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1.
Collybia fusipes is the cause of a root rot of Quercus petraea (sessile oak), Q. robur (pedunculate oak) and Q. rubra (red oak). This parasite is often reported to cause problems in stands of red oaks and field evidence suggests that this North American oak species is more susceptible than the two European oak species. Young saplings of the three oak species and of chestnut, Castanea sativa, in the glasshouse, and also mature sessile and red oaks growing in the same stand were inoculated with C. fusipes to compare their susceptibility. Red oak, both as young seedlings and mature trees, was more susceptible to C. fusipes than sessile oak. Chestnut seedlings were as susceptible as sessile oak. Susceptibility of pedunculate oak seedlings was intermediate between red oak and sessile oak. In one experiment this species was significantly less susceptible than red oak, and in the other it was as susceptible.  相似文献   

2.
A new record is reported of the oak gallwasp Aphelonyx persica on oaks (Quercus cerris, Q. ithaburensis, Q. trojana) in the Inland Aegean Region of Turkey. This species is recorded for the first time on Q. cerris and Q. trojana. Details are given of the geographical distribution, hosts and phenology.  相似文献   

3.
Pestalotiopsis isolates obtained from the foliage, stem-base and roots of hardy ornamentals grown on commercial nurseries in the UK were identified and characterised according to pathogenicity and colony morphology. All 18 isolates were identified as Pestalotiopsis sydowiana on the basis of conidia morphology, and confirmation of identification was made by experts at CABI Bioscience. Isolates were pathogenic on the host from which originally isolated. Typical symptoms included foliar browning of foliage and stems, and the presence of black or greenish-black acervuli on diseased tissue. Isolates were not host specific and infected other species of hardy ornamentals. Three colony types on potato dextrose agar were distinguished according to colour and production of acervuli by individual isolates.Three selected isolates of P. sydowiana were characterised by examining the effects of growth media, temperature, pH, and water potential on hyphal extension. Isolates grew well on commonly used growth media, including PDA, Sabouraud dextrose agar (SDA), V8 juice agar (V8), malt extract agar (MEA) and Czapek Dox agar (CDA). The optimum temperature for growth on PDA was in the range 20–25°C, with little or no growth occurring below 5°C or above 30°C. Hyphal extension occurred over a pH range between 2.6–8.6, with optimum values occurring at pH 5.5. In general, decreases in osmotic and matric potential caused a reduction in growth. Hyphal extension on media adjusted osmotically as NaCl ceased between –9.9 and –10.5MPa. Isolates were more tolerant of osmotic than matric potential, with no growth occurring at –6.5MPa on media adjusted with polyethylene glycol.  相似文献   

4.
In Portugal, the oak pinhole borer Platypus cylindrus and its mycobiota have been associated with cork oak (Quercus suber) death, but no knowledge exists regarding the associated bacterial community. However, it is known that some bacteria are important for ambrosia beetle symbiosis and play a role in oak tree health. To explore the bacteria associated with this beetle and its host, with the ultimate goal of highlighting potential roles in oak decline, this study used a culture-dependent approach for strain isolation and phylogenetic identification using 16S rRNA gene sequencing and multilocus sequence analysis (MLSA). The bored galleries of different cork oak trees from a cork stand in Alentejo, together with the body and mycangia of adult beetles, were investigated. The samples revealed a diverse community comprising 500 isolates with 64 distinct types of bacterial colonies. Sixty-eight strains were selected for sequencing and used for phylogenetic analysis, 40 from wood galleries and 28 from beetles. Thirty-two genera of bacteria were identified, 18 of which were described for the first time within oak–beetle interactions. Major taxonomic groups were Actinobacteria in beetles and Enterobacterales in wood galleries. Although specific oak bacterial pathogens were not detected, a group of distinct strains detected in wood galleries, potentially belonging to a new Pectobacteriaceae species, were able to produce mild symptoms on cork oak plantlets. This study reports for the first time the biodiversity of culturable bacteria associated with the Q. suber–P. cylindrus interaction, their relevance to both organisms and the possible contribution to oak decline.  相似文献   

