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1.
The fungus Leptosphaeria maculans causes blackleg (phoma stem canker), one of the most serious diseases of oilseed rape. The role of pycnidiospores produced during asexual reproduction is poorly documented and limits the understanding of the pathogen's population dynamics. The objectives of this study were to assess rain-splash dispersal of pycnidiospores of L. maculans from phoma leaf spots, and transmission of the disease from oilseed rape stubble carrying pycnidia. The work was conducted in still air with either a drop generator or a rain simulator. The impact of simulated incident drops on phoma leaf spots resulted in the dispersal of L. maculans pycnidiospores within splash droplets. Ninety per cent of the spores were collected within 14 cm of the source and a few were regularly observed up to 40 cm. Pycnidiospores produced on oilseed rape stubble and dispersed by simulated rain infected oilseed rape trap plants in a spatial pattern that matched the spatial dispersal of the pycnidiospores. In the field, rain-splash dispersal of pycnidiospores could increase the pathogen population and may enhance sexual reproduction by facilitating the mating of initially spatially separated isolates of opposite mating type.  相似文献   

2.
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   

3.
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   

4.
The distribution of the highly virulent and weakly virulent types ofLeptosphaeria maculans, causal agent of blackleg of oilseed rape, was studied in two fields in southern Ontario. Using a polymerase chain reaction-based assay with primers specific for these virulence types, plant tissues were directly examined for the occurrence of the pathogen. The highly virulent type was detected in leaf, stem and crown tissue at most of the sampling sites. The weakly virulent type was detected only in leaf lesions at 50% of the sites in field 1 and 30% of the sites in field 2. Of 96 leaf lesions examined, 48 contained the highly virulent type, 12 contained the weakly virulent type and 16 contained both the highly virulent and weakly virulent types.Sclerotinia sclerotiorum was isolated from all leaf lesion that did not react withL. maculans virulence type-specific primers. Coinfection of single blackleg leaf lesions by bothL. maculans virulence types thus occurred in oilseed rape plants in the field. Only the highly virulent type was detected in pseudothecia on stubble. Approximately 1% of the seed collected from these two fields containedL. maculans, and both the highly virulent and weakly virulent types were detected. The highly virulent type was more prevalent and non-specific in the kind of plant tissue it infected, whereas the weakly virulent type appeared to be limited to infecting leaves and seed. This study illustrates an application of polymerase chain reaction with virulence type-specific oligonucleotide primers to study the epidemiology of blackleg of oilseed rape.  相似文献   

5.
Blackleg disease (phoma stem canker) of Brassica napus (canola, oilseed rape) is caused by the fungus Leptosphaeria maculans . In some regions of Australia, resistance in oilseed rape cultivars derived from B. rapa subs . sylvestris (e.g. cv. Surpass 400) became ineffective within three years of commercial release. The genetic control of avirulence in L. maculans towards cv. Surpass 400 is described. When Australian field isolates were screened on this cultivar, three phenotypic classes were observed; virulent, intermediate and avirulent. Analysis of crosses between fungal isolates varying in their ability to infect cv. Surpass 400 demonstrated the presence of two unlinked avirulence genes, AvrLm1 and AvrLmS . Complementation of isolates (genotype avrLm1 ) with a functional copy of AvrLm1 , and genotyping of field isolates using a molecular marker for AvrLm1 showed that virulence towards Rlm1 is necessary, but not sufficient, for expression of a virulent phenotype on cv. Surpass 400. Taken together, these data strongly suggest that cv. Surpass 400, with ' sylvestris -derived' resistance, contains at least two resistance genes, one of which is Rlm1 .  相似文献   

6.
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   

7.
采用常规平板分离法, 从进境澳大利亚大麦中夹杂的油菜籽上获得1株疑似油菜茎基溃疡病菌的菌株01829?通过致病性测定?形态学观察?特异性引物扩增?ITS序列比对分析, 对01829进行了种类鉴定?结果表明:菌株01829在PDA培养基上生长较慢, 菌落边缘不整齐, 产生大量分生孢子器和分生孢子; 采用特异性引物对LMR1-D和Lmb分别进行PCR检测, 结果均有预期扩增片段产生; 基于ITS序列构建的系统发育树中, 菌株01829和GenBank中其他油菜茎基溃疡病菌相关序列聚在同一分支; 菌株01829接种油菜子叶和茎基部, 在子叶和茎基部接种部位分别引起叶斑和凹陷溃疡斑?根据上述试验结果, 将菌株01829鉴定为油菜茎基溃疡病菌, 这是我国口岸首次从进境澳大利亚大麦中截获油菜茎基溃疡病菌?  相似文献   

