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1.
In October 2009, vein yellowing disease was observed on the weeds Crassocephalum crepidioides and Ageratum conyzoides in a subtemperate region in northern India. Ageratum enation virus (AEV), along with a nanovirus like satellite DNA 1, was found to be associated with both weeds. The isolates had 99% identity with each other and with an isolate of AEV reported from Zinnia elegans from this region. To the best of our knowledge, this report is the first of any begomovirus infection in C. crepidioides in India and the first on AEV infecting C. crepidioides worldwide and A. conyzoides in India.  相似文献   

2.
Begomovirus infection was suspected in tomato plants exhibiting symptoms of curling and deformation of leaves observed in a survey conducted in northern and central Peru. Rolling circle amplification and restriction fragment length polymorphism analyses suggested that a begomovirus was present in symptomatic plants. The full-length sequence of a begomovirus DNA component was determined, comprising 2591 nucleotides. Based on its genome organization, we suggest it corresponds to the DNA-A of a New World begomovirus. Less than 89% nucleotide sequence identity to known begomoviruses was found, indicating that it corresponds to an isolate of a distinct begomovirus species for which the name tomato leaf deformation virus (ToLDeV) is proposed. Different stretches of the genomic component have the highest sequence identity with different viruses compatible with a recombinant origin. Sequence segments shared common ancestors with isolates of either soybean blistering mosaic virus, tomato yellow spot virus, or tomato chino La Paz virus. Partial sequence analysis of begomovirus isolates present in symptomatic tomato samples collected in northern and central Peru suggested widespread occurrence of this new begomovirus. This is the first confirmation of a begomovirus infection in tomatoes in Peru.  相似文献   

3.
Quantitative PCR revealed that Tomato chlorotic dwarf viroid (TCDVd) was present in substantial amounts in viroid-infected tomato flowers. Healthy tomato plants were arranged in two different glasshouses, and plants were mechanically inoculated with TCDVd. Bumblebees (Bombus ignitus) were then introduced into the glasshouses to reveal whether the viroid was transmitted from infected source plants to neighbouring healthy plants. TCDVd infection was found in neighbouring tomato plants more than 1 month after the introduction of the bees, some of which expressed symptoms, in both glasshouses. Thus, bumblebees transmitted TCDVd from tomato to tomato by pollination activities.  相似文献   

4.
A conventional PCR and a SYBR Green real-time PCR assays for the detection and quantification of Phytophthora cryptogea, an economically important pathogen, have been developed and tested. A conventional primer set (Cryp1 and Cryp2) was designed from the Ypt1 gene of P. cryptogea. A 369 bp product was amplified on DNA from 17 isolates of P. cryptogea. No product was amplified on DNA from 34 other Phytophthora spp., water moulds, true fungi and bacteria. In addition, Cryp1/Cryp2 primers were successfully adapted to real-time PCR. The conventional PCR and real-time PCR assays were compared. The PCR was able to detect the pathogen on naturally infected gerbera plants and on symptomatic artificially infected plants collected 21 days after pathogen inoculation. The detection limit was 5 × 103 P. cryptogea zoospores and 16 fg of DNA. Real-time PCR showed a detection limit 100 times lower (50 zoospores, 160 ag of DNA) and the possibility of detecting the pathogen in symptomless artificially infected plants and in the re-circulating nutrient solution of closed soilless cultivation systems.  相似文献   

5.
Nicandra physaloides, a common weed in South America, was found to be infected by an isolate of Tomato severe rugose virus (ToSRV), a bipartite begomovirus. The plants developed severe yellow rugose mosaic and were collected in São Paulo State, Brazil. This isolate of ToSRV was transmitted by Bemisia tabaci B biotype from infected plants of N. physaloides to healthy plants of N. physaloides and tomato in a glasshouse. This is the first report of natural infection of N. physaloides by ToSRV in Brazil.  相似文献   

