Rapid-cycling Brassica Research Articles

Climate change and plant rhizosphere microbiomes: an experiential course-embedded research project.

The current and ongoing challenges brought on by climate change will require future scientists who have hands-on experience using advanced molecular techniques, can work with large data sets, and can make correlations between metadata and microbial diversity. A course-embedded research project can prepare students to answer complex research questions that might help plants adapt to climate change. The project described herein uses plants as a host to study the impact of climate change-induced drought on host-microbe interactions through next-generation DNA sequencing and analysis using a command-line program. Specifically, the project studies the impact of simulated drought on the rhizosphere microbiome of Fast Plants rapid cycling Brassica rapa using inexpensive greenhouse supplies and 16S rRNA V3/V4 Illumina sequencing. Data analysis is performed with the freely accessible Python-based microbiome bioinformatics platform QIIME 2.

Floral morphology of 'Anand' rapid cycling Brassica oleracea .

Abstract The 'Anand' type of cytoplasmic male sterility (CMS) was introduced to Brassica oleracea through protoplast fusion (Cardi and Earle, 1997), providing a source of male sterility that is of value in producing F1 hybrid varieties of this species without the cold sensitivity of 'Ogura' cytoplasm. In this species, as in others in which it has been introduced, 'Anand' mitochondria are associated with flower abnormalities. The best lines have been used by commercial breeders. This paper describes 'Anand' flower abnormalities in further detail. Rapid cycling brassica with 'Anand' cytoplasm may have promise as a model system for research on floral patterning. Materials and Methods. Three lines of rapid cycling B. oleracea carrying the 'Anand' cytoplasm and one wild type were grown. The flower morphology of 'Anand' lines was classified as good in F25-F-1A, fair in F25-F-6B, and poor in F23-F-1B (Cardi and Earle, 1997). Seedlings were started in an indoor growth room, but were maintained in a naturally lit greenhouse at 20° night, 25° day during flowering. Five flowers on 5 plants of each line were examined. Results. Morphological abnormalities affected all floral parts (Table 1). There was substantial variation among flowers on individual plants and among lines but little within lines. Conclusions. "Good" flowers have large petals that push open the sepals before the carpel elongates. Female fertility could be reduced due to occlusion of the stigma or physical damage caused by the stigma pressing against the end of a sepal and kinking the style. Female fertility in some flowers was unlikely because the carpel suture failed to fuse. In some cases the edge of the split carpel was sepal-like, consistent with the absence of SEPALLATA expression. The stigma on a sepal represents the converse. Stamens were most strongly affected, with outer stamens most reduced. This whorl is the one most frequently suppressed in flowering plants (Masters, 1869). The number of stamens was reduced to varying degrees. First to be lost was one or both of the pair outside the petals. Then the outer pair inside the petals was affected. One or both of these stamens could either be lost or doubled to give 3 to 5 stamens. Again a positional cue for stamens appears to be weakened. Anther development was often limited, the expected and desired consequence of the Anand genotype. Some undehisced " good " anthers contained pollen. There is variation even among the lines initially described as " good ". Further selection among these may help identify those that are most promising for further use in hybrid production.

Sef1, rapid-cycling Brassica napus for large-scale functional genome research in a controlled environment.

We demonstrated a short-cycle B. napus line, Sef1, with a highly efficient and fast transformation system, which has great potential in large-scale functional gene analysis in a controlled environment. Rapeseed (Brassica napus L.) is an essential oil crop that accounts for a considerable share of global vegetable oil production. Nonetheless, studies on functional genes of B. napus are lagging behind due to the complicated genome and long growth cycle, this is largely due to the limited availability of gene analysis and modern genome editing-based molecular breeding. In this study, we demonstrated a short-cycle semi-winter-type Brassica napus 'Sef1' with very early-flowering and dwarf phenotype, which has great potential in large-scale indoor planting. Through the construction of an F2 population of Sef1 and Zhongshuang11, bulked segregant analysis (BSA) combined with the rape Bnapus50K SNP chip assay method was used to identify the early-flowering genes in Sef1, and a mutation in BnaFT.A02 was identified as a major locus significantly affecting the flowering time in Sef1. To further investigate the mechanism of early flowering in Sef1 and discover its potential in gene function analysis, an efficient Agrobacterium-mediated transformation system was established. The average transformation efficiency with explants of hypocotyls and cotyledons was 20.37% and 12.8%, respectively, and the entire transformation process took approximately 3 months from explant preparation to seed harvest of transformed plants. This study demonstrates the great potential of Sef1 for large-scale functional gene analysis.

