Development Of Clubroot Disease Research Articles

Impact of Susceptibility on Plant Hormonal Composition during Clubroot Disease Development in Canola (Brassica napus).

Clubroot, caused by Plasmodiophora brassicae, is a soilborne disease of crucifers associated with the formation of large root galls. This root enlargement suggests modulation of plant hormonal networks by the pathogen, stimulating cell division and elongation and influencing host defense. We studied physiological changes in two Brassica napus cultivars, including plant hormone profiles-salicylic acid (SA), jasmonic acid (JA), abscisic acid (ABA), the auxin indole-3-acetic acid (IAA), and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC)-along with their selected derivatives following inoculation with virulent and avirulent P. brassicae pathotypes. In susceptible plants, water uptake declined from the initial appearance of root galls by 21 days after inoculation, but did not have a significant effect on photosynthetic rate, stomatal conductance, or leaf chlorophyll levels. Nonetheless, a strong increase in ABA levels indicated that hormonal mechanisms were triggered to cope with water stress due to the declining water uptake. The free SA level in the roots increased strongly in resistant interactions, compared with a relatively minor increase during susceptible interactions. The ratio of conjugated SA to free SA was higher in susceptible interactions, indicating that resistant interactions are linked to the plant's ability to maintain higher levels of bioactive free SA. In contrast, JA and its biologically active form JA-Ile declined up to 7-fold in susceptible interactions, while they were maintained during resistant interactions. The ACC level increased in the roots of inoculated plants by 21 days, irrespective of clubroot susceptibility, indicating a role of ethylene in response to pathogen interactions that is independent of disease severity. IAA levels at early and later infection stages were lower only in susceptible plants, suggesting a modulation of auxin homeostasis by the pathogen relative to the host defense system.

Integrative Transcriptome, miRNAs, Degradome, and Phytohormone Analysis of Brassica rapa L. in Response to Plasmodiophora brassicae.

Clubroot is an infectious root disease caused by Plasmodiophora brassicae in Brassica crops, which can cause immeasurable losses. We analyzed integrative transcriptome, small RNAs, degradome, and phytohormone comprehensively to explore the infection mechanism of P. brassicae. In this study, root samples of Brassica rapa resistant line material BrT24 (R-line) and susceptible line material Y510-9 (S-line) were collected at four different time points for cytological, transcriptome, miRNA, and degradome analyses. We found the critical period of disease resistance and infection were at 0-3 DAI (days after inoculation) and 9-20 DAI, respectively. Based on our finding, we further analyzed the data of 9 DAI vs. 20 DAI of S-line and predicted the key genes ARF8, NAC1, NAC4, TCP10, SPL14, REV, and AtHB, which were related to clubroot disease development and regulating disease resistance mechanisms. These genes are mainly related to auxin, cytokinin, jasmonic acid, and ethylene cycles. We proposed a regulatory model of plant hormones under the mRNA-miRNA regulation in the critical period of P. brassicae infection by using the present data of the integrative transcriptome, small RNAs, degradome, and phytohormone with our previously published results. Our integrative analysis provided new insights into the regulation relationship of miRNAs and plant hormones during the process of disease infection with P. brassicae.

Expression and Role of Biosynthetic, Transporter, Receptor, and Responsive Genes for Auxin Signaling during Clubroot Disease Development.

