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1.
Local lesion formation on cowpea leaves was more than 50% inhibited by treatment with a 23 kDa RNase-like glycoprotein from Cucumis figarei, figaren, from 24 hr before to 1 hr after inoculation with Cucumber mosaic virus (CMV). CMV accumulation detected by ELISA in tobacco leaves treated with figaren 6 or 0 hr before inoculation with CMV was suppressed. When upper leaves of tobacco plants were treated with figaren and inoculated 10 min later with CMV, mosaic symptoms were delayed for 5–7 days on most of the tobacco plants, and some plants remained asymptomatic. From fluorescence in situ hybridization, infection sites were present in figaren-treated cowpea or melon leaves after inoculation with CMV, though the sites were reduced in number and size compared with those in water-treated control leaves. The amount of CMV RNAs and CMV antigen in melon protoplasts inoculated with CMV and subsequently incubated with figaren similarly increased with time as did that in the control. ELISA and local lesion assays indicated that CMV infection on the upper surfaces of the leaves of tobacco, melon, cowpea and C. amaranticolor whose lower surfaces had been treated with figaren 5–10 min before CMV inoculation was almost completely inhibited. Figaren did not inhibit CMV infection on the opposite untreated leaf halves of melon, cowpea and C. amaranticolor, whereas it almost completely inhibited CMV infection on the untreated halves of leaves of tobacco. CMV infection was not inhibited in the untreated upper or lower leaves of the four plants. These data suggest that figaren does not completely prevent CMV invasion but does inhibit the initial infection processes. It may also induce localized acquired resistance in host plants. Received 10 October 2000/ Accepted in revised form 6 February 2001  相似文献   

2.
Symptoms of Cucumber mosaic virus (CMV) on yellow passion flower ( Passiflora edulis f. flavicarpa ) are characterized by bright yellow mottling on leaves, starting at random points on the vine and diminishing in intensity towards the tip, which becomes symptomless as it grows. To determine whether symptomless portions of vines are CMV-free or represent latent infection, leaves with and without symptoms were collected from infected vines in the field. Biological, serological (plate-trapped antigen enzyme-linked immunosorbent assay, PTA-ELISA), Western blot and dot-blot hybridization assays showed that portions of the vines without symptoms were CMV-free. Vegetatively propagated vines with symptoms showed remission of symptoms on newly developed leaves. One year later, no CMV was detected in the upper leaves of these plants. Mechanically inoculated passion flower seedlings behaved similarly; symptoms were shown by few leaves after inoculation. Afterwards, plants became symptomless and CMV was not detected in the upper leaves or root system, 40 or 85 days after inoculation. The mechanism responsible for remission of symptoms accompanied by CMV disappearance is not known.  相似文献   

3.
Cucumber mosaic virus (CMV) was isolated from a mosaic diseased plant of Eucharis grandiflora. The virus caused mosaic symptoms on leaves and slight distortion of flower petals in E. grandiflora by either mechanical or aphid inoculation. The virus was identified as a strain of CMV subgroup I from its biological and serological characteristics.  相似文献   

4.
A spray inoculation of the first leaf of 2-leaf stage cucumber plants with a non-pathogenic isolate of Alternaria cucumarina or Cladosporium fulvum before a challenge inoculation with the pathogen Sphaerotheca fuliginea induced systemic resistance to powdery mildew on leaves 2–5. Systemic resistance was expressed by a significant (p < 0.05) reduction in the number of powdery mildew colonies produced on each leaf of the induced plants, as compared with water-sprayed plants. Systemic resistance was evident when a prior inoculation with each of the inducing fungi was administered 1, 3 or 6 days before the challenge inoculation with S. fuliginea. Increasing the inoculum concentration of A. cucumarina or C. fulvum enhanced the systemic protection and provided up to 71.6% or 80.0% reduction, respectively, in the number of colonies produced on upper leaves, relative to controls. Increasing the inoculum concentration of S. fuliginea used for challenge inoculation, increased the number of powdery mildew colonies produced on both induced and non-induced plants. Pre-treated plants, however, were still better protected than controls, indicating that the level of systemic protection was related to the S. fuliginea inoculum concentration. The induction of systemic resistance against powdery mildew by biotic agents, facilitates the development of a wide range of disease management tools.  相似文献   

