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1.
The host range of beet necrotic yellow vein virus (BNYVV) and Polymyxa betae was determined by growing plants in naturally infested soils from rhizomania outbreaks in England. Apart from Beta vulgaris , plant species infected by BNYVV were included in the families Chenopodiaceae ( Atriplex patula, Chenopodium bonus-henricus, C. hybridum, C. polyspermum and Spinacia oleracea ), Amaranthaceae ( Amaranthus retroflexus ) and Caryophyllaceae ( Silene alba, S. vulgaris, S. noctiflora and Stellaria graminea ). Only P. betae isolates from B. vulgaris, C. polyspermum and S. oleracea were found to be able to transmit BNYVV back to sugar beet. When a range of weed plants from infected fields were tested, none were found to be infected by BNYVV. Therefore, it seems likely that the weed hosts play only a minor role in the spread of rhizomania disease compared to that of sugar beet, other Beta vulgaris crop types or spinach.  相似文献   

2.
A molecular method is described to aid identification of the obligate parasite Polymyxa and discriminate between species ( P. betae and P. graminis ) and isolates. DNA was extracted from zoospores, resting spores and roots infected with P. betae and P. graminis and compared with that from negative control plants that were not inoculated with Polymyxa but were grown at the same time under the same conditions. The ribosomal internal transcribed spacers and 5.8S rDNAs were amplified by the polymerase chain reaction and digested with restriction enzymes to detect molecular differences between the species and isolates. There were differences between P. betae and P. graminis and two subgroups within P. graminis but so far this has not been correlated with any other biological property.  相似文献   

3.
Twenty common arable weed species were inoculated using Myzus persicae to transmit beet yellows virus (BYV), beet mild yellowing virus (BMYV), and an isolate of beet western yellows viruses (BWYV) that did not infect beet. The viruses were detected by enzyme-linked immunosorbent assay (ELISA), in which monoclonal antibodies distinguished between BMYV and BWYV, and by aphid transmissions to indicator host plants. Spergula arvensis, Stellaria media, Lamium purpureum and Papaver rhoeas were susceptible to all three viruses whereas Senecio vulgaris, Capsella bursa-pastoris, Anagallis arvensis and Chrysanthemum segetum were susceptible to both BMYV and BWYV, and Matricaria perforata, Raphanus raphanistrum, Veronica persica, Urtica urens and Viola arvensis were susceptible to BWYV only. Atriplex patula, Chenopodium album and Portulaca oleracea were susceptible to BYV only. Myosotis arvensis, Silene alba, Poa annua and Solanum nigrum were not susceptible to any of the viruses. Portulaca oleracea was shown for the first time to be a host of BYV, and C. segetum a host of BMYV and BWYV. In spring 1991, 8% of weeds sampled in a field of autumn-sown oilseed rape contained BWYV. Tests on weeds collected from an area of 'set-side' adjacent to sugar beet showed that 3% contained BMYV and 3% BWYV. No sampled weeds were infected with BYV. The role of weeds in the epidemiology of sugar beet virus yellows is discussed.  相似文献   

4.
稻区杂草上的梨孢菌与稻瘟病发生的关系   总被引：5，自引：0，他引：5  
 新发现的稻曲病菌白化菌株其分生孢子座白色,厚垣孢子表面光滑,大小为3.5-6.0×3.5-6.8μm。在麦芽糖-稻芽浸渍液中可产生较多的分生孢子。pH值为6时生长最好。普通培养基中加入几种供试碳源和氮源均有利于菌落生长,以蔗糖为碳源,浓度为2%或以L-天门冬酰胺为氮源浓度为0.2%~0.3%时时其菌落生长有促进作用。培养过程中可产生对稻种萌发有抑制作用的毒素,而固体培养时产毒能力高于液体培养。白化菌株回接到水稻上可重新产生白色稻曲球。该菌和稻曲病菌的酯酶同功酶和RAPD扩增谱带明显不同。可见白化菌株具有独立于稻曲病菌的新的分类地位。  相似文献   

