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1.
A new pathogen of pyrethrum (Tanacetum cinerariifolium) causing anthracnose was described as Colletotrichum tanaceti based on morphological characteristics and a four‐gene phylogeny consisting of rDNA‐ITS, β‐tubulin (TUB2), glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH) and actin (ACT) gene sequences. The fungus produced perithecia in culture, requiring an opposite mating type isolate in a heterothallic manner. The initial infection strategy on pyrethrum leaves involved the formation of appressoria followed by production of multilobed infection vesicles in the epidermal cells. Infection and colonization then proceeded through thinner secondary hyphae, which resulted in the initial production of water‐soaked lesions followed by black necrotic lesions. The infection process was suggestive of a hemibiotrophic infection strategy. Moreover, phylogenetic analysis clearly showed that C. destructivum, C. higginsianum and C. panacicola were separate species that also had similar intracellular hemibiotrophic infection strategies as C. tanaceti, which all clustered in the C. destructivum complex. Colletotrichum spp. were detected at 1% incidence in seed of 1 of 19 seed lines, indicating the potential for seed as a source of inoculum into crops. Colletotrichum tanaceti was detected in leaf lesions from 11 of 24 pyrethrum fields surveyed between April and July 2012, at a frequency of 1·3–25·0% of lesions. Anthracnose probably contributes to the complex of foliar diseases reducing green leaf area in pyrethrum fields in Australia.  相似文献   

2.
The isolation frequency of Microsphaeropsis sp. in spring in association with necrotic lesions on leaves in Tasmanian pyrethrum (Tanacetum cinerariifolium) fields has increased substantially since first identification in 2001. Examination of morphological features and sequencing of the internal transcribed spacer region (ITS) resulted in the identification of a new species, herein described as Microsphaeropsis tanaceti sp. nov. The pathogenicity of three M. tanaceti isolates to two pyrethrum cultivars was confirmed by inoculating glasshouse‐grown plants in three experiments. No significant differences in the susceptibility of the two cultivars to infection by M. tanaceti were found. Symptoms were tan‐coloured spots which coalesced around the margins of the leaves. Therefore, the name ‘tan spot’ is proposed for this new disease of pyrethrum. The sensitivity of seven M. tanaceti isolates to difenoconazole and azoxystrobin, commonly used fungicides for the management of foliar diseases in spring, was assessed under in vitro conditions. Sensitivity testing for difenoconazole was conducted using a mycelial growth assay on potato dextrose agar, whilst testing for sensitivity to azoxystrobin used a conidial germination assay on water agar. Microsphaeropsis tanaceti was found to be more sensitive to azoxystrobin than difenoconazole, with complete inhibition of conidial germination at concentrations above 0·625 µg a.i. mL?1. By comparison, concentrations of 50 µg a.i. difenoconazole mL?1 or greater were required for significant inhibition of mycelial growth. It therefore appears likely that there is currently some control of tan spot as a result of the use of azoxystrobin and to a lesser extent, difenoconazole, for the control of other diseases.  相似文献   

3.
Two new pathogens of pyrethrum, described as Paraphoma chlamydocopiosa and Paraphoma pye, isolated from necrotic leaf lesions on pyrethrum plants in northern Tasmania, Australia, were identified using morphological characters, phylogenetic analysis of the internal transcribed spacer (ITS), elongation factor 1‐α (EF1‐α) and β‐tubulin (TUB) genes, and pathogenicity bioassays. Bootstrap support in the combined and individual gene region phylogenetic trees supported the two species that were significantly different from the closely related P. chrysanthemicola and P. vinacea. Morphological characteristics also supported the two new species, with conidia of P. chlamydocopiosa being considerably longer and wider than either P. chrysanthemicola or P. vinacea, and P. pye being distinct in forming bilocular pycnidia. Glasshouse pathogenicity tests based on root dip inoculation resulted in P. chlamydocopiosa and P. pye infecting the crown and upper root tissues of pyrethrum plants, and significant reduction in biomass 2 months after inoculation. Both of these Paraphoma species caused leaf lesions during in vitro and in vivo bioassays 2 weeks after foliar spray inoculation. Although P. chlamydocopiosa and P. pye were shown to be crown rot pathogens, they were also commonly isolated from leaves of diseased plants in pyrethrum fields of northern Tasmania.  相似文献   

