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1.
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   

2.
Pectinases extract (PE) from the fermentation product ofPenicillium oxalicum BZH-2002 was tested for its ability to induce protection against scab caused byCladosporium cucumerinum on cucumber (Cucumis sativus L.) plants. Seedlings with one true leaf were sprayed with various concentrations of PE (10–200 units ml−1) 3 days before inoculation withC. cucumerinum. Results showed that the induced local protection against the pathogen was dose-dependent when the concentrations of PE were between 20 and 120 units ml−1; systemically induced resistance against the pathogen was not observed. Boiled PE had a slight effect on disease reduction. Commercial pectinases prepared fromAspergillus niger showed lower protection against scab compared with PE when they were used at the same concentration of enzyme activity. No inhibitory activity was observed on conidial germination or germ-tube growth ofC. cucumerinum. PE was further evaluated for its enhancement of defense-related enzymes. Peroxidase (PO), polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL) increased in cucumber seedlings after treatment with PE. PO and PPO remained at a higher level in PE-pretreated seedlings throughout the experiment period whether pathogen-inoculated or non-inoculated, whereas PAL activity began to decrease 2 days after PE treatment. http://www.phytoparasitica.org posting July 14, 2004.  相似文献   

3.
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   

4.
Sclerotinia sclerotiorum is a worldwide ascomycete fungal plant pathogen, which causes enormous yield losses on major economic crops such as crucifers, grain legumes and several other plant families. The objective of this research was to isolate and characterise some bioactive products from cultures of fungi associated with the marine sponge Axinella sp. In total, nine fungal isolates were obtained from the marine sponge Axinella sp. collected from the South China Sea. A group of test strains, including two G+ strains (Bacillus subtilis and Staphylococcus aureus), two G− strains (Escherichia coli and Pseudomonas aeruginosa) and three fungi including two plant pathogenic fungi Sclerotinia sclerotiorum and Magnaporthe grisea and Saccharomyces cerevisiae, were employed as the indicator organisms for bioactivity screening. Using antagonistic tests and bioactive screening of the ethyl acetate (EtOAc) extracts of the corresponding cultures, fungal isolate JS9 showed the stronger efficacy against the test indicator strains, especially the indicator fungal pathogens. Isolate JS9 was further identified as Myrothecium sp. by a combination of morphological features and 18S rDNA BLAST on GenBank. Two macrocyclic trichothecenes, roridin A (compound 1) and roridin D (compound 2) were purified by tracking the activity of the EtOAc extract fractions and characterised with spectral analyses including MS, 1H-NMR, 13C-NMR and disortionless enhancement by polarization transfer (DEPT). In vitro antifungal tests showed that the two macrocyclic trichothecenes were bioactive against S. cerevisiae, M. grisea and S. sclerotiorum with minimal inhibitory concentrations of 31.25, 125 and 31.25 μg ml−1 for roridin A, and 62.5, 250 and 31.25 μg ml−1 for roridin D, respectively. The present investigation demonstrated that two antifungal trichothecenes including roridin A and roridin D produced by the fungus Myrothecium sp. isolated from the marine sponge Axinella sp. could be potential inhibitors against the plant pathogen S. sclerotiorum. Lian Wu Xie and Shu Mei Jiang contributed equally to this work.  相似文献   

5.
In a field experiment between 2004 and 2006, 14 winter wheat varieties were inoculated with either a mixture of three isolates of F. poae or a mixture of three isolates of F. avenaceum. In a subsequent climate chamber experiment, the wheat variety Apogee was inoculated with individual single conidium isolates derived from the original poly conidium isolates used in the field. Disease symptoms on wheat heads were visually assessed, and the yield as well as the fungal incidence on harvested grains (field only) was determined. Furthermore, grains were analysed using LC-MS/MS to determine the content of Fusarium mycotoxins. In samples from field and climate chamber experiments, 60 to 4,860 μg kg−1 nivalenol and 2,400 to 17,000 μg kg−1 moniliformin were detected in grains infected with F. poae and F. avenaceum, respectively. Overall, isolate mixtures and individual isolates of F. avenaceum proved to be more pathogenic than those of F. poae, leading to a higher disease level, yield reductions up to 25%, and greater toxin contamination. For F. poae, all variables except for yield were strongly influenced by variety (field) and by isolate (climate chamber). For F. avenaceum, variety had a strong effect on all variables, but isolate effects on visual disease were not reflected in toxin production. Correlations between visual symptoms, fungal incidence, and toxin accumulation in grains are discussed.  相似文献   

