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1.
Sclerotinia stem rot (SSR) of oilseed rape (OSR, Brassica napus), caused by Sclerotinia sclerotiorum, is a serious problem in the UK and worldwide. As fungicide‐based control approaches are not always reliable, identifying host resistance is a desirable and sustainable approach to disease management. This research initially examined the aggressiveness of 18 Sclerotinia isolates (17 S. sclerotiorum, one S. subarctica) on cultivated representatives of B. rapa, B. oleracea and B. napus using a young plant test. Significant differences were observed between isolates and susceptibility of the brassica crop types, with B. rapa being the most susceptible. Sclerotinia sclerotiorum isolates from crop hosts were more aggressive than those from wild buttercup (Ranunculus acris). Sclerotinia sclerotiorum isolates P7 (pea) and DG4 (buttercup), identified as ‘aggressive’ and ‘weakly aggressive’, respectively, were used to screen 96 B. napus lines for SSR resistance in a young plant test. A subset of 20 lines was further evaluated using the same test and also in a stem inoculation test on flowering plants. A high level of SSR resistance was observed for five lines and, although there was some variability between tests, one winter OSR (line 3, Czech Republic) and one rape kale (line 83, UK) demonstrated consistent resistance. Additionally, one swede (line 69, Norway) showed an outstanding level of resistance in the stem test. Resistant lines also had fewer sclerotia forming in stems. New pre‐breeding material for the production of SSR resistant OSR cultivars relevant to conditions in the UK and Europe has therefore been identified.  相似文献   

2.
Sclerotinia trifoliorum, an important pathogen of cool season legumes, displays both homothallism and heterothallism in its life cycle, unique among members of the genus Sclerotinia. Very little is known about its genetic diversity and population structure. A sample of 129 isolates of S. trifoliorum from diseased chickpea in California was investigated for genetic diversity, population differentiation and reproductive mode. Genetic diversity was estimated using mycelial compatibility (MCG) phenotypes, rDNA intron variation, and allelic diversity at seven microsatellite loci. Genetic analysis revealed high levels of genotypic diversity demonstrated by high genotypic richness (0·88). Similarly, high levels of gene diversity (mean expected heterozygosity HE = 0·68) were observed at the microsatellite loci. Geographic populations of S. trifoliorum were highly admixed as evident from low FST values (0–0·11), suggesting high contemporary or historical gene flow. Hierarchical analysis of molecular variance showed that more than 92% of the genetic variation occurred among isolates within populations. Bayesian clustering analysis identified four cryptic genetic populations that were not correlated to geographic location, and index of multilocus association was non‐significant in each of the four genetic populations. However, the presence of identical haplotypes within and among populations indicates clonal reproduction. The high levels of haplotype diversity and population heterogeneity, a lack of correspondence between MCG and microsatellite haplotype, and low levels of population differentiation suggest that populations of S. trifoliorum in chickpea have been undergoing extensive outcrossing and migration events probably shaped by human‐mediated dissemination, the underlying diverse cropping systems, and chickpea disease management practices.  相似文献   

3.
The soilborne fungus Sclerotinia sclerotiorum infects many important crop plants. Central to the success of this pathogen is the production of sclerotia, which enables survival in soil and constitutes the primary inoculum. This study aimed to determine how crop plant type and S. sclerotiorum isolate impact sclerotial production and germination and hence inoculum potential. Three S. sclerotiorum isolates (L6, L17, L44) were used to inoculate plants of bean, carrot, lettuce, oilseed rape (OSR) and potato, and the number and weight of sclerotia per plant quantified. Carpogenic germination of sclerotia collected from different hosts was also assessed for L6. Production of sclerotia was dependent on both crop plant type and S. sclerotiorum isolate, with OSR and lettuce supporting the greatest number (42–122) and weight (1.6–3.0 g) of sclerotia per plant. The largest sclerotia were produced on OSR (33–66 mg). The three S. sclerotiorum isolates exhibited a consistent pattern of sclerotial production irrespective of crop type; L6 produced large numbers of small sclerotia while L44 produced smaller numbers of large sclerotia, with L17 intermediate between the two. Germination rate and percentage was greatest for larger sclerotia (4.0–6.7 mm) and also varied between host plants. Combining sclerotial production data and typical field crop densities suggested that infected carrot and OSR could produce the greatest number (3944 m?2) and weight (73 g m?2) of S. sclerotiorum sclerotia, respectively, suggesting these crops potentially contribute a greater increase in inoculum. This information, once further validated in field trials, could be used to inform future crop rotation decisions.  相似文献   

