Root exudates of potato onion are involved in the suppression of clubroot in a Chinese cabbage-potato onion-Chinese cabbage crop rotation

Clubroot, caused by Plasmodiophora brassicae, has emerged as a serious disease threatening cruciferous crop production throughout the world. Crop rotation with non-host species is commonly practised to avoid clubroot, but it is not known whether rotation crops can control clubroot when the resting spores of P. brassicae remain unaffected. Pot experiments were performed to investigate the response of clubroot in Chinese cabbage to crop rotation with potato onion. The results showed that Chinese cabbage rotated with potato onion exhibited less clubroot disease than Chinese cabbage monoculture. Compared with residues from potato onion, the addition of root exudates from potato onion significantly decreased the disease incidence and index of clubroot (p ≤ 0.05). Potato onion root exudates decreased the number of secondary plasmodia of P. brassicae and the expression of the PRO1 gene of P. brassicae. These results suggest that root exudates from potato onion may play an important role in suppressing clubroot in a Chinese cabbage-potato onion-Chinese cabbage rotation system.     

Survival of <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> pv<Emphasis Type="Italic">. vitians</Emphasis> on lettuce in crop debris,irrigation water,and weeds in south Florida

Clubroot, caused by Plasmodiophora brassicae, has become a serious threat to canola (Brassica napus) production in western Canada. Experiments were conducted to evaluate the effect of rate of metam sodium fumigant (dithiocarbamate; sodium N-methyldithiocarbamate; trade name Vapam) and application methods including watering, soil surface covering, and soil incorporation on clubroot of canola. At higher rates (0.4–1.6 mL^?1 L soil) metam sodium increased canola seedling emergence and plant health, and reduced root hair infection, gall weight and clubroot severity under greenhouse conditions. Metam sodium application improved subsequent plant growth and reduced clubroot severity, but land preparation and volume of water applied did not affect efficacy. The incorporation of metam sodium into the soil and plastic covering after application improved fumigant efficacy. The study showed that soil fumigation with metam sodium can reduce clubroot severity and improve plant health in the subsequent canola crop.     

Potential biological control of clubroot on canola and crucifer vegetable crops

Clubroot caused by Plasmodiophora brassicae is an emerging threat to canola (Brassica napus) production in western Canada, and a serious disease on crucifer vegetable crops in eastern Canada. In this study, seven biological control agents and two fungicides were evaluated as soil drenches or seed treatments for control of clubroot. Under growth cabinet conditions, a soil‐drench application of formulated biocontrol agents Bacillus subtilis and Gliocladium catenulatum reduced clubroot severity by more than 80% relative to pathogen‐inoculated controls on a highly susceptible canola cultivar. This efficacy was similar to that of the fungicides fluazinam and cyazofamid. Under high disease pressure in greenhouse conditions, the biocontrol agents were less effective than the fungicides. Additionally, all of the treatments delivered as a seed coating were less effective than the soil drench. In field trials conducted in 2009, different treatments consisting of a commercial formulation of B. subtilis, G. catenulatum, fluazinam or cyazofamid were applied as an in‐furrow drench at 500 L ha^?1 water volume to one susceptible and one resistant cultivar at two sites seeded to canola in Alberta and one site of Chinese cabbage in Ontario. There was no substantial impact on the susceptible canola cultivar, but all of the treatments reduced clubroot on the susceptible cultivar of Chinese cabbage, lowering disease severity by 54–84%. There was a period of 4 weeks without rain after the canola was seeded, which likely contributed to the low treatment efficacy on canola. Under growth cabinet conditions, fluazinam and B. subtilis products became substantially less effective after 2 weeks in a dry soil, but cyazofamid retained its efficacy for at least 4 weeks.     

Effects of growing leafy daikon (Raphanus sativus) on populations of Plasmodiophora brassicae (clubroot)

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.     

Reduction of Spore Density of Plasmodiophora brassicae in Soil by Decoy Plants

The severity of clubroot (Plasmodiophora brassicae) on Chinese cabbage was reduced by growing plants such as oats, spinach and leafy daikon prior to Chinese cabbage in pot experiments. Resting spore densities of P. brassicae in the soil were 29–62%, depending on the pervious crop, as compared to unplanted control plot after ploughing under the previously cultivated plants. Root hairs of the preceding plants were infected with P. brassicae, but clubbed roots were not formed on these plants. The results indicate that these plants functioned as decoy plants reducing the resting-spore density in soil and thereby suppressing disease severity. Received 21 February 2000/ Accepted in revised form 5 September 2000     