Auxins play a pivotal role in clubroot development caused by the obligate biotroph Plasmodiophora brassicae. In this study, we investigated the pattern of expression of 23 genes related to auxin biosynthesis, reception, and transport in Chinese cabbage (Brassica rapa) after inoculation with P. brassicae. The predicted proteins identified, based on the 23 selected auxin-related genes, were from protein kinase, receptor kinase, auxin responsive, auxin efflux carrier, transcriptional regulator, and the auxin-repressed protein family. These proteins differed in amino acids residue, molecular weights, isoelectric points, chromosomal location, and subcellular localization. Leaf and root tissues showed dynamic and organ-specific variation in expression of auxin-related genes. The BrGH3.3 gene, involved in auxin signaling, exhibited 84.4-fold increase in expression in root tissues compared to leaf tissues as an average of all samples. This gene accounted for 4.8-, 2.6-, and 5.1-fold higher expression at 3, 14, and 28 days post inoculation (dpi) in the inoculated root tissues compared to mock-treated roots. BrNIT1, an auxin signaling gene, and BrPIN1, an auxin transporter, were remarkably induced during both cortex infection at 14 dpi and gall formation at 28 dpi. BrDCK1, an auxin receptor, was upregulated during cortex infection at 14 dpi. The BrLAX1 gene, associated with root hair development, was induced at 1 dpi in infected roots, indicating its importance in primary infection. More interestingly, a significantly higher expression of BrARP1, an auxin-repressed gene, at both the primary and secondary phases of infection indicated a dynamic response of the host plant towards its resistance against P. brassicae. The results of this study improve our current understanding of the role of auxin-related genes in clubroot disease development.

Expression and Role of Response Regulating, Biosynthetic and Degrading Genes for Cytokinin Signaling during Clubroot Disease Development.

The obligate biotroph Plasmodiophora brassicae causes clubroot disease in oilseeds and vegetables of the Brassicaceae family, and cytokinins play a vital role in clubroot formation. In this study, we examined the expression patterns of 17 cytokinin-related genes involved in the biosynthesis, signaling, and degradation in Chinese cabbage inoculated with the Korean pathotype group 4 isolate of P. brassicae, Seosan. This isolate produced the most severe clubroot symptoms in Chinese cabbage cultivar “Bullam-3-ho” compared to three other Korean geographical isolates investigated. BrIPT1, a cytokinin biosynthesis gene, was induced on Day 1 and Day 28 in infected root tissues and the upregulation of this biosynthetic gene coincided with the higher expression of the response regulators BrRR1, on both Days and BrRR6 on Day 1 and 3. BrRR3 and 4 genes were also induced during gall enlargement on Day 35 in leaf tissues. The BrRR4 gene, which positively interact with phytochrome B, was consistently induced in leaf tissues on Day 1, 3, and 14 in the inoculated plants. The cytokinin degrading gene BrCKX3-6 were induced on Day 14, before gall initiation. BrCKX2,3,6 were induced until Day 28 and their expression was downregulated on Day 35. This insight improves our current understanding of the role of cytokinin signaling genes in clubroot disease development.

Role of Cytokinins in Clubroot Disease Development

Clubroot, caused by the obligate biotrophic protist Plasmodiophora brassicae is a devastating disease of crucifers that causes substantial economic loss worldwide. The disease is characterized by the formation of galls in the root and hypocotyl of infected plants which restricts host vascular cambium development inhibiting efficient water and nutrient uptake by the plant. The pathogen- driven interference of hormonal homeostasis, particularly of cytokinin, in the root tissue is intricately linked with induction of hypertrophy and cell divisions leading to formation of galls. Levels of cytokinins and cell division generally increase at the onset of the disease which declines at the later stages of gall formation. The genes involved cytokinin biosynthesis such as cytokinin oxidase/ dehydrogenases and isopentenyl transferases shows differential expressions during clubroot infection and gall expansion in root tissues. Wider understanding of the roles of cytokinins and associated genes along the development of the disease will be helpful in unravelling plants defense mechanism against clubroot disease.

Jasmonic Acid-Mediated Aliphatic Glucosinolate Metabolism Is Involved in Clubroot Disease Development in Brassica napus L.

