products remains a challenge. Management of laurel wilt in commercial avocado production areas is discussed.  相似文献   

13.
Improvement of cultivar resistance is the key strategy to control the host-specialized pathogen Verticillium longisporum in oilseed rape (OSR). A special feature of this pathogen is its systemic, non-homogenous and delayed colonization of the plant xylem resulting in an extended symptomless period of latency. As a result, severity of infection in the field is difficult to score as it becomes apparent only at crop maturity stages when it may be confused with natural senescence. Assessment of Verticillium disease severity in OSR by visual scoring of microsclerotia on harvested stubbles unsatisfactorily reflects genotypic resistance as it is strongly affected by the ripening stage of the plant. To overcome these limitations, we developed a qPCR method, which unambiguously differentiates levels of quantitative resistance to V. longisporum in OSR genotypes under field conditions. The specificity and sensitivity of two primer pairs targeting ITS or tubulin loci in the V. longisporum genome were tested. While tubulin primers showed a high specificity to V. longisporum isolates, ITS primers exhibited a significantly higher sensitivity in detecting fungal DNA in stem tissue (limit of quantification =0.56 fg DNA) of field-grown pre-symptomatic plants. The best discrimination of resistant and susceptible OSR cultivars based on fungal DNA analysis in stem tissue was achieved at growth stage 80, at the transition of fungal vascular growth in viable plants to saprotrophic colonization of senescent stem tissues. Field screening data obtained with qPCR at growth stage 80 confirmed results from greenhouse testing thus corroborating the relevance and reliability of seedling assays for determining cultivar responses to V. longisporum in the field, as a useful tool for breeders in first selection of elite OSR genotypes with improved resistance to Verticillium.  相似文献   

14.
Arceuthobium sichuanense is an aerial parasitic plant (dwarf mistletoe) which causes severe damage to spruce forests on the Qinghai-Tibet Plateau. Picea crassifolia and Picea purpurea, two main host species of A. sichuanense, have different growth characteristics and elevational distributions. The effects of A. sichuanense infection on P. crassifolia and P. purpurea trees were evaluated by examining needle and current-year shoot morphology, needle water use efficiency and needle nitrogen concentration, with 30 needle samples, 30 current-year shoot samples and 10 A. sichuanense aerial shoot samples for each host species. The most apparent effects were significant reductions in both needle size and current-year shoot length. The high degree of correlation in foliar δ 15N values between the dwarf mistletoe and its host trees indicated that nitrogen in the dwarf mistletoe was derived entirely from its host. Percent reductions in needle and current-year shoot length were smaller for P. purpurea than for P. crassifolia, possibly suggesting that P. purpurea exhibits a lesser capacity to accommodate the parasitic effects of mistletoe infection by adjusting the growth of needles and current-year shoots. The reductions in needle nitrogen concentration and δ 13C values were lower in P. purpurea than in P. crassifolia, indicating that P. purpurea suffered more nitrogen and water stresses and exhibited lower vigor compared to P. crassifolia. Our results demonstrated that P. purpurea may suffer more negative effects induced by dwarf mistletoe infections at needle and branch levels than P. crassifolia.  相似文献   

15.
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16.
Fusarium wilt, one of the destructive diseases of cucumber can be effectively controlled by using biocontrol agents such as Trichoderma harzianum. However, the mechanisms controlling T. harzianum-induced enhanced resistance remain largely unknown in cucumber plants. Here we screened the potent T. harzianum isolate TH58 that could effectively control F. oxysporum (FO). Glasshouse efficacy trials also showed that TH58 decreased disease incidence by 69.7 %. FO induced ROS over accumulation, while TH58 inoculation suppressed ROS over accumulation and improved root cell viability under F. oxysporum infection. TH58 inoculation could reverse the FO-induced cell division block and regulate the proportional distribution of nuclear DNA content through inducing 2C fraction. Moreover, the expression levels of cell cycle-related genes such as CDKA, CDKB, CycA, CycB, CycD3;1 and CycD3;2 in TH58 - pre-inoculated seedlings were up-regulated compared with those infected with FO alone. Taken together, these results suggest that T. harzianum improved plant resistance against Fusarium wilt disease via alterations in nuclear DNA content and cell cycle-related genes expression that might maintain a lower ROS accumulation and higher root cell viability in cucumber seedlings.  相似文献   