4.
F. Liu  M. Wang  J. Wen  B. Yi  J. Shen  C. Ma  J. Tu  T. Fu 《Plant pathology》2015,64(6):1407-1416
Sclerotinia stem rot (SSR) is a severe disease of oilseed rape, which severely impacts the crop productivity worldwide. Sclerotinia sclerotiorum causes SSR, resulting in the secretion of oxalic acid (OA), which can be further degraded to carbon dioxide (CO2) and hydrogen peroxide (H2O2) by oxalate oxidase (OXO). In the present investigation, the barley oxalate oxidase (BOXO, Y14203) gene was introduced into oilseed rape by Agrobacterium‐mediated transformation to investigate the mechanism by which OXO promotes resistance to S. sclerotiorum. Compared to the control 72 h post‐inoculation, there were c. 15–61% fewer lesions on leaves of the transgenic oilseed rape, which thus exhibited a detectable level of partial resistance in leaf tissue to S. sclerotiorum. Transgenic oilseed rape also showed decreased oxalate and increased hydrogen peroxide levels compared to the control, and the expression of defence response genes involved in the hydrogen peroxide signalling pathway was also induced. Therefore, the improved resistance of oilseed rape could be attributed to the enhanced OA metabolism, production of hydrogen peroxide and the hydrogen peroxide‐mediated defence levels during infection.  相似文献   

5.
Brassica crops are of global importance, with oilseed rape (Brassica napus) accounting for 13% of edible oil production. All Brassica species are susceptible to sclerotinia stem rot caused by Sclerotinia sclerotiorum, a generalist fungal pathogen causing disease in over 400 plant species. Generally, sources of plant resistance result in partial control of the pathogen although some studies have identified wild Brassica species that are highly resistant. The related pathogen S. subarctica has also been reported on Brassica but its aggressiveness in relation to S. sclerotiorum is unknown. In this study, detached leaf and petiole assays were used to identify new sources of resistance to S. sclerotiorum within a wild Brassica ‘C genome’ diversity set. High‐level resistance was observed in B. incana and B. cretica in petiole assays, whilst wild B. oleracea and B. incana lines were the most resistant in leaf assays. A B. bourgeai line showed both partial petiole and leaf resistance. Although there was no correlation between the two assays, resistance in the detached petiole assay was correlated with stem resistance in mature plants. When tested on commercial cultivars of B. napus, B. oleracea and B. rapa, selected isolates of S. subarctica exhibited aggressiveness comparable to S. sclerotiorum indicating it can be a significant pathogen of Brassica. This is the first study to identify B. cretica as a source of resistance to S. sclerotiorum and to report resistance in other wild Brassica species to a UK isolate, hence providing resources for breeding of resistant cultivars suitable for Europe.  相似文献   

6.
The success of the necrotrophic fungus Sclerotinia sclerotiorum is largely dependent on its major virulence factor, oxalic acid (OA). Virulence is lost in transgenic plants that express OA degrading enzymes, e.g. oxalate oxidase (OxO). The histopathology of S. sclerotiorum infection and OA accumulation was examined in a transgenic soybean line over‐expressing OxO (OxO‐OE) and its isogenic parent (WT). In situ flower inoculation showed that the OxO‐OE plants were highly resistant to the pathogen while the WT parents were susceptible. This difference in resistance was not apparent in the floral tissues, as aggressive hyphal activity was similar on both hosts, showing that high OxO activity and low OA accumulation in OxO‐OE was not a deterrent. However, the process of fungal infection on excised leaf tissue differed on the two hosts. Primary lesions developed and showed similar severe ultrastructural damage on both hosts but rapid lesion expansion (colonization) proceeded only on the WT, concomitant with OA accumulation. Oxalic acid rose in OxO‐OE 1 day post‐inoculation and did not change over the following 3 days, showing that colonization can be blocked by maintaining low levels of OA. However, OxO degradation of OA did not deter initial host penetration and primary lesion formation. This shows that OA, the major virulence factor of S. sclerotiorum, is critical for host colonization but may not be required during primary lesion formation, suggesting that other factors are contributing to the establishment of the primary lesion.  相似文献   

