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1.
A study was conducted to assess the effect of temperature on infection and development of Plasmodiophora brassicae in root hairs of Shanghai pak choi (Brassica rapa subsp. chinensis) and on initiation of clubroot symptoms. Ten‐day‐old seedlings were grown in liquid‐sand culture, inoculated with resting spores and maintained in growth cabinets at 10, 15, 20, 25 and 30°C. Seedlings were harvested at 2‐day intervals, starting 2 days after inoculation (DAI) and continuing until swelling of the tap root was observed (maximum 28 days). Roots were assessed for root hair infection (RHI), stage of development of infection (primary plasmodia, zoosporangia, release of zoospores, secondary plasmodia), symptom development, and for clubroot severity at 24 DAI. Temperature affected every stage of clubroot development; RHI was highest and visual symptoms initiated earliest at 25°C, intermediate at 20 and 30°C, and lowest and latest at 15 and 10°C. Root hair infection was observed at every temperature, but clubroot symptoms developed only above 15°C. A substantial delay in the development of the pathogen was observed at 10 and 15°C. No symptoms were observed at 28 DAI in plants grown at 10°C. Swelling of the tap root was visible at 28 DAI in plants at 15°C, 14 DAI at 20 and 30°C, and 10 DAI at 25°C. These results support and explain the observation in companion studies that cool temperatures result in slower development of clubroot symptoms in brassica crops.  相似文献   

2.
The differences in physiological response of Brassica oleracea to infection and growth of Plasmodiophora brassicae in infected tissue were studied in clubroot resistant and susceptible hosts, grown in sand solution culture artificially inoculated with spores of P. brassicae (108 spores mL−1). Primary (root hair) and secondary (cortical) stages of P. brassicae occurred in both resistant and susceptible hosts. Symptoms of cortical invasion by P. brassicae in resistant and susceptible hosts included cell wall breaks, presence of vesicles or inclusion bodies within the cell walls, cell wall thickening in association with plasmodesmata and enlarged and/or disorganized host nuclei. The main difference between the resistant and susceptible host reaction was the absence of degradation of the secondary thickening and cell walls of the xylem in the resistant host. This study supports the existence of an amoeboid form of the pathogen in addition to the recognized two-phase life history of P. brassicae. Furthermore, it suggests that resistance in B. oleracea does not prevent the development of this amoeboid form. A reduced number of cell wall breakages suggests movement of the amoeboid form, may have been restricted but not prevented in the resistant host.  相似文献   

3.
Clubroot disease, caused by Plasmodiophora brassicae Woronin, affects various cruciferous crops. Variations in pathogenicity and virulence are present among field populations of P. brassicae. Many races (pathotypes) have been reported in Japan as well as in other countries using various differential systems. Populations can be classified into four pathotypes using two clubroot-resistant (CR) cultivars of Chinese cabbage as differential hosts in Japan. However, it was recently indicated that each population is often heterogenic and composed of multiple genotypes (races or pathotypes). Breakdown in CR cultivars of Chinese cabbage is a problem in some areas of Japan and may contribute to the selective propagation of minor pathogenic genotypes on the CR cultivars. Clubroot has also been recorded on five species of cruciferous weeds in Japan. In particular, clubroot of Cardamine flexuosa is widely distributed in Japan. Some populations of C. flexuosa are often moderately pathogenic on Chinese cabbage and turnip. Therefore, the epidemiological relationship between clubroot of cruciferous crops and that of the weed has been noted but not thoroughly clarified. The relationship between pathogenic and genetic variations has also been examined among populations from cruciferous crops and weeds in Japan. The result implies an interesting genetic relationship among Williams’ races, among pathotypes determined using CR cultivars of Chinese cabbage and among populations from crops and C. flexuosa. This review includes an introduction of the status of studies on pathogenic and genetic diversity in P. brassicae from Japan.  相似文献   

