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1.
Ultrastructural observations showed that the European race of Gremmeniella abietina var. abietina can secrete several cell wall–degrading enzymes that help the invasion of Pinus banksiana and P. contorta shoot tip tissues. Alterations in the content or distribution of cellulose were obvious, indicating that colonization might be achieved primarily through the action of glucanases. Polygalacturonases seemed more abundant in the cortex and the phloem of the stem, suggesting they are among the first enzymes secreted by the pathogen during infection. Production of laccases and peroxidases was also revealed but always close to fungal cells or in areas where host wall degradation was obvious. In places where there was an accumulation of phenolic compounds in the infected zones of the shoot, particularly in or near the transition zone, immunolocalization of both enzymes was limited or absent. Laccases and polygalacturonases were regularly detected over the extracellular sheath of G. abietina, and this indicates that the sheath could play a significant role during host wall degradation. Finally, examination of G. abietina wall constituents, such as chitin and β‐1,3‐glucans, suggests that the composition of the pathogen wall changes during the infection process. This change may be associated with the secretion of fungal enzymes but could also be linked to host reactions altering the integrity of pathogen cell walls.  相似文献   

2.
The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is an important insect pest of canola, Brassica napus L., in Ardabil, Iran. Host plant resistance is an essential component of integrated management of P. xylostella. We investigated the preferences and performance of P. xylostella on nine commercial cultivars of canola, namely Zarfam, RGS003, Adder, Okapi, Opera, Hyola401, Ebonite Option500 and Elite under greenhouse conditions at 23 ± 1°C, 50 ± 5% RH and 14L:10D. In free-choice situation, oviposition was lowest on Opera (23.5) and highest on Zarfam (44.7). In the life table study, fecundity of new generation female moths was lowest on Opera (95.4) and highest on Adder (145.7). Survival from egg to adult was significantly lower on Opera, Option500 and Hyola401 than on other tested cultivars. The intrinsic rate of natural increase (r m) and population growth rate (λ) were lowest on Opera and highest on Zarfam. The generation time (T) was shortest on Zarfam (17.2 days) and longest on Hyola401 (19.9 days) whereas doubling time (DT) was longest on Opera (3.9 days) and shortest on Zarfam (3.0 days). Our results clearly suggest that Opera was the most resistant host among the tested cultivars and has the potential to be used in the integrated management of P. xylostella.  相似文献   

3.
Wilt disease caused by Fusarium solani is a serious constraint to Dalbergia sissoo (shisham) plantations in northern India. In this study, the antagonistic potential of 40 bacterial isolates recovered from rhizophere soil of healthy shisham trees, and a well‐characterized Trichoderma species (Trichoderma virens) were tested for their possibility as biocontrol agents for F. solani. Two promising isolates (S1 and S15) were identified which inhibited pathogen growth, caused chitin degradation, produced siderophores and solubilized phosphate in vitro. Isolate S15 scored highest for hydrogen cyanide (HCN) production while isolate S1 was a non‐HCN producer. These two isolates were identified as Serratia marcescens (S1) and Pseudomonas azotoformans (S15) following sequence analysis of 16S rDNA. In dual culture assays, T. virens caused 80% inhibition of mycelial growth of the test fungus. The three selected antagonists when tested in planta in the glasshouse completely suppressed production of wilt symptoms on 12‐month‐old shisham plants. Further work is needed to ascertain the potential of these isolates to be used as biocontrol agents to manage shisham wilt under field conditions.  相似文献   

4.
Cell wall-degrading enzymes produced by Rigidoporus lignosus in vitro and in vivo. Secretion of 3 polysaccharide degrading enzymes (cellulase, xylanase, endopolygalacturonase) by R. lignosus, responsible for white root rot of Hevea, was studied in culture and during pathogenesis.  相似文献   

5.
Hymenoscyphus pseudoalbidus is the causal agent of ash dieback, a disease that is presently endangering Fraxinus spp. throughout most of Europe. The phytotoxin, viridiol, was previously isolated from culture extracts of H. pseudoalbidus and found to be toxic to leaves of F. excelsior. Thus, we were interested in learning to what extent viridiol is responsible for pathogenicity of H. pseudoalbidus and investigated this using twelve isolates of H. pseudoalbidus. We also included five isolates of the closely related avirulent species, Hymenoscyphus albidus, in our studies. Some, but not all, isolates of H. pseudoalbidus and H. albidus produced measurable quantities of viridiol in culture. Three tests were used to determine to what extent viridiol concentration correlates with virulence: culture extracts were tested for activity in leaf segment tests and for inhibition of germination of seedlings of Fraxinus excelsior; virulence of the isolates was tested following infection of axenically cultured ash seedlings. Activity of the culture extracts varied, as did virulence of the isolates following inoculation into seedlings. No correlations were found between viridiol concentration and activities of culture extracts in leaf segment tests or in the germination test, nor between viridiol concentration and disease symptoms when inoculated into seedlings. However, activities of culture extracts in leaf segment and in the germination test correlated, as did the results of each of these tests with virulence in the infection experiment. Apparently, as yet unidentified factors other than the concentration of viridiol play important roles in the virulence of H. pseudoalbidus.  相似文献   

