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1.
Fusarium species are soil-borne fungal pathogens that produce a variety of disease symptoms when attacking crop plants. The mode of root colonization of Eucalyptus viminalis seedlings by a pathogenic F. oxyporum strain (Foeu1) at the ultrastructural level and changes in cell wall pectin during host pathogen interactions are described. Root systems of E. viminalis plants were inoculated with F. oxysporum in an in vitro model system. Hyphae of F. oxysporum adhered to the outer epidermal cell walls through fibrillar material, and after penetration they spread into the internal tissues. They developed intercellularly and intracellularly in the root cortex and invaded vascular tissues. Papillae were induced, and the host plasma membrane ruptured in colonized cells, causing rapid host tissue and cell damage. Changes in distribution and occurrence of nonesterified and methyl-esterified pectins were evaluated after root colonization by F. oxysporum using two monoclonal antibodies, JIM 5 and JIM 7, respectively. Nonesterified pectin in control roots was mainly localized in the epidermal cell walls and middle lamellae in parenchymal cortex, whereas methyl-esterified pectin accumulated more in primary cell walls of the cortex and phloem. Decreases in immunodetected nonesterified and methyl-esterified pectins were associated with extensive plant tissue degradation after root colonization by the pathogenic fungus.  相似文献   

2.
In some areas of Japan, yellow spots with white pustules on leaves, stems, petioles, peduncles and calyces were found on Ipomoea nil, I. triloba, I. lacunosa and I. hederacea var. integriuscula. We demonstrated that the diseases on I. nil, I. triloba and I. lacunosa were caused by host-specific strains of Albugo ipomoeae-panduratae and defined three forma speciales of the fungus, respectively, for the three Ipomoea species: “f. sp. nile”, “f. sp. trilobae” and “f. sp. lacunosae”. Because the diseases were new to Japan, we coined the Japanese name “shirosabi-byo”, which means white rust. We also showed that the disease on I. hederacea var. integriuscula was caused by A. ipomoeae-hardwickii. We named this new disease “white rust (shirosabi-byo in Japanese)”.  相似文献   

3.
In the course of pre- and postharvest epidemiological studies on bulbs contamination byAspergillus niger, two Sudanese onion cultivars were tested: ‘Saggai Red’ and ‘El-Hilo White’.A. niger spores, whether seedborne, soilborne or airborne, were avirulent to the healthy growing onion plants. The fungus heavily contaminated the dead onion tissues, mainly the dead leaves followed by the dry scales, the dead roots and, to a lesser extent, the bulb necks, preferring the red-skinned cultivar to the white one. The initial spores carried from naturally contaminated field soil on the dead tissues could germinate and produce massive numbers of new spores on bulbs stored at average climatic conditions of Sudan (23–39°C, 29–93% relative humidity). Under laboratory-controlled conditions, optimal growth occurred at 75–85% r.h. on bulbs with dry scales and maximum losses occurred at 100% r.h. and ambient temperature. Underin vitro conditions, the optimal growth and sporulation temperature forA. niger was in the range of 30–35°C. Early harvesting and removal of the dead onion tissues improved bulb storability in aseptic stores under low temperature and relative humidity conditions. http://www.phytoparasitica.org posting Oct. 20, 2003.  相似文献   

4.
In 2002, a powdery mildew with catenate conidia lacking fibrosin bodies was found on cucumber in a greenhouse in Kanagawa Prefecture, Japan. Morphological observation revealed that the fungus belongs to Oidium subgenus Reticuloidium, anamorph of the genus Golovinomyces. Molecular phylogenetic analyses of the nucleotide sequences of the rDNA ITS regions and D1/D2 domains of the 28S rDNA indicated that the fungus belongs to the clade of G. orontii with other Golovinomyces fungi from a wide range of host plants, suggesting that the fungus was newly transported from abroad. Because there has been no prior report of cucumber powdery mildew caused by Reticuloidium, further research on the physiology, epidemiology, control and resistant cucumber varieties is required.  相似文献   

