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

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。     

Plasmodiophora brassicae resting spore dynamics in clubroot resistant canola (Brassica napus) cropping systems

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.     

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.     

土壤pH对芸薹根肿菌侵染及病害发生的影响

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。     

Effect of temperature on primary infection by Plasmodiophora brassicae and initiation of clubroot symptoms

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.     

Soil management in a mountain agroecosystem and clubroot disease

Clubroot, caused by Plasmodiophora brassicae, is a disease limiting the production of Brassica species. Its severity varies according to the density of the pathogen's resting spores and environmental conditions. Although the soil environment (including its physical, chemical and biological characteristics) is determinant in the development of the disease, little is known regarding these characteristics in tropical regions, such as Brazil. The objective of this study was to investigate the relationships between soil attributes, bacterial population composition and clubroot intensity in a tropical mountain agroecosystem. Soil and plant samples were collected from 17 cauliflower-producing localities in Nova Friburgo, Brazil. The physical and chemical attributes, the bacterial population composition, the number of pathogen resting spores in the soil samples, and the clubroot severity were evaluated. Based on bacterial population composition, two distinct groups of soils were identified, which varied in attributes such as organic matter, potential acidity, pH and disease severity. The organic matter level was associated with differences in soil acidity, bacterial population composition and disease intensity, but there was not a cause and effect relationship between bacterial population composition and clubroot severity. Under the conditions of this agroecosystem, soils with increased organic matter presented higher acidity potential (H + Al), which was strongly correlated to clubroot severity. Thus, high acidity potential could be a key factor leading to clubroot development in mountain regions of Brazil.     

Assessment of the impact of resistant and susceptible canola on Plasmodiophora brassicae inoculum potential

The impact on clubroot severity of growing susceptible canola or mixtures of resistant and susceptible canola genotypes was examined. Bioassays revealed greater clubroot severity and incidence, and reduced plant height, where 100% of a susceptible cultivar had been grown. A higher proportion of susceptible plants within a resistant canola crop increased root hair and secondary infections. Regression analysis of root hair infection and the amount of Plasmodiophora brassicae DNA (as determined by quantitative PCR) revealed strong linear relationships between the two parameters. The linear relationships between root hair infection and P. brassicae DNA were stronger for the resistant cultivar than for the susceptible cultivar when regression analysis was conducted by cultivar over the sampling dates. In conclusion, the cropping of a resistant cultivar reduced clubroot severity, while the presence of susceptible volunteer canola increased inoculum potential. Quantitative PCR was a reliable tool for the quantification of root hair infection.     

根肿病生防放线菌B18发酵条件的研究

B18是一株对十字花科根肿病菌Plasmodiophora brassicae具有抑制作用的优良生防放线菌,其活菌以及发酵液都可抑制根肿病菌休眠孢子萌发.为提高其菌体量以及孢子萌发抑制率,本文以菌体生物量和发酵液抑制根肿病菌休眠孢子活性为指标,通过单因素试验和正交设计优化B18的发酵培养基组分以及培养条件.结果 表明:...     

Clubroot disease in Latin America: distribution and management strategies

Clubroot caused by Plasmodiophora brassicae is an important disease of cruciferous crops worldwide. In Latin America (from Mexico to Chile, including the Caribbean), most of the area in cruciferous crops is devoted to oilseed rape (Brassica napus; c. 230 600 ha) in Brazil, Chile, Paraguay, Uruguay and Argentina, while cruciferous vegetables such as cabbage, cauliflower, broccoli and Brussels sprouts (40 900 ha) are cropped intensively on small acreages across the region. Although clubroot is present in most Latin American countries, there have been very few studies of P. brassicae. Clubroot research in Latin America has focused mainly on adapting disease management strategies developed in temperate climates to tropical climates, including liming, biological control and genetic resistance. This review summarizes the management strategies used in Latin America to reduce the impact of clubroot, including novel strategies when compared with temperate regions, such as a crop rotation with aromatic plant species and the use of biological control with Trichoderma spp. Latin America has unique characteristics relative to temperate countries such as high humidity, warm temperatures and acidic soil that impact the interaction between P. brassicae and its plant hosts, so more research is required.     