4.
Ray blight disease of pyrethrum (Tanacetum cinerariifolium) is caused by Stagonosporopsis tanaceti, with infected seed being a major means of transmission of this fungal pathogen. The infection process of S. tanaceti in pyrethrum seed and seedlings was determined. Infection hyphae only infected the outer and inner layers of the seed coat and not the embryo of naturally infected pyrethrum seed. During the process of germination of infected seed, S. tanaceti from the seed coat infected the developing embryo and cotyledon, resulting in pre‐ and post‐emergence death, depending on the level of infection in the seed coat. Pre‐emergence death occurred due to disintegration of the infected embryo, which was replaced by hyphae and extracellular anthocyanin‐like material (EAM) at 7 days after incubation (dai). Post‐emergence death occurred after both epidermal and cortical tissues of infected cotyledons at the crown/hypocotyl region disintegrated due to colonization by hyphae. Moreover, most of the tissues of the vascular bundles and cortical tissues contained heavy depositions of EAM at 10–14 dai. In 6‐week‐old infected seedlings, hyphae were confined to the epidermis and the cortical tissues at the crown/hypocotyl regions; the vascular bundles of both infected and uninfected regions, and cortical tissues of the uninfected regions of the seedlings were completely free from infection hyphae and EAM. These findings provide a better understanding of the early stages of the disease cycle of S. tanaceti and will lead to improved control measures for seedborne infection using seed treatments.  相似文献   

5.
Ray blight caused by Stagonosporopsis tanaceti is one of the most important diseases of pyrethrum (Tanacetum cinerariifolium), a perennial herbaceous plant cultivated for the extraction of insecticidal pyrethrins in Australia. The disease is responsible for complete yield loss in severe outbreaks. Infected seed is considered as the principal source of S. tanaceti. Infection hyphae remain only in the seed coat and not in the embryo, resulting in pre- and post-emergence death of seedlings and latent infection. Therefore, quantification of the level of infection by S. tanaceti within seed using a qPCR assay is important for efficient management of the disease. Stagonosporopsis tanaceti completes its life cycle within 12 days after leaf infection through production of pycnidia and can infect every tissue of the pyrethrum plant except the vascular and root tissues. Ray blight epidemics occur in pyrethrum fields through splash dispersal of pycnidiospores between adjacent plants. Besides steam sterilization, thiabendazole/thiram and fludioxonil are effective seed-treating chemicals in controlling S. tanaceti before planting begins. Ray blight is currently managed in the field through the foliar application of strobilurin fungicides in the first 1–2 years of crop establishment. Later on, difenoconazole and multisite specific fungicides in the next 2–3 years during early spring successfully reduce ray blight infestation. Avoiding development of resistance to fungicides will require more sustainable management of ray blight including the development and deployment of resistant cultivars.  相似文献   

6.
Pyrethrum seed has an important role in the transmission of Stagonosporopsis tanaceti, the cause of ray blight disease of pyrethrum. A TaqMan probe based polymerase chain reaction (PCR) assay was developed to quantify the level of S. tanaceti inocula in pyrethrum seed and seedlings. Primer pair (St_qF3, St_qR2) was designed based on the intergenic spacer (IGS) region of S. tanaceti, which produced a 125 bp amplicon specific to S. tanaceti. TaqMan PCR assay using St_qF3, St_qR2 and a probe St_qP was highly specific against the genomic DNA of S. tanaceti, but did not amplify DNA of 14 related Stagonosporopsis species or other foliar pathogens of pyrethrum. The sensitivity limit of this assay was measured using the cycle threshold (Ct) value which ranged from 17.59 for 10 nanograms (ng) to 36.34 for 100 femtograms (fg) genomic DNA of S. tanaceti. There was a significant negative correlation (r = ?0.999, P < 0.001) between the Ct value and the percent of S. tanaceti infected seed. In addition, this TaqMan PCR assay detected latent infection within seedlings. This assay could be applied to test commercial seed and seedlings before deciding on the appropriate management practices.  相似文献   