5.
Quercus ilex is one of the European forest species most susceptible to root rot caused by the oomycete Phytophthora cinnamomi. This disease contributes to holm oak decline, a particularly serious problem in the ‘dehesas’ ecosystem of the southwestern Iberian Peninsula. This work describes the host–pathogen interaction of Q. ilex and P. cinnamomi, using new infection indices at the tissue level. Fine roots of 6‐month‐old saplings inoculated with P. cinnamomi were examined by light microscopy and a random pool of images was analysed in order to calculate different indices based on the measured area of pathogen structures. In the early stages of invasion, P. cinnamomi colonizes the apoplast and penetrates cortical cells with somatic structures. On reaching the parenchymatous tissues of the central cylinder, the pathogen develops different reproductive and survival structures inside the cells and then expands through the vascular system of the root. Some host responses were identified, such as cell wall thickening, accumulation of phenolic compounds in the middle lamella of sclerenchyma tissues, and mucilage secretion blocking vascular cells. New insights into the behaviour of P. cinnamomi inside fine roots are described. Host responses fail due to rapid expansion of the pathogen and a change in its behaviour from biotrophic to necrotrophic.  相似文献   

6.
Forty eight isolates of Phytophthora cinnamomi from various host plants in France (35 isolates) and in other countries were tested for pathogenicity. Seedlings of chestnut, northern red oak, pine and eucalyptus were infected by soil contamination. Taproots, stems and bark strips of plants of chestnut and different oak species were inoculated with mycelium agar disks. Results of the different experiments were in good agreement. All isolates appeared pathogenic to all the different test species but with variable levels of virulence. Isolates with consistent low or high level of virulence, which could be used as standards in further studies, were identified. Interaction between P. cinnamomi isolates and host plant species was significant in terms of lesion lengths. These interactions could not be related to host from which P. cinnamomi was isolated. Consistent with this, in Quercus rubra, the isolate-provenance interaction was not significant. This feature is encouraging for provenance screening for resistance to P. cinnamomi in this species. The variation in virulence was not related to other isolate characteristics (mating type, electrophoretic type, age).  相似文献   

7.
One isolate each of Trichoderma viride, Epicoccum nigrum, Fusarium tricinctum, Alternaria alternata, Sclerotinia sclerotiorum and Cytospora (teleomorph: Valsa sp.) present in epigeous declining oak tissues was evaluated for its ability to control Diplodia corticola (isolate 79). This fungus is the causal agent of cankers, vascular necrosis and dieback on various oak species. Among the isolates tested, T. viride and F. tricinctum showed maximum in vitro inhibition of mycelial growth of D. corticola (isolate 79). Species were also evaluated for their ability to reduce mortality caused by D. corticola (isolate 79) of Quercus cerris and Q. pubescens seedlings under controlled conditions. Two series of inoculations were carried out through wounds in the stem; in the first, the distance between the point of inoculation of the antagonist and the pathogen was 6 cm, whereas in the second series the distance was shortened to 3 cm. In seedlings of Q. cerris and Q. pubescens at a distance of 3 cm, inoculation with F. tricinctum and A. alternata significantly reduced mortality caused by D. corticola (isolate 79). Inoculation of T. viride through artificial cuticular wounds in the stem of seedlings prevented the proliferation of D. corticola (isolate 79) only on seedlings of Q. cerris. All Q. pubescens seedlings treated with T. viride manifested pathological symptoms subsequent to proliferation of D. corticola (isolate 79). These observations indicate that the interactions between endophytes in planta and D. corticola (isolate 79) are complex and merit further study.  相似文献   

8.
Quambalaria shoot blight, caused by the fungal pathogen Quambalaria pitereka, is a serious disease of eucalypt plantations in Australia. The aggressiveness of four Q. pitereka isolates was compared on a range of host genera, species, provenances and clones. Isolates differed substantially in their aggressiveness, with two consistently showing higher levels of aggressiveness based on incidence and severity of disease and lesion size. Isolates derived from Corymbia citriodora subsp. variegata (Ccv) and C. torelliana were shown to have a relatively restricted host range, with lesions but no sporulation found on Eucalyptus species, Angophora species other than A. costata and Corymbia species other than Ccv, the host of origin. The level of aggressiveness toward the different provenances of spotted gum and C. torelliana varied between isolates and there was evidence of some isolate × host interaction within provenances of Ccv. The two methods of inoculation used in this study, spray and spot inoculation, gave similar results. However, the fact that the spot inoculation method was labour‐intensive was a disadvantage limiting the numbers of isolates and hosts that can be tested.  相似文献   