芸薹根肿菌（Plasmodiophora brassicae）单孢分离接种及生理小种的鉴定

芸薹根肿菌(Plasmodiophora brassicae)单孢分离接种方法曾有报道,本试验改进了国外单孢分离技术.将休眠孢子悬浮液稀释到1个/0.5 μL,滴在一块消过毒的载玻片上,放置在显微镜下反复检查,以确保它精确只含有一个孢子.用微管将孢子吸入接种在2日龄白菜幼苗根毛上,营养液培养3周.为使其更接近田间发病环境条件,后期将疑似发病根在无菌土中继续进行病菌增繁.该方法能够有效地加快病菌繁殖感染,提高单孢分离接种成功率.对不同地区病菌进行大量单孢分离接种.本试验对3个地区的病菌单孢接种共950株,接种成功27株,使用Williams根肿病菌鉴别寄主鉴定,共9个生理小种.     

Effect of host and non‐host crops on Plasmodiophora brassicae resting spore concentrations and clubroot of canola

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.     

Variation in the development of secondary dormancy in oilseed rape genotypes under conditions of stress

Summary A substantial amount of seed is left in the fields before and during harvest of oilseed rape. Although this crop exhibits little or no primary dormancy, the absence of certain environmental cues that promote germination of imbibed seeds induces secondary dormancy. The work reported investigated the extent to which environmental stress conditions, including osmotic stress, low oxygen stress and anaerobiosis, induce secondary dormancy in oilseed rape, and examined the variation in development of secondary dormancy between and within genotypes. Osmotic stress was most effective in inducing dormancy. Anaerobic treatment produced very few dormant seeds, as did an atmosphere low in oxygen and high in nitrogen. The development of secondary dormancy under osmotic stress varied considerably between and within genotypes. Dormancy ranged from almost zero to about 60% for winter genotypes and about 85% for spring types. Within genotypes, variations occurred between seed lots and years of harvest. Temperature variations affected the percentage of dormant seeds. More dormant seeds were likely to be produced with incubation under water stress at 20 °C than at 12 °C. In winter genotypes, fewer dormant seeds were produced when incubation temperature and germination test temperatures differed. Thus, incubating at 20 °C and 12 °C, followed by germination tests at 20 °C and 12 °C, respectively, produced most dormant seeds. Also, in the winter genotypes, the potential development of secondary dormancy was positively correlated with the pattern and speed of germination of untreated seeds.     

Relationship between severity of blackleg (Leptosphaeria maculans/L. biglobosa species complex) and subsequent primary inoculum production on oilseed rape stubble

The relationship between severity of blackleg, or phoma stem canker ( Leptosphaeria maculans/L. biglobosa ), and subsequent primary inoculum production on oilseed rape ( Brassica napus ) stubble was investigated at two sites in France over 3 years. The quantity of primary inoculum produced in the following year increased with canker severity, from 1·9 to 10·8 pseudothecia cm⁻² on stubble with the least and most severe cankers, respectively. Stubble incubated at Le Rheu (cooler, more rain) had 1·7 times more pseudothecia than stubble incubated at Grignon. Stubble collected at Grignon had 2·7 times more pseudothecia than that collected at Le Rheu. The use of Darmor, a cultivar with a good level of quantitative resistance, reduced the severity of canker in the field, but not the subsequent inoculum production for stubble of the same canker severity class. At both sites, maturation of pseudothecia occurred after 63–75 days of incubation and increased with canker severity with a mean of 0·5 and 3% mature pseudothecia appearing per favourable day, on stubble with the least and most severe cankers, respectively. A simplified procedure for pseudothecial quantification proved satisfactory: for all three observers, most (91–96%) of the fructifications counted as pseudothecia were real pseudothecia. Only a few (4–14%) of the fructifications considered as non-pseudothecia were in fact pseudothecia of L. maculans . The total area occupied by pseudothecia, which was simpler and faster to evaluate, was correlated (coefficient of determination, R ² = 71%) with the number of counted pseudothecia. The results presented here make it possible to forecast the quantity of available primary inoculum for a given disease severity.     