Glucosinolate (GSL) is associated with clubroot disease, which is caused by the obligate biotrophic protist Plasmodiophora brassicae. Due to the complicated composition of GSLs, their exact role in clubroot disease development remains unclear. By investigating clubroot disease resistance in cruciferous plants and characterizing the GSL content in seeds, we can determine if clubroot disease development is related to the components of GSLs. The difference in the infection process between Matthiola incana L. (resistant) and Brassica napus L. (susceptible) was determined. Root hair infection was definitely observed in both resistant and susceptible hosts, but no infection was observed during the cortical infection stage in resistant roots; this finding was verified by molecular detection of P. brassicae via PCR amplification at various times after inoculation. Based on the time course detection of the contents and compositions of GSLs after P. brassicae inoculation, susceptible roots exhibited increased accumulation of aliphatic, indolic, and aromatic GSLs in B. napus, but only aromatic GSLs were significantly increased in M. incana. Gluconapin, which was the main aliphatic GSL in B. napus and present only in B. napus, was significantly increased during the secondary infection stage. Quantification of the internal jasmonic acid (JA) concentration showed that both resistant and susceptible plants exhibited an enhanced level of JA, particularly in susceptible roots. The exogenous JA treatment induced aliphatic GSLs in B. napus and aromatic GSLs in M. incana. JA-induced aromatic GSLs may be involved in the defense against P. brassicae, whereas aliphatic GSLs induced by JA in B. napus likely play a role during the secondary infection stage. Three candidate MYB28 genes regulate the content of aliphatic GSLs identified in B. napus; one such gene was BnMYB28.1, which was significantly increased following both the treatment with exogenous JA and P. brassicae inoculation. In summary, the increased content of JA during the secondary infection stage may induce the expression of BnMYB28.1, which caused the accumulation of aliphatic GSLs in clubroot disease development.

Managing clubroot disease (caused byPlasmodiophora brassicaeWor.) by exploiting the interactions between calcium cyanamide fertilizer and soil microorganisms

SUMMARYCalcium cyanamide is a nitrogenous fertilizer used predominantly for over a century in field and glasshouse vegetable and salad production. The current review draws together, for the first time, knowledge concerning the biological properties of the compound that benefit crop production by encouraging sustainable soil health and quality. This is achieved through the increase of microorganisms antagonistic to plant pathogens. The review also reports on the natural occurence and degradation of cyanamide. The literature survey provides a perspective of research from the early 1900s to current studies. This identifies that nitrogen is released steadily into the rhizosphere from this fertilizer. Calcium is also readily available for plant roots and promotes the alkaline soil conditions beneficial to benign microorganisms. Consequently, soil suppressiveness towards organisms such asPlasmodiophora brassicae, the cause of clubroot disease in brassicas, develops. The effects of calcium and accompanying changes in soil pH values are discussed in relation to the life-cycle stages ofP. brassicaeand the development of clubroot disease. Formulations of calcium cyanamide contain the dimeric form, dicyandiamide. This compound slows soil nitrification and subsequent nitrate leaching into ground waters, reducing potential pollution. Calcium cyanamide is normally used for growing specialized fresh produce and is not available in quantities comparable with ammoniacal fertilizers. It is contended, however, that it has properties deserving wider assessment because of their implications for sustainable cropping.

Putative role of IAA during the early response of Brassica napus L. to Plasmodiophora brassicae

This study examined the role of indole-3-acetic acid (IAA) during the early stage of infection of rapeseed (Brassica napus L.) by the obligate biotrophic protist Plasmodiophora brassicae Woron., which causes clubroot disease. Treatment of infected B. napus seedlings with exogenous IAA promoted the development of clubroot disease, including an increase in the number and size of galls, whereas treatment with N-1-naphthylphthalamic acid (NPA) attenuated the disease and altered the location and size of the root nodules, resulting in a reduced disease index. An increased level of free IAA was detected in the roots at 3 and 7 days after inoculation (DAI) compared with the control, suggesting the activation of IAA signaling in the early stage of P. brassicae infection. Moreover, IAA treatment caused no significant change in the germination rate of the resting spores but resulted in enhanced root hair infection. RT–PCR and quantitative real-time PCR (qPCR) were used to analyze the expression of IAA homeostasis-related genes (3, 7, and 10 DAI) to identify gene expression patterns in the roots and leaves of B. napus after inoculation. Five IAA biosynthesis-related genes examined in this study were induced in the roots after inoculation with P. brassicae but not in the leaves. The rapid induction of BnAAO4 expression at 3 DAI may be responsible for the overproduction of IAA during the early stages of infection. This study suggests that IAA acts as a signaling molecule that putatively stimulates root hair infection in the early response of B. napus to P. brassicae infection.

Differential expression of miRNAs in Brassica napus root following infection with Plasmodiophora brassicae.