9.
Isolates of plant reoviruses causing severe stunting and dark leaf symptoms on wheat in Hebei province, on maize in Hubei province and on rice in Zhejiang province, China have been characterized. Four of the ten genome segments corresponding to Rice black-streaked dwarf virus (RBSDV) S7, S8, S9, S10 were amplified by RT-PCR from the Hebei and Zhejiang isolates and sequenced. Sequences of S9 and S10 were also obtained from the Hubei isolate. Sequences of corresponding segments of the Chinese isolates were very similar to each other (94.0–99.0% identical nucleotides and 96.3–100% identical amino acids) and were closer to those of a previously reported Japanese RBSDV isolate (90.0–94.9% identical nucleotides and 91.1–98.6% identical amino acids) than to those of an Italian Maize rough dwarf virus isolate (85.1–88.1% identical nucleotides and 85.5–94.3% identical amino acids). The Chinese isolates should be classified as RBSDV.  相似文献   

10.
Pathogenicity and genetic variation were investigated within a collection of 104 banana-infecting isolates of Cylindrocladium (teleomorph Calonectria) originating from different countries and representing previously described morphological taxa or species. These root-rot fungi, along with endoparasitic nematodes, have been reported to be causal agents of necrotic lesions that induce root breakage and toppling of banana plants. Little is known about the individual pathogenic effects of the species involved or their genetic diversity. In the present study, among the five morphological taxa found in the banana rhizosphere, only isolates showing an atypical morphology relative to Cylindrocladium gracile (named Cy. gracile-like isolates) and Cy. spathiphylli isolates were pathogenic on banana cultivar Grande Naine. When comparing the latter isolates with others of the same species, but originating from different hosts, an analysis of rDNA spacer polymorphism partitioned isolates of Cy. spathiphylli by host into a banana – tea group and a Heliconia – Spathiphyllum group. Furthermore, isolates from Heliconia were not pathogenic on banana. A pathogenicity assessment of representative isolates from the Cy. gracile-like and the Cy. spathiphylli taxa on six different banana cultivars yielded no evidence of differential interactions between isolates and banana genotypes. Significant differences in susceptibility between banana genotypes were nevertheless detected that could potentially be exploited by breeders. Random amplified polymorphic DNA analysis revealed a genetic similarity ranging from 70% to 100% within Cy. spathiphylli isolates from bananas regardless of the geographic origin. Moreover, Cy. gracile-like isolates were highly similar but showed only 60% similarity relative to the Cy. gracile reference isolates, thus raising questions about their species status.  相似文献   

11.
ABSTRACT The drippy nut disease of oak was first described in California in 1967 and, since then, the causal agent has not been reported in any other area. This study describes for the first time in Europe the isolation of Brenneria (Erwinia) quercina from bark canker in addition to drippy bud and drippy nut in Quercus ilex and Q. pyrenaica. The bark canker and drippy bud symptoms were not previously described as caused by this bacterium. No fungal pathogens were associated with any of the symptoms. Physiological and biochemical characterization identified the pathogenic isolates from Spain as belonging to B. quercina, similar to the reference strain CFBP 1266. Fatty acid profiles of the Spanish isolates also were similar to the strain of B. quercina from California. Serological analysis by indirect immunofluorescence and enzyme-linked immunosorbent assay using polyclonal antisera against the reference strain of B. quercina and one Spanish oak isolate revealed some antigenic heterogeneity between isolates of different origins. Pathogenicity tests demonstrated that the Spanish isolates were able to reproduce internal symptoms of necrosis and acorn exudation in Q. ilex and Q. pyrenaica and suggest that B. quercina may be associated, among other causes, with the oak decline syndrome affecting Spanish oak forests.  相似文献   

12.
A study was undertaken to examine the main source of inoculum of Bipolaris sorokiniana responsible for its reappearance in rice–wheat cropping regions of eastern India. Soil samples were collected at monthly intervals during April–October in the years 2000 and 2001 from fields having rice–wheat cropping. Bipolaris sorokiniana conidia were isolated and their viability was found to decline sharply with the onset of flooding in the month of August. In contrast to 82% in April, viability was 4% and <1% in August and September, respectively. Viable conidia were multiplied in the laboratory and inoculated on to susceptible cv. Sonalika under controlled conditions for test of pathogenicity. Appearance of symptoms typical to spot blotch were recorded after 7 days. Twenty-two different species (weeds and grasses) normally found to be associated with rice–wheat fields were tested for the presence of B. sorokiniana to evaluate their possible role as alternative hosts. Only three species, i.e. Setaria glauca, Echinochloa colonum and Pennisetum typhoids, were found to naturally harbour B. sorokiniana. Isolates from these hosts were tested for pathogenicity and also for their possible spread to wheat. When reisolated from these hosts, the pathogen did not infect wheat. Seeds of 25 different wheat genotypes were tested for B. sorokiniana infection. All genotypes were infected and the incidence of infection varied from 26% to 86%. Five isolates of wheat and one isolate from each of the three species (S. glauca, E. colonum and P. typhoids) were subjected to RAPD analysis. Two broad clusters were formed, suggesting that the wheat isolates were different from the isolates originating from other hosts. The results indicate that seeds are the most important source of inoculum for the reappearance of spot blotch of wheat in rice-wheat cropping systems in eastern India.  相似文献   

