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1.
Low and high glucosinolate cultivars of oilseed rape were analysed for variation in both individual and total glucosinolate content up to 27 days after inoculation with turnip mosaic virus. Both infected and control plants of the two cultivars differed in the concentration of aliphatic, aromatic and indole glucosinolates. The biggest differences in glucosinolate content between the cultivars were found in the aliphatic and aromatic glucosinolate groups. Infected plants of the high glucosinolate cultivar, Solida, possessed lower amounts of glucosinolates, than did healthy control plants. Similar results were obtained with a low glucosinolate cultivar, S1. No significant difference was found between the two cultivars in resistance to turnip mosaic virus, using qualitative and quantitative ELISA to determine virus content in their tissues.  相似文献   

2.
Effects of pretreatment of Brassica napus leaves with ascospores of Leptosphaeria biglobosa or chemical defence activators [acibenzolar- S -methyl (ASM) or menadione sodium bisulphite (MSB)] on infection by ascospores of Leptosphaeria maculans (phoma stem canker) and development of disease were studied in controlled-environment (phoma leaf spot) and field (phoma leaf spot and stem canker) experiments. In controlled-environment experiments, pretreatment of oilseed rape leaves (cv. Madrigal) with L. biglobosa , ASM or MSB delayed the appearance of L. maculans phoma leaf spot lesions. These pretreatments also decreased the phoma leaf spot lesion area in both pretreated leaves (local effect) and untreated leaves (systemic effect). In winter oilseed rape field experiments in the 2002/03 and 2003/04 growing seasons, pretreatment with L. biglobosa or ASM in October/November decreased not only the number of phoma leaf spot lesions per leaf caused by L. maculans in autumn/winter, but also the severity of phoma stem canker in the subsequent spring/summer. Effects were greater in 2002/03 (when natural L. maculans ascospore release began in September 2002) than in 2003/04 (when ascospore release began in December following a period of dry weather in August/September 2003). These results suggest that pretreatment with biological or chemical defence activators can induce local and systemic resistance to L. maculans , with both short-term effects on the development of phoma leaf spotting and long-term effects on the development of stem canker 8 months later.  相似文献   

3.
Tests on samples of oilseed rape seed ( Brassica napus ) sown in the UK between 1981 and 1984 indicated that on average 25% of samples were infected with Alternaria brassicae and 61% with Leptosphaeria maculans , with maximum incidences of infection of 19 and 4.2% respectively. Much infection by Alternaria spp. occurred on vegetable and forage brassica seed produced in the UK between 1979 and 1983. In B. oleracea types A. brassicicola occurred most frequently, affecting 88% of samples and up to 55% of seeds. A. brassicae was detected in 44% of B. oleracea samples and in up to 13% of seeds. Little Alternaria infection occurred in swede or forage rape samples (B. napus ), but A. brassicae affected up to 8–5% of seeds in turnip samples ( B. campestris ). L. maculans occurred in 44% of samples of vegetable and forage brassica seed produced in the UK, with a maximum of 4–6% infected seeds. A. brassicicola was present in 73% of samples of imported B. oleracea seed, affecting up to 25.5% of seeds. A. brassicae was absent from these samples and little L. maculans was detected. Pathogenicity tests on isolates of L. maculans from infected seeds indicated that virulent pathotypes were present in 16 rape seed samples but in only one sample (swede) of vegetable or forage brassica seed. The high incidence of seed infection by these pathogens emphasizes the importance of applying fungicide treatments to all types of brassica seed.  相似文献   

4.
Quantitative resistance to Leptosphaeria maculans in Brassica napus was investigated in field and controlled environments using cultivars Darmor (with quantitative resistance) and Eurol (without quantitative resistance). In field experiments, numbers of phoma leaf spot lesions in autumn/winter and severity of stem canker the following summer were assessed in three growing seasons. There were no differences between Darmor and Eurol in number of leaf lesions in autumn/winter. However, stem cankers were less severe on Darmor than Eurol at harvest the following summer. In controlled-environment experiments, development of leaf lesions at different temperatures (5–25°C) and wetness durations (12–72 h) was investigated using ascospore inoculum; symptomless growth of L. maculans along leaf petioles towards the stem was quantified using quantitative PCR and visualized using GFP-expressing L. maculans ; growth of L. maculans within stem tissues was investigated using GFP-expressing L. maculans . There were more leaf lesions on Darmor than Eurol, although there was no difference between Darmor and Eurol in L. maculans incubation period. There were no differences between Darmor and Eurol in either distance grown by L. maculans along leaf petioles towards the stem or quantity of L. maculans DNA in leaf petioles, but L. maculans colonized stem tissues less extensively on Darmor than Eurol. It was concluded that quantitative resistance to L. maculans operates during colonization of B. napus stems by the pathogen.  相似文献   