8.
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   

9.
Stem canker of crucifers is caused by an ascomycete species complex comprising of two main species, Leptosphaeria maculans and L. biglobosa. These are composed of at least seven distinct subclades based on biochemical data or on sequences of internal transcribed spacer (ITS), the mating type MAT1-2 or fragments of actin or beta-tubulin genes. In the course of a wide-scale characterization of the race structure of L. maculans from Western Australia, a few isolates from two locations failed to amplify specific sequences of L. maculans, i.e., the mating-type or minisatellite alleles. Based on both pathogenicity tests and ITS size, these isolates were classified as belonging to the L. biglobosa species. Parsimony and distance analyses performed on ITS, actin and beta-tubulin sequences revealed that these isolates formed a new L. biglobosa subclade, more related to the Canadian L. biglobosa 'canadensis' subclade than to the L. biglobosa 'australensis' isolates previously described in Australia (Victoria). They are termed here as L. biglobosa 'occiaustralensis'. These isolates were mainly recovered from resistant oilseed rape cultivars that included the Brassica rapa sp. sylvestris-derived resistance source, but not from the susceptible cv. Westar. The pathogenicity of L. biglobosa 'occiaustralensis' to cotyledons of most oilseed rape genotypes was higher than that of L. biglobosa 'canadensis' or L. biglobosa 'australensis' isolates.  相似文献   

10.
The survival of Leptosphaeria maculans , which causes phoma stem canker (blackleg), on oilseed rape residues ( Brassica napus ) in South Australia was investigated. Using a quantitative polymerase chain reaction (PCR) assay for L. maculans DNA, the pathogen was mainly detected in the upper 5 cm of the soil profile, including residues on the soil surface. As the size of organic matter particles in the soil decreased, so did the quantity of L. maculans detected in them. To obtain representative data for a field, at least 30 subsamples needed to be collected over the 0·81 ha area studied. In a survey of 49 commercial fields in South Australia, most L. maculans was detected in fields 1 year after oilseed rape had been grown, with less detected after 2 years and negligible amounts 3 years or more after cropping. The diagnostic DNA-based assay for L. maculans reduced the time and cost of studying L. maculans survival in soil and increased the sensitivity and accuracy of results compared with estimates of propagule number of colony-forming units on a semiselective medium.  相似文献   

11.
Phoma stem canker (blackleg), caused by Leptosphaeria maculans , is an important disease on oilseed rape (canola, rapeseed, Brassica napus , Brassica juncea , Brassica rapa ) causing seedling death, lodging or early senescence in Australia, Canada and Europe, but not in China. The two forms of L. maculans (A group and B group) that occur on oilseed rape are now considered to be separate species. The epidemiology and severity of phoma stem canker differs between continents due to differences in the pathogen population structure, oilseed rape species and cultivars grown, climate and agricultural practices. Epidemics are most severe in Australia, where only the A group occurs, and can be damaging in Canada and western Europe, where both A and B groups occur, although their proportions vary within regions and throughout the year. Epidemics are slight in China, where the A group has not been found. Dry climates (Australia, western Canada) lengthen the persistence of infected debris and may synchronize the release of airborne ascospores (after rain) with seedling emergence. L. maculans spreads from cotyledon and leaf infections down petioles to reach the stem, with infections on cotyledons and leaves early in the season producing the most damaging stem cankers at the stem base (crown). Development of both crown cankers and phoma stem lesions higher up stems is most rapid in regions with high temperatures from flowering to harvest, such as Australia and Canada. Breeding for resistance (genetic, disease escape or tolerance), stubble management, crop rotation and fungicide seed treatments are important strategies for control of phoma stem canker in all areas. Fungicide spray treatments are justified only in regions such as western Europe where high yields are obtained, and accurate forecasts of epidemic severity are needed to optimize their use.  相似文献   

12.
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   

13.
Virulent and non-virulent pathotypes of Leptosphaeria maculans were differentiated on the basis of cultural characteristics and virulence to cabbage plants. Surveys of isolates obtained from oilseed rape crops grown in England in 1982 and 1983 showed that virulent pathotypes predominated in some areas whereas in others they were infrequent or absent. Overall 41% of isolates from this crop were of the virulent type. Virulent types usually occurred most frequently in areas with a long history or a high density of oilseed rape. In vegetable and forage brassica seed crops in Essex virulent isolates formed a small proportion of the population, except in one swede crop from which 95% of isolates were virulent. Host specificity was not detected in cross-infection experiments using isolates from different hosts and localities.  相似文献   

14.
The A and B groups (aggressive and non-aggressive) of Leptosphaeria maculans were compared in studies of host range, infection phenotypes and epidemiology. Isolates of both groups infected a wide range of cruciferous hosts including Brassica napus, B. rapa, B. oleracea, B. juncea, B. carinata. B. nigra, Thlaspi arvense and Raphanus sativus. On cotyledons, B-group isolates were generally more aggressive than A-group isolates, causing local lesions and subsequent systemic invasion of the majority of test species. On susceptible stems, A-group isolates caused cortical lesions; B-group isolates, if they reached the stem, usually caused pith lesions with no external symptoms. In a susceptible line of B. napus , CrGC5, systemic infections of the leaf and petiole were similar with both groups, but the B-group rarely entered the stem to form cortical lesions or cankers. At two different field locations, natural epidemics caused by the two groups on oilseed rape leaves were similar in overall pattern, B-group lesions occurred slightly later but the incidence increased more rapidly and reached a maximum slightly earlier than that of the A group. The two groups differed markedly in stem infection patterns. Infection of the cortex near the base of the stem and the development of a typical stem canker was caused entirely by the A group. However the B group often caused considerable damage to the pith. Superficial chlorotic lesions on stems and inflorescences were mainly attributable to the B group. In view of the stem pith infection by the B group without external symptoms, its importance on oilseed rape may have been underestimated previously.  相似文献   

