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1.
Spores and infection structures such as germ tubes and appressoria of Magnaporthe oryzae, the fungus causing blast disease of wheat, produced an extracellular matrix (ECM) on the surfaces of host leaves during fungal differentiation. The chemical components and function of the ECM were studied to understand the pathological roles using two immunological techniques and ECM-digesting enzymes. The ECM was characterized by fibrous and amorphous materials, located in the spaces between fungal cell walls and plant cuticles. Immunohistochemical and immunoelectron microscopy suggested that ECM includes components positively reacted with antibodies of four animal cell adhesion factors (collagen VI, vitronectin, fibronectin and laminin) and an animal integrin α3. ECM, incubated on a cellulose membrane, was rapidly digested by matrix metalloproteinases (collagenase and gelatinase B), resulting in the detachment of most infection structures from membrane surfaces. Both ultrastructural observation and immunological responses showed that more ECM was located at the appressoria than at the spores and germ tubes. This result suggested that appressoria needed a powerful adhesion force for aggressive action of penetration pegs into plant cuticles. An erratum to this article can be found at  相似文献   

2.
The age of a leaf at the time of inoculation affected both development of infection structures on the leaf surface and subsequent sporulation. In the case of the susceptible genotypes, cv. Caturra and line NC-169, there was a decrease in the number of appressoria formed, with an increase in age of fully expanded leaves. On the selected resistant line, NP-547, significantly fewer appressoria were formed on the fourth leaf pair than on younger or older leaf pairs. Appressoria were formed significantly more readily over stomata of leaf pairs one, two, three, four and six than over five and seven of the susceptible selections. On the youngest leaf pair a significantly large percentage of appressoria formed away from stomata compared with the percentages obtained for older leaf pairs, where a large proportion of germinated uredospores did not form appressoria. The reaction type of the susceptible genotypes was a greater value on younger than older leaf pairs, and the reverse was true of the resistant genotype. The latent period (inoculation to sporulation) was shorter on NC-169 than on cv. Caturra. No uredospores formed on NP-547. Uredosorus density decreased with an increase in leaf age on the susceptible genotypes.  相似文献   

3.
Ethirimol, a hydroxypyrimidine fungicide active against powdery mildews only, inhibited the formation of appressoria during primary infection of barley powdery mildew, Erysiphe graminis f.sp hordei. It also affected other stages of mildew development. Several adenine analogs had similar effects and ethirimol-resistant mildew strains were generally cross-resistant to these. Adenine and adenosine reduced the fungitoxicity of ethirimol. During the formation of appressoria [3H]adenine was incorporated into RNA but [14C]glycine was not, suggesting that purine biosynthesis did not occur. Ethirimol inhibited this RNA synthesis and it is concluded that the fungicide may interfere with adenine metabolism at some site subsequent to its synthesis.  相似文献   

4.
小麦叶锈菌在感病寄主上发育的组织病理学和超微结构研究   总被引：14，自引：0，他引：14  
 应用荧光显微技术、微分干涉技术和生物电镜技术,系统地研究了小麦叶锈菌在感病寄主上的发育过程及其超微结构特征。小麦叶锈菌在感病品种上的发育过程可分为几个明显的阶段,即孢子的萌发、附着胞的形成、气孔下囊的分化、初生菌丝和次生菌丝的形成和生长、吸器母细胞和吸器的形成、夏孢子床和夏孢子堆的产生以及夏孢子的形成。小麦叶锈菌的胞间菌丝呈丝状,生长和分枝通常沿寄主细胞壁进行。胞间菌丝与寄主细胞的接触诱导了吸器母细胞的分化,吸器母细胞在与寄主细胞壁的接触部位发育形成入侵栓,穿透寄主细胞壁后于细胞内形成吸器。胞间菌丝和吸器母细胞均含有双核,而成熟吸器则含有单核。经常规染色后,胞间菌丝和吸器母细胞的壁与隔膜均可分辨出由多层构成。  相似文献   