5.
The differential interactions of V. longisporum (VL) and V. dahliae (VD) on the root surface and in the root and shoot vascular system of Brassica napus were studied by confocal laser scanning microscopy (CLSM), using GFP tagging and conventional fluorescence dyes, acid fuchsin and acridin orange. VL and VD transformants expressing sGFP were generated by Agrobacterium-mediated transformation. GFP signals were less homogenous and GFP tagging performed less satisfactory than the conventional fluorescence staining when both were studied with CLSM. Interactions of both pathogens were largely restricted to the root hair zone. At 24 h post-inoculation (hpi), hyphae of VL and VD were found intensely interwoven with the root hairs. Hyphae of VL followed the root hairs towards the root surface. At 36 hpi, VL hyphae started to cover the roots with a hyphal net strictly following the grooves of the junctions of the epidermal cells. VL started to penetrate the root epidermal cells without any conspicuous infection structures. Subsequently, hyphae grew intracellularly and intercellularly through the root cortex towards the central cylinder, without inducing any visible plant responses. Colonisation of the xylem vessels in the shoot with VL was restricted to individual vessels entirely filled with mycelium and conidia, while adjacent vessels remained completely unaffected. This may explain why no wilt symptoms occur in B. napus infected with VL. Elevated amounts of fungal DNA were detectable in the hypocotyls 14 days post-inoculation (dpi) and in the leaves 35 dpi. Root penetration was also observed for VD, however, with no directed root surface growth and mainly an intercellular invasion of the root tissue. In contrast to VL, VD started ample formation of conidia on the roots, and was unable to spread systemically into the shoots. VD did not form microsclerotia in the root tissue as widely observed for VL. This study confirms that VD is non-pathogenic on B. napus and demonstrates that non-host resistance against this fungus materializes in restriction of systemic spread rather than inhibition of penetration.  相似文献   

6.
Isolates of an unidentified Rhizoctonia sp. (UR isolates) were obtained from creeping bentgrass and Kentucky bluegrass with reddish brown sheath and foliar rots. Because the UR isolates anastomosed with isolates of three varieties of Waitea circinata (var. oryzae, var. zeae, and var. circinata), colony morphology, hyphal growth rate at different temperatures, pathogenicity, sequence analysis of the internal transcribed spacers (ITS) region of ribosomal RNA genes (rDNA) were compared. The colony color of mature UR isolates was distinct from isolates of the other three varieties of W. circinata. In pathogenicity tests on creeping bentgrass, the severity of the disease caused by UR isolates was significantly higher than that caused by the three varieties of W. circinata. Sequence similarities of the rDNA-ITS region between UR isolates and between isolates within each variety were high (97–100%), but they were lower among isolates from UR and the varieties of W. circinata (88–94%). In a phylogenetic tree based on the rDNA-ITS sequences, UR isolates formed a cluster separate from each of the clusters formed by the three varieties of W. circinata. These results indicate that the UR isolates clearly differ from the three varieties of W. circinata. We therefore propose that the UR isolates be classified as new Rhizoctonia sp. that are closely related to W. circinata and that the disease on creeping bentgrass should be called Waitea reddish-brown patch disease (Sekikasshoku-hagusare-byo in Japanese).  相似文献   

7.
Wasabi (Wasabia japonica) is grown for its highly-valued rhizome which is used as a condiment in Japanese food. Symptoms of vascular blackening in the rhizome were first observed in 2005 in plants grown in British Columbia, Canada. Microscopic observations and microbial isolation from infected tissues revealed that most of the xylem tracheid cells were blackened and bacteria were consistently associated with symptomatic plants. The bacterium most frequently recovered was identified as Pectobacterium carotovorum subsp. carotovorum (Pcc) using BioLog™ and sequencing of a specific ~510 bp IGS region. Pathogen-free plants obtained using meristem-tip micropropagation were inoculated with a wasabi isolate of Pcc. Vascular blackening symptoms developed in the rhizome after 8 weeks when the rhizome was first wounded by stabbing or cutting, or if the roots were pre-inoculated with Pythium species isolated from rhizome epidermal tissues, followed by inoculation with Pcc at 1 × 108 cells ml−1. Xylem tracheid cells were blackened and Pcc was reisolated from all diseased tissues. The highest frequency of rhizome vascular blackening occurred at 22°C and 27°C and these tissues occasionally succumbed to soft rot at higher temperatures, but not when inoculated tissues were incubated at 10°C. The rooting medium used by growers for vegetative propagation of wasabi was shown to contain Pcc but the pathogen was not recovered from the irrigation water. Entry of Pcc through wounds on wasabi rhizomes and the host tissue response result in symptoms of vascular blackening.  相似文献   