5.
ABSTRACT Introgressions into Brassica napus from the B genome, either the B. nigra chromosome B4 or the B. juncea fragment carrying the Jlm1 gene, have given rise to the B. napus-B. nigra addition line (LA4+) and the B. napus-B. juncea recombinant line (MXS), respectively. The resistance of these two lines to Leptosphaeria maculans is characterized by a hypersensitive reaction (HR) on both the cotyledons and leaves, while the collar displays a high degree of resistance. Responses induced in cotyledons of the two lines by L. maculans inoculation were investigated with emphasis on cytological events underlying the HR and on host defense reactions. Features of host cell changes including condensation and lobing of nuclei, fragmentation of chromatin, disruption of the nuclear membranes, and plasma membrane withdrawal were reminiscent of HR cell death in MXS and LA4+ plants. Restriction of pathogen growth to the infection areas in LA4+ was correlated to reinforcement of cell wall barriers, including wall apposition, papillae, and vessel plugging. In MXS, the lower expression of resistance was associated with a delay in plant responses. These results indicate that mechanisms underlying the HR in the B. napus recombinant and addition lines are differently controlled according to the introgressed genes.  相似文献   

6.
The potential use of DNA-based methods for detecting airborne inoculum of Leptosphaeria maculans and Pyrenopeziza brassicae , both damaging pathogens of oilseed rape, was investigated. A method for purifying DNA from spores collected using Hirst-type spore samplers and detecting it using polymerase chain reaction (PCR) assays is described. For both pathogens, the sensitivities of the DNA assays were similar for spore-trap samples and pure spore suspensions. As few as 10 spores of L. maculans or P. brassicae could be detected by PCR and spores of both species could be detected against a background of spores of six other species. The method successfully detected spores of P. brassicae collected using spore traps in oilseed rape crops that were infected with P. brassicae. Leptosphaeria maculans spores were detected using spore traps on open ground close to L. maculans -infected oilseed rape stems. The potential use of PCR detection of airborne inoculum in forecasting the diseases caused by these pathogens is discussed.  相似文献   

7.
The influence of competitive effects between two isolates, of the number of infection sites on cotyledons and of host polygenic resistance on the systemic growth of Leptosphaeria maculans , the cause of phoma stem canker in oilseed rape ( Brassica napus ), were investigated. Controlled-condition experiments were conducted with two oilseed rape doubled haploid lines, one susceptible and the other with a high level of polygenic resistance, inoculated via wounded cotyledons with conidial suspensions obtained from two isolates. Expression of cankers in plants was enhanced by exposing inoculated plants to low temperature (6°C) followed by warm temperature (20°C). The fungus was detected by PCR amplifications of three minisatellite markers in all stems with visible canker symptoms and also in the stems of 14 of the 59 plants without visible cankers on the hypocotyls. Disease severity increased with the number of infection sites on cotyledons: in one of the three replicate experiments, the mean external necrosis length on the hypocotyl ranged from 6·47 to 35·3 mm for one and eight infections sites on cotyledons, respectively. The probability of an isolate reaching the hypocotyl from inoculated cotyledons decreased with increasing competing inoculum load on cotyledons: for instance, for isolate A290v it decreased from 1 when inoculated alone to 0·28 when coinoculated with six drops of competing isolate P27d. Polygenic resistance significantly reduced disease incidence and severity. For instance, in one of the three replicate experiments, disease incidence ranged from more than 74% in susceptible plants to 16% in resistant ones, while mean external necrosis length was up to 35·3 and 6·5 mm on susceptible and on resistant plants, respectively. This study offers new possibilities for assessing levels of polygenic resistance to stem canker in B. napus and studying the aggressiveness of L. maculans isolates.  相似文献   