5.
ABSTRACT The initial penetration process of appressoria of Colletotrichum acutatum on almond leaves was studied using digital image analysis of light micrographs and scanning electron microscopy. For image analysis, a series of sequential, partially focused digital micrographs of appressoria was analyzed to generate a single, completely focused montage image with a continuous in-focus depth of field. In studies on the development of the internal light spot (ILS), we observed that 50.4% of the appressoria formed an ILS after leaves were inoculated and incubated for 12 h at 20 degrees C, and that this increased to 95.8% after 24 h. Comparative image analyses of appressoria with and without ILSs using depth relief mapping and line profile software options showed that the ILS had a depth relief that was below that of the leaf surface. Depth relief analysis in the ILS region during incubation revealed an increase in depth in this area of up to 1.8 mum in some of the appressoria. A comparative morphological study of the ILS in montage images and the penetration pore of appressoria in scanning electron micrographs showed similar shapes and dimensions of the two structures in the appressorium. Light micrographs of histological sections confirmed fungal penetration and internal vesicle formation in almond leaves within 36 h after inoculation and incubation at 20 degrees C. This study represents the first direct evidence that the ILS in appressoria corresponds to the penetration pore and the developing penetration peg using a rapid, digital image analysis technique.  相似文献   

6.
A comparison of rates of germination and appressorium formation by an isolate of Colletotrichum gloeosporioides on mango leaves, fruit surfaces and cellophane membranes showed that behaviour was broadly similar on all three substrates. Frequency of appressorium formation was slightly higher on cellophane membranes, and both hyaline and melanized appressoria were formed. Only melanized appressoria were formed on mango surfaces. In vitro experiments on membranes showed comparative differences in physiological behaviour with temperature for two Philippine isolates of C. gloeosporioides . The most stimulatory temperature for production of appressoria differed in isolates I-2 and I-4 (25 and 20°C, respectively). At 30°C more appressoria became melanized than at lower temperatures, but the frequency of formation of penetration pegs was highest at 25°C. Conidia of C. gloeosporioides germinated on cellophane membranes at relative humidities as low as 95%, but the percentage of conidia germinating and forming appressoria increased as the RH approached 100%. Approximately 18% of conidia of C. gloeosporioides I-2 held at 62 and 86% RH for 4 weeks retained viability, and some were capable of forming appressoria when placed at 100% RH. These results have implications for epidemiological models for disease control.  相似文献   

7.
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8.
The early stages of development of Bremia lactucae (lettuce downy mildew) were examined on lettuce cultivars possessing high (Iceberg and Regina di Maggio) and low (Great Lakes and Plenos) levels of field resistance. Germ tubes, appressoria, penetration, primary and secondary vesicles, intercellular hyphae and haustoria were observed 3. 6 and 24 h after inoculation of cotyledons and of leaf discs from adult plants. Differences were observed between cv. Iceberg and susceptible genotypes in the percentage of spores germinating and the incidence and speed of development of infection structures. Secondary vesicles were first observed 24 h and 6 h after inoculation in Iceberg and susceptible genotypes, respectively. The lowest incidence of secondary vesicle formation 24 h after inoculation (48 and/or 43%) was recorded in Iceberg and Regina di Maggio, and the highest incidence (68%) occurred in Plenos. The formation of intercellular hyphae and haustoria was not observed in cv. Iceberg some 24 h after inoculation. There were significant differences in the lengths of germ tubes formed on different cultivars. Those on cv. Iceberg were longer than those formed on susceptible cultivars. The results indicate that the field resistance of B. lactucae may result from mechanisms which are effective in the early stages of infection.  相似文献   