8.
Nonpathogenic isolates of Fusarium oxysporum can be successful antagonists of pathogenic forms of the same fungal species that commonly attacks crop plants. The characteristics that distinguish nonpathogenic from pathogenic forms are not well understood. In this study, the mode of root colonization of Eucalyptus viminalis seedlings by a nonpathogenic F. oxysporum strain is described at the ultrastructural level. Root systems of E. viminalis plants were inoculated with nonpathogenic F. oxysporum strain Fo47 in an in vitro model system. Changes in the occurrence of nonesterified and methyl-esterified pectins in colonized E. viminalis roots were evaluated by in situ immunolabeling using two monoclonal antibodies, JIM 5 and JIM 7. Modes of penetration and root colonization patterns in E. viminalis seedlings by the nonpathogenic fungus were similar to those described for pathogenic forms of F. oxysporum. However, root interactions differed in that the nonpathogenic fungus did not induce host tissue damage. No papilla-like appositions were observed in host cells in response to invading hyphae, which did not disrupt the host plasma membrane in many cases, suggesting that a biotrophic relationship was established. Root colonization by the nonpathogenic strain did not induce alteration in JIM 7 labeling of methyl-esterified pectin in E. viminalis cell walls, whereas nonesterified pectin was detected to a significantly greater extent in cell walls of roots colonized by the fungus. Pectin components decreased slightly only at points of hyphal contact with host cells. Because nonpathogenic strains utilize pectin in pure culture, host control over enzyme activity or production by the fungi may at least partly explain their compatible interactions with host tissues.  相似文献   

9.
Fusarium solani is a fungal pathogen that infects many different genera of plants. It represents one of the two Fusarium spp. commonly isolated from agricultural soils and plant tissues in Ethiopia. To determine the diversity of F. solani in Ethiopia, we studied 43 isolates using Amplified Fragment Length Polymorphism (AFLP) and nucleotide sequences of the Translation Elongation Factor 1α (TEF-1α) and β-tubulin genes. TEF-1α sequences from GenBank, representing previously described species and clades of the F. solani-Haematonectria haematococca complex, were also included for comparative purposes. Phylogenetic analyses of the TEF-1α data separated the isolates into three groups corresponding with the three previously described clades (Clades 1–3) for this fungus. The Ethiopian isolates aggregated into one group corresponding to Clade 3. TEF-1α, β-tubulin and AFLPs further separated the Ethiopian isolates into a number of clusters and apparently novel phylogenetic lineages. Although the biological and ecological significance of these lineages and clusters is unclear, our data show that the Ethiopian agricultural environment is rich in species and lineages of the F. solani-H. haematococca complex.  相似文献   

10.
Feeding sites induced by the root-knot nematodeMeloidogyne artiellia in turnip (Brassica rapa), cabbage (Brassica oleracea) and barley (Hordeum vulgare) were examined by light and electron transmission microscopy, and compared with those formed byM. javanica andM. hapla. The feeding cells ofM. artiellia in turnip and cabbage showed hypertrophy, hyperplasia and vacuolization, and became multinucleate giant cells. In contrast to the typical simple-shaped giant cells ofM. javanica andM. hapla, those ofM. artiellia had an amoeboid structure containing ‘protuberances’, which are distinct from previously reported ‘projects’ of giant cells induced byM. incognita in other plants. Protuberances expanding between vascular cells were observed in young and developed giant cells. Since no cell-wall fragments were found at the bases of the protuberances, either by light or electron microscopy, it is strongly indicated that these structures were caused by local expansion of the giant cells rather than by fusion with adjacent cells. The giant cells ofM. artiellia in barley had regular shapes of giant cells without protuberances, and resembled those induced byM. javanica orM. hapla in turnip and cabbage. http://www.phytoparasitica.org posting Sept. 17, 2006.  相似文献   