15.
Williams  & Fitt 《Plant pathology》1999,48(2):161-175
Stem canker or blackleg of brassicas, caused by Leptosphaeria maculans , is one of the most damaging diseases of winter oilseed rape in the UK. Airborne ascospores, released in autumn and winter, initiate leaf infections which may lead to colonization of the petiole and, later in the season, formation of stem lesions and cankers. Although isolates of the pathogen differ in ability to cause damaging stem cankers, this is not readily apparent from leaf spotting or stem lesion symptoms. However, several cultural, biochemical and genetic characteristics appear to be associated with the ability to form damaging stem cankers and isolates can be assigned to one of two groups, termed A and B, on the basis of differences in these characteristics. To investigate the relationship between leaf spotting symptoms and subsequent stem canker formation, and to improve understanding of the epidemiology of this pathogen, it is desirable to differentiate between the stem canker forming A group and the less damaging B group of L. maculans . Characterization of isolate type is also important in seed testing and crop breeding programs, particularly in countries such as Canada and Poland where the A type is not ubiquitous. This article reviews methods, including plant assays, assessments of growth characteristics in vitro , isozyme analyses, secondary metabolite profiling, serology, and nucleic acid analyses, that can be used to differentiate the A and B groups.  相似文献   

16.
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   

17.
In controlled environment experiments to study early development of light leaf spot, lesions developed with leaf wetness durations of 16 to 48 h after inoculation of oilseed rape with conidial suspensions of Pyrenopeziza brassicae at 12 or 18°C, but not with leaf wetness durations of 0 to 13h. The incubation period was 21 to 22 days at 12°C and 14 to 18 days at 18°C for leaf wetness durations of 16 to 48 h. The latent period was 21 to 23 days at 12°C and 18 to 19 days at 18°C, and the total number of lesions increased with increasing leaf wetness duration at both temperatures. In field experiments, light leaf spot always developed on oilseed rape with a leaf wetness duration of 48 h after inoculation in both 1990/1991 and 1991/1992, but the percentage leaf area affected was less on plants placed in an oilseed rape crop than on those placed in a glasshouse. Plants moved to an oilseed rape crop immediately after inoculation nearly always developed light leaf spot symptoms when they were inoculated between 19 October 1990 and 1 March 1991 or between 27 September 1991 and 14 February 1992, but plants inoculated between 31 August and 16 October 1990 or on 20 September 1991, when estimated leaf wetness duration was less than 16 h for several days after they were placed in crops, did not develop symptoms. The latent period of light leaf spot on plants transferred to the oilseed rape crop was 15 to 40 days, and there was an approximately linear relationship between 1 (latent period) and mean temperature during this period. The accumulated temperature during the latent period ranged from c. 150 to 250 day-degrees. The severity of lesions on these plants increased with increasing temperature from 5 to 15°C.  相似文献   

18.
Seedlings of 13 cultivars of oilseed rape ( Brassica napus ) were inoculated with 10 isolates of Leptosphaeria maculans. Three virulent isolates were identified which gave a resistant reaction on some cultivars normally considered susceptible. Further experiments to compare these with standard isolates confirmed the existence of a differential host-pathogen interaction. The breeding line 78/271, plus the cultivars Quinta, Garant, Norli and possibly Elvira differentiated the isolates tested while Jet Neuf, Rafal, Primor, Doral, Hercules, Rapora, Liraglu and Erra did not. The relevance of these findings to breeding for canker resistance in oilseed rape is discussed.  相似文献   

19.
油菜黑胫病菌和茎基溃疡病菌的LAMP检测方法的建立   总被引：1，自引：0，他引：1  
油菜黑胫病和油菜茎基溃疡病分别由子囊菌Leptosphaeria biglobosa和L.maculans引起.我国油菜产区仅发现L.biglobosa,未发现L.maculans.因而,L.maculans是我国的对外检疫性对象.这两种真菌形态相似,引起的病害症状相似,给田间快速准确鉴定带来难度.本研究基于环介导等温...  相似文献   

20.
The hypothesis that enhancing the level of glucosinolates in leaves of oilseed rape would increase resistance to two fungal pathogens was tested. Thirty-three Brassica napus lines with variable leaf glucosinolate contents were assessed for susceptibility to infection by Leptosphaeria maculans and Alternaria spp. under field conditions. The data clearly showed that there was not a simple positive relation between glucosinolate content and resistance, and that the hypothesis can be refuted. The level of Alternaria infection of both leaves and pods was positively correlated with glucosinolate content, while for L. maculans there was no significant relationship between the two variables. It is suggested that these pathogens have become specialists on glucosinolate-containing taxa in an analogous way to insect herbivores.  相似文献   

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