Canola (oilseed rape, Brassica napus L.) is susceptible to infection by the biotrophic protist Plasmodiophora brassicae, the causal agent of clubroot. To understand the roles of microRNAs (miRNAs) during the post-transcriptional regulation of disease initiation and progression, we have characterized the changes in miRNA expression profiles in canola roots during clubroot disease development and have compared these to uninfected roots. Two different stages of clubroot development were targeted in this miRNA profiling study: an early time of 10-dpi for disease initiation and a later 20-dpi, by which time the pathogen had colonized the roots (as evident by visible gall formation and histological observations). P. brassicae responsive miRNAs were identified and validated by qRT-PCR of miRNAs and the subsequent validation of the target mRNAs through starBase degradome analysis, and through 5′ RLM-RACE. This study identifies putative miRNA-regulated genes with roles during clubroot disease initiation and development. Putative target genes identified in this study included: transcription factors (TFs), hormone-related genes, as well as genes associated with plant stress response regulation such as cytokinin, auxin/ethylene response elements. The results of our study may assist in elucidating the role of miRNAs in post-transcriptional regulation of target genes during disease development and may contribute to the development of strategies to engineer durable resistance to this important phytopathogen.

Reduction of clubroot (Plasmodiophora brassicae) formation in Arabidopsis thaliana after treatment with prohexadione‐calcium, an inhibitor of oxoglutaric acid‐dependent dioxygenases

Recently, flavonoids were shown to modulate the outcome of clubroot development in Arabidopsis thaliana after infection with the obligate biotrophic pathogen Plasmodiophora brassicae. Therefore, the development of clubroot disease was investigated in Arabidopsis after treatment with prohexadione‐calcium (ProCa), an inhibitor of ascorbic acid/2‐oxoglutaric acid‐dependent dioxygenases such as flavanone‐3‐hydroxylase. The treatment resulted in a reduction of the flavonols quercetin and kaempferol in clubroots, whereas the precursor naringenin highly accumulated. The root system of ProCa‐treated plants was better developed although galls were still visible. Thus, ProCa treatment resulted in reduced gall size. Flavonoids are thought to inhibit polar auxin transport by modulating auxin efflux carriers. It was investigated whether the auxin response might change as a consequence of the accumulation of naringenin in ProCa‐treated plants. In the areas of gall development an auxin response was indicated by the auxin‐responsive promoter DR5 coupled to the reporter β‐glucuronidase (GUS), whereas very little staining was found in healthy root parts. No differences in GUS activity were found between P. brassicae‐infected and ProCa‐treated plants, and plants only infected with P. brassicae, indicating that the effect of ProCa treatment on clubroot reduction is not via changes in auxin responses. As ProCa is also an inhibitor of late steps in gibberellin biosynthesis, a specific gibberellin biosynthesis inhibitor, chlormequatchloride (CCC), was tested on club development. However, CCC did not reduce disease symptoms, indicating that the observed reduced gall development was not because of gibberellin biosynthesis inhibition by ProCa.

Isoform-Specific Localization of Brassica rapa Nitrilases in Root Infected with Plasmodiophora brassicae Revealed Using In Situ Hybridization Probes Improved with Locked Nucleic Acids

We established an in situ hybridization (ISH) technique by modification of hybridization probes with locked nucleic acids (LNAs) and demonstrated isoform-specific localization of transcripts of Brassica rapanitrilase (BrNIT-T) genes in clubroot tissue infected with Plasmodiophora brassicae. Chimeric oligo DNA probes containing LNAs demonstrated highly improved specificities and could discriminate between BrNIT-T1 and BrNIT-T2. These LNA-containing probes were applied to ISH. BrNIT-T1 was strongly expressed in cells containing expanding secondary plasmodia of P. brassicae, but not in cells containing resting spores. On the other hand, BrNIT-T2 transcripts were localized in noninfected cells rather than infected cells during the clubroot growth phase but coexisted with mature resting spores at a later phase of clubroot development. Immunostaining for indole-3-acetic acid (IAA) revealed IAA accumulation in cells containing growing plasmodia. IAA immunostaining in infected cells was reduced as the pathogen formed resting spores, but the signal was again enhanced in cells containing mature resting spores at a later phase of infection, suggesting that IAA is involved in both the early growth and the latest maturation phase of clubroot development. Expression of BrNIT-T1 and BrNIT-T2 in turnip roots was upregulated by exogenous treatment with cytokinin and jasmonic acid, respectively. Thus, these two phytohormones are possible triggers of abnormal IAA production in clubroot tissue via induction of the respective nitrilase. Given these results, we propose a model for isoform-specific roles of B. rapa nitrilases in auxin biosynthesis involved in phytohormone crosstalk during development of clubroot disease.