7.
Leaf blotch and fruit spot of apple caused by Alternaria species occur in apple orchards in Australia. However, there is no information on the identity of the pathogens and whether one or more Alternaria species cause both diseases in Australia. Using DNA sequencing and morphological and cultural characteristics of 51 isolates obtained from apple leaves and fruit with symptoms in Australia, Alternaria species groups associated with leaf blotch and fruit spot of apples were identified. Sequences of Alternaria allergen a1 and endopolygalacturonase gene regions revealed that multiple Alternaria species groups are associated with both diseases. Phylogenetic analysis of concatenated sequences of the two genes resulted in four clades representing A. arborescens and A. arborescens‐like isolates in clade 1, A. tenuissima/A. mali isolates in clade 2, A. alternata/A. tenuissima intermediate isolates in clade 3 and A. longipes and A. longipes‐like isolates in clade 4. The clades formed using sequence information were supported by colony characteristics and sporulation patterns. The source of the isolates in each clade included both the leaf blotch variant and the fruit spot variant of the disease. Alternaria arborescens‐like isolates were the most prevalent (47%) and occurred in all six states of Australia, while A. alternata/A. tenuissima intermediate isolates (14%) and A. tenuissima/A. mali isolates (6%) occurred mostly in Queensland and New South Wales, respectively. Implications of multiple Alternaria species groups on apples in Australia are discussed.  相似文献   

8.
Rust fungi in the genus Melampsora usually cause disease on hosts in the Salicaceae. Identification of Melampsora species is often complicated due to few differences in spore morphology and little publicly available comparative sequence data. Weeping willow trees (primarily Salix babylonica and its hybrids) have been reported to be infected by 11 Melampsora species; however, most of these records are based on morphological characterization. New collections of rust fungi on weeping willows from the central USA were analysed using a combination of morphology, ITS and LSU rDNA sequencing, and host data to determine that they represent an undescribed rust fungus, Melampsora ferrinii sp. nov. Additional studies of herbarium material revealed that M. ferrinii has occasionally been collected but identified as M. epitea. In addition to North America, M. ferrinii is also present in South America and has been infecting weeping willows there since at least the 1990s.  相似文献   

9.
Phyllosticta citricarpa (teleomorph Guignardia citricarpa) is the causal agent of citrus black spot, a disease causing lesions on fruits and leaves of different Citrus species in Asia, Australia, South Africa and South America. It is a quarantine organism in the European Union and the USA and hence a reliable differentiation between this species and other Phyllosticta species found on Citrus is essential. A differentiation based on morphology is often problematic, hence a range of molecular tests have been developed to distinguish P. citricarpa from other species present on citrus fruits, especially the endophyte Phyllosticta capitalensis (teleomorph Guignardia mangiferae). However, these tests cannot distinguish P. citricarpa from the closely related Phyllosticta citriasiana, the causal agent of tan spot disease. In this study, a real‐time PCR was designed which is specific for P. citricarpa and does not amplify P. citriasiana or P. capitalensis DNA.  相似文献   

10.
Tomato bacterial spot is caused by Xanthomonas euvesicatoria, X. vesicatoria, X. perforans and X. gardneri. In order to determine the distribution, frequency of occurrence, and diversity of these species in the Brazilian commercial tomato fields, a survey was conducted between 2009 and 2012. In this period, 204 strains were obtained from 33 counties (22 with processing tomatoes and 11 with fresh‐market tomatoes). Pathogenicity tests, BOX‐PCR, PCR with species‐specific primers, and sequence analysis of the avirulence gene avrXv3 were performed in order to identify the strains at species and race level. Xanthomonas perforans predominated among the strains (92%) and was present in most counties. In addition, this species was prevalent in most areas of both fresh‐market tomatoes (63.6% of counties surveyed) and processing tomatoes (95.4% of counties surveyed). Fifteen strains (7.5%) were identified as X. gardneri, which was found mostly in fresh‐market fields located at regions with altitude higher than 900 m, and only one strain of X. euvesicatoria (0.5%) was found in a processing tomato field. High genetic diversity was observed within X. perforans, with 137 BOX‐PCR haplotypes. Race T3 prevailed (97.5%), but reported here for the first time is the occurrence of five strains identified as race T4 in fresh‐market fields in the state of São Paulo. The race T4 phenotype of these strains resulted from the presence of an 859 bp insertion in the avirulence gene avrXv3. This insertion is related to amino acid sequences of a transposase found in X. gardneri, and to amino acid sequences of X. campestris.  相似文献   