6.
Virus-like symptoms—red ringspots on stems and leaves, circular blotches or pale spots on fruit—were found on commercial highbush blueberry (Vaccinium corymbosum) cultivars Blueray, Weymouth, Duke and Sierra in Japan. In PCR testing, single DNA fragments were amplified from total nucleic acid samples of the diseased blueberry bushes using primers specific to Blueberry red ringspot virus (BRRV). Sequencing analysis of the amplified products revealed 95.7–97.7% nucleotide sequence identity with the BRRV genome. This paper is the first report of blueberry red ringspot disease caused by BRRV in Japan. The nucleotide sequence data reported in this paper are available in the GenBank/EMBL/DDBJ database as accessions AB469884 to AB469893 for BRRV isolates from Japan.  相似文献   

7.
Botrytis cinerea is a non-specific, necrotrophic pathogen that attacks many plant species, including Arabidopsis and tomato. Since senescing leaves are particularly susceptible to infection by B. cinerea, we hypothesized that the fungus might induce senescence as part of its mode of action and that delaying leaf senescence might reduce the severity of B. cinerea infections. To examine these hypotheses, we followed the expression of Arabidopsis SAG12, a senescence-specific gene, upon infection with B. cinerea. Expression of SAG12 is induced by B. cinerea infection, indicating that B. cinerea induces senescence. The promoter of SAG12, as well as that of a second Arabidopsis senescence-associated gene, SAG13, whose expression is not specific to senescence, were previously analyzed in tomato plants and were found to be expressed in a similar manner in the two species. These promoters were previously used in tomato plants to drive the expression of isopentenyl transferase (IPT) from Agrobacterium to suppress leaf senescence (Swartzberg et al. in Plant Biology 8:579–586, 2006). In this study, we examined the expression of these promoters following infection of tomato plants with B. cinerea. Both promoters exhibit high expression levels upon B. cinerea infection of non-senescing leaves of tomato plants, supporting our conclusion that B. cinerea induces senescence as part of its mode of action. In contrast to B. cinerea, Trichoderma harzianum T39, a saprophytic fungus that is used as a biocontrol agent against B. cinerea, induces expression of SAG13 only. Expression of IPT, under the control of the SAG12 and SAG13 promoters in response to infection with B. cinerea resulted in suppression of B. cinerea-induced disease symptoms, substantiating our prediction that delaying leaf senescence might reduce susceptibility to B. cinerea. Contribution from the Agriculture Research Organization, The Volcani Center, Bet Dagan, Israel, No. 127/2006 series.  相似文献   

8.
In 2006, stem rot and blue-green crusty lesions were found on the stems of tomato plants in Chiba Prefecture, Japan. Penicillium oxalicum was isolated repeatedly from the diseased plants. The causal fungus reproduced natural symptoms after artificial inoculation of tomato plants and was re-isolated from symptomatic plant tissue. P. oxalicum is a new pathogen that causes blue mold on tomato plants in Japan.  相似文献   

9.
Pymetrozine, a novel compound belonging to the class pyridine-azomethines, is a feeding inhibitor labeled for use against plant pests in the order Hemiptera. Pymetrozine was evaluated for its ability to interfere with whitefly transmission of the begomovirusTomato yellow leaf curl virus (TYLCV). Pymetrozine was applied as Fulfill TM 50 WG at two rates (0.291 and 0.582 g formulationl −1) to tomato seedlings with four to six true leaves. Viruliferous whiteflies (three to five per plant) were added 1, 4, 7 and 11 d after a single application of pymetrozine, and transmission rates were determined 4 wk after the addition of whiteflies. Pymetrozine provided protection against transmission of TYLCV by viruliferous whiteflies for up to 1 wk after a single apliation. No phytotoxicity was observed on tomato transplants. These results indicate that pymetrozine could be an effective tool for tomato transplant producers to protect susceptible transplants from infection by begomoviruses, such as TYLCV. Pymetrozine might also work well as part of an integrated approach to begomovirus management in greenhouse tomato fruit production. http://www.phytoparasitica.org positing Oct. 20, 2003.  相似文献   

10.
Colletotrichum isolates isolated from cowpea in the Hangzhou area of China were identified as C. destructivum based on morphological characteristics, pathogenicity tests, sequence analysis of the internal transcribed spacer (ITS)1, 5.8S RNA gene and ITS2 regions of ribosomal DNA and the infection process. The ability of the C. destructivum isolates to infect Arabidopsis thaliana was investigated under laboratory conditions and showed a two-phase hemibiotrophic infection process. In addition, the sequences of the rDNA ITS region of C. destructivum isolates from cowpea were identical with 100% similarity to that of isolates of C. higginsianum originating from cruciferous plants. This article presents new evidence in support of C. higginsianum as a synonym of C. destructivum.  相似文献   