6.
Wasabi (Wasabia japonica) is grown for its highly-valued rhizome which is used as a condiment in Japanese food. Symptoms of vascular blackening in the rhizome were first observed in 2005 in plants grown in British Columbia, Canada. Microscopic observations and microbial isolation from infected tissues revealed that most of the xylem tracheid cells were blackened and bacteria were consistently associated with symptomatic plants. The bacterium most frequently recovered was identified as Pectobacterium carotovorum subsp. carotovorum (Pcc) using BioLog™ and sequencing of a specific ~510 bp IGS region. Pathogen-free plants obtained using meristem-tip micropropagation were inoculated with a wasabi isolate of Pcc. Vascular blackening symptoms developed in the rhizome after 8 weeks when the rhizome was first wounded by stabbing or cutting, or if the roots were pre-inoculated with Pythium species isolated from rhizome epidermal tissues, followed by inoculation with Pcc at 1 × 108 cells ml−1. Xylem tracheid cells were blackened and Pcc was reisolated from all diseased tissues. The highest frequency of rhizome vascular blackening occurred at 22°C and 27°C and these tissues occasionally succumbed to soft rot at higher temperatures, but not when inoculated tissues were incubated at 10°C. The rooting medium used by growers for vegetative propagation of wasabi was shown to contain Pcc but the pathogen was not recovered from the irrigation water. Entry of Pcc through wounds on wasabi rhizomes and the host tissue response result in symptoms of vascular blackening.  相似文献   

7.
Essential oils extracted fromEucalyptus blakelyi (1,8-cineole, 77.5%),Melaleuca fulgens (1,8-cineole, 56.9%) and 1,8-cineole were shown to have fumigant toxicity against different development stages ofSitophilus oryzae. The eggs ofS. oryzae were the most tolerant, followed by pupae, larvae and adults in that order.M. fulgens oil,E. blakelyi oil and 1,8-cineole at 100 μl per liter of air gave, respectively, LT50 values of 16.2, 17.4 and 9.1 h for adults, 31.1, 19.3 and 17.5 h for larvae, 55.6, 75.2 and 39.7 h for pupae, and required >7 days for eggs. Only 1,8-cineole (200 μl −1 air) gave a significant egg kill by 7 days and the LT95 was 134.5 h. 1,8-Cineole could be a useful new fumigant. http://www.phytoparasitica.org posting Oct. 3, 2004.  相似文献   

8.
Significant antibacterial activity was observed in the essential oil (E.O.) ofRosa damascena Mill. and the Minimum Bactericidal Concentration (MBC) of the E.O. was determined as 1386.5 μg ml−1 forErwinia amylovora, the causal agent of fire blight disease. Ooze formation on immature pears and lesion formation in artificially inoculated shoots were completely (100%) prevented by the essential oil ofR. damascena (1500 μg ml−1), essential oil ofThymbra spicata var.spicata (500 μg ml−1) and streptomycin (100 μg ml−1). Copper oxychloride plus maneb significantly reduced ooze formation and lesion formation, but the control was less than that obtained with the essential oils or streptomycin. The essential oil ofR. damascena may be a useful natural bactericide for the control of the fire blight pathogen,E. amylovora. http://www.phytoparasitica.org posting July 14, 2004.  相似文献   

9.
A botanical natural product,AkseBio2, was evaluated under laboratory conditions for its oviposition deterrent, ovicidal and larvicidal (nymphicidal) effects against the pear psyllaCacopsylla pyri (L.) (Hemiptera: Psyllidae). The product exhibited a strong oviposition deterrent effect for winterform and summerform females and caused a reduction in the total number of eggs laid in both choice and no-choice assays. Significant mortalities in freshly laid eggs (0–48 h) and various nymphal stages of the pest were recorded in toxicity assays. At a concentration of 0.1% (formulation), the highest biological activity of the product was recorded against the young (1st and 2nd) nymphal stages (up to 87.4% mortality) in comparison with the other biological stages of the pest. It was less active against the older (3rd-5th) nymphs, causing 62.1% mortality at the same concentration. In assays with non-target organisms, a significant negative effect was not observed. There were no significant changes on treated plants up to 7 days after treatment in any trial, nor was there any phytotoxicity on plant tissue as a result ofAkseBio2 treatments. The results suggest that the product can be used in psylla control instead of synthetic insecticides and may serve as an integrated pest management (IPM) component in pear orchards. http://www.phytoparasitica.org posting July 14, 2004.  相似文献   