Overexpression of rice acyl-CoA-binding protein OsACBP5 protects Brassica napus against seedling infection by fungal phytopathogens

Context Class III acyl-CoA-binding proteins such as those from dicots (Arabidopsis and grapevine) play a role in defence against biotrophic pathogens. The overexpression of the monocot Oryza sativa (rice) OsACBP5 in Arabidopsis and rice has been demonstrated to enhance broad-spectrum disease resistance against selected phytopathogens in OsACBP5-overexpressing (OsACBP5-OE) lines. Aims We aimed to develop transgenic rapid-cycling Brassica napus (B. napus-RC) and canola cv. Westar OsACBP5-OEs using tissue culture-based Agrobacterium-mediated transformation and to evaluate transgenic plants for resistance against Alternaria blight, blackleg and Sclerotinia rot diseases. Methods Transgenic B. napus-RC and cv. Westar OsACBP5-OEs were generated through Agrobacterium-mediated transformation using Agrobacterium strain LBA4404 harbouring a plasmid with the rice complementary DNA encoding OsACBP5 driven by the cauliflower mosaic virus 35S promoter. Alternaria blight and blackleg pathogen assays were based on infecting young cotyledons, while detached leaf assay was used to test the tolerance of B. napus plants toward Sclerotinia sclerotiorum. Key results Average transformation efficiencies of 24.2% and 29.1% were obtained for B. napus-RC and B. napus cv. Westar cotyledons respectively. OsACBP5-OE plants exhibited resistance 5 days after inoculation with Alternaria brassicae, 12 days after inoculation with Leptosphaeria maculans, and 24 h after inoculation with S. sclerotiorum. Conclusions Transformation of B. napus-RC was shown herein to be an effective trait testing platform for canola. This study also provides an insight into the usefulness of OsACBP5 in enhancing resistance to necrotrophic phytopathogens. Implications OsACBP5 can be overexpressed in other crops to generate pathogen-resistant varieties.

Rapid-cycling Brassica rapa evolves even earlier flowering under experimental drought.

Changes in climate can impose selection on populations and may lead to rapid evolution. One such climatic stress is drought, which plant populations may respond to with escape (rapid growth and early flowering) or avoidance (slow growth and efficient water-use). However, it is unclear if drought escape would be a viable strategy for populations that already flower early from prior selection. In an experimental evolution study, we subjected rapid-cycling Brassica rapa (RCBr), which was previously selected for early flowering, to four generations of experimental drought or watered conditions. We then grew ancestral and descendant populations concurrently under drought and watered conditions to assess evolution, plasticity, and adaptation. The RCBr populations that evolved under drought had earlier flowering and lower water-use efficiency than the populations that evolved under watered conditions, indicating evolutionary divergence. The drought descendants also had a trend of earlier flowering compared to ancestors, indicating evolution. Evolution of earlier flowering under drought followed the direction of selection and increased fitness and was consistent with studies in natural and experimental populations of this species, suggesting adaptive evolution. We found rapid adaptive evolution of drought escape in RCBr and little evidence for constraints on flowering time evolution, even though RCBr already flowers extremely early. Our results suggest that some populations may harbor sufficient genetic variation for evolution even after strong selection has occurred. Our study also illustrates the utility of combining artificial selection, experimental evolution, and the resurrection approach to study the evolution of functional traits.