4.
5.
不同杀菌剂对油菜根肿病的防效及对油菜产量损失的影响   总被引:3,自引:0,他引:3  
本研究使用5种杀菌剂和1种微肥于油菜苗期2~3片真叶期进行灌根处理,以传统的石灰处理方法比较,评价不同处理对油菜根肿病的防治效果和对油菜产量损失的影响。5种杀菌剂处理、微肥以及石灰处理均对油菜根肿病有较好的防效,其中50%多菌灵可湿性粉剂防效达90.82%;从产量损失方面比较,10%氰霜唑悬浮剂、50%多菌灵可湿性粉剂,75%百菌清可湿性粉剂和60%硫磺·敌磺钠可湿性粉剂处理可显著减少根肿病引起的产量损失;50%氟啶胺悬浮剂处理较对照增产不显著,而且对油菜生长有抑制作用;油菜根肿病的病情指数与油菜产量呈显著的负相关性,相关系数r=-0.796 2,油菜产量(y)与病情指数(x)的回归方程为y=-32.65x+2 372。  相似文献   

6.
Clubroot, caused by Plasmodiophora brassicae, has become a serious threat to canola (Brassica napus) production in western Canada. Experiments were conducted under greenhouse and field conditions to assess the effect of Vapam fumigant (dithiocarbamate; sodium N‐methyldithiocarbamate) on primary and secondary infection by P. brassicae, clubroot severity, and growth parameters in canola. Preliminary trials showed a 12–16‐fold reduction in primary and secondary infection and clubroot severity at all of the Vapam application rates (0·4–1·6 mL L?1 soil) assessed. Vapam was also found to be effective in reducing clubroot severity and improving seed yield of canola under field conditions. Application of Vapam at soil moisture levels in the range of 10–30% (v:v) had a large effect on both disease severity and infection rates and plant growth parameters. The results suggest that Vapam can effectively reduce clubroot severity and may be useful for the treatment of transplant propagation beds in brassica vegetable production, and for the containment of small, localized clubroot infestations in commercial canola crops.  相似文献   

7.
An evaluation of 404 Brassica oleracea cultivars for susceptibility to Plasmodiophora brassicae (clubroot) at one field site in northern Scotland over the four years 1979-82 is reported. The population of P. brassicae at this site possessed a high degree of virulence to B. oleracea as determined by seedling tests in a glasshouse environment, using the European Clubroot Differential series. No statistically significant differences in susceptibility were consistently identified between cultivars when tested under field conditions. Data over years and over crops were analysed by the residual maximum likelihood technique. Differences between cultivars were small compared with cultivar x year interactions. No obvious differences were identified in susceptibility between the crop types Brussels sprout, cabbage, calabrese and cauliflower. Disease levels as analysed over all field trials increased markedly in years three and four of this experiment compared with the first two years.  相似文献   

8.
Plasmodiophora brassicae, causal agent of clubroot of crucifers, poses a serious threat to Canadian canola production. The effects of fallow (F) periods and bait crops (clubroot‐susceptible canola (B) and perennial ryegrass (R)) on clubroot severity and P. brassicae resting spore populations were evaluated in five sequences: R–B, B–R, R–F, B–F and F–F. Both host and non‐host bait crops reduced clubroot severity in a subsequent crop of a susceptible canola cultivar compared with fallow. Resting spore and P. brassicae DNA concentrations decreased in all treatments, but were lowest for the R–B and B–R bait crop sequences. In addition, two studies were conducted in mini‐plots under field conditions to assess the effect of rotation of susceptible or resistant canola cultivars on clubroot severity and P. brassicae resting spore populations. One study included three crops of susceptible canola compared with a 2‐year break of oat–pea, barley–pea, wheat–wheat or fallow–fallow. The other study assessed three crops of resistant canola, two crops of resistant canola with a 1‐year break, one crop of resistant canola and a 2‐year break, and a 3‐year break with barley followed by a susceptible canola. The rotations that included non‐host crops of barley, pea or oat reduced clubroot severity and resting spore concentrations, and increased yield, compared with continuous cropping of either resistant or susceptible canola. Growing of a susceptible canola cultivar contributed 23–250‐fold greater gall mass compared with resistant cultivars.  相似文献   

9.
The expression of 12 cDNAs from Plasmodiophora brassicae , among them two novel sequences, was determined during clubroot development on Arabidopsis thaliana . The aim was to find cDNAs expressed at distinct stages of pathogenesis. The relative amount of infection with active plasmodia could be estimated using Pb Actin cDNA as an internal standard. Two cDNAs, Pb Brip9 and Pb CC249, were strongly expressed at stages of disease development corresponding to the occurrence of sporulating plasmodia. Therefore, it should be possible in the future to find more cDNAs which could be used as markers for certain stages of clubroot development.  相似文献   