10.
The clustered hrp genes encoding the type III secretion system in the Japanese strains MAFF301237 and MAFF311018 of Xanthomonas oryzae pv. oryzae were sequenced and compared. The strains differ in their pathogenicity, location, and year of isolation. A 30-kbp sequence comprising 29 open reading frames (ORFs) was identical in its structural arrangement in both strains but differed from X. campestris pv. campestris, X. axonopodis pv. citri, and X. axonopodis pv. glycines in certain genes located between the hpaB-hrpF interspace region. The DNA sequence and the putative amino acid sequence in each ORF was also identical in both X. oryzae pv. oryzae strains as were the PIP boxes and the relative sequences. These facts clearly showed that the structure of the hrp gene cluster in X. oryzae pv. oryzae is unique.  相似文献   

11.
A mulberry epiphytic Enterobacter cloacae MUL1 harbors plasmid pMUL1 encoding five drug-resistance genes. This plasmid was examined upon its conjugal transfer into epiphytic Erwinia herbicola on the phylloplane of mulberry and 12 species of weeds. The plasmid was transferred into Er. herbicola at a frequency of 10–5–10–3/recipient in mulberry and Lolium multiflorum LAM. 1–8 days after wound inoculation with 106–108/ml suspensions. In Chenopodium album L. and C. album L. var. centrorubrum, however, it was transferred only after wound inoculation with a 108/ml suspension, but not with 107/ml or 106/ml suspensions, owing to the weak epiphytic fitness of Ent. cloacae on these weeds. Transconjugants were also obtained for seven other species of weeds in the case of inoculation with a 108/ml suspension. In contrast, when bacterial suspensions were sprayed on mulberry leaves with or without fresh wounds, transconjugants were obtained only in wounded leaves, which were considered suitable for bacterial conjugation. These findings suggest that epiphytic bacteria, including Ent. cloacae and Er. herbicola, may be carriers of drug-resistance genes distributed among plant pathogenic bacteria in nature.  相似文献   

12.
Strains of Xanthomonas campestris pv. vesicatoria Dye 1978 (Xcv), the causal agent of bacterial spot, have been classified into two groups based on their ability to hydrolyze starch. Three monoclonal antibodies (MAbs), 7AH10, 5HB3, and 4AD2, were produced immunized against the living bacteria and were specific to and could distinguish Xcv strains able or unable to hydrolyze starch (Amy+ or Amy–). The MAb 7AH10, obtained against strain UPB141(Amy–) reacted in an enzyme-linked immunosorbent assay with all the Amy– strains (n = 19) and 1 of 11 Amy+ strains. Against Xcv 2625, an Amy– unusual phenotype strain, MAb 5HB3, recognized 97% of our worldwide collection of Xcvs (n = 30). Also against that strain, the MAb 4AD2 reacted with none of the homologous Amy– phenotypes and with 90% (n = 11) of the heterologous Amy+ phenotypes. For all the MAbs, cross reactions with other pathovars or species were less than 4% (n = 67). By assaying a Japanese collection of strains against the three MAbs, the Amy+ strains were distinguished from the Amy– strains, and their relation with other world strains could be demonstrated. All the MAbs reacted with the lipopolysaccharide fraction of the bacterial cell wall during immunoblotting.  相似文献   