8.
A total of 101 Brassica napus ssp. oleifera accessions with seed differing in glucosinolate and erucic acid contents were screened for resistance to four isolates of Peronospora parasitica at the cotyledon stage. Two groups of accessions with different resistance factors were identified. Lines that were homogeneous for resistance were selected from seedling populations of accessions that exhibited a heterogeneous reaction to some isolates. The resistance of one group differs from that of cv, Cresor, the only oilseed rape cultivar reported to have an isolate-specific gene for resistance to P. parasitica. The isolate specificity of the second group was identical to that of cv, Cresor, A comparison of the response of host accessions which expressed moderate to full susceptibility at the cotyledon stage, with no clear differential response to any of the four P. parasitica isolates, indicated that those with high glucosinolate and high erucic acid contents (12 accessions) were slightly but significantly less susceptible than those with high glucosinolate and low erucic acid (19 accessions), or low glucosinolate and low erucic acid contents (28 accessions). The mean differences between accessions with low erucic acid but differing in glucosinolate content were inconsistent. The last result was further confirmed by investigating the expression of resistance to three isolates of P. parasitica at three different seedling growth stages among 11 accessions of oilseed rape with seeds low in erucic acid but differing in glucosinolate content.  相似文献   

9.
Development of stem cankers in seedlings of Brassica napus var. oleifera inoculated with Leptosphaeria maculans was studied in growth cabinets. As the pathogen progressed from the petiole into the stem, hyphae invaded parenchyma cells for the first time, initiating a necrotrophic phase which resulted in the formation of a lesion. Ultimate containment of the pathogen was associated with a sequence of host reactions including lignification, cambium formation and callose deposition at the perimeter of the lesion. Two isolates of L. maculans differed in the pattern of stem infection. One was confined to the cortex and the other passed through the leaf gap into the pith. Variation in response between cultivars Rapora, Primor and Jet Neuf modified these two colonization patterns but did not eliminate the main differences. There were qualitative and quantitative differences in host cell reactions. The significance of these findings is discussed in relation to differences in resistance of the cultivars in the field.  相似文献   

10.
Field experiments in Europe have shown that Chinese cultivars of winter oilseed rape ( Brassica napus ) are very susceptible to the pathogen Leptosphaeria maculans (cause of phoma stem canker). Climatic and agronomic conditions in China are suitable for L. maculans since the closely related but less damaging pathogen L. biglobosa occurs on the winter and spring oilseed rape crops there. Major gene resistance to L. maculans is not durable; when introduced into commercial oilseed rape cultivars it is rapidly rendered ineffective by changes in the pathogen population. The threat to Chinese oilseed rape production from L. maculans is illustrated by the way in which L. maculans has spread into other areas of the world where previously only L. biglobosa was present, such as Canada and Poland. Models were developed to describe the spread (in space and time) of L. maculans across Alberta province, Canada, based on survey data collected over a 15-year period. These models were used to estimate the potential spread of L. maculans across the Yangtze river oilseed rape growing areas of China and its associated costs. Short-term strategies to prevent occurrence of severe phoma stem canker epidemics in China include training of extension workers to recognise symptoms of the disease and use of PCR-based diagnostics to detect the pathogen on imported seed. Long-term strategies include the introduction of durable resistance to L. maculans into Chinese oilseed rape cultivars as a component of an integrated disease management programme. The costs of such strategies in relation to costs of a phoma stem canker epidemic are discussed.  相似文献   

11.
In June/July 2001, 2002, 2003 and 2006, regional variation in distribution of the pathogens Leptosphaeria maculans and L. biglobosa that are causally associated with phoma stem canker was surveyed on winter oilseed rape crops in England. In 2001–2003, when isolates from basal cankers were visually identified as L. maculans or L. biglobosa based on cultural morphological characteristics, 70% were L. maculans and 30% L. biglobosa . In 2001, 2002, 2003 and 2006, when amounts of DNA of each species in basal cankers were determined by quantitative PCR, the abundance of L. maculans DNA was greater than that of L. biglobosa DNA in 77% of samples. When regional differences in amounts of L. maculans and L. biglobosa DNA were mapped geostatistically, quantities of L. maculans DNA were greater in cankers from southern England and those of L. biglobosa DNA were greater in northern England. A comparison with geostatistically mapped predictions made using a weather-based model describing stages in development of phoma stem canker epidemics suggested that these differences in Leptosphaeria populations may have been a consequence of differences in temperature after onset of leaf spotting between northern and southern England. Both PCR and morphological evidence suggested that the abundance of L. maculans in England has increased since the last surveys in the 1980s. Implications of these surveys for control of phoma stem canker are discussed.  相似文献   