7.
Sclerotinia stem rot (SSR) caused by the phytopathogenic fungus Sclerotinia sclerotiorum is a major disease of oilseed rape (Brassica napus). During infection, large, white/grey lesions form on the stems of the host plant, perturbing seed development and decreasing yield. Due to its ability to produce long‐term storage structures called sclerotia, S. sclerotiorum inoculum can persist for long periods in the soil. Current SSR control relies heavily on cultural practices and fungicide treatments. Cultural control practices aim to reduce the number of sclerotia in the soil or create conditions that are unfavourable for disease development. These methods of control are under increased pressure in some regions, as rotations tighten and inoculum levels increase. Despite their ability to efficiently kill S. sclerotiorum, preventative fungicides remain an expensive gamble for SSR control, as their effectiveness is highly dependent on the ability to predict the establishment of microscopic infections in the crop. Failure to correctly time fungicide applications can result in a substantial cost to the grower. This review describes the scientific literature pertaining to current SSR control practices. Furthermore, it details recent advances in alternative SSR control methods including the generation of resistant varieties through genetic modification and traditional breeding, and biocontrol. The review concludes with a future directive for SSR control on oilseed rape.  相似文献   

8.
The plant‐pathogenic fungus Sclerotinia sclerotiorum has a broad host range and a worldwide distribution. Boscalid, an inhibitor of succinate dehydrogenase in the electron transport chain of fungi, is highly effective in controlling sclerotinia stem rot caused by S. sclerotiorum. The current study characterized the S. sclerotiorum boscalid‐resistant (BR) mutants obtained by fungicide induction. Among the bioactive fungicides against S. sclerotiorum, cross‐resistance was not detected between boscalid and dimethachlon, fluazinam or carbendazim; positive cross‐resistance was detected between boscalid and carboxin; and negative cross‐resistance was detected between boscalid and kresoxim‐methyl. Compared to their parental isolates, BR mutants had slower radial growth, no ability to produce sclerotia, lower virulence and oxalic acid content but higher mycelial respiration and succinate dehydrogenase (SDH) activity. Moreover, BR mutants had decreased sensitivity to salicylhydroxamic acid (SHAM) but not to oxidative stress. All the results indicated that the risk of resistance to boscalid in S. sclerotiorum is low to moderate. DNA sequence analysis showed that all of the BR mutants had the same point mutation A11V (GCA to GTA) in the iron sulphur protein subunit (SDHB). Interestingly, expression of the cytochrome b (cytb) gene was reduced to different degrees in the BR mutants, and this might be correlated with the negative cross‐resistance between boscalid and kresoxim‐methyl. Such information is vital in the design of resistance management strategies.  相似文献   

9.
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10.
White mould, caused by Sclerotinia sclerotiorum, is one of the most threatening fungal diseases occurring across major bean production regions worldwide. In Argentina, under favourable weather conditions, up to 100% seed yield losses occur on susceptible common bean cultivars. The aim of this study was to characterize the diversity of S. sclerotiorum isolates from six dry bean fields in the main production area of Argentina by means of molecular, morphological (mycelium colour, number and pattern of sclerotia distribution) and pathogenic approaches. Among 116 isolates analysed, high genotypic and morphological variability was observed. A total of 52 mycelial compatibility groups (MCGs) and 59 URPs (universal rice primers) molecular haplotypes were found. All the MCGs were location specific, while only 12% of the URP haplotypes were shared among locations. The molecular analysis of variance revealed a significant differentiation among populations, with higher genetic variability within the populations analysed than among them. The aggressiveness of the isolates towards bean seedlings was assessed in the greenhouse. Most of the isolates were highly aggressive, while no variation among locations was observed. The information generated in the present study provides, for the first time, information on the variability of S. sclerotiorum associated with white mould in the main common bean production area in Argentina. In addition, the findings suggest the occurrence of both clonal and sexual reproduction in the populations analysed. This work contributes to the development of sustainable management strategies in bean production aimed to minimize yield losses due to white mould.  相似文献   