13.
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14.
Ageratum conyzoides L. is an annual herb in the tropics and subtropics whose extracts are known to possess pharmacological and biocidal activity. We report on the bioactivity of a secondary metabolite (a chromene) isolated from the shoots ofA. conyzoides against some plant pathogenic fungi. Organic solvent extracts from the shoots were tested for antifungal activity against the plant pathogenic fungiRhizoctonia solani, Sclerotium rolfsii, Botryodiplodia theobromae, Phomopsis theae andFusarium species growingin vitro on potato dextrose agar medium. The cruden-hexane extract completely inhibited the growth ofR. solani andS. rolfsii. Then-hexane extract was chromatographed over a column of silica gel followed by activity-guided fractionation to give an antifungal principle. Structure elucidation by detailed analysis of1H,13C NMR and mass spectroscopy identified the active compound as precocene II. The growth ofR. solani andS. rolfsii was completely inhibited by precocene II at a concentration of 80–100 ppm. The sclerotia ofR. solani andS. rolfsii were also completely suppressed by 150 ppm of precocene II. Sub-culture of these inhibited fungi onto precocene II-free medium restored growth of the fungus, indicating that precocene II is fungistatic. Crude or refined extracts fromA. conyzoides offer the possibility of biocontrol of plant pathogenic fungi. http://www.phytoparasitica.org posting Feb. 11, 2004.  相似文献   

15.
The present study was conducted to determine if there is specificity in the host-pathogen relationship between the isolates of Xanthomonas oryzae pv. oryzae, the causal bacterium for rice blight and Leersia grasses, the alternative weed hosts of the disease. Plants of three species of Leersia, namely, L. sayanuka, L. oryzoides and L. japonica, were collected from various parts of Japan and were inoculated with the X. oryzae pv. oryzae isolates obtained from various locations in Japan and from 11 Asian countries. Four L. sayanuka plants were found susceptible to all Race II isolates and some Race I isolates, but were resistant to all Race III isolates. Race III is known to have a wider range pathogenicity to rice cultivar groups compared with Race I and II. Although the reactions of two L. oryzoides plants to Race I and II isolates were similar to that of L. sayanuka, the L. oryzoides plant collected from Niigata Prefecture showed a susceptible reaction to some Race III isolates. On the other hand, L. japonica plants gave reactions different those of L. sayanuka and L. oryzoides, with two plants of L. japonica found to be resistant to all test isolates collected from Japan. The Asian isolates exhibited a wide host range against the international differential rice cultivars, but almost all of them were avirulent to Leersia plants. These results indicate that the relationship between the pathogenicity of the causal bacterium and the resistance of host plants is very complex, and suggest that pathogenic diversity of X. oryzae pv. oryzae might be related to the resistance of Leersia spp.  相似文献   

16.
Eighteen toxins produced byFusarium species were tested at different concentrations onOrobanche ramosa seeds to evaluate their effectiveness in inhibiting germination. Many of the toxins were active at the highest concentration used. Seven of them,viz. fusarenon X, nivalenol, deoxynivalenol, T-2 toxin, HT-2 toxin, diacetoxyscirpenol and neosolaniol, were highly active at 10μM, causing 100% inhibition of germination. Many of them were still active when assayed at a concentration ten times lower, with T-2, HT-2, nivalenol, neosolaniol and diacetoxyscirpenol still able to cause total inhibition; the last mentioned was very active also at 0.1μM, causing more than 90% inhibition. The results show that the use of toxic secondary metabolites could represent a useful alternative strategy in the management of parasitic weeds, by interfering with the induced germination process, and that fungal culture extracts could be an interesting source of new compounds acting as natural and original herbicides. http://www.phytoparasitica.org posting Sept. 18, 2002.  相似文献   

17.
Random insertional mutagenesis using a marker DNA fragment is an effective method for identifying fungal genes relevant to morphogenesis, metabolism, and so on. Agrobacterium tumefaciens-mediated transformation (AtMT) has long been used as a tool for the genetic modification of a wide range of plant species. Recent study has indicated that A. tumefaciens could transfer T-DNA not only to plant cells but also to fungal cells. In this study, AtMT was applied to Colletotrichum lagenarium for random insertional mutagenesis. We constructed a binary vector pBIG2RHPH2 carrying a hygromycin-resistant gene cassette between the right and left borders of T-DNA. Optimal co-cultivation of C. lagenarium wild-type 104-T with pBIG2RHPH2-introduced A. tumefaciens C58C1 led to the production of 150–300 hygromycin-resistant transformants per 106 conidia. Southern blot analysis revealed that T-DNA was mainly integrated at a single site in the genome and at different sites in transformants. The T-DNA inserts showed small truncations of either end, but the hygromycin-resistant gene cassette inside the T-DNA was generally intact. The mode of T-DNA insertion described above resulted in highly efficient gene recovery from the transformants by thermal asymmetrical interlaced-polymerase chain reaction. The fungal genomic DNA segments flanking T-DNA were identified from five of eight mutants that had defective melanin biosynthesis. The sequence from one of the segments was identical to that of the melanin biosynthesis gene PKS1 of C. lagenarium, which we previously characterized. These results strongly support our notion that AtMT is a possible tool for tagging genes relevant to pathogenicity in the plant pathogenic fungus C. lagenarium.  相似文献   