Effects of application of organic materials on the development of clubroot disease caused by Plasmodiophora brassicae

Effects of application of organic materials on the development of clubroot disease caused by Plasmodiophora brassicae

정식 후 초기 관수횟수 감소에 따른 배추 뿌리혹병 발생 억제효과

배추재배에서 뿌리혹병은 세계적으로 가장 문제가 되고 있는 병 중 하나이다. 본 연구는 배추 정식 후 관수횟수가 뿌리혹병의 발생 정도에 미치는 영향을 평가하기 위하여 폿트와 포장에서 실시되었다. 토양수분장력 별 시험에서 토양수분장력 별 관수횟수는 적을수록 발병도가 낮은 경향이었다. 상품수량은 0.06 MPa 처리구에서 10a당 5,306 kg으로서 다른 처리보다 증수하여 가장 경제적인 관수개시점으로 나타났다. 향후 적정 살균제 처리조합 혹은 저항성 품종 재식시의 관수 횟수에 대한 보강 연구가 필요할 것으로 보인다. Clubroot of Chinese cabbage, caused by Plasmodiophora brassicae, is one of the most serious plant diseases in the world. The objectives of this study were to investigate the effect of the irrigation times on the development of club root after planting and to evaluate the effect of clubroot disease on yield of chinese cabbage in pot and field. The clubroot disease gradually increased with increasing irrigation frequency after planting. The growth characters and yield of chinese cabbage by irrigation times varied according to soil moisture and clubroot disease severity. Based on marketable yield and control value, an ideal irrigation point was at the soil matric potential of 0.06 MPa. These results suggest that the suppression on clubroot disease development could be achieved by initially reduced irrigation times after planting. Future studies on irrigation times using fungicide treatment and resistant cultivar under natural field conditions are required to improve the control effect of clubroot.

Transcriptome Analysis of Arabidopsis Clubroots Indicate a Key Role for Cytokinins in Disease Development

The clubroot disease of the family Brassicaceae is caused by the obligate biotrophic protist Plasmodiophora brassicae. Infected roots undergo a developmental switch that results in the formation of aberrant roots (clubs). To investigate host gene expression during the development of the disease, we have used the Arabidopsis ATH1 genome array. Two timepoints were chosen, an early timepoint at which the pathogen has colonized the root but has induced only very limited change of host cell and root morphology and a later timepoint at which more than 60% of the host root cells were colonized and root morphology was drastically altered. At both timepoints, more than 1,000 genes were differentially expressed in infected versus control roots. These included genes associated with growth and cell cycle, sugar phosphate metabolism, and defense. The involvement of plant hormones in club development was further supported; genes involved in auxin homeostasis, such as nitrilases and members of the GH3 family, were upregulated, whereas genes involved in cytokinin homeostasis (cytokinin synthases and cytokinin oxidases/dehydrogenases) were already strongly downregulated at the early timepoint. Cytokinin oxidase/dehydrogenase overexpressing lines were disease resistant, clearly indicating the importance of cytokinin as a key factor in clubroot disease development.

Changes in gene expression of putative isopentenyltransferase during clubroot development in Chinese cabbage ( Brassica rapa L.)