5.
Bemisia tabaci (Gennadius), the sweetpotato whitefly, has only one known entomophthoralean pathogen,Erynia radicans (Entomophthoraceae). Two new pathogens have been isolated recently from a glasshouse population of this pest:Conidiobolus coronatus and another, undescribed species ofConidiobolus (Entomophthorales: Ancylistaceae). Artificial inoculation experiments revealed that eggs ofB. tabaci are practically immune to infection by either species. Second-instar larvae are highly resistant, only high doses of conidia causing between <1% and 4.6% mortality. Adults were found to be much more susceptible. Doses of 60 conidia/mm2 ofC. coronatus caused average mortalities ofca 95%. The maximum mortality of adults caused byConidiobolus sp. was much lower,ca 30%, at a dose of 210 conidia/mm2. The incubation period (inoculation to death) for both species, under our experimental conditions, is very short: 18–24 h forC. coronatus and 30 h forConidiobolus sp. Both fungi produced loricoconidia (conidia metamorphosed into resting spores) on cotton leaves and other dry surfaces. This ability allowedConidiobolus sp. to remain viable for 17–21 days on cotton leaves, in glasshouse conditions and in the absence of hosts, whileC. coronatus persisted for 10–14 days.  相似文献   

6.
Among 153 isolates ofRhizoctonia spp. obtained from 95 soil samples collected from different fields in the USA, 42 (27.5%) isolates were hypovirulent or non-pathogenic on cabbage (tested on tap water agar plus 250 μg/ml chloramphenicol plates). Of these, 14 (33.3% of the np-R) isolates protected >60% of the cabbage seedlings againstR. solani, and the best eight isolates protected 73–95% of the cucumber seedlings. The np-R isolates RU56-8 (AG-P) and RU89-1 [AG-B(o)] induced the highest resistance against hypocotyl challenge inoculation with virulentR. solani (38.3–85.7%), whereas most of the challenged control seedlings (85–100%) collapsed. Similarly, isolates RU56-8 and RU89-1 induced the highest resistance (22.2–87.5%) against hypocotyl challenge inoculation withPythium aphanidermatum, whereas most of the challenged control seedlings collapsed (90–100%). Isolates RU56-8 and RU89-1 significantly reduced the lesion numbers and area/leaf (to 8.9–42.0% of the control) caused by challenge inoculation of the first true leaves withPseudomonas syringae pv.lachrymans. No np-R isolate could be recovered from the upper hypocotyls or from the leaves, indicating that there was no contact between the inducer and the pathogen. Root colonization with some np-R increased seedling tolerance to low soil moisture levels.  相似文献   

7.
Momordica charantia L. plants systemically infected with Cucumber mosaic virus (CMV) were found in Oita Prefecture. The virus isolated from the host plant was characterized by biological, serological, and molecular biological methods. The purified virus was used to mechanically inoculate the host and produced green mottle, green mosaic, and/or chlorotic spots in the noninoculated upper leaves of the host. The virus was identified as an isolate of CMV containing genomic RNA3 derived from subgroup IA by several lines of evidence based on electron microscopy, serological detection, host range, symptoms, and the entire nucleotide sequence of RNA3.  相似文献   

8.
When lower leaves of rice plants were inoculated with powder formulation of a saprophytic strain ofPseudomonas fluorescens, Pfl, upper leaves, in addition to the inoculated lower leaves, showed resistance to the rice bacterial blight pathogenXanthomonas oryzae pv.oryzae. When the leaves were challenge-inoculated withX. oryzae pv.oryzae 4 days afterP. fluorescens application on lower leaves, the disease intensity in upper leaves decreased from 6.7 to 1.1. When rice seeds were treated with the formulation ofP. fluorescens Pfl and sown, 30-day-old seedlings showed resistance toX. oryzae pv.oryzae and the disease intensity decreased from 6.8 to 1.2. The induced resistance was transient; leaves sprayed withP. fluorescens Pfl at 30 days after treatment and leaves of 60-day-old seedlings fromP. fluorescens-treated seeds did not show resistance to the pathogen. In field trials, seed treatment followed by foliar application of the powder formulation ofP. fluorescens Pfl effectively controlled rice bacterial blight and increased the yield. In the induced resistant leaves a sharp increase in lignification and activities of peroxidase, phenylalanine ammonia-lyase and 4-coumarate: CoA ligase was observed when the leaves were challenge-inoculated withX. oryzae pv.oryzae. An approximately threefold increase in lignin content, peroxidase activity and phenylalanine ammonia-lyase activity and a fivefold increase in 4-coumarate: CoA ligase activity were observed 5 days after challenge inoculation withX. oryzae pv.oryzae in rice leaves pretreated withP. fluorescens for 5 days. A similar increase in defense-related activities was not observed in susceptible interactions or inP. fluorescens-treated plants at later stages of interactions when no resistance to the pathogen was observed.  相似文献   