9.
ABSTRACT Experiments were conducted in three prune orchards in California. In each orchard, inoculations with Monilinia fructicola, the causal agent of brown rot of stone fruits, were performed on branches of trees at bloom and fruit developmental stages. Five inoculum concentrations were used in each inoculation. Six and four wetness durations were created for each inoculum concentration at bloom and fruit developmental stages, respectively. Fruit were harvested 3 weeks before commercial harvest. The overnight freezing incubation technique was used to promote sporulation and to determine incidence of latent infection (ILI) of fruit brown rot. No differences in ILI among locations were found. A seasonal pattern of bloom and fruit susceptibility to latent infection was determined. Susceptibility to latent infection at bloom stage was at a moderate level and increased to reach the highest level at pit hardening stage. Subsequently, fruit susceptibility to latent infection decreased, reaching the lowest level in early June at embryo growth stage. Thereafter, the susceptibility increased again with fruit development and maturity until harvest. Linear relationships between ILI and inoculum concentration were obtained for most combinations of growth stage and wetness duration. Incidence of latent infection increased linearly with increased wetness duration at bloom stage and increased exponentially with increased wetness duration at early and late fruit developmental stages. The optimum temperatures for latent infection at pit hardening stage ranged from 14 to 18 degrees C, but the effect of temperature on latent infection was reduced at resistant stages. The temperature range favorable to latent infection varied for different wetness durations.  相似文献   

10.
Steiner U  Oerke EC 《Phytopathology》2007,97(10):1222-1230
ABSTRACT During formation of appressoria produced from conidia and ascospores of Venturia inaequalis, a dark brown ring structure was detected at the base of appressoria. This melanized appressorial ring structure (MARS) was attached to the leaf surface like a sealing ring and formed the fungus-plant interface; it is believed to be required for pathogen penetration of the cuticle. Neither germ tubes nor infection structures beneath the cuticle were found to be visibly melanized. MARS were formed not only on apple leaves but also on leaves of nonhost plants and artificial surfaces differing in hydrophobicity; the formation of appressoria and MARS was confined to hard surfaces. The melanin nature of the ring was confirmed by using melanin biosynthesis inhibitors. Applications prior to inoculation largely inhibited the melanization and reduced infection rate by 45 to 80%; curative applications were not effective. Transmission electron microscopy verified a localized melanization of the cell wall around the penetration pore, and melanin was incorporated into all layers of the fungal cell wall. Appressoria without MARS were not able to infect the plant, suggesting that this structure can be considered to be a pathogenicity factor in V. inaequalis.  相似文献   

11.
ABSTRACT Grape berries are highly susceptible to powdery mildew 1 week after bloom but acquire ontogenic resistance 2 to 3 weeks later. We recently demonstrated that germinating conidia of the grape powdery mildew pathogen (Uncinula necator) cease development before penetration of the cuticle on older resistant berries. The mechanism that halts U. necator at that particular stage was not known. Several previous studies investigated potential host barriers or cell responses to powdery mildew in berries and leaves, but none included observation of the direct effect of these factors on pathogen development. We found that cuticle thickness increased with berry age, but that ingress by the pathogen halted before formation of a visible penetration pore. Cell wall thickness remained unchanged over the first 4 weeks after bloom, the time during which berries progressed from highly susceptible to nearly immune. Autofluorescent polyphenolic compounds accumulated at a higher frequency beneath appressoria on highly susceptible berries than on highly resistant berries; and oxidation of the above phenolics, indicated by cell discoloration, developed at a significantly higher frequency on susceptible berries. Beneath the first-formed appressoria of all germinated conidia, papillae occurred at a significantly higher frequency on 2- to 5-day-old berries than on 30- to 31-day-old fruit. The relatively few papillae observed on older berries were, in most cases (82.8 to 97.3%), found beneath appressoria of conidia that had failed to produce secondary hyphae. This contrasted with the more abundantly produced papillae on younger berries, where only 35.4 to 41.0% were located beneath appressoria of conidia that had failed to produce secondary hyphae. A pathogenesis-related gene (VvPR-1) was much more highly induced in susceptible berries than in resistant berries after inoculation with U. necator. In contrast, a germin-like protein (VvGLP3) was expressed within 16 h of inoculation in resistant, but not in susceptible berries. Our results suggest that several putative barriers to infection, i.e., cuticle and cell wall thickness, antimicrobial phenolics, and two previously described pathogenesis-related proteins, are not principal causes in halting pathogen ingress on ontogenically resistant berries, but rather that infection is halted by one or more of the following: (i) a preformed physical or biochemical barrier near the cuticle surface, or (ii) the rapid synthesis of an antifungal compound in older berries during the first few hours of the infection process.  相似文献   