5.
Highly specific rabbit polyclonal antibodies for the obligate sugar-beet root parasite, Polymyxa betae , were produced using a novel recombinant DNA approach. Parasite cDNA was selectively isolated from infected roots, expressed in vitro , and the purified protein used to raise antibodies. This produced clean, precisely targeted antibodies, and allowed for rigorous screening of candidate genes and their products at the molecular level prior to animal immunization. This approach selects for genes whose products are highly expressed by the parasite in planta , and five such candidate genes from Polymyxa betae were identified and cloned. Polyclonal antiserum developed using the product of one such gene was found to react specifically with P. betae in sugar-beet roots and with the closely related Polymyxa graminis in barley roots, and to cross-react with Plasmodiophora brassicae in cabbage roots, without the need for further purification. No cross-reaction was detected with protein extracts from potato roots infected by the plasmodiophoromycete Spongospora subterranea . In all cases, there was no interaction with proteins from host plants, or from other microorganisms found in association with uninoculated sugar-beet, barley, cabbage and potato roots.  相似文献   

6.
Summary. The effectiveness of pre-emergence applications of 2,4-D for weed control in maize was studied In five experiments, in comparison with other herbicide treatments. 2,4-D-aimne applied before crop emergence gave satisfactory weed control if the subsequent conditions were wet, but post-emerge nee applications only killed some species ( Chenopodium album and Atriplex patula. ) A combination of 2,4-D-amine, applied pre-emergence to a moist soil and subsequently as a foliar spray, controlled completely C. album, A. patula, Stellaria media and Veronica spp. Pre-emergence applications of simazine gave better weed control with less need for rain soon after application. Only A. patula was usually resistant. Pre-emergence treatments of atrazine killed all weeds whilst linuron controlled S. media, A. patula., C. album and Sonchus oleraceus but not Veronica spp.
Irrigation experiments showed that weed competition for water was largely responsible for the depressions in the early growth of maize when the conditions were dry. Final yield largely reflected the degrees of weed control attained by the herbicidal treatments. Only 2,4-D applied pre-emergence, and followed by heavy rain caused a direct depression in yield.
Effects des herbicides sur la productivityé du mals fourrage avec référence particuliére aux applications en pré-levée du 2,4-D amine  相似文献   

7.
An ELISA test was developed for the quantitative detection of the obligate parasite Polymyxa betae , the vector of Beet necrotic yellow vein virus (BNYVV), in infected sugarbeet roots. The test used monoclonal and polyclonal antibodies raised to a recombinantly expressed glutathione-S-transferase (GST) from P. betae . A close correlation was found between the number of P. betae zoospores in serially diluted suspensions and absorbance values in the ELISA test. Time-course studies of plants grown in naturally infested soils in controlled environment tests demonstrated the value of the ELISA test in screening for P. betae resistance. In preliminary tests, P. betae -resistant accessions of the wild sea beet ( Beta vulgaris ssp. maritima ), which might be used to restrict the transmission of BNYVV, were identified.  相似文献   

8.
A rapid method for direct detection of Polymyxa DNA in soil   总被引：1，自引：0，他引：1  
Polymyxa spp. are vectors for a number of economically important soilborne plant viruses. The development of a technique to detect virus and vectors directly in soil would be useful for epidemiological studies and assessment of disease risk prior to planting. A rapid method was developed to extract and quantify Polymyxa spp. DNA from soils. DNA was extracted from three soils infested with Polymyxa betae and three infested with P. graminis using an EDTA lysis buffer in combination with a MagneSil™ DNA extraction kit and Kingfisher™ magnetic particle processor. Primers and probes designed to correspond to sequences within the internal transcribed spacer region 2 (ITS2) of ribosomal DNA enabled recovery and amplification of P. betae and P. graminis DNA using real-time PCR and TaqMan chemistry. For the P. graminis- infested soils, the purity of DNA obtained was sufficient to allow Polymyxa DNA to be amplified without dilution to remove inhibitors, but with P. betae- infested soils, amplification was only achieved if the DNA was diluted 1:10. Using TaqMan PCR, a standard curve was constructed from uninfested soil spiked with known numbers of P. betae cystosori; the quantity of P. betae inoculum from naturally infested soil was then extrapolated from the curve. This technique offers a sensitive method of extracting, detecting and quantifying Polymyxa spp. DNA in soil.  相似文献   