11.
Ninety-six isolates of sunflower Sclerotinia sclerotiorum (Lib.) de Bary from Inner Mongolia (IM) in China, from Canada and the United Kingdom (UK) were sampled to investigate the genetic diversity and structure using Sequence-Related Amplified Polymorphism. A total of 123 polymorphic bands were obtained, ranging in size from 100 to 500 base pairs. The five populations of S. sclerotiorum isolated from the three countries showed various levels of genetic variability. The percentage of polymorphic loci varied from 30.89% in the UK population to 97.56% in the Middle IM population. The values of Shannon index (i) varied from 0.1876 in the UK population to 0.5301 in the West IM population. The heterozygosity of the five geographic populations obtained by estimating allele frequency varied from 12.91% in the UK population to 35.44% in the West IM population. The genetic identity, as indicated by the Nei unbiased identity index, ranged from 0.9744 between populations from Canada and East IM to 0.6477 between populations from West IM and UK. UPGMA cluster analysis using Nei’s genetic distance gave distances ranging from 0.0259 to 0.4343. The rates of gene flow among five geographic populations ranged from 1.5406 between West IM and UK populations to 18.4149 between West IM and Middle IM populations. The four populations from West IM, Middle IM, East IM and Canada were clustered into one subgroup in which the isolates from West and Middle IM belonged to one population, whereas those from East IM and Canada essentially were another population. The isolates from the UK formed a population that was significantly distinct from other populations.  相似文献   

12.
Environmental conditions in Sardinia (Tyrrhenian Islands) are conducive to fusarium root rot (FRR) and fusarium head blight (FHB). A monitoring survey on wheat was carried out from 2001 to 2013, investigating relations among these diseases and their causal agents. FHB was more frequently encountered in the most recent years while FRR was constantly present throughout the monitored period. By assessing the population composition of the causal agents as well as their genetic chemotypes and EF‐1α polymorphisms, the study examined whether the two diseases could be differentially associated to a species or a population. Fusarium culmorum chemotypes caused both diseases and were detected at different abundances (88% 3‐ADON, 12% NIV). Fusarium graminearum (15‐ADON genetic chemotype) appeared only recently (2013) and in few areas as the causal agent of FHB. In F. culmorum, two haplotypes were identified based on an SNP mutation located 34 bp after the first exon of the EF‐1α partial sequence (60% adenine, 40% thymine); the two populations did not segregate with the chemotype but the A‐haplotype was significantly associated with FRR in the Sardinian data set (P = 0·001), suggesting a possible fitness advantage of the A‐haplotype in the establishment of FRR that was neither dependent on the sampling location nor the sampling year. The SNP determining the Sardinian haplotype is distributed worldwide. The question whether the A‐haplotype segregates with characters facilitating FRR establishment will require further validation on a specifically sampled international data set.  相似文献   

13.
A recent study on fungal mating type genes revealed two MAT alleles within homothallic Sclerotinia sclerotiorum differentiated by an inversion, Inv? (inversion negative) and Inv+ (inversion positive). An analysis of mating type in closely related S. minor was conducted to shed light on the evolution of this MAT inversion. Inv? and Inv+ MAT alleles were identified in S. minor and were characterized. Both MAT alleles in S. minor were flanked by APN2 and SLA2, and consisted of two idiomorphs fused as in other homothallic ascomycetes. However, in the Inv+ MAT, the 3·6 kb MAT region was inverted relative to the Inv? MAT. Except for the inversion, both Inv? and Inv+ MAT in S. minor were equal in size and identical in nucleotide sequence. The MAT inversion in Inv+ S. minor was at exactly the same place as in Inv+ S. sclerotiorum and affected three of four MAT genes: MAT1‐1‐1 was truncated and MAT1‐2‐4 and MAT1‐2‐1 were inverted. Unlike S. sclerotiorum, expression of MAT genes did not differ between Inv? and Inv+ S. minor. The 250 bp inverted repeat motif that flanked the inverted MAT region in S. sclerotiorum and believed responsible for the MAT inversion was also found in S. minor, but was 256 bp. Depending on the MAT genes, 93–96% nucleotide identity was observed between Sclerotinia species. Both Inv+ and Inv? MAT S. minor and S. sclerotiorum isolates were commonly found in lettuce fields of Arizona along with MAT heterokaryons.  相似文献   