拮抗链霉菌26B的筛选及其在不同含水量土壤中对白菜软腐病的防病效果

为挖掘防治白菜软腐病的生防菌,本研究采用牛津杯法从38株白菜根际放线菌中筛选到一株拮抗放线菌26B,通过形态学观察和16S rRNA基因序列分析将菌株26B初步鉴定为链霉菌。该菌除菌发酵滤液对供试的白菜软腐病菌Pectobacterium carotovorum subsp. brasiliensis BC1及3种马铃薯黑胫病菌均表现较高的抑菌活性,其中对白菜软腐病菌抑菌直径达到23.97mm。萌发试验表明,白菜种子经26B除菌发酵滤液浸种后发芽势、发芽指数、根长及鲜重显著增加。采用浸根法测定菌株26B除菌发酵滤液对软腐病菌荧光标记菌株BC1-gfp在白菜根部定殖量的影响,浸根处理后48h,白菜根上BC1-gfp的数量达到2.3×109CFU/g;未从26B除菌发酵滤液与BC1-gfp菌悬液混和处理（体积比10%）的白菜根上检测到病原菌。盆栽防病试验结果表明,在含水量为14%和20%的土壤中,菌株26B除菌发酵滤液对白菜软腐病的防效分别达96.0%和89.8%。上述结果表明,链霉菌26B是一株具有潜在开发应用价值的生防菌株,将链霉菌26B应用与土壤水分管理相结合可进一步提高其防病效果。     

芸薹根肿菌次生游动孢子侵染致病分析

为明确芸薹根肿菌Plasmodiophora brassicae Woron.在其它寄主中是否广泛存在无性短循环及次生游动孢子的侵染致病性,以不结球白菜为寄主培养3批幼苗(G1、G2和G3),用休眠孢子悬浮液接种G1,被侵染的G1接种G2,被侵染的G2接种G3,采用离心管水培法研究其侵染致病性。结果显示,无性短循环研究中,G1、G2和G3根毛均被侵染,除G3并株接种侵染率为33.33%外,其它处理侵染率均在50.00%以上,根毛里有明显的游动孢子囊;次生游动孢子能侵染不结球白菜的皮层组织,致使不结球白菜发病形成明显的肿根;G1、G2和G3水培发病率为20.00%、15.00%和6.00%,砂培发病率为22.50%、18.75%和7.50%;G3肿根病理切片中可观察到休眠孢子。表明芸薹根肿菌侵染不结球白菜时,其生活史中存在无性短循环,次生游动孢子具有侵染致病作用。     

Standorteigenschaften und Anbaumanagement erklären regionale Unterschiede im Kohlherniebefall in Deutschland

In the years 2013 and 2014 the presence and the infestation level of Plasmodiophora brassicae in six federal states of Germany were assessed using a bioassay method. Soils were sampled from 237 oilseed rape fields and the farmers provided information about the soil type, the soil pH values and the last year of oilseed rape cultivation. Clubroot was detected in 66 % of the fields investigated with a mean disease severity (BI) of 0.34. Between and within the federal states differences in presence and infestation level of P. brassicae were detected. In Schleswig-Holstein significantly more fields were infected by P. brassicae (90 %) and BI was relatively high (0.49) compared to Lower Saxony, Mecklenburg-Western Pomerania and North Rhine-Westphalia with 50 % infected fields and a mean BI of 0.27. Highly infested fields (BI > 0.8) were prevalent on 15 and 25 % of fields investigated in every federal state. Within the federal states the soil climate regions (BKR) differed significantly from each other. In BKR with light and sandy soils P. brassicae was less widespread compared to neighboring BKR with loamy soils. In addition, BKR with high infestation levels on fields investigated revealed a high presence of clubroot infested fields within this BKR. The infestation level in our study was significantly influenced by soil type, content of sand and soil pH value: soil types with a sand content of 30–35 % and a pH values lower than 5.6 showed high clubroot severity and disease incidences.     

三株生防菌对甘蓝根肿病的防治效果及促生作用研究

极长链霉菌SL01、淡紫紫孢菌QLP12和非致病镰刀菌Fo47是具有广谱抑菌和促生作用的生防菌。为明确其对甘蓝根肿病的防效及对甘蓝的促生作用,通过种子萌发及苗期生长试验明确了3株生防菌最佳育苗期的使用浓度。温室试验表明,生防菌灌根处理可有效提高对甘蓝根肿病的防效,菌株Fo47和SL01处理的防效可达到90.38%,显著高于药剂处理;菌株QLP12处理的防效为69.78%,显著高于清水处理。田间试验中,菌株Fo47、QLP12和SL01均能表现出较好的生防效果,防效分别可达66.17%、60.20%和51.58%,甘蓝结球鲜重分别比对照增加了29.13%、43.69%和16.5%。品质试验中,3株生防菌都能提高叶片还原糖含量,菌株Fo47和SL01能降低叶片硝酸盐含量。研究表明,3株生防菌能促进甘蓝生长、提高叶片品质,同时对甘蓝根肿病具有很好的防效,为生物菌肥的开发利用提供理论依据。     