9.
The genome of most Beet necrotic yellow vein virus (BNYVV) isolates is comprised of four RNAs. The ability of certain isolates to overcome Rz1-mediated resistance in sugar beet grown in the United States and Europe is associated with point mutations in the pathogenicity factor P25. When the virus is inoculated mechanically into sugar beet roots at high density, the ability depends on an alanine to valine substitution at P25 position 67. Increased aggressiveness is shown by BNYVV P type isolates, which carry an additional RNA species that encodes a second pathogenicity factor, P26. Direct comparison of aggressive isolates transmitted by the vector, Polymyxa betae, has been impossible due to varying population densities of the vector and other soilborne pathogens that interfere with BNYVV infection. Mechanical root inoculation and subsequent cultivation in soil that carried a virus-free P. betae population was used to load P. betae with three BNYVV isolates: a European A type isolate, an American A type isolate, and a P type isolate. Resistance tests demonstrated that changes in viral aggressiveness towards Rz1 cultivars were independent of the vector population. This method can be applied to the study of the synergism of BNYVV with other P. betae-transmitted viruses.  相似文献   

10.
In recent years several interspecific hybrids have been reported in the plant pathogenic oomycete genus Phytophthora. Due to the large genotypic and phenotypic changes, these hybrids might have broader or more limited host ranges compared with their parental species. It is crucial to understand the host range of Phytophthora hybrids to minimize the economic losses caused by their infection. The potential host range of four hybrids belonging to Clade 8a of the Phytophthora phylogenetic tree was investigated in this study. Thirty species of herbaceous plants as well as eight species of woody plants were inoculated and monitored for any symptom of infection. In addition, the detached twigs of 32 tree species, fruits of six plant species, tubers of potato, and roots of carrot and sugar beet were investigated for susceptibility to these hybrids. Almost all hybrids caused severe rot on all tested fruits, tubers, and roots, although different isolates showed different pathogenicity on detached tree twigs. All hybrids tested had a different host range compared with their parental species: they were able to infect plants outside the host range of their parents, infect hosts of both parental species, although these parents did not have overlapping hosts, or, in some cases, they were not able to infect hosts infected by the parents.  相似文献   

11.
The effects of soil temperature on infection of sugar-beet roots by the soil-borne fungus Polymyxa betae were investigated in controlled environments. Pre-germinated seeds were sown in pots of naturally infested soil and seedlings sampled at frequent intervals over a period of several weeks. Within the range 10-30°C, the optimum soil temperature for infection was c. 25°C; the time between sowing and the first detectable infection was shortest and the subsequent rate of infection most rapid at this temperature. No infection was observed over 80 days at 10°C.
Both root and shoot dry weight were reduced on plants growing in infested soil at 15, 20 and 25 C compared with those growing in uninfested soil. In general, root growth was more severely affected than shoot growth and the effects were most pronounced at 20°C. These results were confirmed in a subsequent experiment in which P. betae -infected root material was used as the inoculum. In addition to its role as the vector of beet necrotic yellow vein virus (the cause of Rhizomania disease), the significance of P. betae as a plant pathogen in its own right is discussed.  相似文献   