9.
The effect of microclimate variables on development ofClonostachys rosea and biocontrol ofBotrytis cinerea was investigated on rose leaves and crop residues. C.rosea established and sporulated abundantly on inoculated leaflets incubated for 7–35 days at 10°, 20° and 30°C and then placed on paraquat—chloramphenical agar (PCA) for 15 days at 20°C. On leaflets kept at 10°C, the sporulation after incubation on PCA increased from 60% to 93% on samples taken 7 to 21 days after inoculation, but decreased to 45% on material sampled after 35 days. A similar pattern was observed on leaves incubated at either 20° or 30°C. The sporulation ofC. rosea on leaf disks on PCA was not affected when the onset of high humidity occurred 0, 4, 8, 12 or 16 h after inoculation. However, sporulation was reduced to 54–58% on leaflets kept for 20–24 h under dry conditions after inoculation and before being placed on PCA. The fungus sporulated on 68–74% of the surface of leaf disks kept for up to 24 h at high humidity after inoculation, but decreased to 40–51% if the high humidity period before transferral to PCA was prolonged to 36–48 h. The growth ofC. rosea on leaflets was reduced at low inoculum concentrations (103 and 104 conidia/ml) because of competition with indigenous microorganisms, but at higher concentrations (105 and 106 conidia/ml) the indigenous fungi were inhibited. Regardless of the time of application ofC. rosea in relation toB. cinerea, the pathogen’s sporulation was reduced by more than 99%. The antagonist was able to parasitize hyphae and conidiophores ofB. cinerea in the leaf residues. AsC. rosea exhibited flexibility in association with rose leaves under a wide range of microclimatic conditions, and in reducingB. cinerea sporulation on rose leaves and residues, it can be expected to suppress the pathogen effectively in rose production systems.  相似文献   

10.
Phosphites (Phi) are alkali metal salts of phosphorous acid, with the ability to protect plants against different pathogens. In this research, the effect of Phi applied to potato plants on severity of three important potato diseases in Argentina was assessed. Seed tubers and foliage of potato cvs Shepody and Kennebec were treated with Phi to assess effects on resistance against Phytophthora infestans, Fusarium solani and Rhizoctonia solani. Protection resulting from Phi treatment in seed tubers was high against P. infestans, intermediate against F. solani, and low against R. solani. In addition, seed tubers treated with calcium or potassium phosphites (CaPhi and KPhi, respectively) at 1% of commercial product emerged earlier than untreated ones. When Phi were foliarly applied two or four times at different doses, high levels of protection against P. infestans were achieved in both cultivars. Higher protection was observed in Kennebec when CaPhi was applied, while in Shepody this was true for KPhi. Expression of β-1,3-glucanases was induced at different times after treatment but no correlation between β-1,3-glucanases expression and foliar protection level was found. On the other hand, Phi positive protection effects did not produce negative effects in plant growth. Leaves from CaPhi-treated plants showed a darker green colour than leaves from control plants; also an increase in Rubisco protein and a delay in crop senescence was observed.  相似文献   

11.
The objective of this research was to study the levels of some organic solutes, such as total protein, total soluble sugars, starch and proline in leaves, as well as abscisic acid concentration in xylem of pepper plants inoculated with Verticillium dahliae Kleb. Healthy and inoculated plants were always kept well watered. Measurements were made at time intervals after inoculation. Leaf water potential rapidly decreased as a consequence of fungal infection. However, relative water content in leaves only changed significantly from day 20 after inoculation, and such decreases coincided with a sharp build up of proline and total soluble sugars in leaves. Starch and protein levels, as well as abscisic acid concentration in xylem, declined in healthy and inoculated peppers as they became older. However, such decreases were more pronounced in infected plants, especially soon after inoculation. Results suggest that proline and total soluble sugars accumulation could be sensors of the damage caused by the fungal infection.  相似文献   