11.
The fungal genus Alternaria comprises a large number of asexual taxa with diverse ecological, morphological and biological modes ranging from saprophytes to plant pathogens. Understanding the speciation processes affecting asexual fungi is important for estimating biological diversity, which in turn affects plant disease management and quarantine enforcement. This study included 106 isolates of Alternaria representing five phylogenetically defined clades in two sister sub‐generic groups: section Porri (A. dauci, A. solani and A. limicola) and section Alternaria (A. alternata/tenuissima and A. arborescens). Species in section Porri are host‐specific while species in section Alternaria have wider host ranges. For each isolate, DNA sequences of three genes (Alt a1, ATPase, Calmodulin) were used to estimate phylogenies at the population and species levels. Three multilocus haplotypes were distinguished among A. dauci isolates and only one haplotype among A. solani and A. limicola isolates, revealing low or no differentiation within each taxon and strong clonal structure for taxa in this section. In contrast, 37 multilocus haplotypes were found among A. alternata/tenuissima isolates and 21 multilocus haplotypes among A. arborescens isolates, revealing much higher genotypic diversity and multiple clonal lineages within taxa, which is not typical of asexual reproducing lineages. A species tree was inferred using a Yule Speciation model and a strict molecular clock assumption. Species boundaries were well defined within section Porri. However, species boundaries within section Alternaria were only partially resolved with no well‐defined species boundaries, possibly due to incomplete lineage sorting. Significant association with host specificity seems a driving force for speciation.  相似文献   

12.
Recent disease surveys in the Western Cape province of South Africa have revealed a previously unknown and serious stem canker disease on native Rapanea melanophloeos (Myrsinaceae, Ericales) trees. Cankers commonly result in the death of branches or entire stems. Fruiting structures typical of fungi in the Cryphonectriaceae were observed on the surfaces of cankers. In this study, the fungus was identified and its pathogenicity to R. melanophloeos was tested. Multigene phylogenetic analyses based on DNA sequences of the partial LSU gene, ITS region of the nuclear ribosomal DNA gene and two regions of the β‐tubulin (BT) gene, showed that the fungus represents a formerly undescribed genus and species in the Cryphonectriaceae. The fungus was also morphologically distinct from other genera in this family. Inoculation trials showed that the fungus described here as Immersiporthe knoxdaviesiana gen. et sp. nov. is an aggressive pathogen of R. melanophloeos trees.  相似文献   

13.
Cucurbit powdery mildew caused by Golovinomyces orontii is a serious disease that affects cucurbit crops in temperate areas. In northern Italy, the species is responsible for the early infections at the beginning of the growing season. However, chasmothecia have never been recorded in Italy and the impact of either asexual or sexual reproduction of G. orontii remains to be determined. To investigate and compare the genetic structure of Italian populations with those from the Czech Republic, where chasmothecia are sporadically recorded, seven housekeeping gene fragments (tef‐1α, csI, ITS, H3, tub2, IGS and mtLSU) were amplified and used in a multilocus sequence typing (MLST) approach. The four‐gamete test was performed to detect recombination between and within populations. Phylogeny was inferred using both Bayesian and minimum evolution analyses. Results from MLST revealed the presence of 141 single nucleotide polymorphisms and the existence of 13 different haplotypes. Phylogenetic analysis revealed the existence of two main distinct phylogenetic groups that were also highly genetically different, confirming that G. orontii is a species complex. Recombination was detected within both the phylogenetic groups and the geographical populations, indicating that sexual reproduction could have occurred. However, considering the lower haplotype diversity and the high frequency of ST3 (17 isolates) and ST7 (eight isolates) haplotypes, the Italian population could be predominantly clonal, while sexual reproduction may occasionally occur due to the introduction of genotypes similar to those from the Czech Republic.  相似文献   