12.
Northern corn leaf blight (NCLB) caused by Setosphaeria turcica is a major foliar disease of maize. The early-stage infection events of this pathogen on maize leaves are unclear. We investigated the optimum temperature for conidial germination and appressorium formation, and characterized penetration and growth of S. turcica in maize leaf sheath and onion epidermis cells, including use of histological staining to assess plant cell viability. The results showed that the optimum temperature for conidial germination and appressorium formation was 20°C. On the maize leaf sheath, the appressoria were formed by germinated conidia, and penetration on the epidermal cells occurred at 8 h postinoculation (hpi). Round vesicles developed beneath the appressoria. Between 16 and 24 hpi, the branched invasive hyphae invaded three to five adjacent cells at most infection sites. The invasive hyphae tended to move along the cell wall and crossed from one cell to another. In the onion epidermis cells, the appressoria formed at 8 hpi, and in most cases the epidermal cells were penetrated through the juncture of the cell walls. At 16–24 hpi, the primary hyphal terminus swelled to a vesicle. The maize leaf sheath cells died at 8 hpi, whereas the onion cells did not. Our findings documented in detail the penetration and invasive hyphal growth in maize leaf sheath and onion epidermis, as well as viability of plant cells, at the early stages of infection, and provide a foundation for elucidating the underlying mechanism of S. turcica–maize interactions.  相似文献   

13.
Lee MH  Bostock RM 《Phytopathology》2006,96(10):1072-1080
ABSTRACT Monilinia fructicola, which causes brown rot in stone fruit, forms appressoria on plant and artificial surfaces. On nectarine, the frequency of appressoria produced by conidial germlings depends to a large degree on the stage of fruit development, with numerous appressoria formed on immature (stage II) nectarine fruit, and no appressoria observed on fully mature fruit (late stage III). On polystyrene surfaces, appressorium formation was increased from <10% of germinated conidia to >95% of germinated conidia when the conidia were washed to remove residual nutrients and self-inhibitors. M. fructicola appressorium formation also appears to be regulated by the topography of the plant surface. On fruit, appressoria formed on stomatal guard cell lips, on the grooves of lateral cells adjacent to stomata or between two epidermal cells, and on the convex surfaces of epidermal cells. Pharmacological effectors indicate that cyclic AMP-, MAP kinase-, and calcium/calmodulin-dependent signaling pathways are involved in the induction and development of appressoria. KN-93, an inhibitor of calmodulin-dependent protein kinase II, did not inhibit conidial germination but did inhibit appressorium formation and brown rot development on flower petals, suggesting that appressoria are required for full symptom development on Prunus spp. petals.  相似文献   