10.
The early stages of infection of canola roots by the clubroot pathogen Plasmodiophora brassicae were investigated. Inoculation with 1 × 105 resting spores mL?1 resulted in primary (root hair) infection at 12 h after inoculation (hai). Secondary (cortical) infection began to be observed at 72 hai. When inoculated onto plants at a concentration of 1 × 104 mL?1, secondary zoospores produced primary infections similar to those obtained with resting spores at a concentration of 1 × 105 mL?1. Secondary zoospores caused secondary infections earlier than resting spores. When the plants were inoculated with 1 × 107 resting spores mL?1, 2 days after being challenged with 1 × 104 or 1 × 105 resting spores mL?1, secondary infections were observed on the very next day, which was earlier than the secondary infections resulting from inoculation with 1 × 107 resting spores mL?1 alone and more severe than those produced by inoculation with 1 × 104 or 1 × 105 resting spores mL?1 alone. Compared with the single inoculations, secondary infections on plants that had received both inoculations remained at higher levels throughout a 7‐day time course. These data indicate that primary zoospores can directly cause secondary infection when the host is under primary infection, helping to understand the relationship and relative importance of the two infection stages of P. brassicae.  相似文献   

11.
通过设置不同pH梯度,研究土壤pH对根肿菌侵染及病害发生的影响。结果表明:土壤酸性时病菌侵染速度快,碱性时慢,而强酸性和碱性土壤条件则抑制孢子萌发;pH为6.0时最有利于根肿菌休眠孢子萌发,萌发率最高,为53.96%;碱性条件可使初级原生质团变形凝结成球状,不能正常分裂或延迟形成游动孢子囊,从而不利于根肿菌侵染。白菜发病率与病情指数随pH升高,呈先上升后下降趋势。其中,pH为5.0时,发病率和病情指数最高,pH 7.0~8.0时发病轻。因此,适宜的偏酸性环境条件下,通过作用于病菌休眠孢子萌发和侵染,提高病害危害程度,而中性或碱性条件干扰该过程并降低病害发生。  相似文献   

12.
Clubroot disease, caused by Plasmodiophora brassicae, has become a major problem in the production of cruciferous crops worldwide. In this study, a population of 121 doubled haploid (DH) lines derived from a crossing between a resistant and a susceptible canola (Brassica napus) genotype was subjected to phenotypic and genotypic studies to determine the inheritance and location of the resistance gene(s). After inoculation with pathotype 3 of P. brassicae, the lines showed a 1:1 segregation ratio for resistance, indicating that resistance in this population is controlled by a single gene. Fifteen PCR‐based markers that were known to be linked to clubroot resistance (CR) genes were screened against genomic DNA from parents and resistant and susceptible bulks. Marker GC1680, linked to the CR gene CRa, exhibited polymorphism between the parents and between the resistant and susceptible bulks. CRa target primers were used to amplify fragments from the two parents and the resultant sequences were compared. A high degree of sequence similarity was found between the parents in the nucleotide binding site domain of CRa. In contrast, sequence polymorphisms were detected in the leucine‐rich repeat (LRR) domain. One pair of primers that amplify a band from the LRR region of the resistant parent but not the susceptible parent was used to screen the DH population. Amplicons were obtained from 60 of the 61 resistant lines and two of the 60 susceptible lines; thus, three recombinants were found. Based on these results, a resistance locus linked to CRa was found.  相似文献   