6.
In 2010–2011, Phytophthora lateralis was isolated from diseased Chamaecyparis lawsoniana exhibiting dieback and mortality at eight geographically separate forest, parkland and shelterbelt locations in England, Scotland and Northern Ireland. In 2011, P. lateralis was also isolated from young symptomatic nursery plants of C. lawsoniana and Thuja occidentalis recently imported into Scotland from mainland Europe. These are the first findings of P. lateralis in the UK. At six of the field sites, only collar and root lesions were observed. However, at two sites, large stem and branch lesions unconnected to the collar region were also observed. Phytophthora lateralis was readily isolated from both aerial and basal lesions. In artificial inoculation experiments, two Scottish isolates of the pathogen caused lesions on C. lawsoniana shoots and were readily reisolated from the lesions, their pathogenicity being comparable to that of P. lateralis isolates originating from outside the UK. Isolates from six field sites and the two nursery interceptions exhibited ITS and cox II sequences identical to published sequences of French and North American isolates. However, the isolates from two field sites shared an ITS sequence with Taiwanese isolates and differed from North American, French and Taiwanese isolates by a single‐base substitution in cox II, suggesting a separate evolutionary history. It is clear that P. lateralis now presents a significant threat to C. lawsoniana in Britain. The main source of the outbreaks is likely to be imported infested nursery stock.  相似文献   

7.
The fungus Ceratocystis huliohia was detected for the first time in dead and dying Metrosideros polymorpha trees on the Island of Kaua?i, Hawai?i, U.S.A. Fungal isolates were recovered from diseased trees into culture, and identities were confirmed by diagnostic qPCR assay and DNA sequencing. Growth chamber inoculations confirmed C. huliohia pathogenicity on M. polymorpha seedlings and subsequently the same fungus was recovered, completing Koch's postulates. DNA sequence analysis revealed a unique ITS haplotype for Kaua?i isolates of C. huliohia that has not been found on Hawai?i Island.  相似文献   

8.
The fungus Pseudobeltrania cedrelae, the type species of the genus, is the causal agent of an important leaf spot in seedlings and adult plant of cedar (Cedrela fissilis). Due to the contradictory phylogenetic position of the genus Pseudobeltrania, epitypification of P. cedrelae was carried out based on a culture obtained from the same locality and host of the original type. Samples were collected, and 10 isolates of P. cedrelae associated with lesions on cedar leaflets were obtained. For morphological characterization, conidia, conidiophores, conidiogeneous cells, conidiogeneous loci and basal cells were taken both from the fungus obtained from leaf lesions and from that obtained in slide culture. Mycelial growth rates and sporulation were evaluated in six different culture media. For molecular phylogeny, maximum parsimony analyses were performed from the ITS and 28S sequences of the isolates. Both the morphological characteristics of the fungal structures obtained from symptomatic leaves and the slide culture technique presented variations. In foliar lesions, isolates presented the same morphological characteristics as the type material. Mycelial growth rate and sporulation of P. cedrelae were greatest on malt extract agar and V8 juice agar. Pseudobeltrania cedrelae was pathogenic when inoculated into healthy cedar plants. According to the phylogenetic tree, isolates grouped in the same clade, but in a distinct clade of Pseudobeltrania ocoteae. The results suggested that P. ocoteae belongs to the genus Hemibeltrania. This paper presents new information on P. cedrelae that contributes to clarifying the phylogeny of the Beltraniaceae.  相似文献   