12.
白术矮化病毒病病原的分子鉴定和部分序列分析   总被引：2，自引：0，他引：2  
 本试验在生物学接种的基础上,利用非序列依赖性PCR扩增(sequence-independent amplification,SIA)对白术矮化病毒病病原进行了分子鉴定,序列测定及分析。结果发现,具有矮化症状的白术为黄瓜花叶病毒(Cucumber mosaic virus,CMV)所侵染。为明确CMV白术分离物(CMV-Am)的分类地位,本研究进一步克隆了CMV-Am的外壳蛋白基因(CP)和移动蛋白基因(MP)全序列。序列比对分析表明,CMV-Am与CMV亚组ⅠB中株系XJ2序列同源性最高,核苷酸、氨基酸序列同源性分别为98.9%、99.1%。氨基酸序列同源性聚类分析表明,CMV-Am与中国大多数CMV分离物一样,属于CMV亚组ⅠB。  相似文献   

13.
The aim of this work was to correlate the appearance of the symptoms, multiplication and spread of virus after mechanical inoculation of potato (Solanum tuberosum L.) cultivars showing different levels of susceptibility and sensitivity to Potato virus YNTN (PVYNTN). The potato cultivars used were the resistant cultivar Sante and susceptible cultivars Igor, Pentland squire and Désirée. The spread of the virus PVYNTN in infected plants was monitored using different methods: DAS-ELISA, tissue printing, immuno-serological electron microscopy and real-time PCR. In all three susceptible cultivars, the virus was detected in the inoculated leaves 4–5 days after inoculation. From there virus spread rapidly, first into the stem, then more or less simultaneously to the upper leaves and roots. Real-time PCR was shown to be very sensitive and enabled viral RNA to be detected in non-inoculated leaves of susceptible cultivar Igor earlier than other methods. Therefore, for exact studies of plant–virus interaction, a combination of methods which detect viruses on the basis of their different properties (coat protein, morphology or RNA) should be used to monitor the spread of viruses.  相似文献   

14.
Leaves of powdery mildew-susceptible barley (Hordeum vulgare cv. Ingrid) and related near-isogenic lines bearing various resistance genes (Mla12, Mlg or mlo5) were inoculated with Blumeria graminis f. sp. hordei race A6. Fungal attack induced several-fold increases in ethylene emission and electrolyte leakage in leaves of susceptible Ingrid beginning 3 days after inoculation. Activities of peroxidase, superoxide dismutase, glutathione S-transferase, ascorbate peroxidase and glutathione reductase enzymes were induced markedly in susceptible leaves 5–7 days after inoculation. Similar, but less pronounced pathogen-induced changes were detected in inoculated leaves of Mla-type resistant plants that show hypersensitive cell death upon inoculation, and, to an even lesser extent, in the Mlg and mlo lines, where no visible symptoms accompanied the incompatible interaction. Glutathione content increased only in susceptible barley 7 days after inoculation. Catalase activity, total ascorbate content and redox state were not influenced by inoculation in any of the genotypes. The activity of dehydroascorbate reductase was significantly reduced 3–5 days after inoculation in the susceptible parental plants and after 5 days in Mla and Mlg lines, while it was stable in the mlo barley. Slightly elevated levels of H2O2 were observed in the inoculated resistant plants. In contrast, H2O2 content decreased in the susceptible line 7 days after pathogen attack. These data indicate that high levels of antioxidants are involved in the compatible interaction of susceptible barley and powdery mildew by protecting the pathogen from oxidative damage.  相似文献   

15.
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16.
Tomato plants infected with Potato spindle tuber viroid (PSTVd) had severe leaf curling and vein necrosis. The disease symptoms began to diminish during the late stages of infection, however, and almost healthy-looking leaves began to appear on the upper portion of the plants. PSTVd concentrations reached their highest levels in leaves with severe symptoms and decreased in upper leaves recovering from severe symptoms. PSTVd-specific short interfering RNAs (siRNAs), characteristic of RNA silencing, accumulated in all leaves in which PSTVd reached a detectable level, suggesting that recovery from severe disease was induced by RNA silencing via sequence-specific degradation of PSTVd.  相似文献   

17.
为明确南方根结线虫Meloidogyne incognita效应蛋白MiV901在其寄生过程中的生物学功能,通过构建MiV901基因的植物表达载体,利用根癌农杆菌Agrobacterium tumefaciens介导的花序浸染法将其转化拟南芥Arabidopsis thaliana,并采用室内人工接种法测定转基因植株对灰葡萄孢 Botrytis cinerea侵染及南方根结线虫寄生的影响。结果显示：经Southern blot检测,MiV901基因以不同的拷贝数插入到转基因拟南芥株系901-6、901-8和901-12的基因组中,且qPCR检测结果证实 MiV901基因能够正常表达。3个转基因拟南芥株系901-6、901-8和901-12叶部接种灰葡萄孢3 d后,叶片上形成的病斑平均直径分别为1.00、1.06、1.05 cm,比野生型对照扩大了9.9%~16.5%。相比野生型对照,转基因拟南芥株系901-12、901-6和901-8接种南方根结线虫2龄幼虫后根系上产生了更多的雌虫和卵块,雌虫数分别显著增加了45.4%、34.4%和23.7%,卵块数分别显著增加了51.2%、 46.3%和31.7%。表明异源表达MiV901基因能够抑制植物免疫,增加拟南芥对灰葡萄孢和南方根结线虫侵染的敏感性。  相似文献   