14.
Leaf blotch is a globally important disease of barley crops and other grasses that is caused by at least five host‐specialized species in the fungal genus Rhynchosporium. The pathogen R. commune (specialized to barley, brome‐grass and Italian ryegrass) has long been considered to reproduce only by asexual means, but there has been accumulating evidence for recombination and gene flow from population genetic studies and the detection of complementary MAT1‐1 and MAT1‐2 isolates in a c. 1:1 ratio in the field. Here, it is demonstrated that 28 isolates of the closely related species R. agropyri (on couch‐grass) and R. secalis (on rye and triticale), collected from Europe, were also either of MAT1‐1 or MAT1‐2 genotype and that the distribution of mating types did not deviate significantly from a 1:1 ratio. Evidence is then provided for MAT1‐1‐1 and MAT1‐2‐1 gene expression during mycelial growth for all three species. By contrast, 27 isolates of the more distantly related R. orthosporum (on cocksfoot) and R. lolii (on Italian and perennial ryegrasses) from Europe were exclusively of the MAT1‐1 genotype, and expression of the MAT1‐1‐1 gene could not be detected during mycelial growth. These data suggest that cryptic sexual cycles are more likely to exist for R. commune, R. agropyri and R. secalis than for either R. orthosporum or R. lolii. A phylogenetic analysis of partial MAT1‐1 idiomorph sequences resolved these five species into two distinct groups (R. commune, R. agropyri and R. secalis versus R. orthosporum and R. lolii) but provided only limited resolution within each group.  相似文献   

15.
Thielaviopsis and related taxa are responsible for losses in several agricultural crops. In carrot these pathogens can cause black rot, mainly after harvesting. Molecular studies using species-specific DNA sequences are the principal tools for accurate identification of these pathogens. The objective of this work was to investigate which taxa are associated with black rot in carrot in Brazil using gene markers and Bayesian phylogenetic analysis. Eighteen isolates were obtained from carrots with symptoms of black rot. Through morphological characteristics all isolates were classified as Thielaviopsis-like. Bayesian inference using only MCM7 sequences and a concatenated data set (LSU, MCM7 and 60S rRNA) allowed identification of all isolates as belonging to Berkeleyomyces basicola. All isolates induced black rot in carrot. Although our studies include a small number of isolates, the results indicate the likely predominance of B. basicola in causing black rot in carrot in Brazil, and that MCM7 sequences are enough to distinguish the Berkeleyomyces species by Bayesian inference.  相似文献   

16.
Greeneria uvicola causes bitter rot on Vitis vinifera (bunch grapes) and Muscadinia rotundifolia (muscadine grapes) in warm moist temperate and subtropical regions. This study investigated the phylogenetic relationship of G. uvicola representatives from Australia (67 isolates), the USA (31 isolates), India (1 isolate) and Costa Rica (1 isolate) and compared their pathogenicity and fungicide sensitivity. Differences in cultural and conidial morphology were observed between the isolates from Australia and the USA. Phylogenetic relationships were determined based on three gene regions: the ribosomal DNA (rDNA) internal transcribed spacer 1 (ITS1–5?8S–ITS2), 28S large subunit (LSU) nuclear rDNA and β‐tubulin‐2. Greeneria uvicola isolates were clearly differentiated into four groups: isolates from Australia and India; USA isolates from V. vinifera; USA isolates from M. rotundifolia; and the isolate from Costa Rica. All isolates were pathogenic on V. vinifera (cv. Chardonnay) berries although those originating from M. rotundifolia were not as aggressive as isolates from V. vinifera, irrespective of geographical origin. Sensitivity to pyraclostrobin and salicylhydroxamic acid (SHAM) was studied. Despite differences in fungicide applications, hyphal growth inhibition was not significantly different for geographical location, cultivar, tissue, year of collection or different spray regimes. For the Australian and USA isolates, fungal growth inhibition was significantly greater for pyraclostrobin than for SHAM, and was significantly greater for the combined treatment than for each of the fungicides applied singly. The aetiological and epidemiological knowledge of bitter rot collected through this study will aid better prediction and management strategies of this pathogen.  相似文献   