Efficient and Economical Targeted Insertion in Plant Genomes via Protoplast Regeneration.

Versatile genome editing can be facilitated by the insertion of DNA sequences into specific locations. Current protocols involving CRISPR and Cas proteins rely on low efficiency homology-directed repair or non-homologous end joining with modified double-stranded DNA oligonucleotides as donors. Our simple protocol eliminates the need for expensive equipment, chemical and enzymatic donor DNA modification, or plasmid construction by using polyethylene glycol-calcium to deliver non-modified single-stranded DNA oligonucleotides and CRISPR-Cas9 ribonucleoprotein into protoplasts. Plants regenerated via edited protoplasts achieved targeted insertion frequencies of up to 50% in Nicotiana benthamiana and 13.6% in rapid cycling Brassica oleracea without antibiotic selection. Using a 60 nt donor containing 27 nt in each homologous arm, 6/22 regenerated N. benthamiana plants showed targeted insertions, and one contained a precise insertion of a 6 bp HindIII site. The inserted sequences were transmitted to the next generation and invite the possibility of future exploration of versatile genome editing by targeted DNA insertion in plants.

Damage and recovery from drift of synthetic-auxin herbicide dicamba depends on concentration and varies among floral, vegetative, and lifetime traits in rapid cycling Brassica rapa

Herbicides can drift from intended plants onto non-target species. It remains unclear how drift impacts plant functional traits that are important for fitness. To address this gap, we conducted an experiment where fast cycling Brassica rapa plants were exposed to one of three drift concentrations (0.5%, 1%, 10%) of synthetic-auxin dicamba. We evaluated damage to and capacity of floral and vegetative traits to recover as well as lifetime fitness by comparing treated plants to controls. Response to dicamba exposure was concentration-dependent across all traits but varied with trait type. At 0.5% dicamba, three out of five floral traits were affected, while at 1% dicamba, four floral traits and one out of two vegetative traits were negatively impacted. At 10% dicamba all floral and vegetative traits were stunted. Overall, floral traits were more responsive to all dicamba drift concentrations than vegetative traits and displayed a wide range of variation ranging from no response (e.g., pistil length) to up to 84% reduction (ovule number). However, despite floral traits were more affected across the dicamba drift concentrations they were also more likely to recover than the vegetative traits. There was also variation among lifetime traits; the onset of flowering was delayed, and reproductive fitness was negatively affected in a concentration-dependent manner, but the final biomass and total flower production were not affected. Altogether, we show substantial variation across plant traits in their response to dicamba and conclude that accounting for this variation is essential to understand the full impact of herbicide drift on plants and the ecological interactions these traits mediate.

Draft Genome Assembly and Transcriptome Dataset for European Turnip (Brassica rapa L. ssp. rapifera), ECD4 Carrying Clubroot Resistance.

Draft Genome Assembly and Transcriptome Dataset for European Turnip (Brassica rapa L. ssp. rapifera), ECD4 Carrying Clubroot Resistance.

Targeting Cytokinin Homeostasis in Rapid Cycling Brassica rapa with Plant Growth Regulators INCYDE and TD-K.

Modifying the cytokinin content in plants is a means of improving plant productivity. Here, we report the development and biological activity of compound TD-K (1-(furan-2-ylmethyl)-3-(1,2,3-thiadiazol-5-yl)urea)which is related to thidiazuron. TD-K—which exhibited extremely high antisenescence activity in the wheat leaf bioassay—and INCYDE (2-chloro-6-(3-methoxyphenyl)aminopurine)—a plant growth regulator reported to inhibit cytokinin oxidase/dehydrogenase (CKX), an enzyme involved in the degradation of the plant hormone cytokinin—were selected for investigation of their effects on the model plant Rapid Cycling Brassica rapa (RCBr). We monitored the expression of BrCKX and isopentenyl transferase (BrIPT), which codes for the key cytokinin biosynthesis enzyme, in developing leaves following INCYDE and TD-K application. Growth room experiments revealed that INCYDE increased RCBr seed yield per plant, but only when applied multiple times and when grown in 5 mM KNO3. Expression in control leaves showed transient, high levels of expression of BrCKX and BrIPT at true leaf appearance. Following INCYDE application, there was a rapid and strong upregulation of BrCKX3, and a transient downregulation of BrIPT1 and BrIPT3. Interestingly, the upregulation of BrCKX3 persisted in a milder form throughout the course of the experiment (16 days). TD-K also upregulated BrCKX3. However, in contrast to INCYDE, this effect disappeared after two days. These results suggest that both compounds (CKX inhibitor and cytokinin TD-K) influenced cytokinin homeostasis in RCBr leaves, but with different mechanisms.