18.
Among the factors affecting the quality and yield of garlic production, blue mold caused by -- Penicillium spp. -- is responsible for economical losses in many countries. Allicin, present in garlic bulbs, has been suggested as having antifungal activity against some Penicillium species. This study was conducted to evaluate the response of garlic accessions against Penicillium hirsutum infection and to compare this response with bulb allicin content. Twelve garlic accessions were inoculated with P. hirsutum, and assayed in greenhouse and growth chamber experiments. Plant growth parameters and the fungal production of conidia were evaluated. Significant differences were found among the accessions. Accessions Castaño and Morado were most resistant whereas AR-I-125 and Fuego were always severely affected by the disease. A low correlation was found (r = 0.17) between allicin content and tolerance, indicating that allicin is not the main factor involved in the resistance against P. hirsutum.  相似文献   

19.
Organic management of soils is generally considered to reduce the incidence and severity of plant diseases caused by soil-borne pathogens. In this study, take-all severity on roots of barley and wheat, caused by Gaeumannomyces graminis var. tritici, was significantly lower in organically-managed than in conventionally-managed soils. This effect was more pronounced on roots of barley and wheat plants grown in a sandy soil compared to a loamy organically-managed soil. Fluorescent Pseudomonas spp. and in particular phlD+ pseudomonads, key factors in the take-all decline phenomenon, were represented at lower population densities in organically-managed soils compared to conventionally-managed soils. Furthermore, organic management adversely affected the initial establishment of introduced phlD+ P. fluorescens strain Pf32-gfp, but not its survival. In spite of its equal survival rate in organically- and conventionally-managed soils, the efficacy of biocontrol of take-all disease by introduced strain Pf32-gfp was significantly stronger in conventionally-managed soils than in organically-managed soils. Collectively, these results suggest that phlD+ Pseudomonas spp. do not play a critical role in the take-all suppressiveness of the soils included in this study. Consequently, the role of more general mechanisms involved in take-all suppressiveness in the organically-managed soils was investigated. The higher microbial activity found in the organically-managed sandy soil combined with the significantly lower take-all severity suggest that microbial activity plays, at least in part, a role in the take-all suppressiveness in the organically-managed sandy soil. The significantly different bacterial composition, determined by DGGE analysis, in organically-managed sandy soils compared to the conventionally-managed sandy soils, point to a possible additional role of specific bacterial genera that limit the growth or activity of the take-all pathogen.  相似文献   

20.
Incorporation into soil of dry mycelium ofPenicillium chrysogenum, a waste product of the pharmacological industry, enhanced plant growth and reduced root galling caused by the root-knot nematodeMeloidogyne javanica in cucumber and tomato plants. Incorporation into sandy loam soil in pots of dry mycelium at a concentration of 0.25% (w/w) resulted in complete protection of cucumber plants from the nematode. The number of juveniles recovered from soils containing dry mycelium was greatly reduced even at a concentration of 0.1% (w/w). In microplot studies conducted at two sites in two seasons, with three or four doses, dry mycelium caused a dose-dependent reduction in root galling index (GI) and promotion of plant growth of cucumber and tomato plants. Inin vitro studies, the water extract of dry mycelium immobilized nematode juveniles and reduced the egg hatching rate, but these effects were partly reversible after a rinse in water. Soil-drenching of cucumber and tomato seedlings with water extract of dry mycelium did not reduce GI or number of root-invading juveniles. The results show that dry mycelium promotes plant growth and protects plants against nematode infection. Protection, however, does not operatevia induced resistance. http://www.phytoparasitica.org posting April 6, 2003.  相似文献   

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