13.
Thirteen strains ofPhytophthora porri from five different hosts were compared with respect to their morphology, cardinal temperatures for growth, pathogenicity to leek and cabbage and restriction fragment patterns of mitochondrial DNA. Morphology of vegetative growth was rather similar in most isolates. Those characters which differed among isolates showed overlapping variability and could not be used to distinguish groups, with the exception of production of oogonia and sporangia and the antheridium type. Considerable differences were found in restriction patterns of mitochondrial DNA, isolates from the same host mostly showing identical patterns. Isolates from differentAllium species showed relatively similar restriction patterns if compared to the other isolates. Isolates fromBrassica oleracea proved to be a homogeneous group, quite different from the others with respect to restriction patterns, production of sporangia, production of oogonia, antheridium type and pathogenicity. One isolate, CBS 366.59, isolated from and pathogenic toA. porrum, deviated in many characters from the other isolates. It showed the restriction patterns ofPhytophthora nicotianae and also the high cardinal temperatures for growth typical for this species. The sporangia, however, were distinctly non-papillate and the majority of antheridia was of the paragynous type.  相似文献   

14.
In southern Poland during 1986–1989, six species of Ceratocystis were found on sick and dead Quercus robur. The frequency of their occurrence in above-ground portions and roots of trees is given. The possibility is discussed whether oak decline, caused by a complex of abiotic and biotic factors, is intensified when trees are colonized by Ceratocystis.  相似文献   

15.
Twenty-eight Pyricularia isolates from two wild foxtails—green foxtail (Setaria viridis) and giant foxtail (S. faberii)—in Japan were taxonomically characterized by DNA analyses, mating tests, and pathogenicity assays. Although most of the isolates failed to produce perithecia in mating tests with Magnaporthe oryzae, a diagnostic polymerase chain reaction-restriction fragment length polymorphism phenotype of M. oryzae was detected in the beta-tubulin genomic region in all isolates. The pathogenicity assays revealed that host ranges of the isolates were similar to those of isolates from foxtail millet (S. italica), which were exclusively pathogenic on foxtail millet. In addition to the 28 isolates from wild foxtails, 22 Pyricularia isolates from 11 other grasses were analyzed by RFLP using single-copy sequences as probes. In a dendrogram constructed from the RFLP data, isolates that were previously identified as M. oryzae formed a single cluster. All the wild foxtail isolates formed a subcluster with foxtail millet isolates within the M. oryzae cluster. From these results, we conclude that Pyricularia isolates from the wild foxtails are closely related to isolates from foxtail millet and should be classified into the Setaria pathotype of M. oryzae.  相似文献   

16.
The rDNA-ITS sequence of Rhizoctonia solani AG 1-ID was determined and compared to those of R. solani AG 1-IA, AG 1-IB, and AG 1-IC. The similarity of the isolates from each AG 1 subgroup was almost identical (99%–100%), whereas it was lower between subgroups (91%–95%) than within subgroups. Phylogenetic analysis indicated that isolates of AG 1-ID and other subgroups were separately clustered. Isolates of R. solani AG 1 were clearly separated from R. solani AG 2-1, AG 4, and binucleate Rhizoctonia AG-Bb and AG-K. These results showed that analysis of the rDNA-ITS sequence is an optimal criterion for differentiating R. solani AG 1-ID from other subgroups of R. solani AG 1.  相似文献   