Agrobacterium-mediated vacuum infiltration and floral dip transformation of rapid-cycling Brassica rapa

BackgroundRapid-cycling Brassica rapa (RCBr), also known as Wisconsin Fast Plants, are small robust plants with a short lifecycle that are widely used in biology teaching. RCBr have been used for decades but there are no published reports of RCBr genetic transformation. Agrobacterium-mediated vacuum infiltration has been used to transform pakchoi (Brassica rapa ssp. chinensis) and may be suitable for RCBr transformation. The floral dip transformation method, an improved version of vacuum infiltration, could make the procedure easier.ResultsBased on previous findings from Arabidopsis and pakchoi, plants of three different ages were inoculated with Agrobacterium. Kanamycin selection was suboptimal with RCBr; a GFP screen was used to identify candidate transformants. RCBr floral bud dissection showed that only buds with a diameter less than 1 mm carried unsealed carpels, a key point of successful floral dip transformation. Plants across a wide range of inflorescence maturities but containing these immature buds were successfully transformed, at an overall rate of 0.1% (one per 1000 T1 seeds). Transformation was successful using either vacuum infiltration or the floral dip method, as confirmed by PCR and Southern blot.ConclusionA genetic transformation system for RCBr was established in this study. This will promote development of new biology teaching tools as well as basic biology research on Brassica rapa.

Colonization of siliques and seeds of rapid cycling Brassica oleracea plants by Xanthomonas campestris pv. campestris after spray-inoculation of flower clusters

Glasshouse experiments were conducted to study the colonization of seedpods (siliques) and seeds of rapid cycling Brassica oleracea plants after spraying inoculum on clusters of recently opened flowers with Xanthomonas campestris pv. campestris (Xcc) at densities of 107–108 cfu ml−1. A green fluorescent protein (GFP) tagged Xcc strain was used to allow visualization of the bacteria by epifluorescence stereo microscopy (ESM) and confocal laser scanning microscopy (CLSM). The GFP-tagged strain showed reduced virulence compared to the untagged parental strain, but was still able to cause black rot symptoms. Two to three days after spray-inoculation, sepals, stamen and petals were colonized by Xcc, as observed by ESM. In green siliques a GFP-signal was observed on valves, septa and seeds, despite the fact that a high percentage of Xcc cells had lost their ability to express GFP as found by dilution-plating. Densities of Xcc in infected silique tissues were up to 109 cfu g−1. A fluorescent signal using ESM was found in seeds harvested from symptomatic siliques after incubation of seeds on blotting paper wetted with broth to enhance the multiplication of Xcc. Xcc was found in association with the seed coat and in a single seed, also in the endosperm and embryo, indicating deep-seated seed infection. The estimated incidence of contaminated seeds in both years was ca. 7%. The estimated incidence of deep-seated infections, still detectable after warm water treatment of seeds, was also high (2–3.8%). It is concluded that spray-inoculation of flower clusters with Xcc can result in the infection of sepals and reproductive organs, and in deep-seated seed infections.