The obligate biotroph Plasmodiophora brassicae induces club formation on roots of various species of the Brassicaceae family. This hypertrophy is dependent on increased amount of auxins and cytokinins. To investigate the involvement of cytokinin biosynthesis by the plant in clubroot development, we isolated cDNA fragments of five putative cytokinin synthase genes from Brassica rapa ( BrIPT1, 3, 5, 7, and 8) and examined their expression using Northern blot analysis. Observations at 5-day intervals revealed the first visible club formation (only near the base of the root) at 20 days post-inoculation (dpi). Compared with control roots, the expression of BrIPT1, 3, 5, and 7 was increased at 20 dpi in parts of the inoculated root that lacked visible symptoms (>2 cm below the base of the root) but at which large clubs formed later in the progress of the disease. However, these genes were less expressed in clubs that formed 0–2 cm below the base of the root than in the control at 20 dpi. These results suggest that P. brassicae infection transiently stimulates the transcription of BrIPT1, 3, 5, and 7 before club formation, after which the expression is repressed in clubs. No signals corresponding to BrIPT8 were detected in either inoculated or uninoculated roots. These results suggest that cytokinin biosynthesis by the plant is related to the primary development of clubroot disease, although it is unlikely to contribute to club enlargement.

The Interaction of Plasmodiophora brassicae and Arabidopsis thaliana: Parameters for Disease Quantification and Screening of Mutant Lines

AbstractThe soil‐borne obligate pathogen Plasmodiophora brassicae causes clubroot disease in species of Brassicaceae, including Arabidopsis thaliana. The host–pathogen interaction was studied with respect to the age of the plant at the time point of inoculation and to different infection pressures in order to establish a standardization of infection parameters and evaluation of disease extent for A. thaliana lines. Spore number per root weight, root and shoot weight of inoculated and non‐inoculated plants as well as infection rate and disease index (DI) were analysed and correlated. The disease extent of different lines was comparable as measured by the relation of root weight of inoculated and non‐inoculated plants (Ri/Rni index) and the DI. Most of the 71 screened A. thaliana lines turned out to be susceptible. However, the mutant lines tu8, tu3, det1‐1, and rhd3‐1 showed a certain degree of tolerance under specific culture conditions. The reactions of rhd3‐1 indicate that hypertrophy is a prerequisite for maturation of the pathogen. The reactions of the tu3 and tu8 mutants indicate a role of indole glucosinolates and indole‐3‐acetonitrile/IAA in development of clubroot disease.

Indole glucosinolate and auxin biosynthesis in Arabidopsis thaliana (L.) Heynh. glucosinolate mutants and the development of clubroot disease.

Mutants and wild type plants of Arabidopsis thaliana were analysed for differences in glucosinolate accumulation patterns, indole-3-acetic acid (IAA) biosynthesis and phenotype. A previously identified series of mutants, termed TU, with altered glucosinolate patterns was used in this study. Only the line TU8 was affected in shoot phenotype (shorter stems, altered branching pattern). Synthesis of IAA and metabolism were not much affected in the TU8 mutant during seedling development, although the content of free IAA peaked earlier in TU8 during plant development than in the wild type. Indole glucosinolates and IAA may, however, be involved in the development of clubroot disease caused by the obligate biotrophic fungus Plasmodiophora brassicae since the TU3 line had a lower infection rate than the wild type, and lines TU3 and TU8 showed decreased symptom development. The decline in clubroot formation was accompanied by a reduced number of fungal structures within the root cortex and slower development of the fungus. Indole glucosinolates were lower in infected roots of TU3 and TU8 than in control roots of these lines, whereas in wild-type plants the differences were not as prominent. Free IAA and indole-3-acetonitrile (IAN) were increased in infected roots of the wild type and mutants with normal clubroot symptoms, whereas they were reduced in infected roots of mutants TU3 and TU8. These results indicate a role for indole glucosinolates and IAN/IAA in relation to symptom development in clubroot disease.