马铃薯品种对枯萎病菌的抗性鉴定

通过室内接种试验与田间接种试验,调查评价供试马铃薯品种对枯萎病菌的抗性。结果显示,供试的马铃薯品种中没有免疫品种,脱毒组培苗接种病原菌测定的19个品种中,表现为中抗的品种有2个,占供试品种的10.53%;表现为中感的品种有10个,占供试品种的52.63%;表现为高感的品种7个,占供试品种的36.84%。田间接种病原菌测定的20个品种中,中抗及以上品种有9个,占供试品种的45%,中感及高感品种11个,占供试品种的55%。     

湖南白菜和红菜薹根肿病菌生理小种鉴定

为了弄清湖南省白菜和红菜薹根肿病菌生理小种组成和分布,2013年采集长沙、湘潭、益阳、怀化4个地区的十字花科作物白菜、红菜薹根肿病株27个,用Williams根肿病鉴别品种对其进行生理小种鉴定。初步鉴定出5个生理小种,即1号、5号、8号、9号和11号,它们在湖南病区中出现的频率分别为22.3%、18.5%、14.8%、33.3%和11.1%。按寄主生理小种组成,湖南白菜根肿病菌生理小种有1号、5号、9号、11号,红菜薹根肿病菌为8号、9号和11号;按地区生理小种分布,长沙白菜根肿病菌生理小种为5号和9号,湘潭白菜和红菜薹根肿病菌生理小种分别1号、8号和11号,怀化白菜根肿病菌为生理小种9号;益阳白菜和红菜薹根肿病菌分别为生理小种1号、11号、8号和9号。目前,在湖南4个市白菜和红菜薹根肿病菌生理小种是9号。     

Characterization of the suppressive effects of the biological control strain VAR03-1 of <Emphasis Type="Italic">Rhizobium vitis</Emphasis> on the virulence of tumorigenic <Emphasis Type="Italic">R. vitis</Emphasis>

Rhizobium vitis: strain VAR03-1 is a biological control agent that suppresses grapevine crown gall disease caused by a tumorigenic strain of R. vitis (Ti). Both acetosyringone-induced expression of a virulence gene and the growth of Ti were suppressed in vitro when it was cultivated in the VAR03-1 culture filtrate. These inhibitory effects were reduced by high-temperature treatment or incubation for 72 h. Both activities were detected in the high molecular weight fraction (>?100 kDa) of the filtrate. Our results suggest that the antagonistic effects of VAR03-1 on Ti are mediated by large particle(s) released in the culture media.     

Survival of <Emphasis Type="Italic">Curtobacterium flaccumfaciens</Emphasis> pv. <Emphasis Type="Italic">flaccumfaciens</Emphasis> in the soil under Brazilian conditions

Mustard clubroot, caused by Plasmodiophora brassicae, is a serious disease that affects Brassica juncea var. tumida Tsen, a mustard plant that is the raw material for a traditional fermented food manufactured in the Chongqing Municipality, People’s Republic of China. To find antagonistic bacteria for P. brassicae, 124 bacteria were obtained from the rhizosphere soil of B. juncea var. tumida grown in Fuling, Chongqing. Isolates were preliminarily chosen by evaluating the inhibition rate of the P. brassicae resting spore germination. The biocontrol effects of three antagonistic bacteria against clubroot on B. juncea var. tumida were evaluated in a greenhouse experiment. B18 showed the highest control efficiency, at 63.4% in the greenhouse test. In a field trial, B18 was also effective in controlling clubroot, but only at a 49.7% efficiency rate. According to 16S rDNA sequence analysis, strain B18 had a 100% sequence similarity with type strain Zhihengliuella aestuarii DY66^T (EU939716). Based on morphological, cultural, physiological and biochemical characteristics, the DNA G + C content, polar lipids, fatty acids, cell wall analysis, as well as DNA–DNA hybridization, strain B18 was identified as Z. aestuarii B18. Thus, the isolate B18 might have a potential biocontrol application for clubroot. We report for the first time that Z. aestuarii B18 can control clubroot.     