Development and Application Effect of Open Inquiry Program for Elementary School Students Using Rapid-cycling Brassica rapa

Development and Application Effect of Open Inquiry Program for Elementary School Students Using Rapid-cycling Brassica rapa

Genome-wide analysis of gene expression to distinguish photoperiod-dependent and -independent flowering in Brassicaceae

Photoperiod is the most important environmental cue for the regulation of flowering time, a highly important agronomic trait for crop productivity. To help elucidate the photoperiodic control of flowering in Brassicaceae, we performed microarray experiments using species-specific oligo-arrays with the long day (LD) plant Arabidopsis thaliana and the photoperiod-independent plant rapid cycling Brassica rapa (RCBr). Enrichment analysis of the gene ontologies of differentially expressed genes (DEGs) did not uncover clear differences in gene expression between photoperiod-dependent and -independent plants. Most genes that were up-regulated under LD conditions in Arabidopsis were also up-regulated in RCBr. In addition, most genes associated with light signaling and the circadian clock showed similar expression patterns between Arabidopsis and RCBr, implying that most components known to be key regulators in the photoperiodic flowering pathway are not responsible for the photoperiod independence of RCBr. Nonetheless, we identified one clock-associated gene, PSEUDO-RESPONSE REGULATOR9 (PRR9), as a candidate gene explaining the photoperiod independence of RCBr. The mechanism underlying the role of PRR9 in photoperiodic control and genomic polymorphisms should be further explored using different B. rapa species.

'식물의 한살이' 단원에서 속성배추를 활용한 뇌기반 진화적 접근법이 초등학생의 흥미에 미치는 영향

The purpose of this study is to analyze the effects of elementary science instruction applying a Brain-Based Evolutionary (ABC-DEF) approach using Rapid-cycling Brassica rapa (RcBr) on the interests of elementary school students. For this study, two elementary school classes in Seoul and one elementary school class in Gyeonggi-do were selected. Comparison group received instruction using textbook and teacher's guidebook. A class taught using only brain-based evolutionary approach is experimental group A, and a class taught through brain-based evolutionary approach using RcBr is experimental group B. In order to analyze the quantitative differences about the interests of students, three kinds of test were administered to the students: 'Applied Unit-Related Interests', 'Follow-up Interests' and 'Interests in the observation material'. To get more information, qualitative data such as portfolios and interviews were analyzed. The major findings are as follows. First, for the test of applied unit-related interests, a statistically significant difference was found between comparison group and experimental group A, and between comparison group and experimental group B. As the results of interviews, the students have shown that the intensified exploration activities on plant in Brain-Based Evolutionary approach applied to experimental groups A and B had a positive effect. Second, for test of follow-up interests, we classified the students' follow-up interests into three types: extended-developed-deepened (EDD) type, simply expanded-maintained (SEM) type, and stopped or decreased (SD) type. Both experimental group A and experimental group B showed the highest percentage of EDD. Also, observation journal applying the evolutionary process (DEF) showed a positive effect on the students' interest. Comparison group showed the highest percentage of SEM. Third, for test of applied interests in the observation material, a statistically significant difference was found between comparison group and experimental group A, and comparison group and experimental group B. Experimental group B using RcBr showed the highest average score, while experimental group A showed a higher score than comparison group. Based on these findings, educational implications of Brain-Based Evolutionary approach and using RcBr are discussed.

The Gene Encoding Dihydroflavonol 4-Reductase Is a Candidate for the anthocyaninless Locus of Rapid Cycling Brassica rapa (Fast Plants Type).

Rapid cycling Brassica rapa, also known as Wisconsin Fast Plants, are a widely used organism in both K-12 and college science education. They are an excellent system for genetics laboratory instruction because it is very easy to conduct genetic crosses with this organism, there are numerous seed stocks with variation in both Mendelian and quantitative traits, they have a short generation time, and there is a wealth of educational materials for instructors using them. Their main deficiency for genetics education is that none of the genetic variation in RCBr has yet been characterized at the molecular level. Here we present the first molecular characterization of a gene responsible for a trait in Fast Plants. The trait under study is purple/nonpurple variation due to the anthocyaninless locus, which is one of the Mendelian traits most frequently used for genetics education with this organism. We present evidence that the DFR gene, which encodes dihyroflavonol 4-reductase, is the candidate gene for the anthocyaninless (ANL) locus in RCBr. DFR shows complete linkage with ANL in genetic crosses with a total of 948 informative chromosomes, and strains with the recessive nonpurple phenotype have a transposon-related insertion in the DFR which is predicted to disrupt gene function.