9.
Penicillium adametzii significantly inhibited the growth of Heterobasidium annosum sensu stricto on 2% potato dextrose agar after 10 days at 20–25°C. Chloroform extracts from P. adametzii culture filtrate and from culture grown on rice often decreased the dry weight of Armillaria colony and diameter of Heterobasidion colony in vitro. The effect depended on species and isolate of Armillaria, Heterobasidion and P. adametzii and concentration of the extract. Higher concentration of chloroform extract increased the dry weight of stems and roots of Pinus sylvestris plants inoculated with either of two isolates of Armillaria ostoyae and one isolate of Armillaria gallica. Lower concentrations of chloroform extract increased the dry weight of stems and roots of P. sylvestris inoculated with another isolate of A. gallica. Culture filtrate of P. adametzii decreased the length of necrosis on P. sylvestris stem inoculated with either of two of four isolates of H. annosum s.s., but if applied 1 month before inoculation, it increased the length of necrosis caused by another H. annosum s.s. isolate. Twenty fractions from the P. adametzii chloroform extract were separated by thin layer chromatography. Carboxylic acids, flavonoids and glycosides were detected in chloroform extract of P. adametzii by high performance liquid chromatography/mass spectrometer analysis. This is the first report of interactions between P. adametzii and either Armillaria or Heterobasidion with P. sylvestris.  相似文献   

10.
The antagonist ability of four fungal endophytes isolated from elms (Trichoderma atroviride GF13, Diaporthe eres GF2, Diplodia ulmi GF5 and Alternaria alternata GF6) and two fungi from a collection (Trichoderma harzianum and Trichoderma virens) was evaluated against six strains of Ophiostoma novo‐ulmi (1, 10, 19, 32, 43 and O‐Va), the causal agent of Dutch elm disease. Dual culture tests were established in PDA and MA culture media to test the interactions between pathogenic fungi and potential antagonist ones. The fungi showed varying levels of antagonist capacity against O. novo‐ulmi. Among them, T. atroviride and T. harzianum had the greatest inhibiting effect (around 50%). Culture filtrates and previously inoculated cellophane discs from T. harzianum and T. atroviride also caused growth inhibition of O. novo‐ulmi, with less intensity in strains 10 and 19. The control mechanisms involved in the process were competition, mycoparasitism and the production of soluble and diffusible antifungal metabolites. The new isolate T. atroviride GF13 was efficient as antagonist. It showed antagonist ability against non‐elm‐derived fungi such as Verticillium, Fusarium, Aspergillus, Rhizopus and Penicillium. These results suggest interesting application possibilities in the biological control of Dutch elm disease.  相似文献   

11.
The pine nematode Bursaphelenchus mucronatus has been associated with pine wilt in China. This work was intended to investigate the role of the pathogenicity‐related β‐1,4‐endoglucanase gene of B. mucronatus in the infection of pines. In this study, the full‐length cDNA of the Bm‐eng‐1 gene was cloned and characterized from a B. mucronatus isolate. Phylogenetic analysis suggested that the Bm‐eng‐1 gene of B. mucronatus may be acquired from fungi through horizontal gene transfer. The function of the gene was demonstrated using RNA interference. RNA interference indicated that Bm‐eng‐1 was involved in the dispersal, reproductive ability and pathogenicity of B. mucronatus. In situ hybridization showed that Bm‐eng‐1 was specifically expressed in the oesophageal gland of B. mucronatus. Furthermore, to investigate the relation between β‐1,4‐endoglucanase activities and virulence of different isolates, the β‐1,4‐endoglucanase activities and the expression levels of Bm‐eng‐1 were detected in six B. mucronatus isolates with different virulence. β‐1,4‐Endoglucanase activity was generally higher in pathogenic isolates than in non‐pathogenic isolates, and the Bm‐eng‐1 expression levels in different isolates were positively correlated with the β‐1,4‐endoglucanase activity. These findings suggested that β‐1,4‐endoglucanase plays important roles in the pathogenic process of B. mucronatus, and the differential expression of the gene may underlie the different activity levels of β‐1,4‐endoglucanase, subsequently influencing variations in virulence of B. mucronatus isolates.  相似文献   

12.
The epidemic of bud rot disease affecting oil palm in Colombia is primarily caused by Phytophthora palmivora. The pathogen has a cosmopolitan presence that includes Southeast Asia, but to date, bud rot has not been reported in this region. This study provides an overview of the potential risk of Malaysian P. palmivora isolates cross‐infecting other host species, including cocoa, durian, rubber and Malaysian oil palm planting materials (Dura × Pisifera, D × P). On cocoa pods, the durian isolate PP7 caused dark brown necrotic lesions. Detached leaf bioassays showed that P. palmivora isolates PP3 and PP7 infected different hosts, except rubber foliage without wounding. Inoculation tests on cocoa, durian and rubber seedlings caused brown necrotic lesions when stems were wounded, with 10% mortality in cocoa and durian at 17 days post‐inoculation (dpi). However, no further infection was observed, and lesions closed within 14–28 dpi on the non‐wounded seedlings. Pathogenicity tests of oil palm seedlings inoculated with isolates PP3 and PP7 indicated that Malaysian P. palmivora isolates were not pathogenic to oil palms based on localized infection observed only through wounding. Overall, the work demonstrated that Malaysian P. palmivora isolates were able to cross‐infect multiple hosts but did not show severe infections on oil palms.  相似文献   