17.
Y Wang  Z W Fan  Y D Shen  X X Li  Y Liu  Q Q Huang 《Weed Research》2019,59(6):419-426
Invasive plants may be more plastic than non‐invasive plants and maintain high fitness under various environmental conditions. Previous studies mainly focused on the comparisons between invasive and native plants, and comparisons between highly invasive and less invasive exotic species are still relatively rare, especially for comparisons at the subspecies level. This study examined the effects of nutrient addition and shading on the performance of the highly invasive Mimosa invisa and its less invasive subspecies M. invisa var. inermis under either isolated or competitive conditions. Nutrient addition increased biomass and plant height and decreased root‐to‐shoot ratio (R/S). Shading decreased biomass and R/S and increased plant height. Under isolated conditions, the two invaders did not differ in R/S, plant height and plasticity of these traits in response to nutrient addition or shading, and the two invaders also did not differ in biomass production under each of the nutrient and light treatments. When the two invaders competed with each other, M. invisa outcompeted M. invisa var. inermis under high soil nutrient conditions, and the two invaders did not differ in performance under other growth conditions. Thus, only considering competition may we find out the difference between highly invasive species and their closely related, less invasive subspecies. Management of M. invisa should focus on habitats with high soil nutrient availability, in which M. invisa is more likely to dominate.  相似文献   

18.
A homothallic Phytophthora species was found to be consistently associated with a rot of mature fruits of two local cultivars of olive (Olea europaea) in Calabria, southern Italy. The phylogenetic analysis of sequences of the ITS1‐5.8S‐ITS2 region and cox1 gene enabled its identification as a new species of clade 2, with a basal position compared to previously described subclades. The new species is described formally with the epithet Phytophthora oleae, referring to the natural matrix from which it was isolated. A unique combination of molecular and morphological characters clearly separates P. oleae from other already described Phytophthora species. This new species produced semipapillate, occasionally bipapillate, persistent sporangia on simple sympodially branching sporangiophores as well as globose and smooth‐walled oogonia, paragynous antheridia and spherical, plerotic oospores. The pathogenicity of P. oleae was confirmed in inoculation trials on fruits of three olive cultivars, including the two local cultivars from which the pathogen had been isolated.  相似文献   

19.
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20.
Roses produced or grown in the field, as well as pot‐grown and cut roses, are attacked by different fungal pathogens causing leaf spot diseases. The incorrect identification and scoring of these pathogens and the lack of information about their genetic and pathotype diversity hamper resistance breeding. This is especially true for the hemibiotrophic ascomycete Sphaceloma rosarum, which is often confused with other fungi. Here for the first time, the genetic variability between isolates at both the molecular and morphological level is analysed. Eighty leaf spot samples were collected from different rose genotypes at five different locations, and 15 single conidial isolates established. All of the samples showed high morphological similarities to the reference isolate CBS 213.33 that was obtained from a public repository. By sequencing a part of the large subunit (LSU) of the 28S ribosomal RNA and phylogenetic analysis, high sequence similarities were shown to other Sphaceloma species for 13 of the isolates and the CBS reference. One of the isolates clustered with Septoria species and another clustered with Seimatosporium species. UPGMA clustering with 145 polymorphic AFLP markers resulted in five distinct groups in the majority rule consensus tree for the 14 S. rosarum isolates, including the CBS reference. Jaccard similarities ranged from 0·31 to 0·91. A detached leaf assay using a differential set of five rose genotypes led to the classification of the five tested isolates as five distinct pathotypes. Therefore, grouping depending on the avirulence gene diversity was clearly different from clustering using selectively neutral AFLP markers that were evenly distributed throughout the genome.  相似文献   

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