13.
This study investigated the ability of an endophytic fungus Acremonium alternatum to reduce clubroot formation in the model plant Arabidopsis thaliana, which is highly susceptible to Plasmodiophora brassicae . Quantitative PCR demonstrated that A. alternatum colonized the P. brassicae -infected roots and shoots of the host plant. When Arabidopsis plants were co-inoculated with P. brassicae and A. alternatum , gall formation was reduced as shown by the reduction of the disease index (DI) by up to 50% compared to plants only infected with P. brassicae, whereas the infection rate was lowered by about 20% only in several, but not all, experiments. Clubroot was similarly suppressed when plants were inoculated with autoclaved A. alternatum spores or spore extracts, showing that viable spores were not needed. However, A. alternatum spores did not inhibit P. brassicae resting spore germination. Compared to the normal root galls, the smaller root galls on A. alternatum -inoculated plants contained fewer resting spores of the clubroot pathogen. It was thus hypothesized that inoculation with A. alternatum delayed the development of P. brassicae . Using quantitative RT-PCR to monitor the expression of P. brassicae genes differentially expressed during the development of the disease, a delayed pathogen development was corroborated. Furthermore, greenhouse experiments identified a time window in which the endophyte had to be administered, where the latest effective time point was 5 days before inoculation with P. brassicae and the optimum treatment was to administer A. alternatum and P. brassicae at the same time. These results indicate that A. alternatum and perhaps similar endophytes could be useful for the management of clubroot disease.  相似文献   

14.
The clubroot pathogen Plasmodiophora brassicae is an obligate biotrophic protist that lives in close relationship with its host cell. The roots of the host plants are colonized and the plant growth is altered upon infection. While shoots can be stunted and show wilt symptoms after longer infection periods, the root system is converted to a tumorous root tissue, called ‘clubroot’, by alterations of the plant growth promoting hormones auxin, cytokinin and brassinosteroid. Because the life cycle occurs largely within the host cells, this leads to dramatic changes in host root morphology and anatomy. Thus, the identification of the respective protist structures in the host tissue by microscopy is challenging. Different staining methods as well as fluorescence and electron microscopy of thin sections can reveal specific life stages of P. brassicae and can yield additional information on the changes in the host tissues concerning, for example, cell wall properties. In addition, promoter–reporter fusions, immunostaining methods and in situ hybridization techniques can be used to gain additional information on the changes in the host roots.  相似文献   

15.
In this study, the ability of two organic plant growth stimulants, mainly based on algal extracts, amino acids and phosphonate, to reduce clubroot formation in the model plant Arabidopsis thaliana and two economically important Brassica species, Brassia rapa (Chinese cabbage) and Brassica napus (oilseed rape) was investigated. A commercial liquid (Frutogard®) and a granulate (PlasmaSoil®) formulation were used to find optimum conditions for both control of the pathogen and plant growth. Both formulations were able to significantly reduce gall formation after Plasmodiophora brassicae infection on Chinese cabbage, but PlasmaSoil® gave better effects, possibly as a result of the continuous supply of the components to the soil. Individual components did not have the same effect. Clubroots on oilseed rape could also be reduced. In contrast, club formation was not reduced in the model plant Arabidopsis thaliana. This points to interesting differences in the induction of resistance in the different species. Cross‐sections of infected and treated roots stained for different macromolecules (callose, lignin, suberin) indicated differences in anatomy as a result of the two formulations. The results indicate an application for the granulate formulation PlasmaSoil® in clubroot control.  相似文献   

16.
Control of some soilborne pathogens may be achieved by use of decoy or catch crops. These stimulate the germination of resting spores, resulting in limited expression of disease symptoms. Results achieved using this approach are reported here using leafy daikon (radish, Raphanus sativus var. longipinnatus ) for control of Plasmodiophora brassicae , the cause of clubroot disease of Brassicaceae. Disease indices of Chinese cabbage plants grown in pots that had previously contained leafy daikon were lower compared with pots where no plants had been grown before (control pots). Numbers of resting spores of P. brassicae in soil in pots after cultivation with leafy daikon were reduced by 71% compared with control pots when resting spores were recovered and counted directly. In a field experiment, numbers of resting spores were reduced by 94% compared with the start of the experiment when leafy daikon was grown in advance of Chinese cabbage, but there was no reduction in disease severity in the Chinese cabbage. Plasmodiophora brassicae infected the root hairs of leafy daikon and those of Chinese cabbage, but no clubs were found on leafy daikon roots. The results from pot trials indicate that leafy daikon may be useful as a decoy crop for the control of clubroot disease in field crops.  相似文献   