12.
A 2-year survey of soils from a total of 208 fields, using sugar-beet seedlings as bait plants, showed Polymyxa betae to be ubiquitous in the sugar-beet-growing areas of Britain. It was detected in some soils which had not grown a host crop for up to 17 years. However, infection of roots was relatively infrequent in plant samples taken from 134 survey fields in early summer and the density of colonization always low. Three other non-mycelial fungi, Olpidium brassicae, Lagena radicicola and Rhizophydium graminis were also common parasites of sugar-beet roots detected in soil bioassays. Infection of plant samples by O. brassicae was particularly severe.  相似文献   

13.
Polymyxa betae is the fungal vector of beet necrotic yellow vein virus (BNYVV), which is the causal agent of the sugar beet disease rhizomania. The within-season dynamics of the fungus are a crucial factor in the occurrence and severity of rhizomania. Late infection of the host by viruliferous fungi enables host resistance to the virus to develop and hence limits crop damage. A previously published mechanistic model for the dynamics of Polymyxa betae is extended in this paper to incorporate the effect of temperature on the germination of resting spores, and on the latent periods between infection and the production of secondary zoospores and new resting spores. It is shown that, for UK temperature conditions, the effect of sowing date on infection is greater than that of year-to-year variations in temperature associated with a single representative sowing date. The variation in inoculum build-up predicted when temperature data from a range of soil types were used in the model agreed with field observations, where higher levels of infection are observed on sandy soils than on black fen peat soils. The difference was most distinct when daily maximum soil temperature values were used to drive the model rather than rolling 24-hour average values.  相似文献   

14.
ABSTRACT Five Capsicum species were tested for susceptibility to Tomato yellow leaf curl virus (TYLCV) and the mild strain of TYLCV (TYLCV-Mld). TYLCV was able to infect 30 of 55 genotypes of C. annuum, one of six genotypes of C. chinense, one of two genotypes of C. baccatum, and the only genotype of C. frutescens tested but was unable to infect the one genotype of C. pubescens tested. This is the first evidence for the susceptibility of C. baccatum, C. chinense, and C. frutescens to TYLCV. Unlike TYLCV isolates, TYLCV-Mld was unable to infect C. chinense. No host differences were observed between the Israeli and Florida isolates of TYLCV. None of the Capsicum species showed symptoms after infection with TYLCV or TYLCV-Mld. TYLCV was detected in fruits of C. annuum, but whiteflies were unable to transmit virus from fruits to plants. White-flies were able to transmit both TYLCV and TYLCV-Mld from infected pepper plants to tomato plants. Pepper plants in research plots were found infected with TYLCV at rates as much as 100%. These data demonstrate the ability of some genotypes of pepper to serve as reservoirs for the acquisition and transmission of TYLCV and TYLCV-Mld.  相似文献   

15.
The host range of Polymyxa graminis isolates originating from peanut clump-infested areas in India (Andhra Pradesh and Rajasthan), Pakistan and Senegal was studied on monocotyledonous and dicotyledonous cultivated species, using known quantities of sporosori as inoculum. Profuse multiplication occurred only on some graminaceous species, but the various isolates showed different host specificity. All the isolates produced high infection on sorghum and pearl millet, and all but one isolate from Rajasthan infected maize. Wheat, rye and barley were susceptible to some of the tested isolates. The isolates from Rajasthan and Pakistan produced moderate to severe infection on at least one of these species. On rice, groundnut and sugar beet, only traces of infection by some isolates were detected, whereas no infection was observed on mustard and sunflower. Differences of susceptibility in Pennisetum spp. and Sorghum spp. were demonstrated. The variations in host specificity among isolates from peanut clump-infested areas may result from an adaptation of P. graminis populations to various biotopes. The implications of these results for the management of peanut clump disease are discussed. A comparison of the host ranges of isolates of P. graminis and P. betae from temperate areas demonstrated that distinct types of Polymyxa might be identified based on their relative ability to multiply on susceptible species. Nevertheless, overlapping in the host ranges among the different Polymyxa types, characterised by distinct ecological and genomic features, raises doubts about the host range as a classification criterion for the Polymyxa genus.  相似文献   