12.
ABSTRACT Leptosphaeria maculans, the causal agent of stem canker of oilseed rape, develops gene-for-gene interactions with its hosts. To date, eight L. maculans avirulence (Avr) genes, AvrLm1 to AvrLm8, have been genetically characterized. An additional Avr gene, AvrLm9, that interacts with the resistance gene Rlm9, was genetically characterized here following in vitro crosses of the pathogen. A worldwide collection of 63 isolates, including the International Blackleg of Crucifers Network collection, was genotyped at these nine Avr loci. In a first step, isolates were classified into pathogenicity groups (PGs) using two published differential sets. This analysis revealed geographical disparities as regards the proportion of each PG. Genotyping of isolates at all Avr loci confirmed the disparities between continents, in terms of Avr allele frequencies, particularly for AvrLm2, AvrLm3, AvrLm7, AvrLm8, and AvrLm9, or in terms of race structure, diversity, and complexity. Twenty-six distinct races were identified in the collection. A larger number of races (n = 18) was found in Australia than in Europe (n = 8). Mean number of virulence alleles per isolate was also higher in Australia (5.11 virulence alleles) than in Europe (4.33) and Canada (3.46). Due to the diversity of populations of L. maculans evidenced here at the race level, a new, open terminology is proposed for L. maculans race designation, indicating all Avr loci for which the isolate is avirulent.  相似文献   

13.
Pretreatment of the first true leaves of oilseed rape plants ( Brassica napus cv. Bristol) with menadione sodium bisulphite (MSB) locally and systemically induced resistance, as shown by reduced lesion size and number, to infection by the fungal pathogen Leptosphaeria maculans , the causal agent of stem canker. Using a known systemic activator of salicylic acid-dependent PR-1 induction, acibenzolar- S -methyl (BTH; S -methylbenzo[1,2,3]thiadiazole-7-carbothiate) as a comparison, real-time PCR expression analysis of genes encoding a pathogenesis-related protein 1 ( PR-1 ) and an ascorbate peroxidase ( APX ) demonstrated a systemic enhancement of APX expression in MSB-pretreated plants, with no effect on PR-1 expression, suggesting augmented reactive oxygen species production in MSB-pretreated plants. The results demonstrate MSB to be an effective resistance activator in oilseed rape, and potentially useful for the control of stem canker.  相似文献   

14.
ABSTRACT The inheritance of resistance to Leptosphaeria maculans, the causal agent of black leg of crucifers, was studied in Brassica juncea. Three resistant accessions (UM3021, UM3043, and UM3323) and one susceptible accession (UM3132) of B. juncea were crossed in a complete diallel. Parents, F(1), and F(2) progenies were evaluated for all crosses using both cotyledon and stem inoculation. Cotyledon reaction was evaluated with two isolates of L. maculans, but stem reaction was evaluated with one isolate. Disease reactions observed for individual plants were the same for both inoculation methods and for both isolates of the pathogen for cotyledon reaction. No segregation was observed for the crosses between resistant accessions (UM3043 x UM3323 and UM3021 x UM3323), but a few susceptible plants were observed in the F(2) progeny of crosses between resistant parents (UM3021 x UM3043). This was probably due to heterozygosity in some parental plants of UM3021. For crosses be tween the susceptible parent and resistant parents, F(1) plants for two crosses were all resistant. For cross UM3132 x UM3021, some susceptible plants occurred, which was also suggestive of heterozygosity in UM3021. Although resistance in F(1) was dominant, for F(2) populations, segregation fit either 13:3, 3:1, or 1:3 ratios, indicating that resistance can be either adominant or recessive trait. F(3) families derived from some susceptible F(2) plants from crosses UM3021 x UM3132 and UM3043 x UM3132 were evaluated using the cotyledon inoculation method only. Segregation of F(2) plants and F(3) families in crosses involving resistant and susceptible parents indicated that the resistance to L. maculans in B. juncea is controlled by two nuclear genes with dominant recessive epistatic gene action.  相似文献   