14.
Exserohilum turcicum is the causal agent of northern leaf blight, a devastating foliar disease of maize and sorghum. Specificity of E. turcicum to either maize or sorghum has been observed previously, but molecular evidence supporting host specialization is lacking. The aim of this study was to compare the genetic structure of E. turcicum isolates collected from adjacent maize and sorghum fields in Delmas and Greytown in South Africa. In addition, the mode of reproduction of this pathogen was investigated. Isolates from maize (N = 62) and sorghum (N = 64) were screened with 12 microsatellite markers as well as a multiplex mating type PCR assay. No shared haplotypes were observed between isolates from different hosts, although shared haplotypes were detected between isolates from maize from Delmas and Greytown. Population structure and principal coordinate analyses revealed genetic differentiation between E. turcicum isolates from maize and sorghum. Analysis of molecular variance indicated higher among‐population variation when comparing populations from different hosts, than comparing populations from different locations. Lack of shared haplotypes, high proportion of private alleles, greater among‐population variance between hosts than locations and significant pairwise population differentiation indicates genetic separation between isolates from maize and sorghum. The high haplotypic diversity in combination with unequal mating type ratios and significant linkage equilibrium indicates that both sexual and asexual reproduction contributes to the population genetic structure of E. turcicum in South Africa.  相似文献   

15.
The genetic structure of 276 Sclerotinia sclerotiorum isolates representing 37 field populations from four provinces in northern Iran were analysed with six polymorphic microsatellite loci. In total, 80 haplotypes were detected with 19 haplotypes (23.7%) shared amongst at least two regional populations. None of the haplotypes were shared among all four regional populations. Of the 80 haplotypes, 32 haplotypes (40%) occurred in low frequencies represented by only one isolate. Moderate levels of gene diversity (H = 0.51 to 0.61) and genotypic diversity (Ĝ = 12.0 to 22.0; clonal fraction = 0.39 to 0.67) for regional populations were observed. Genotypic diversities (Ĝ) did not differ significantly among populations. All regional populations were in linkage equilibrium indicating the occurrence of outcrossing. Low to moderate levels of population subdivision (0.03 to 0.07), were observed among regional populations. Only one large panmictic population was inferred by Structure, indicating no significant population structure. A Mantel test showed no significant isolation by distance (r = −0.43; P = 0.18), indicating anthropogenic movement of inoculum. The results demonstrated that S. sclerotiorum populations in northern Iran, are randomly mating and have a number of shared haplotypes among regional populations; this possibly represents recent founder populations and/or a high occurrence of anthropogenic migration of infected plant material among populations.  相似文献   

16.
Sclerotinia stem rot (Sclerotinia sclerotiorum) is a serious disease in oilseed Brassica crops worldwide. In this study, temperature adaptation in isolates of S. sclerotiorum collected from differing climatic zones is reported for the first time on any crop. Sclerotinia sclerotiorum isolates from oilseed rape (Brassica napus) crops in warmer northern agricultural regions of Western Australia (WW3, UWA 7S3) differed in their reaction to temperature from those from cooler southern regions (MBRS‐1, UWA 10S2) in virulence on Brassica carinata, growth on agar, and oxalic acid production. Increasing temperature from 22/18°C (day/night) to 28/24°C increased lesion diameter on cotyledons of B. carinataBC054113 more than tenfold for warmer region isolates, but did not affect lesion size for cooler region isolates. Mean lesion length averaged across two B. carinata genotypes (resistant and susceptible) fell from 4·6 to 2·4 mm for MBRS‐1 when temperature increased from 25/21°C to 28/24°C but rose for WW3 (2·35 and 3·21 mm, respectively). WW3, usually designated as low in virulence, caused as much disease on stems at 28/24°C as MBRS‐1, historically designated as highly virulent. Isolates collected from cooler areas grew better at low temperatures on agar. While all grew on potato dextrose agar between 5 and 30°C, with maximum growth at 20–25°C, growth was severely restricted above 32°C, and only UWA 7S3 grew at 35°C. Oxalate production increased as temperature increased from 10 to 25°C for isolates MBRS‐1, WW3 and UWA 7S3, but declined from a maximum level of 101 mg g?1 mycelium at 20°C to 24 mg g?1 mycelium at 25°C for UWA 10S2.  相似文献   