16.
The effect of sowing date on the infection of sugar-beet seedlings by Polymyxa betae was examined in a small-plot experiment on a naturally infested site. Seed was sown on seven occasions at weekly intervals from late March to early May. From each sowing, plant samples were taken at approximately weekly intervals over a period of 7 weeks. The extent of root infection by P. betae and the dry weight of plants was determined at each sampling date, and the progress of infection and rate of plant growth were examined against time and thermal time. Infection occurred sooner after sowing and the subsequent rate of fungal development was more rapid in late-sown than in early-sown plants. Early sowing allowed germination and growth of sugar beet at temperatures too low for fungal infection. The growth of late-sown plants appeared to be reduced by P. betae infection. The implications of these findings for the development of rhizomania disease are discussed.  相似文献   

17.
甜菜多粘菌传带甜菜坏死黄脉病毒的细胞定位研究   总被引：1，自引：0，他引：1  
 利用砂培体系继代培养不同病区甜菜多粘菌(Polymyxa betae),经酶联检测,分离得到2个带毒率高的分离株N,HR12。应用甜菜坏死黄脉病毒(BNYVV)抗血清和免疫金标记技术分析了甜菜根中P.betae不同发育阶段与病毒的关系。在初生原质体、游动孢子囊以及未成熟的游动孢子中观察到被金颗粒标记的病毒粒子,在休眠孢子外围也观察到金标记的病毒粒子,但在休眠孢子内未直接观察到病毒粒子,只是在其内壁及液泡中常见有标记上的金颗粒。  相似文献   

18.
The potential role of 10 frequently occurring weed species found amongst Spanish lettuce crops as host plants for the two viruses associated with the lettuce big-vein disease, Lettuce big-vein associated virus (LBVaV) and Mirafiori lettuce big-vein virus (MLBVV), was studied. The results showed that both viruses can infect naturally growing Sonchus oleraceus (common sowthistle) plants, the unique susceptible species detected among the analysed weeds. The sequences of the coat protein (CP) genes of the LBVaV and MLBVV isolates recovered from S. oleraceus plants were determined. Phylogenetic studies revealed a very close relationship between the CP sequences from these weed isolates and those from Spanish lettuce. Moreover, we showed that S. oleraceus can act as a source of lettuce infection by means of Olpidium brassicae, the vector fungus of both viruses.  相似文献   

19.
Samples of effluent were taken at various stages in a range of waste-water treatment systems from seven sugarbeet factories and 14 vegetable processors and tested by a seedling-baiting method. None of the systems examined appeared completely to remove Polymyxa betae , the fungal vector of beet necrotic yellow vein furovirus, the cause of rhizomania disease of sugarbeet. In laboratory experiments, neither anaerobic conditions, raising the pH to 12 nor treating with peracetic acid had any discernible effect on P. betae viability. It is concluded that there is a risk that rhizomania disease could be spread by waste water from processing infected sugarbeet or vegetables from infested land, although there is some evidence that this risk is reduced where systems involving extensive settlement are used.  相似文献   

20.
A STUDY OF THE COMPETITIVE ABILITY OF CHENOPODIUM ALBUM L.   总被引：1，自引：0，他引：1  
T. WILLIAMS 《Weed Research》1964,4(4):283-295
Summary. Experiments arc reported that demonstrate that there is mutual interference between kale and Chenopodium album when grown in association. As the plants grow, those at high density, whether in mixtures or in pure stands, interfere with each other and individual plant weight and leaf area are reduced. By changing the time:of Introduction of one of the species into a mixture it was shown that kale suffered heavy mortality when C. album had an initial advantage. When kale was introduced before C. album the weed remained stunted but there was no mortality. The weed exerted an early effect of kale. The ability of C. album to interfere with kale, seems to be related to its plasticity. It is able to grow rapidly, to trap light effectively and even under adverse conditions to set seed.
Etude sur le pouvoir de compétition de Chenopodium album L. I. Recherches sur la compétition enire les choux et C. album  相似文献   

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