17.
Wang  Yao  Luo  Wenbo  Huang  Yun  Xu  Luyang  Yin  Yong 《植物病害和植物保护杂志》2017,124(1):67-71
Journal of Plant Diseases and Protection - The mixtures of 10 % cyazofamid SC and 25 % methiadinil SC were selected at different concentrations in root irrigation treatment of...  相似文献   

18.
Flusulfamide (2, 4-dichloro-,,-trifluoro-4-nitro-m-toluenesulfonanilide) was investigated for its mode of action against Plasmodiophora brassicae Woronin. Seedlings of Chinese cabbage (Brassica rapa L. subsp. pekinensis) were grown for 14 and 21 days in soil infested with P. brassicae and then transplanted into soil containing flusulfamide (0.9µg a.i.g–1 dry soil). Clubroot was not suppressed by this treatment, indicating that the fungicide is ineffective against P. brassicae established within cortical cells of the host root. Where seedlings were grown in soil infested with resting spores which had previously been treated with flusulfamide, root-hair infection and club formation were suppressed. This indicates that flusulfamide directly acts against resting spores. When placed in root exudates of Chinese cabbage, untreated resting spores germinated at a high frequency while flusulfamide-treated resting spores hardly germinated at all. Use of the Evan's blue staining assay indicated that flusulfamide-treated resting spores remained viable. Flusulfamide was detected by high performance liquid chromatography on resting spores treated with flusulfamide for 30min. This indicates that the chemical is adsorbed onto resting spores. These results suggest that flusulfamide suppresses clubroot disease by inhibiting germination of P. brassicae resting spores through adsorption onto their cell walls.  相似文献   

19.
The soilborne pathogen Plasmodiophora brassicae, causal agent of clubroot of canola (Brassica napus), is difficult to manage due to the longevity of its resting spores, ability to produce large amounts of inoculum, and the lack of effective fungicides. The cropping of clubroot resistant (CR) canola cultivars is one of the few effective strategies for clubroot management. This study evaluated the impact of the cultivation of CR canola on P. brassicae resting spore concentrations in commercial cropping systems in Alberta, Canada. Soil was sampled pre-seeding and post-harvest at multiple georeferenced locations within 17 P. brassicae-infested fields over periods of up to 4 years in length. Resting spore concentrations were measured by quantitative PCR analysis, with a subset of samples also evaluated in greenhouse bioassays with a susceptible host. The cultivation of CR canola in soil with quantifiable levels of P. brassicae DNA resulted in increased inoculum loads. There was a notable lag in the release of inoculum after harvest, and quantifiable P. brassicae inoculum peaked in the year following cultivation of CR canola. Rotations that included a ≥2-year break from P. brassicae hosts resulted in significant declines in soil resting spore concentrations. A strong positive relationship was found between the bioassays and qPCR-based estimates of soil infestation. Results suggest that CR canola should not be used to reduce soil inoculum loads, and crop rotations in P. brassicae infested fields should include breaks of at least 2 years away from B. napus, otherwise the risk of selecting for virulent pathotypes may increase.  相似文献   

20.
To elucidate the mechanism of clubroot suppression under neutral soil pH, a highly reproducible germination assay system under soil culture conditions was designed based on the hypothesis that germinated spores of Plasmodiophora brassicae could be identified by the absence of a nucleus (i.e. having released a zoospore to infect a root hair of the host plant). Brassica rapa var. perviridis seedlings were inoculated with a spore suspension of P. brassicae at a rate of 2·0 × 106 spores g−1 soil and grown in a growth chamber for 7 days. The spores were recovered from rhizosphere and non-rhizosphere soils and stained with both Fluorescent Brightener 28 (cell-wall-specific) and SYTO 82 orange fluorescent nucleic-acid stain (nucleus-specific stain). Total numbers of spores were counted under UV-excitation, and spores with a nucleus that fluoresced orange under G-excitation were counted. The significant increase in the percentage of spores without a nucleus (germinated spores) in the rhizosphere after 7 days' cultivation and the correlation with root-hair infections validated the assay system. Applications of calcium-rich compost or calcium carbonate to neutralize the soil significantly reduced the percentage of germinated spores in the rhizosphere, as well as the number of root-hair infections. The present study provides direct evidence that the inhibition of spore germination is the primary cause of disease suppression under neutral soil pH.  相似文献   

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