根肿病生防菌Zhihengliuella aestuarii B18定殖能力及防效分析

Zhihengliuella aestuarii B18是一株对十字花科根肿病菌Plasmodiophora brassicae具有抑制作用的优良生防菌株。为探明其生防潜能,本文通过抗生素抗性标记法、盆栽试验和田间小区试验研究了B18在不同土壤pH、土壤温度、土壤含水量、初始接种浓度、蔬菜作物以及不同土壤类型中的定殖动态。灭菌土试验结果表明:调节土壤pH 7.5～8.5,含水量10%～30%,放置于10～25℃,70 d后B18定殖菌量保持在105～107 cfu/g。盆栽试验结果表明:初始接种菌液浓度为109 cfu/mL时,45 d后根际土中定殖菌量可稳定在104～105cfu/g。将50 mL浓度为2×109 cfu/mL的生防菌菌液接种于田间不同类型土壤后,第30天定殖菌量分别为病田8.7×105cfu/g,病土1.02×105cfu/g,健田8.5×104cfu/g,健土2.6×104cfu/g,即定殖能力由强到弱依次为:病田＞病土＞健田＞健土。且病田中B18在根际土中可存活至45 d且菌量保持在104 cfu/g,根内可存活至31 d且菌量保持在104 cfu/g。田间调查结果显示B18在病田和病土中对榨菜根肿病的防效分别为42.01%和47.53%,增产率分别为37.24%和40.22%。     

Growth and movement of secondary plasmodia of Plasmodiophora brassicae in turnip suspension-culture cells

Growth of secondary plasmodia of the clubroot pathogen Plasmodiophora brassicae was studied in dual culture of P. brassicae and turnip suspension cells. Suspension culture of P. brassicae -infected turnip cells was achieved by using P. brassicae -infected callus in Murashige and Skoog medium supplemented with 0·1 mg 2,4-D L⁻¹ and 0·02 mg kinetin L⁻¹. The shape of secondary plasmodia in suspension cells was spherical-to-subspherical. A few young plasmodia divided and became numerous spherical, small plasmodia which eventually formed a plasmodial cluster. The plasmodia fused and became vegetative plasmodia. Infected cells were significantly larger than noninfected cells. Secondary plasmodia moved within transformed turnip suspension host cells by cytoplasmic streaming of the host cells. Secondary plasmodia divided in synchrony with the transformed turnip cells.     

Spread and development of quambalaria shoot blight in spotted gum plantations

The aim of this study was to examine the disease development of quambalaria shoot blight, caused by the fungal pathogen Quambalaria pitereka, in plantation‐grown spotted gum (Corymbia citriodora subsp. citriodora, C. citriodora subsp. variegata, C. henryi and C. maculata) in south‐east Queensland, Australia. The results showed that native spotted gums are a primary source of inoculum followed rapidly by the production of secondary inoculum from infected trees in the plantation. The rate of spread and development of Q. pitereka within plantations increased exponentially over time as additional trees became infected and produced secondary inoculum. Spore concentration was shown to play an important role in disease development, with disease severity increasing with increasing disease incidence on individual trees and incidence across the plantation.     

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.     