15.
ABSTRACT Two types of genetic resistance to Leptosphaeria maculans usually are distinguished in Brassica napus: qualitative, total resistance expressed at the seedling stage and quantitative, partial resistance expressed at the adult plant stage. The latter is under the control of many genetic factors that have been mapped through quantitative trait loci (QTL) studies using 'Darmor' resistance. The former usually is ascribed to race-specific resistance controlled by single resistance to L. maculans (Rlm) genes. Three B. napus-originating specific Rlm genes (Rlm1, Rlm2, and Rlm4) previously were characterized. Here, we report on the genetic identification of two novel resistance genes, Rlm3 and Rlm7, corresponding to the avirulence genes AvrLm3 and AvrLm7. The identification of a novel L. maculans- B. napus specific interaction allowed the detection of another putative new specific resistance gene, Rlm9. The resistance genes were mapped in two genomic regions on LG10 and LG16 linkage groups. A cluster of five resistance genes (Rlm1, Rlm3, Rlm4, Rlm7, and Rlm9) was strongly suggested on LG10. The relation between all these specific resistance genes and their potential role in adult-plant field resistance is discussed. These two Rlm-carrying regions do not correspond to major QTL for Darmor quantitative resistance.  相似文献   

16.
In controlled environment experiments, ascospores of Leptosphaeria maculans (stem canker) infected oilseed rape (cv. Nickel) leaves and caused phoma leaf spots at temperatures from 8°C to 24°C and leaf wetness durations from 8 h to 72 h. The conditions that produced the greatest numbers of leaf spot lesions were a leaf wetness duration of 48 h at 20°C; numbers of lesions decreased with decreasing leaf wetness duration and increasing or decreasing temperature. At 20°C with 48 h of leaf wetness, it was estimated that one out of four spores infected leaves to cause a lesion whereas with 8 h of leaf wetness only one out of 300 spores caused a lesion. As temperature increased from 8°C to 20°C, the time from inoculation to the appearance of the first lesions (a measure of the incubation period) decreased from 15 to 5 days but leaf wetness duration affected the length of the incubation period only at sub-optimal temperatures. Analyses suggested that, within the optimal ranges, there was little effect of temperature or wetness duration on incubation period expressed as degree-days; the time until appearance of 50% of the lesions was ca. 145 degree-days. A linear regression of % leaves with lesions (Pl) (square-root transformed) on % plants with lesions (Pp) accounted for 93% of the variance: Pl=1.31+0.061Pp. This relationship was also investigated in winter oilseed rape field experiments in unsprayed plots from October to April in 1995/96 (cv. Envol), 1996/97 (cv. Envol), 1997/98 (cvs Bristol and Capitol) and 1998/99 (cvs Apex, Bristol and Capitol) seasons. The linear regression of % leaves with lesions (square-root transformed) on % plants with lesions accounted for 90% of the variance and had a similar slope to the controlled environment relationship: Pl=0.81+0.051Pp. These results were used to examine relationships between the development of phoma leaf spot on plants in winter oilseed rape crops, the incubation period of L. maculans and the occurrence of infection criteria (temperature, rainfall) in the autumns of 1996, 1997 and 1998.  相似文献   

17.
为研究稻瘟病菌Magnaporthe oryzae不同菌株间的相互作用,选择与单抗性基因系水稻IRBL5-M （携带抗性基因Pi5）表现为亲和性的菌株HN52与非亲和性的菌株HN119为研究对象,将其单独或混合接种到单抗性基因系水稻IRBL5-M中,并通过荧光显微镜观察接种后水稻叶鞘的发病情况及病斑面积,测定接种后水稻内相关抗性基因OsWRKY45、OsNPR1、OsPR10、OsMAPK2的表达量以及活性氧的变化。结果显示,相较于单独接种亲和性菌株,混合接种后单抗性基因系水稻IRBL5-M病斑发病面积减少;混合接种中亲和性菌株HN52菌丝侵染能力降低,侵染菌丝细胞间扩展率显著降低73.13%;同时单抗性基因系水稻IRBL5-M中OsWRKY45、OsNPR1、OsPR10和OsMAPK2抗性基因表达量显著增加,水稻叶片中活性氧含量增加,表明在菌株混合侵染过程中,非亲和性菌株可通过激发水稻的抗性反应来降低亲和性菌株对水稻的侵染程度。  相似文献   