14.
为明确苹果炭疽叶枯病病原菌围小丛壳Glomerella cingulata的侵染致病特征,在分离获得该病原菌的基础上,采用形态学观察、ITS序列分析和致病性测定对其进行了鉴定,并利用光学和扫描电子显微镜对病原菌在嘎啦苹果叶片上的侵染过程进行了研究.结果表明,在陕西咸阳地区分离获得的9株病原菌均为围小丛壳G.cingulata.25 ℃下接种9 h后,分生孢子中间产生隔膜,双胞化,并萌发产生芽管和附着胞;24 h后分生孢子的2个细胞均可萌发并形成芽管及附着胞,部分芽管顶端可产生次级分生孢子;48 h后次级分生孢子萌发形成附着胞;72 h后,附着胞下形成的侵染钉可直接入侵寄主,在表皮细胞内形成初生菌丝和次生菌丝,此时叶片表面已出现褐色斑点.接种7 d后叶片病斑处出现分生孢子盘和子囊壳.表明陕西省近年出现的苹果炭疽叶枯病病原菌为围小丛壳G.cingulata,该病菌在嘎啦叶片上的一些特殊侵染行为可能是导致该病害易在短时间内暴发的重要原因.  相似文献   

15.
ABSTRACT The early infection and colonization processes of Colletotrichum acutatum on leaves and petals of two almond cultivars with different susceptibility to anthracnose (i.e., cvs. Carmel and Nonpareil) were examined using digital image analysis of light micrographs and histological techniques. Inoculated tissue surfaces were evaluated at selected times after inoculation and incubation at 20 degrees C. Depth maps and line profiles of the digital image analysis allowed rapid depth quantification of fungal colonization in numerous tissue samples. The results showed that the early development of C. acutatum on petals was different from that on leaf tissue. On petals, conidia germinated more rapidly, germ tubes were longer, and fewer appressoria developed than on leaves. On both tissues, penetration by the pathogen occurred from appressoria and host colonization was first subcuticular and then intracellular. On petals, colonizing hyphae were first observed 24 h after inoculation and incubation at 20 degrees C, whereas on leaves they were seen 48 to 72 h after inoculation. Intercellular hyphae were formed before host cells became necrotic and macroscopic lesions developed on petals >/=48 h and on leaves >/=96 h after inoculation. Histological studies complemented data obtained by digital image analysis and showed that the fungus produced infection vesicles and broad hyphae below the cuticle and in epidermal cells. In both tissues, during the first 24 to 48 h after penetration fungal colonization was biotrophic based on the presence of healthy host cells adjacent to fungal hyphae. Later, during intercellular growth, the host-pathogen interaction became necrotrophic with collapsed host cells. Quantitative differences in appressorium formation and host colonization were found between the two almond cultivars studied. Thus, on the less susceptible cv. Nonpareil fewer appressoria developed and host colonization was reduced compared with that on cv. Carmel.  相似文献   

16.
Histopathological assessment of infection by the crown rot pathogen Fusarium pseudograminearum in wheat seedling tissues was performed using fluorescence microscopy. The coleoptiles and leaf sheaths of four host cultivars of differing susceptibility were examined. Leaf sheaths were most frequently penetrated via stomata, indicated by initial lesions forming at the guard cells. Internally, cell wall penetration was facilitated by penetration structures which appeared as hyphal swellings or septate foot‐shaped appressoria. Colonization of leaf sheaths resulted in the re‐emergence of hyphae from stomata on both surfaces of the sheath. These hyphae are hypothesized to have two major roles; first as exploratory hyphae for colonization of new tissues, and secondly as sites of profuse conidial production. The formation of conidia on the leaf sheath surface was only recorded on the most susceptible bread wheat genotype. No other major differences in host–pathogen interactions were observed among these cultivars. Almost all cell types in the leaf sheath tissues were extensively colonized, except for the vascular bundles and silica cells. This investigation provides the first comprehensive assessment of F. pseudograminearum infection structures and growth patterns during the infection of wheat seedlings.  相似文献   