Virulence and inoculum density‐dependent interactions between clubroot resistant canola (Brassica napus) and Plasmodiophora brassicae

To mitigate the impact and dissemination of clubroot in western Canada, canola (Brassica napus) producers have relied on clubroot resistance traits. However, in 2013 and 2014, new strains of the clubroot pathogen, Plasmodiophora brassicae, emerged that are virulent on most clubroot‐resistant (CR) canola genotypes. Novel strains of the pathogen were inoculated onto two susceptible canola cultivars, one resistant line and six CR cultivars. Although all cultivars/lines showed a susceptible response to inoculation with the new strains of P. brassicae, the severity of disease reaction, root hair infection rates and the amount of P. brassicae DNA present in each canola genotype varied depending on the strain. In addition, the effect of inoculum density on disease severity and gall formation was recorded for one of these new strains on a universally susceptible Chinese cabbage cultivar and one susceptible and 10 resistant canola genotypes. Although root galls were observed at an inoculum density of 10³ spores per mL of soil, clear differentiation of susceptible and resistant reactions among canola cultivars/lines was not observed until the inoculum density reached 10⁵ spores mL^?1. At a spore density of 10⁶ spores mL^?1 and above, all cultivars/lines developed susceptible reactions, although there was some differentiation in the degree of reaction. This study shows the potential to develop a unique disease profile for emergent clubroot pathotypes and shows a useful range of spore densities at which to study new P. brassicae strains.     

防治烟草根黑腐病拮抗芽孢菌株的筛选

由基生根串珠霉菌(Thielaviopsis basicola)引起的烟草根黑腐病是烟草生产上重要根部真菌病害,近年在我国烟草种植区有加重危害的趋势,目前防治措施主要依赖化学药剂,给卷烟卫生带来一系列问题[1].探索该病生物防治途径,克服农药残留和病原菌抗药性十分重要.芽孢杆菌是土壤和植物微生态区系的优势生物种群,具有优良生防特性[2],采用芽孢杆菌作为烟草根黑腐病生防因子尚未见报道.本研究从烟草根际土壤中分离筛选对烟草根黑腐病病菌有较强拮抗作用的芽孢菌株,研究其抑菌活性、控病作用及其分类学地位.     

大白菜软腐病拮抗菌的筛选、鉴定及其防效研究

为筛选对大白菜软腐病具有较好拮抗效果的生防菌株,采用对峙平板法分别从作物根际土、发酵池以及本实验室菌种库得到6株拮抗性较强的菌株ASR-12、ASR-23、ASR-31、ASR-54、ASR-55、ASR-150。在离体叶柄软腐防效试验中,采用注射接种法获得了拮抗性较强的3株拮抗菌ASR-12、ASR-23和ASR-150,48 h的防效分别达到了87.64%、80.90%和70.79%。温室防效试验的结果表明:菌株ASR-12、ASR-23和ASR-150防治效果分别为59.22%、59.21%和55.00%,显著高于72%农用链霉素可湿性粉剂的防效(39.15%),具有很好应用前景。依据形态、生理生化和分子鉴定,菌株ASR-12被鉴定为解淀粉芽胞杆菌Bacillus amyloliquefaciens。     

Efficacy of Vapam fumigant against clubroot (Plasmodiophora brassicae) of canola

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.     

叶面喷施枯草芽胞杆菌XF-1防治大白菜根肿病

为了建立简易、有效的根肿病生防体系,本研究采用浇灌和喷施枯草芽胞杆菌XF-1的绿色荧光蛋白标记菌株XF-1-gfp,测定其在大白菜植株内的定殖能力,并用野生型菌株XF-1发酵液研究其防治根肿病和挽回产量效果。结果表明,叶面喷施XF-1-gfp发酵液后,标记菌在大白菜根、茎、叶等组织内的密度呈现出"先上升后下降最后趋于平稳"的趋势,最终稳定在约10~3 cfu/g组织;盆栽试验结果表明,与空白对照相比,所有处理发病率和病情指数均显著下降,喷施XF-1发酵液后最佳防治效果为56.4%,浇灌化学杀菌剂10%氰霜唑悬浮剂2 000倍液及1×10~7 cfu/mL的XF-1发酵液防效分别为78.6%与70.7%。大田试验结果表明,喷施XF-1发酵液后防治效果达52.6%,与浇灌化学杀菌剂10%氰霜唑悬浮剂(64.6%)及XF-1发酵液(74.0%)相比无显著差异。此外,与空白对照、浇灌10%氰霜唑悬浮剂及XF-1发酵液相比,喷施XF-1发酵液后大白菜单株产量分别增加了74.0%、35.1%及23.6%。试验结果表明叶面喷施XF-1发酵液是一种有效的防控大白菜根肿病及增产增收的方法。     

Pathogenic and genetic diversity in Plasmodiophora brassicae (clubroot) from Japan

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.     

Suppression of the clubroot pathogen Plasmodiophora brassicae by plant growth promoting formulations in roots of two Brassica species

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.