Multigenerational exposure to cerium oxide nanoparticles: Physiological and biochemical analysis reveals transmissible changes in rapid cycling Brassica rapa

The unique redox chemistry on the surface of cerium oxide nanoparticles (CeO2NPs) and their broad applications in society have caused many concerns over the release and accumulation of these materials in the environment. Many investigations have been conducted with regard to the environmental health and safety effect of CeO2NPs, including their impact on plant health. However, most previous studies were conducted on the early seedling development stage, with a small number of recent investigations examined the impact of CeO2NPs throughout the life cycle of plants (e.g. from seed to seed). However, the long term, multigenerational impact of CeO2NPs on plants remains unclear. The main aim of this study was to assess the physiological and biochemical consequences of multi-generational (three) CeO2NPs exposure over a range of concentrations (0–1000mg/L) on B. rapa. The results showed that plants in the second and third generation displayed slower plant growth and smaller biomass. The Brassica plants also bore 39%, 59% and 61% less siliques after two generations of exposure to 10, 100 and 1000mg/L of CeO2NPs. The numbers of seeds produced per silique were also reduced in the third generation plant by over 50% following the exposure to 100 and 1000mg/L of CeO2NPs. In addition, plants in the later generations generally contained higher concentrations of hydrogen peroxide (H2O2) in their tissues. Altogether, our results suggest that the second and third generation plants might have experienced higher oxidative stress than the first generation plants. This study provided first evidence that the impact of CeO2NPs varied across generations and long term evaluation extending several generations of plant growth is necessary to obtain a realistic understanding on the long term impact of engineered nanoparticles.

IMPACT OF SELENIUM FERTILIZATION ON GLUCOSINOLATE CONCENTRATION IN ARABIDOPSIS THALIANA AND RAPID CYCLING BRASSICA OLERACEA

Brassica vegetables are a significant source of glucosinolates (GSs), which are sulfur (S)-containing phytonutrients exhibiting, upon hydrolysis by endogenous myrosinase, antioxidant and anti-carcinogenic activity. Selenium (Se) is an essential micronutrient in mammalian health exhibiting antioxidant activity by inhibiting experimental carcinogenesis in animal models and reducing cancer incidence in human clinical trials. Selenium is readily accumulated in both Brassica species and Arabidopsis thaliana, a model species with similar S-metabolism. The research objectives for this project were to: 1) compare the impact of Se fertilization on GS concentrations between Arabidopsis thaliana and rapid cycling Brassica oleracea; and 2) determine the level of Se fertilization needed to optimize plant tissue Se concentration to maximize potential human health benefits. Both S and Se concentrations increased in A. thaliana and B. oleracea tissues in response to increasing Se treatments. Concentrations of glucoiberin, glucoraphanin, aliphatic, and total GS differed significantly between A. thaliana and B. oleracea. Data demonstrates that anti-carcinogenic GSs can be modified through changes in Se treatment concentrations, yet high levels of anti-carcinogenic GSs can be maintained while increasing Se concentration to 0.8 mg Se L-1. Thus, it is feasible to increase Se to beneficial dietary levels without compromising GS concentrations.