13.
The overall aim of this study was to develop a new, reliable and rapid diagnostic assay for differentiating six European Armillaria species based on variation in their elongation factor‐1 alpha (EF‐1 α) gene sequences and to verify a set of species‐specific primers on 61 Armillaria isolates from Europe. Partial sequences of the EF‐1 α gene obtained in Armillaria borealis, Armillaria cepistipes, Armillaria gallica, Armillaria mellea, Armillaria ostoyae and Armillaria tabescens revealed sufficient interspecific variation to distinguish among species using nested primers. These primers gave unambiguous bands when tested on representative isolates of five of these species. However, the EF‐1 α sequences of European A. borealis isolates clustered into two distinct clades, termed here AbX and AbY. Specific primers were subsequently designed and tested successfully on both AbX‐type and AbY‐type A. borealis isolates. The taxonomy of A. borealis needs to be elucidated to determine whether a new, as yet unnamed Armillaria taxon exists in Europe. Three A. borealis isolates were also found to have heterozygous sites in their EF‐1 α sequences, which suggests that the gene could exist in more than one copy or that these isolates contain hybrid sequences. A pyrosequencing method was also developed, targeting a small region of EF‐1 α intron 4, which was able to differentiate European Armillaria isolates to the species level and additionally could distinguish AbX‐type and AbY‐type A. borealis isolates.  相似文献   

14.
Apple scab caused by Venturia inaequalis is the most destructive disease of apple worldwide. In this study, genetic diversity of 101 V. inaequalis isolates from cultivated apples and ornamental crabapples in Pennsylvania (PA, USA) was characterized using 14 microsatellite markers. A total of 157 alleles ranging from 5 (Vitg9/99) to 26 (Vica10/154) per locus were detected. Regardless of the host of origin, isolates were grouped into five clusters, which were largely supported by STRUCTURE and principal coordinate analysis. Cluster analyses based on genetic distances and population structure analysis suggest very small differentiation (PhiPT ranging from 0.016 to 0.103, depending on the population comparison) between apple and crabapple isolates of V. inaequalis. Pairwise comparisons among populations from different locations showed very low differentiation, and POPGENE analysis indicated frequent migration of alleles (Nm = 1.47). In pathogenicity tests using a detached leaf assay, isolates of V. inaequalis from crabapple caused characteristic scab symptoms on apple and were highly virulent. Results of the study indicate that scab lesions in crabapple trees in close vicinity to apple orchards could serve as reservoirs for spread of the pathogen. Movement of inoculum among locations and between hosts may be responsible for the limited population structure observed. Understanding the population structure of V. inaequalis isolates is significant for apple scab management as crabapples are often used as pollinizers and rootstock in apple orchards, and as ornamental trees.  相似文献   

15.
Damage symptoms, were expressed on detached shoots of Salix repens within 24 hours of exposure to toxin preparations from culture filtrates of Rosellina desmazieresii. Many of these symptoms, which resembled those observed on diseased plants, could also be obtained in the test system by exposure to cytochalasin E solutions. This toxic compound is produced by R. desmazieresii and may be important in symptom development, since culture filtrate preparations from isolates producing little cytochalasin E induced few symptoms. Toxin preparations from R. desmazieresii induced damage on detached shoots of several woody species, including both hosts and non-hosts of this fungus.  相似文献   

16.
Trichoderma isolate T05, collected and isolated from a poplar (Populus simonii × Populus nigra) stand in the province of Heilongjiang, China, was tested for its efficacy in controlling Cytospora chrysosperma in vitro and Cytospora canker of poplar in the field. Trichoderma isolate T05 was identified as Trichoderma longibrachiatum in sect. Longibrachiatum based on both morphological characteristics and phylogenetic analysis of the nuclear ribosomal internal transcribed spacer (ITS1 and ITS2) oligonucleotide sequences and the short intron of tef1. During dual culturing, the inhibitory effect of T. longibrachiatum T05 on C. chrysosperma increased over time, and inhibition up to 81% was observed 120 h after inoculation. Hyphae of T. longibrachiatum T05 grew alongside, coiled and sporulated around the pathogen hyphae, which were generally observed to be wrinkled, collapsed, disrupted and degraded. Culture filtrates of T. longibrachiatum T05 that were sterilized by either bacterial filtration or autoclaving suppressed the growth of the pathogen colony. Filtrate sterilized by filtration showed greater inhibitory activity than the autoclaved filtrate, which still had some inhibitory activity, demonstrating that some inhibitory substances were heat unstable and some heat stable. Cytospora chrysosperma C01 colony growth was also reduced by volatile antibiotics produced by T. longibrachiatum T05, with inhibition of 54% observed after 96 h. In a field trial, Cytospora canker on poplar trunks was controlled with efficacy similar to that of routine chemical control by applying a T. longibrachiatum preparation.  相似文献   