11.
Five primer/probe sets to identify the tomato wilt pathogen, Fusarium oxysporum f. sp. lycopersici (FOL), and its three races selectively were designed based on the rDNA-intergenic spacer and avirulence genes. Real-time PCR using genomic DNA from mycelia and soil DNA with the primer/probe sets allowed the successful identification of FOL and its races.  相似文献   

12.
Leaf spot of tomato, incited by Pseudomonas syringae pv. syringae, has been reported recently in Italy on grafted and non-grafted tomato plants (scion Cuore di Bue, rootstock Solanum lycopersicum x Solanum hirsutum cv. Beaufort). In some greenhouses, more than 80% of plants were affected, with a marked reduction in yield. This work was undertaken in order to understand the effect of the number of hours of incubation at high relative humidity (r.h.) and temperature as well as the effect of the presence of wounds at infection time on the development of leaf spot. A difference in sensitivity to leaf spot was observed in the various cultivars tested, in terms of severity of P. syringae pv. syringae, with “Cuore di Bue” being the most susceptible of these cultivars. The development of leaf spot is mostly favored by the presence of wounds, at temperatures between 15 and 20°C. The severity of the disease is lower at 10 and 25°C and very low at 30°C. Under the most favorable temperature conditions, the presence of wounds is sufficient to allow the development of the pathogen immediately upon incubation at high r.h. The effect of wounds and the relatively low requirement of hours of incubation at high r.h. suggest the need for careful management and handling of plants when temperatures range between 15 and 25°C, and particularly within 15 and 20°C. All operations carried out, particularly at transplant and immediately after, should avoid the creation of wounds.  相似文献   

13.
In 2004, a damping-off symptom was found on southern star, Oxypetalum caeruleum, in Kochi Prefecture, Japan. Two Phytophthora strains with different colony patterns on potato dextrose agar were isolated, and their pathogenicity was confirmed by inoculation of southern star plants and their reisolation from symptomatic plants. Both fungi were identified as Phytophthora palmivora based on morphology, physiology, and sequence analysis of the internal transcribed spacers of nuclear ribosomal DNA. This is the first report of Phytophthora blight of southern star in the world.  相似文献   

14.
Tomato severe rugose virus (ToSRV) is a serious and prevalent begomovirus that causes severe mosaic and yield loss of tomato plants in Brazil. The virus is transmitted by Bemisia tabaci bitotype B (MEAM1) in a persistent circulative manner. This study evaluated the efficacy of cyantraniliprole foliar spray, cyantraniliprole root drenching, spiromesifen, thiamethoxam, and cartap on the mortality of Bemisia tabaci byotipe B and simulated primary and secondary transmission of ToSRV. None of the insecticides were effective in controlling primary transmission of ToSRV by B. tabaci. Cyantraniliprole root drenching, cartap, and cyantraniliprole foliar spray were effective in controlling secondary transmission of the virus, and infections were reduced by 94.5, 89.6, and 81%, respectively, compared to each of their controls. Thiamethoxam and spiromesifen did not provide effective control of secondary infection. Elimination of external sources of inoculum before starting new plantings and rational use of insecticides to reduce secondary infection may contribute to better disease management of tomato crops.  相似文献   

15.
The biocontrol agent Pythium oligandrum (PO) can suppress bacterial wilt caused by Ralstonia solanacearum (RS) in tomato. To understand the primary biocontrol mechanisms of bacterial wilt by PO, we pretreated tomato plants with sterile distilled water or preinoculated them with PO, followed by inoculation with RS, then observed PO and RS in fixed sections of tomato tissues using a confocal laser-scanning microscope and fluorescence labeling until 14 days after the inoculation with RS. Horizontal and vertical movement of RS bacteria was frequently observed in the xylem vessels of roots and stems of tomato plants (cv. Micro-Tom) that had not been inoculated with PO. In plants that were preinoculated with PO, the movement of RS was suppressed, and bacteria appeared to be restricted to the pit of vessels, a reaction similar to that observed in resistant rootstocks. PO colonization was mainly observed at the surfaces of taproots, the junctions between taproots and lateral roots, and the middle sections of the lateral roots. PO was not observed near wound sites or root tips where RS tended to colonize. However, RS colonization was significantly repressed at these sites in PO preinoculated plants. These observations suggest that the induction of plant defense reactions is the main mechanism for the control of tomato bacterial wilt by PO, not direct competition for infection sites.  相似文献   