Companion Crops for Organic Alfalfa Establishment

In organic cropping systems, companion crops are used for establishment of forage legumes, but a comparison of alternative companion crops for alfalfa (Medicago sativa L.) has not been conducted. We determined the yield of spring‐seeded companion crops and their effect on alfalfa forage yield, weed yield, and net return in five environments. Crops were managed using organic practices. Barley (Hordeum vulgare L.) was among the highest yielding small grains, while annual ryegrass (Lolium multiflorium Lam.) was among the highest yielding forage companion crops. Companion crop effects on alfalfa yields were inconsistent among environments. In the establishment year, in two environments, alfalfa yields were similar for all establishment treatments. In three environments, rapid cycling brassica (Brassica rapa L.), annual ryegrass, and winter wheat (Triticum aestivum L.) companion crop treatments often resulted in alfalfa yields that were greater than those following field pea (Pisum sativum L.), flax (Linum usitatissimum L.), barley, oat (Avena sativa L.), and wheat. In the year following seeding, alfalfa yields in three environments were similar for all treatments, while in two environments, all treatments except field pea had yields equal to a weedy control. Spring‐seeded wheat, barley, and oat companion crops provided greater net returns than the control, field pea, flax, or forage (non‐vernalized winter wheat, annual ryegrass, and rapid‐cycling brassica) companion crop treatments. Small grain companion crops provide high and consistent net returns without adversely affecting alfalfa yields, and should be used for alfalfa establishment in organic crop production systems.

Regulated Changes in the Acetylation of α-Tubulin on Lys40during Growth and Organ Development in Fast Plants,Brassica rapaL.

Recently, we confirmed the widespread occurrence of α-tubulin acetylation on Lys(40) in angiosperms. In the present study, we found that α-tubulin acetylation is regulated in a growth stage- and organ development-dependent manner in the rapid cycling Brassica rapa, also known as Fast Plants. Organ distribution analysis showed that the proportion of acetylated α-tubulin is high in the cotyledons of young plants and in the true leaves and flowers of mature plants. A correlation between the increase in the levels of α-tubulin acetylation and the maturation of true leaves was observed. In the mature leaves, the acetylated α-tubulin showed an uneven distribution pattern, and the cells in the region of the leaf margins contained a high proportion of acetylated α-tubulin. These results indicate that α-tubulin acetylation is dynamically regulated in plant organs during development, and that it might play an important role in microtubule functioning throughout the angiosperm's life cycle.

Reaction of Lines of the Rapid Cycling Brassica Collection and Arabidopsis thaliana to Four Pathotypes of Plasmodiophora brassicae.

The clubroot reaction of five Rapid Cycling Brassica Collection (RCBC) lines (Brassica carinata, B. juncea, B. napus, B. oleracea, and B. rapa) and 84 lines of Arabidopsis thaliana to pathotypes 2, 3, 5, and 6 of Plasmodiophora brassicae (as classified on William's system) was assessed. Also, the reaction of the Arabidopsis lines to a single-spore isolate of each of pathotypes 3 and 6 was compared with that of a field isolate. Seedlings were inoculated with resting spores of P. brassicae, maintained at 25 and 20°C (day and night, respectively), and assessed for clubroot incidence and severity at 6 weeks after inoculation. Several lines of A. thaliana and RCBC exhibited a differential response to pathotype but none of the lines were immune. Among the RCBC lines, B. napus was resistant to all of the pathotypes; B. oleracea was resistant to pathotypes 2, 3, and 5; B. carinata and B. rapa were resistant to pathotypes 2 and 5; and B. juncea was susceptible to pathotypes 5 and 6 and had an intermediate response to pathotypes 2 and 3. Line Ct-1 of A. thaliana was highly resistant to pathotype 2, Pu2-23 was highly resistant to pathotype 5, and Ws-2 and Sorbo were highly resistant to pathotype 6. These results indicate that the lines of RCBC and A. thaliana have potential for use as model crops for a wide range of studies on clubroot, and could be used to differentiate these four pathotypes of P. brassicae. The reaction of the RCBC lines to pathotype 6 was highly correlated with response under field conditions but the reaction to the single-spore isolates of pathotypes 3 and 6 was not strongly correlated with reaction to the field collections in the Arabidopsis lines.