18.
Acibenzolar-S-methyl (Novartis) is a chemical inducer of systemic acquired resistance in several annual plants. The ability of this novel chemical to induce resistance was studied in a perennial plant (apple) affected by fire blight caused by Erwinia amylovora. Acibenzolar-S-methyl (100 and 200mg/l active ingredient) protected Golden Delicious seedlings, scions and trees from artificial infection when applied before inoculation. The protection of apple seedlings was similar to the protection obtained with the standard for fire blight control, plantomycin (100mg/l streptomycin sulfate), applied immediately before inoculation. The mean levels of control in scions in the greenhouse and in trees in orchards were approximately 69% and 50%, respectively. The protection of apple seedlings was constantly associated with the activation of two families of defense-related enzymes, peroxidases and -1,3-glucanases. Accumulation of both enzymes was induced locally in treated leaves and systemically, especially for -1,3-glucanases, in upper untreated leaves, and was sustained for at least 17 days. These results suggest that acibenzolar-S-methyl promotes induced systemic resistance in apple by increasing defense-related compounds. This chemical could provide a new approach of control of fire blight but its practical use needs further investigation.  相似文献   

19.
Viral movement in the leaf tissues of a resistant host, Cucumis figarei, inoculated with the pepo strain of Cucumber mosaic virus (CMV) and incubated at 24°C or 36°C was investigated by fluorescence in situ hybridization (FISH), leaf-press blotting, tissue printing and immunogold-silver staining techniques. Observation by FISH revealed that at 24°C most infection sites with CMV at 0.01 mg/ml or 0.1 mg/ml were limited to a single cell during the incubation period, that the number of infection sites increased from 24hpi (hours post inoculation) to 80 hpi in the leaves inoculated with CMV at 0.5 mg/ml, and that the size as well as the number of infection sites rapidly increased with time in the leaves inoculated with CMV at 2.0 mg/ml. These results suggested that one factor for the resistance of C. figarei at 24°C might be an inhibition of viral movement in and out of the infection sites. Leaf-press blotting and tissue blotting indicated that CMV remained in the infection sites at 24°C, whereas it spread from the inoculated leaves to other parts of the plants through vascular systems at 36°C. Immunogold-silver staining demonstrated that at 24°C CMV infected bundle sheath (BS) cells in minor veins, whereas at 36°C it invaded not only BS cells, but also phloem parenchyma (PP)/ companion cell (CC) or PP/intermediary cell (IC) complexes in minor veins in the regions with chlorotic symptoms. These results indicated that at 24°C CMV had difficulty in passing through the interface between BS and PP/CC or PP/ IC complexes and that viral entry from mesophyll to the phloem pathway was inhibited in the inoculated leaves. Received 26 August 1999/ Accepted in revised form 14 December 1999  相似文献   

20.
为明确超敏蛋白对烟草黄瓜花叶病毒(Cucumber mosaic virus,CMV)的诱导抗性及其生长、品质的影响,采用半叶枯斑法和田间试验研究了10%超敏蛋白对枯斑三生烟和普通烟的诱导抗性及促生作用,并分析了对烤烟经济性状和内在质量的影响。结果表明,10%超敏蛋白在活体外对CMV无钝化作用,但预防、治疗效果显著,接种前48 h喷施预防效果达75.70%,接种后24 h喷施治疗效果达65.45%,均显著高于对照;10%超敏蛋白处理后烟草的株高、茎围、最大叶面积均高于其它处理,单位产量比20%吗啉胍·乙铜可湿性粉剂处理增产211.8 kg/hm2,增值3 519.2元/hm2;经10%超敏蛋白处理后的烤烟化学成分均处于优质烟的适宜质量分数范围内。表明超敏蛋白不仅有利于提高烟草抗性和促进烟株生长,且可以明显提高烟叶经济效益和烟叶内在质量。  相似文献   

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