17.
The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is the most important pest of cultivated Brassica worldwide, including those grown in greenhouses like cauliflower. In this article, we evaluate the potential of various species (and various strains of some species) of Trichogrammatidae (Hymenoptera: Chalcidoidea) to control this pest on cauliflower in greenhouse in France. We assessed the parasitism levels on P. xylostella of 17 Trichogrammatidae strains, belonging to 12 different species (2 indigenous strains from France), under greenhouse conditions. Parasitism levels for each of the Trichogrammatidae species and strains were determined on cauliflower leaves (Brassica oleracea botrytis L., Brassicaceae) infested with P. xylostella eggs. Nine strains parasitized 60% (or more) of the P. xylostella eggs. Compared to previous results in laboratory conditions, climatic conditions of the greenhouse did not influence parasitism levels. The presence of the cauliflower plants may have a positive effect on eight strains, a negative effect on four strains and no effect on five strains. Our study points out the importance of including the host plant of P. xylostella when conducting studies aiming to select the most efficient parasitoid against this pest.  相似文献   

18.
Relative susceptibility of 23 Eucalyptus provenances of 11 species to pink disease caused by Corticium salmonicolor was assessed in culture filtrates of two isolates (CS1 from E. tereticornis and CS2 from E. grandis) of the pathogen, employing cut-shoot bioassay. The results showed statistically significant variation in response among different provenances within a species. Cut shoots of eucalypus giving susceptible response were affected significantly by the culture of filtrates at low dilutions, whereas those giving resistant response tolerated high concentration with little damage to shoots. This evidence clearly indicated an interaction between the host and culture filtrates of the pathogen. The response of CS1 and CS2 culture filtrates gave statistically significant differences in their reactions on various eucalypts, possibly indicating that the isolates are of two different strains. The criticism of cut-shoot bioassay and its significance in laboratory screening of eucalypts to pink disease are discussed.  相似文献   

19.
Mortality of Nothofagus trees in the southern‐central Chile region has been observed for over 30 years. A field survey conducted in 2013 detected partial defoliation and bleeding cankers on Nothofagus obliqua in a pure stand in the Nahuelbuta coastal ranges of the Biobío region. A Phytophthora sp. was isolated from stem cankers and soil samples around symptomatic N. obliqua trees: All isolates were identified as Phytophthora pseudosyringae. These isolates were pathogenic on 1‐year‐old N. obliqua and Nothofagus alpina, and on detached twigs of adult N. obliqua and Nothofagus dombeyi trees. This paper is the first to report association and pathogenicity of P. pseudosyringae with N. obliqua, N. alpina and N. dombeyi native to the Biobío region of Chile. The potential of P. pseudosyringae to cause damage in natural Nothofagus stands in Chile must be determined.  相似文献   

20.
Dothistroma septosporum and D. pini are the causal agents of Dothistroma needle blight (DNB) of Pinus spp. in natural forests and plantations. The main aim of this study was to develop molecular diagnostic procedures to distinguish between isolates within D. septosporum, for use in biosecurity and forest health surveillance programmes. This is of particular interest for New Zealand where the population is clonal and introduction of a new isolate of the opposite mating type could have serious consequences. Areas of diversity in the dothistromin toxin gene clusters were identified in D. septosporum (51 isolates) and D. pini (6 isolates) and used as the basis of two types of diagnostic tests. PCR‐restriction fragment length polymorphism (RFLP) of part of the dothistromin polyketide synthase gene (pksA) enabled distinction between two groups of D. septosporum isolates (A and B) as well as distinguishing D. septosporum and D. pini. The intergenic region between the epoA and avfA genes allowed further resolution between some of the A group isolates in RFLP assays. These regions were analysed further to develop a rapid real‐time PCR method for diagnosis by high‐resolution melting (HRM) curve analysis. The pksA gene enabled rapid discrimination between D. septosporum and D. pini, whilst the epoA–avfA region distinguished the New Zealand isolate from most other isolates in the collection, including some isolates from DNB epidemics in Canada and Europe. Although this study is focused on differences between the New Zealand isolate and other global isolates, this type of diagnostic system could be used more generally for high‐throughput screening of D. septosporum isolates.  相似文献   

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