11.
A new disease of chrysanthemum causing ray speck was found in Okinoerabu island, Kagoshima, Japan in March 2006. Small reddish-brown lesions were observed on the ray florets of the chrysanthemum (cv. Anastasia). The causal fungus was exclusively isolated from the lesions, and typical symptoms were reproduced after inoculation with the isolate. The causal fungus was identified as Stemphylium lycopersici (Enjoji) Yamamoto based on morphology and the sequences of rDNA-ITS and the gpd gene regions. The name, “sho-hanten-byo”, in Japanese is proposed for this ray speck disease.  相似文献   

12.
A boll rot of cotton (Gossypium hirsutum L.) was observed for the first time in Greece in August 1993 in Larissa and Volos counties, and in August and September 1995 in Trikala and Phthiotis counties. Fungi of the genusPhytophthora were isolated from diseased plants. Morphological characteristics of the pathogen were recorded on mounts made directly from the infected tissues or after growth of the isolated fungus on corn meal agar or sterile distilled water. Colony morphology, growth rates, features of asexual and sexual structures and maximum growth temperatures were examined. APhytophthora species new to Europe,Phytophthora boehmeriae Sawada, attacking cotton bolls, was identified. The pathogenicity of the isolates was confirmed by artificial inoculations of detached cotton bolls. Analysis of α-esterase isozymes revealed unique banding patterns for isolates ofP. boehmeriae compared with those ofP. cactorum andP. parasitica, which arePhytophthora species with similar morphology.  相似文献   

13.
Twenty-eight isolates of Fusarium oxysporum f. sp. spinaciae (FOS; the causal agent of spinach wilt) collected from Japan were assessed for mating type and subjected to phylogenetic analysis. Mating type analysis revealed all isolates to be MAT1-2, suggesting that there is no sexual recombination within the population. Phylogenetic analyses based on nucleotide sequences of the ribosomal DNA intergenic spacer (IGS) and the mating type locus (MAT1) suggested that FOS is polyphyletic. The cluster analysis based on IGS showed four phylogenetic groups (S1–S4) among the isolates. Two distinct lineages, S1 and S3, included FOS isolates both of the vegetative compatibility group (VCG) types, 0330 and 0331, demonstrating that VCG differentiation in FOS may not necessarily reflect the phylogenetic relationships based on IGS and MAT1-2-1.  相似文献   

14.
Trichoderma SKT-1 was previously reported as a powerful biological control agent against seedborne pathogens of rice, but the taxonomic disposition of the fungal isolate was not clear. Trichoderma SKT-1 produced irregular pyramidal warts on conidia and had an optimum growth temperature of 30°C. Morphological characteristics and colony growth were identical to those of known species of Trichoderma, including the newly recognized species T. asperellum. The 5.8S rDNA with the internal transcribed spacer (ITS) region (ca. 514 bp) of the fungus was compared with those of known species to determine the phylogenetic placement of the fungus. The length and sequence of the regions from Trichoderma SKT-1 were completely identical to those of an isolate of T. asperellum NRRL 5242 (AJ230669). On the basis of these results, we concluded that Trichoderma SKT-1 was T. asperellum.  相似文献   

15.
Phoma macdonaldii, the causal agent of black stem disease of sunflower (Helianthus annuus), also attacks roots and collars of the plants, resulting in early death. Totally resistant lines do not exist for infection of the aerial parts, but tolerant lines have been characterised. This paper presents a study on colonisation of a partially resistant and a susceptible sunflower line by P. macdonaldii. The fungus was transformed with a constitutively expressed reporter gene encoding the jellyfish green fluorescent protein via Agrobacterium tumefaciens, and colonisation of sunflower roots by this transformed strain was studied by various microscopy techniques including confocal and scanning electron microscopy. The results show that penetration of the fungus into the root occurred through natural fissures or through the epidermis and was similar in both lines. In contrast, the colonisation rate of the stele was reduced in the partially resistant line, and the morphology of the fungal hyphae was also affected. The effect on hyphal morphology was strongest in the stele, indicating a localised production of defence compounds in this line.  相似文献   