17.
小麦与白粉病菌互作中β-1,3-葡聚糖的细胞定位   总被引：5，自引：0，他引：5  
 利用免疫胶体金方法对小麦与白粉病菌互作过程中β-1,3-葡聚糖酶底物,即β-1,3-葡聚糖的合成与分布情况进行了研究。结果发现,白粉病菌的所有器官包括分生孢子、附着胞、入侵栓、吸器和菌丝中均未发现β-1,3-葡聚糖存在;相反,β-1,3-葡聚糖是小麦各种细胞壁的正常组分,在气孔保卫细胞、纤维细胞、导管分子等的细胞壁中含量非常丰富。病原菌的侵染导致植物细胞中β-1,3-葡聚糖的合成增加,但在乳突结构中不含β-1,3-葡聚糖。以上结果说明,往小麦中导入外源β-1,3-葡聚糖酶基因并高效表达,不会对病原菌结构产生直接的破坏和抑制作用;相反,有时可能会影响到某些植物细胞的正常发育。  相似文献   

18.
动物和植物Argonaute蛋白在RNA诱导的基因沉默中发挥重要作用。本研究采用生物信息学方法在全基因组水平鉴定短管赤眼蜂Argonaute蛋白基因家族,鉴定并命名6个TpAGO蛋白。蛋白结构及系统进化分析将TpAGO家族蛋白分为PIWI和Ago两个亚家族。TpAGO蛋白二级结构的数量比例差异不大,分布却存在一定差异,其中α-螺旋分布差异尤为显著。TpAGO蛋白基因结构表现明显的多样性,基因外显子数量差异明显,从1到20个数量不等;Ka/Ks分析表明TpAGO2和TpAGO5,TpAGO3和TpAGO4两对基因间进化动力为正选择作用,其他组合间表现为纯化选择。EST表达分析发现TpAGO基因在昆虫的卵期、幼虫期、蛹期和成虫期均有不同程度的表达,而且靶向EST在同一物种中具有单一性别(雌性或雄性)表达特性,表明短管赤眼蜂TpAGO蛋白基因可参与赤眼蜂性别及发育调控。该研究不仅有助于揭示赤眼蜂产雌孤雌生殖的表观遗传机理,也有助于推动赤眼蜂等天敌的生防应用。  相似文献   

19.
Cereal cyst nematode (CCN), Heterodera avenae, is one of the most important pathogens of wheat worldwide, and causes significant yield losses. Research on CCN–wheat interactions is hampered by the lack of an effective model pathosystem. This study investigated the potential of the model cereal Brachypodium distachyon (Bd21‐3) and diploid wheat 2A (G1812) and 2D (AL8/78) as model hosts for CCN. Nematode infection analysis showed that although some CCN penetrated Bd21‐3 roots, these nematodes failed to develop to the later developmental stages or form cysts, indicating B. distachyon is not a host for CCN. A strong burst of reactive oxygen species (ROS) within Bd21‐3 roots infected with CCN was induced 3 days after infection and the expression of seven ROS‐producing genes was significantly increased. In contrast, CCN completed its life cycle in both diploid wheat 2A and 2D, and formed normal syncytia in these hosts. Although CCN developmental processes within both diploid wheat 2A and 2D were very similar to those in the susceptible control, the number of cysts formed on diploid wheat 2D was less than those formed on diploid wheat 2A and the susceptible control, indicating that diploid wheat 2A was a more suitable host for CCN than 2D. This is the first report of a potential new pathosystem for CCN–host interactions using diploid wheat.  相似文献   

20.
The affinity of various lectins for protoplasts from isolines of wheat differing in their reaction to Puccinia graminis Pers. f. sp. tritici , Ericks and E. Henn. race 21 and for infection structures of the fungus was studied. Protoplasts of both isolines were agglutinated by concanavalin A and soybean lectin and lysed by wheat germ agglutinin. Pokeweed mitogen and wheat germ agglutinin bound to fungal germ tubes and appressoria but not to uredospore walls, substomatal vesicles or infection hyphae.
Viability of protoplasts from either isoline was not affected when they were incubated with uredospores, germlings with and without infection structures or with an extract of the susceptible line, heavily infected by the fungus. No differences between polypeptide fractions prepared from protoplasts of the isolines were detected by sodium dodecyl sulphate polyacrylamide gel electrophoresis.  相似文献   

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