17.
Sclerotinia stem rot of spring oilseed rape (Brassica napus) is caused by Sclerotinia sclerotiorum. In Sweden, the disease leads to severe crop damage that varies from year to year. A real‐time PCR assay was developed and used to determine the incidence of S. sclerotiorum DNA on petals and leaves of spring oilseed rape as well as in air samples, with the aim of finding tools to improve precision in disease risk assessment. Five field experiments were conducted from 2008 to 2010 to detect and study pathogen development. Assessments of stem rot showed significant differences between experimental sites. The real‐time PCR assay proved fast and sensitive and the relationship between percentage of infected petals determined using a conventional agar test and the PCR assay was linear (R2 > 0·76). There were significant differences in S. sclerotiorum incidence at different stages of flowering. The incidence of S. sclerotiorum DNA on the leaves varied (0–100%), with significantly higher incidence on leaves at lower levels. In one field experiment, S. sclerotiorum DNA was not detected on petals during flowering, whereas the pathogen was detected on leaves, with a corresponding stem rot incidence of 7%. The amount of S. sclerotiorum DNA in sampled air revealed that spore release did not coincide with flowering on that experimental site. Thus, using a real‐time PCR assay to determine the incidence of S. sclerotiorum on oilseed rape leaves, rather than on petals, could potentially improve disease risk assessment.  相似文献   

18.
The soilborne fungi Sclerotinia sclerotiorum, Rhizoctonia solani and the oomycete Pythium ultimum are among the most destructive pathogens for lettuce production. The application of the biocontrol agent Paenibacillus alvei K165 to the transplant soil plug of lettuce resulted in reduced S. sclerotiorum, R. solani and P. ultimum foliar symptoms and incidence compared to untreated controls, despite the suppressive effect of the pathogens on the rhizosphere population of K165. In vitro, K165 inhibited the growth of S. sclerotiorum and R. solani but not P. ultimum. Furthermore, the expression of the pathogenesis‐related (PR) gene PR1, a marker gene of salicylic acid (SA)‐dependent plant defence, and of the Lipoxygenase (LOX) and Ethylene response factor 1 (ERF1) genes, markers of ethylene/jasmonate (ET/JA)‐dependent plant defence was recorded. K165‐treated plants challenged with P. ultimum showed up‐regulation of PR1, whereas challenge with R. solani resulted in up‐regulation of LOX and ERF1, and challenge with S. sclerotiorum resulted in up‐regulation of PR1, LOX and ERF1. This suggests that K165 triggers the SA‐ and the ET/JA‐mediated induced systemic resistance against P. ultimum and R. solani, respectively, while the simultaneous activation of the SA and ET/JA signalling pathways is proposed for S. sclerotiorum.  相似文献   

19.
Sclerotinia sclerotiorum is a necrotrophic fungus that causes a devastating disease called white mould, infecting more than 450 plant species worldwide. Control of this disease with fungicides is limited, so host plant resistance is the preferred alternative for disease management. However, due to the nature of the disease, breeding programmes have had limited success. A potential alternative to developing necrotrophic fungal resistance is the use of host‐induced gene silencing (HIGS) methods, which involves host expression of dsRNA‐generating constructs directed against genes in the pathogen. In this study, the target gene chosen was chitin synthase (chs), which commands the synthesis of chitin, the polysaccharide that is a crucial structural component of the cell walls of many fungi. Tobacco plants were transformed with an interfering intron‐containing hairpin RNA construct for silencing the fungal chs gene. Seventy‐two hours after inoculation, five transgenic lines showed a reduction in disease severity ranging from 55·5 to 86·7% compared with the non‐transgenic lines. The lesion area did not show extensive progress over this time (up to 120 h). Disease resistance and silencing of the fungal chs gene was positively correlated with the presence of detectable siRNA in the transgenic lines. It was demonstrated that expression of endogenous genes from the very aggressive necrotrophic fungus S. sclerotiorum could be prevented by host induced silencing. HIGS of the fungal chitin synthase gene can generate white mould‐tolerant plants. From a biotechnological perspective, these results open new prospects for the development of transgenic plants resistant to necrotrophic fungal pathogens.  相似文献   

20.
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