Induction of auxin biosynthetic enzymes by jasmonic acid and in clubroot diseased Chinese cabbage plants

Nitrilase (NIT) and myrosinase are important enzymes for auxin biosynthesis in Brassicaceae, which is increased during clubroot disease. Therefore, NIT and myrosinase levels during club development and possible regulation mechanisms were investigated. In addition, the occurrence of different nitrilase isoforms in Chinese cabbage has been shown. Nitrilase activity was enhanced in infected roots during later stages of club development (35–42 days after inoculation). However, no differences in nitrilase mRNA levels between infected and healthy roots were found during symptom development. Myrosinase expression was increased in clubbed roots at slightly earlier time points (28 days after inoculation) and also at later time points during infection. The activities of tryptophan oxidizing enzyme (TrpOxE), which catalyzes the first step in tryptophan‐dependent auxin biosynthesis in Brassicaceae, and nitrilase were enhanced after treatment with jasmonic acid (JA) and methyl jasmonate. Similarly, the amount of myrosinase mRNA was increased by JA. During clubroot disease the endogenous concentration of JA increased in infected roots 3–5 weeks after inoculation. From our results it can be concluded that: (1) de novo indole‐3‐acetic acid (IAA) biosynthesis plays a role for symptom development of clubroot disease in Brassicaceae during later developmental stages; and (2) JA which increased during club development, may be involved in the up‐regulation of three enzymes important for IAA synthesis.

Glucosinolate content in susceptible and resistant chinese cabbage varieties during development of clubroot disease

The glucosinolate content in Chinese cabbage ( Brassica campestris ssp. pekinensis) during the development of clubroot disease caused by the obligate biotroph Plasmodiophora brassicae was investigated. Two Plasmodiophora-resistant and two susceptible varieties of Chinese cabbage were used and three classes of glucosinolates, aliphatic (=alkenyl), aromatic and indolic were analysed. Between the susceptible varieties ‘Granat’ and ‘Osiris’ and the resistant varieties ‘Parkin’ and ‘Yuki’ there were significant differences in glucosinolate pattern. The total glucosinolate content in roots of the two susceptible varieties was higher throughout the experimental period than in roots of the two resistant varieties. ‘Osiris’ showed the highest glucosinolate content of all the varieties investigated ( ca three-fold higher than ‘Granat’ and ca five-fold higher than ‘Parkin’ and ‘Yuki’). After infection with P. brassicae the indole glucosinolates increased after 14 and 20 days in roots of ‘Granat’ and ‘Osiris’, respectively, whereas ther was no difference between infected and control roots in ‘Parkin’ and ‘Yuki’. The aliphatic glucosinolates were also enhanced in infected roots of ‘Granat’, whereas ‘Osiris’ showed a very high content of aliphatic glucosinolates during the whole experimental period. Roots of ‘Parkin’ and ‘Yuki’ grown in the presence of Plasmodiophora spores showed an elevated concentration of aromatic glucosinolates after 14 and 30 days, respectively, which was not found in ‘Granat’ and ‘Osiris’. Total seed glucosinolate content appeared to be correlated with the susceptibility of the Chinese cabbage varieties tested. Eight different susceptible varieties showed higher total glucosinolate contents than the two resistant varieties. Treatment of plants of the varieties ‘Parkin’ and ‘Granat’ with salicylic acid and jasmonic acid resulted in increased amounts of glucosinolates, although differences in the response were observed between the two treatment. Jasmonic acid induced mainly indole glucosinolates in the leaves, whereas salicylic acid induced indole glucosinolates also in the roots of both varieties. In the variety ‘Parkin’, we also observed induction of aliphatic and aromatic glucosinolates after jasmonate treatment. Although the variety ‘Parkin’ showed no clubroot symptoms, we were able to detect fungal structures within the roots using scanning electron microscopy. We would, therefore, rather describe this variety as tolerant not resistant to clubroot disease. The potential role of different glucosinolates in plant-pathogen interactions is discussed.

Root surface-inhabiting bacteria and the expression of clubroot of radish in controlled environments

The effect of bacteria on the expression of clubroot of radish caused by the obligate parasite, Plasmodiophora brassicae, was studied. Inoculations with the bacterial strains isolated from roots of radish plants increased slightly, decreased slightly or did not change the number of root hairs colonized by P. brassicae in the root hair, i.e. primary phase of colonization. Five of six bacterial strains decreased the incidence of clubroot which was associated with a decrease in the extent of P. brassicae -colonization of the stele, i.e. secondary phase colonization. The role of root surface-inhabiting bacteria in clubroot disease development in radish under controlled environmental conditions is discussed.