Influence of cultivar resistance and inoculum density on root hair infection of canola (Brassica napus) by Plasmodiophora brassicae

The impact of cultivar resistance and inoculum density on the incidence of primary infection of canola root hairs by Plasmodiophora brassicae, the causal agent of clubroot, was assessed by microscopy. The incidence of root hair infection in both a resistant and a susceptible cultivar increased with increasing inoculum density, but was two‐ to threefold higher in the susceptible cultivar; the relationship between root hair infection and inoculum density was also substantially stronger and more consistent in the susceptible cultivar. In the susceptible cultivar, the root hair infection rate peaked between 6 and 8 days after sowing and then declined. In the resistant cultivar, it increased over the 14‐day duration of each study. It appears that examination of root hair infection by microscopy in a bait crop of susceptible canola could serve as a useful tool for estimating P. brassicae inoculum levels in soil. In a separate trial, the relationship between inoculum density and clubroot severity, plant growth parameters, and seed yield was assessed under greenhouse conditions. Inoculum density in the susceptible genotype was strongly and positively correlated with clubroot severity and negatively correlated with plant height and seed yield. In addition, a single cropping cycle of the susceptible cultivar contributed significantly higher levels of resting spores to the soil in a greenhouse test than did a cycle of the resistant cultivar, as assessed by quantitative PCR and microscope analysis.     

Differential responses of red clover cultivars to Sclerotinia trifoliorum under diverse natural climatic conditions

The susceptibility of 15 red clover ( Trifolium pratense ) cultivars to Sclerotinia trifoliorum under natural conditions in field experiments was investigated at sites in Sweden located at latitudes ranging from 60 to 64°N, with corresponding ranges of climatic regimes and lengths of vegetative growth and winter periods. At each site, 10 red clover cultivars were included: five were common, and five were selected according to the regional climate. Clover rot caused by S. trifoliorum from natural sources occurred in all geographical areas studied, and all cultivars included were affected. The numbers of plants of each cultivar killed by the pathogen was estimated at five sites over 2 years. Severe effects were observed in the first winter at these sites, but while incidence of clover rot increased and diseased areas expanded substantially in the second winter in northern Sweden, this pattern was not observed in southern regions. Tetraploidy, late flowering type and previous selection for resistance among cultivars positively influenced survival rates in the field. Estimates of susceptibility of cultivars obtained under field conditions after 2 years showed strong correlation when compared with rankings of susceptibility caused by an aggressive isolate of S. trifoliorum in previously conducted controlled environment laboratory tests. Yields were correlated to the proportion of gaps caused by the pathogen, indicating its economic importance.     

Effects of cyazofamid against Plasmodiophora brassicae Woronin on Chinese cabbage

Cyazofamid (4-chloro-2-cyano-N,N-dimethyl-5-p-tolylimidazole-1-sulfonamide) is a novel fungicide with high levels of activity against Oomycetes fungi and Plasmodiophora brassicae Woronin. The effects of cyazofamid were investigated against P. brassicae, the causal agent of clubroot disease in Chinese cabbage. Cyazofamid at 0.3 mg litre(-1) inhibited resting spore germination of this pathogen by about 80%. Cyazofamid at 3-10 mg litre(-1) exhibited fungicidal activity to resting spores of P. brassicae 1-10 days after treatment. When cyazofamid was applied to infested soil, both root-hair infections and club formation caused by P. brassicae were strongly inhibited at 1-3 mg kg(-1) dry soil. These results suggest that cyazofamid directly inhibits resting spore germination, thereby leading to the inhibition of root-hair infection and club formation. Cyazofamid at 3 mg kg(-1) dry soil also exhibited complete control of clubroot disease. The effect of broadcast soil application using a dust formulation at 2 kg AI ha(-1) (equivalent to 1.3 mg AI kg(-1) dry soil), and plug seedling tray application by a suspension concentrate formulation at 200 and 400 mg AI tray(-1) (30 x 60 x 4 cm3) against P. brassicae was also evaluated. Cyazofamid exhibited good efficacy against the pathogen. The sequential treatment including plug seedling tray application with cyazofamid and pre-plant broadcast soil application with the fungicide fluazinam also exhibited excellent levels of control. These results indicate that cyazofamid has a high potential to be an effective fungicide for the control of clubroot disease.