18.
Pathogens and insects can elicit different sets of plant host responses, supporting the hypothesis for control by different signaling pathways. To evaluate the potential for signal interaction in plants attacked by pathogens and insects, the mRNA abundance for lipoxygenase (LOX), a wound-inducible proteinase inhibitor (PINII), and a pathogenesis-related protein (P4) was evaluated in tomato leaves following challenge with a variety of agents. PINII and P4 expression was determined as these proteins are induced in tomato leaves characteristically following attack by certain insects or pathogens, respectively. Expression studies of LOX, PINII, and P4 indicate that their induction in tomato does not follow a strict pattern based on the type of biologic inducer (insect vs. pathogen) or chemical treatment, with each specific treatment inducing a distinct pattern of gene expression. However, plants induced to express disease resistance with the synthetic salicylate mimic benzothiadiazole-7-carbothioic acid S-methyl ester were compromised in their expression of the wound- or jasmonate-activated PINII, consistent with an observed increase in susceptibility to insect herbivory reported in a companion study. The results do not support the hypothesis for a strict dichotomy of signaling by insects and pathogens of LOX, PINII and P4 in tomato, but point to a potential vulnerability of acquired resistance evident at the levels of gene expression and response to insect attack.  相似文献   

19.
ABSTRACT Leptosphaeria maculans, the causal agent of stem canker of oilseed rape (Brassica napus), develops gene-for-gene interactions with oilseed rape, and four L. maculans avirulence (AVR) genes (AvrLm1, AvrLm2, AvrLm4, and alm1) were previously genetically characterized. Based on the analysis of progeny of numerous in vitro crosses between L. maculans isolates showing either already characterized or new differential interactions, this work aims to provide an overview of the AVR genes that may specify incompatibility toward B. napus and the related species B. juncea and B. rapa. Two novel differential interactions were thus identified between L. maculans and B. napus genotypes, one of them corresponding to a complete resistance to European races of L. maculans. In both cases, a single gene control of avirulence was established (genes AvrLm3 and AvrLm7). Similarly, a single gene control of avirulence toward a B. rapa genotype, also resistant to European L. maculans isolates, was demonstrated (gene AvrLm8). Finally, a digenic control of avirulence toward B. juncea was established (genes AvrLm5 and AvrLm6). Linkage analyses demonstrated that at least four unlinked L. maculans genomic regions, including at least one AVR gene cluster (AvrLm1-AvrLm2-AvrLm6), are involved in host specificity. The AvrLm3-AvrLm4-AvrLm7 region may correspond either to a second AVR gene cluster or to a multiallelic AVR gene.  相似文献   

20.
The activity of key biochemical defense mechanisms in seedlings of winter oilseed rape cultivars, differing in tolerance to infection with Leptosphaeria maculans, was investigated. The studied winter oilseed rape cultivars differed in their biochemical defense potential. In the resistant cultivar, a significant increase in the activity of chitinase and β-1,3-glucanase was observed that can be regarded as a symptom of a systemic defense reaction. In addition, the resistant cultivar had a more efficient antioxidant system, that is, higher activity of specific SOD isoforms and higher level of low-molecular antioxidants. Only the resistant cultivar had three Fe-SOD sub-isoforms. A correlation between the content of cell wall-bound phenolics and hydrogen peroxide in the resistant cultivar may indicate that an important method of H2O2 neutralization was its participation in the process of phenolics incorporation into the cell wall. Elevated content of cell wall-bound phenolics significantly enhances the cell wall integrity, which then becomes a more effective firewall against L. maculans. Moreover, high utilization of soluble sugars during synthesis of the phenolic compounds in the pathogenesis was demonstrated in the resistant cultivar. We conclude that the key factors contributing to a greater tolerance to L. maculans were an effective antioxidant system and higher activity of PR proteins, i.e., chitinase and β-1,3-glucanase.  相似文献   

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