16.
Based on inoculation experiments and morphological and molecular phylogenetic studies, Cylindrocladium damping-off of strawberry and Cylindrocladium blight of coral bells in Japan were demonstrated to be caused by Cylindrocladium canadense. This is the first report of a disease on strawberry and coral bells caused by this fungus.  相似文献   

17.
In arid conditions in India,Ganoderma lucidum (Leyss: Fr.) P. Karsten was found to cause root rot diseases in jojoba (Simmondsia chinensis (Link) Schneider) plants. In the rainy season, 10–15-year-old jojoba plants growing in the proximity of aGanoderma-infectedAcacia tortilis tree, developed disease symptoms. Twigs of affected plants started drying from the top of the branch; leaves turned yellowish brown and finally abscissed; plants dried up within 1 to 3 months. Basidiocarps developed from decaying roots near the collar region and produced colored stalks and fruiting caps. Pathogenicity of the fungus was established by keeping the infected root segments in direct contact with roots of healthy jojoba plants. Root rot symptoms were expressed within 5 months in inoculated plants subjected to moisture stress.  相似文献   

18.
A severe rot was found on the stems and roots of scarlet runner bean (Phaseolus coccineus) in Ibaraki Prefecture (Japan) in August 2004. The causal fungus was identified as Pythium myriotylum. We propose the name of stem and root rot of scarlet runner bean (“Kuki-negusare-byo” in Japanese) for this new disease.  相似文献   

19.
Muskmelon (Cucumis melo cv. Temprano Rochet) and autumn squash (Cucurbita maxima) seedlings were inoculated either with Acremonium cucurbitacearum or Monosporascus cannonballus, two of the soil-borne fungi implicated in ‘melon collapse’. Inoculation was achieved in two different ways: by growing the plants in pots containing infested soil to study the histological changes produced in the infected tissues using light microscopy and by growing seedlings in Petri dishes together with fungal colonies in order to observe the colonisation of the plant tissues using scanning electron microscopy. Both muskmelon and autumn squash roots infected with A. cucurbitacearum showed a suberised layer in the epidermis and the outermost layers of the parenchymatic cortex, but these symptoms developed earlier in the muskmelon plants. Muskmelon plants infected by this fungus also presented hypertrophy and hyperplasia, which led to a progressive separation of the vascular bundles in the lower stems of the affected plants. This response was not observed in autumn squash during the study. On the other hand, few histological changes were observed in tissues infected with M. cannonballus and only a slight increase in the size of cortical intercellular spaces was noted in the lower stems of muskmelon plants, and infected autumn squash tissues remained free of these symptoms throughout the study. The scanning electron microscope observations revealed that both fungi were able to colonise the tissues of the two host plants which were studied. A. cucurbitacearum colonised the epidermis and cortex of both muskmelon and autumn squash. The hyphae grew both inter- and intracellularly, and the density of the colonisation decreased within the endodermis. The same colonisation of host plants was observed as a result of M. cannonballus infection. The xylem vessel lumina of both muskmelon and autumn squash showed hyphae and tylose formation as a result of both fungal infections. However, non-fungal structures were detected in the hypocotyl vascular tissues. The present study demonstrates that both fungi are capable of infecting the tissues of a species which is resistant (autumn squash) and a species which is susceptible (muskmelon) to melon collapse.  相似文献   

20.
In 1982, an anamorphic fungus in the genus Monilia was first isolated as the causal agent of brown rot disease of Japanese apricot or mume (Prunus mume) in Oita Prefecture, Kyushu, Japan. Inoculation of flowers, shoots, and fruit of P. mume with the fungus reproduced brown rot disease symptoms similar to those found in nature. The fungus somewhat resembled the colony appearance of Monilinia (anamorph Monilia) laxa, the apricot brown rot fungus, on PSA plates, but it differed from the latter and the other two brown rot fungi, M. fructigena and M. fructicola, in terms of growth rate, temperature optima for mycelial growth and sporulation, morphology and germination pattern of conidia, nuclear number in the conidium, and nucleotide sequences in the ITS region of ribosomal DNA. It is newly described as Monilia mumecola Y. Harada, Y. Sasaki & T. Sano. A key to anamorphic states of four brown rot fungi of fruit trees is provided.  相似文献   

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