17.
Forests in Europe are threatened by increased diversity of Phytophthora species, but effects on trees of simultaneous infections by Phytophthora and ecological consequences of their coexistence are unknown. This study explored variation in early survival of Quercus ilex to Phytophthora infections and assessed interactions between Phytophthora species when trees were co‐infected. Three Phytophthora species (P. cinnamomi, P. gonapodyides and P. quercina), seeds from 16 populations of Q. ilex (ballota and ilex subspecies) and two infection times were used as sources of variation in two experiments. The influence of Phytophthora species, Q. ilex subspecies and populations on plant germination and survival were analysed using generalized linear mixed models and survival analysis techniques. Germination rates were not influenced by Phytophthora spp. (P = 0.194) but by the subspecies and populations of Q. ilex (P < 0.001). In Phytophthora‐infested soils, Q. ilex subsp. ilex germinated at higher rates than Q. ilex subsp. ballota. Plant survival was strongly influenced by Phytophthora species (P < 0.001), not by the subspecies and populations of Q. ilex. Seedling mortality was reduced and delayed if a less virulent Phytophthora species infected plants prior to infection by a more virulent Phytophthora species. The results help to explain oak decline syndrome and the lack of natural and artificial regeneration of Q. ilex forests. Lack of interspecific variability of early survival to Phytophthora spp. discourages direct sowing for artificial reforestation programmes. Large, thick seeds, giving plants rapid growth, are advantageous traits when soils are infested with Phytophthora spp.  相似文献   

18.
A multitude of bacteria have been isolated from the guts of several insect species. Some of these have been modified to interfere with the development of the host insect or with the development and transmission of plant and animal pathogens transmitted by the host insect. We surveyed the gut flora of the Pacific Coast wireworm,Limonius canus LeConte, a serious pest of potato, at two sites in Oregon and Washington. Isolates were obtained from surface-sterilized triturated larvae by dilution plating on standard media. A rich diversity of species was found in 86 isolates, including spore-formers, non-spore-formers and aerobic and facultatively anaerobic species collected on four sampling dates at each location. Twenty-one of the isolates were identified to species based on rDNA sequence (nine distinct species). An additional 34 isolates were identified to genus from the sequence data while six isolates could be assigned only to family based on sequence comparisons. Twenty-seven additional isolates were identified to species (9), genus (17) or family (1) based on side-by-side morphological comparisons with isolates identified from rDNA sequence. The most frequently isolated bacterium wasBacillus megaterium, followed byRahnella aquatilis. A naturally occurring bacterium found in the gut and/or environment of a targeted insect that is modified to express toxins or other detrimental substances could provide certain advantages (such as persistence and recycling) over inundatively applied microbial control agents, particularly within soil habitats. The hypothesis that these species or others from the survey represent candidates for genetic modification to provide control options forL. canus is discussed.  相似文献   

19.
A monogenic recessive resistance to Rice yellow mottle virus (RYMV) found in the Oryza sativa indica cultivar Gigante and in a few Oryza glaberrima cultivars provided a higher level of resistance than either a polygenic partial resistance found in some japonica cultivars which delayed symptom expression or transgenic resistances which were partial and temporary. This high resistance was overcome by several isolates, but the percentage of such virulent isolates in the fields was low. There was no relationship between the virulence of an isolate towards the high resistance and its aggressiveness in other cultivars. Isolates with either of the two components of pathogenicity – virulence and aggressiveness – were found in each strain and in all regions of Africa, in both wild and cultivated grass species. There was no loss of fitness of resistance-breaking (RB) isolates as they were not counter-selected, impaired or outperformed after serial passages in susceptible cultivars, even in mixture with avirulent quasi-isogenic wild type isolates. Resistance breaking was highly dependent on the amount of virus inoculated and on the mode of transmission. Implications of these results for the durability of the resistances to RYMV and for the development of integrated disease management strategies are discussed.  相似文献   

20.
A new viroid was detected in hops cultivated in Akita Prefecture, Japan where it is prevalent in many hops fields. In a survey of hop samples collected during the 1986–2002 growing seasons, the new viroid was present in the major Japanese hop-cultivating areas as early as the 1980s. A single-stranded circular RNA of 368–372 nucleotides that assume a highly basepaired, stable, rod-like secondary structure, shares 93%–98% sequence homology with Apple fruit crinkle viroid (AFCVd) isolated from apple and 85%–87% with Australian grapevine viroid (AGVd) isolated from grapevine. Taking into account the present concept of viroid species, we conclude that the viroid is AFCVd. Circumstantial evidence suggests that AFCVd from apples and hops were endemic in Japan only where cultivation of the two host plants overlapped, thereby strongly supporting the possibility that AFCVd (or an ancestral viroid) was transmitted across the species barrier from apples to hops or hops to apples somewhere in the region. Phylogenetic analysis of AFCVd from hops, AFCVd from apples, and AGVd together with the other members of the genus Apscaviroid revealed that the Akita isolates of AFCVd from hops (AFCVd-hop) formed a cluster that is distinct from AFCVd-apple and AGVd. Accumulation of host-specific sequence variation following their isolation in different host species may be leading to the formation of two viroid species from a common ancestor.  相似文献   

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