17.
Zonate leaf spot (Gloeocercospora sorghi) is a common disease in Sorghum bicolor producing areas of the U.S., but little is known about its biology, virulence and severity on S. bicolor, Zea mays, and related crop grassweeds. Greenhouse studies were conducted to determine and compare the virulence and severity of G. sorghi on 10 commercially available sorghum hybrids, four Z. mays hybrids and selected grassweed species including Sorghum bicolor (grain sorghum and shattercane biotypes) and Sorghum halepense (Johnsongrass), two of the most problematic arable weeds. Plants from the respective species were inoculated with a local G. sorghi isolate and maintained in a dew-chamber at 24 °C for 24 h and then incubated under greenhouse conditions for 4 weeks. Plants were observed for lesion expression and rated using a modified Horsfall-Barrett scale (0–10). The first symptoms of infection were visible within 24 h following inoculation on shattercane and S. bicolor hybrids. Symptoms consisted of small, non-diagnostic purple lesions on the leaves. Results showed that S. bicolor, S. halepense and shattercane were susceptible to G. sorghi. All other species tested in this study were not infected. More particularly, disease severity, increased from a rating of 3 to 10 on sorghum and from 2 to 7 on S. halepense between 2 and 23 days after inoculation, respectively. However, disease severity on shattercane increased rapidly from 3.5 to 10 between 2 and 8 days after inoculation, respectively. Among the sorghum hybrids tested, FFR-322 appeared to be the most resistant to G. sorghi while Pioneer 83G66 appeared to be the most susceptible. Z. mays hybrids were not infected by the fungus used in this study. G. sorghi could be used effectively to manage shattercane and S. halepense infestations occurring in Z. mays and S. bicolor fields consisting of specific G. sorghi-resistant hybrids.  相似文献   

18.
Miscanthus x giganteus is a fast growing, perennial energy crop for temperate climates. Because of its high annual biomass production rates and its characteristics as a low-input crop, an expansion of field cultivation can be anticipated to cover increasing demands for sustainable biomass production. However, knowledge about pathogens that could have an impact on biomass production is still limited for M. giganteus. Here, we report about the isolation of the filamentous fungus Apinisia graminicola from necrotic leaf lesions of M. giganteus grown on a field trial plot in Northern Germany. Inoculation assays with the isolated A. graminicola strain confirmed its capacity to cause a leaf spot disease on M. giganteus. Additional inoculation assays revealed that A. graminicola also caused necrotic lesions on leaves of the model grass Brachypodium distachyon. Generally, symptoms of A. graminicola-caused leaf spot disease were stronger on B. distachyon compared to M. giganteus. Incubation temperatures above 22 °C during A. graminicola infection resulted in stronger disease symptoms on both, M. giganteus and B. distachyon leaves. Microscopic analysis of cross sectioned, infected leaf tissue revealed an epiphytic mycelium formation on the surface and an endophytic colonization of the mesophyll leave tissue, especially in M. giganteus. Our results revealed that the isolated A. graminicola strain is a causal agent of a leaf spot disease on grass leaves. Its potential on endophytic growth in M. giganteus might open new possibilities in studying this type of plant-fungal interaction on a cellular and molecular level in an energy crop.  相似文献   

19.
Fifty bacterial isolates obtained from compost were tested in vitro against the causal agents of green mould in Agaricus bisporus. Isolate B-38 which induced 48.08% in vitro growth inhibition of T. harzianum T54 and 52.25% of T. aggressivum f. europaeum T77 was identified as Bacillus subtilis, based on 16S rDNA sequence and used in mushroom growing room experiments. B. subtilis B-38 did not decrease mycelial growth rate of Agaricus bisporus A15 in mushroom compost in glass tubes. After applying prochloraz-manganese, B. subtilis B-38 and B. subtilis QST 713, no significant differences in BE values among treatments were found concerning both total yield and the weight of healthy mushrooms. Statistical analyses showed that only inoculation significantly influenced the healthy mushroom yield. In plots inoculated with T. harzianum T54 disease incidence was significantly lower after treatments with prochloraz-manganese (11.81%), B. subtilis QST 713 (12.26%) and B. subtilis B-38 (14.19%) compared to the control (28.16%), as well as in plots inoculated with T. aggressivum f. europaeum T77 11.88%, 12.2% and 15.03%, respectively, in comparison with the control (23.47%). Statistically significant differences were not found among the efficacy values of tested bio-fungicides based on B. subtilis and the commercial fungicide prochloraz-manganese suggesting the use of B. subtilis B-38 and B. subtilis QST 713 as good alternatives to chemical fungicides.  相似文献   

20.
Development ofVerticillium dahliae in potato was modelled by coupling aVerticillium subroutine to an existing potato crop growth model, using mainly biologically meaningful and measurable parameters. The model, written in FORTRAN77, describes disease development in single plants. Stem base infection is modelled as a stochastic process. The average effect on the crop is calculated by taking the average of model reruns. The parameters of the potato crop growth model were calibrated in advance of those of theVerticillium subroutine. By doing so, corrections can be made for lack of fit in the potato growth model. Calibration of theVerticillium subroutine was performed using experimental field data of two years at two microsclerotial density levels. The results of the calibration procedure of theVerticillium subroutine improved strongly when the results of runs of both microsclerotial densities were expressed in one combined goodness of fit value. Simulation of root infection and incidence of stem colonization byV. dahliae were in line with experimental data. However, deviances from data from the literature at inoculum densities which were not used in the calibration procedure indicate that calibration has to be performed using more field data and also incorporating more parameters like those describing fungal dynamics. Optimal runs were obtained at pathozones of c. 30 μm, which may indicate that infections occur only when a microsclerotium is very close to the root.  相似文献   

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