16.
Tomato leaf curl disease (ToLCD) affected 25% of the tomato crop in Chitrakoot, India and symptomatic leaves were collected for molecular assay. The complete sequences of bipartite begomovirus DNA-A and a betasatellite DNA were amplified. In a sequence analysis, begomovirus DNA-A and betasatellite shared highest sequence identity (91–99%) with Tomato leaf curl New Delhi virus (ToLCNDV) DNA-A and chili leaf curl betasatellite (ChLCB), respectively. The virus was transmitted by whitefly to tomato plants and caused ToLCD symptoms with 70% transmission rate. To our knowledge, this is the first report of the natural occurrence of ToLCNDV and ChLCB in India.  相似文献   

17.
In July 2006, black rot was observed on the leaves of 4-leaf-stage seedlings of salt-wort (Salsola komarovii) in Yamagata Prefecture, Japan. We isolated two single-conidial isolates from the diseased leaves. Although colony appearance of the isolates was different from that of each other, both isolates were identified as Colletotrichum truncatum by morphology and molecular similarity. After inoculation of healthy salt-wort plants with the isolates, the isolates were reisolated from symptomatic plants. We thus propose a new disease, anthracnose of salt-wort.  相似文献   

18.
The tomato pathotype of Alternaria alternata (A. arborescens) produces the dark brown to black pigment melanin, which accumulates in the cell walls of hyphae and conidia. Melanin has been implicated as a pathogenicity factor in some phytopathogenic fungi. Here, two genes of the tomato pathotype for melanin biosynthesis, ALM1 and BRM2-1, which encode a polyketide synthetase and a 1,3,8-trihydroxynaphthalene (THN) reductase, respectively, have been cloned and disrupted in the pathogen. The gene-disrupted mutants, alm1 and brm2-1, had albino and brown phenotypes, respectively. The wild-type and the mutants caused the same necrotic lesions on the leaves after inoculation with spores. These results suggest that melanin is unlikely to play a direct role in pathogenicity in the tomato pathotype A. alternata. Scanning electron microscopy revealed that the conidia of both mutants have much smoother surfaces in comparison to the wild-type. The conidia of those mutants were more sensitive to UV light than those of the wild-type, demonstrating that melanin confers UV tolerance.  相似文献   

19.
A real-time PCR assay was designed to quantify seed-borne infection of Pyrenophora graminea in barley (Hordeum vulgare). Conventional tests such as the freezing blotter method cannot distinguish P. graminea from the closely related P. teres. The seed infection threshold for P. graminea is lower than the one for P. teres and is therefore applied for both species although P. graminea may be absent. This results in unnecessary rejections of seed lots. PCR primers and a TaqMan probe were designed to target a P. graminea-specific DNA sequence. The potential of the real-time PCR assay for quantifying seed-borne infection of P. graminea was investigated by examining seed lots harvested from P. graminea-infected fields. The major part (84%) of the variation in the amount of P. graminea DNA measured by real-time PCR could be attributed to variation between seed lots while only about 8% was due to variation within seed lots. DNA quantities of P. graminea were positively correlated with seed infection incidence detected by the freezing blotter method as well as with the infection incidence of plants examined in the greenhouse. Both correlations were highly significant (P < 0.001) but the DNA quantities accounted only for 59% (R 2 = 0.59) and 56% (R 2 = 0.56), respectively, of the variation in the results obtained by the two conventional methods. Seed lots of varieties resistant to P. graminea contained considerable amounts of P. graminea DNA but showed no or only few leaf symptoms in the greenhouse test suggesting that the recommended seed infection thresholds could be raised for resistant varieties.  相似文献   

20.
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