Responses of Erysiphe graminis germlings to contact with artificial and host surfaces

Germling development by Erysiphe graminis f. sp. hordei was compared between conidia held in a simulated air-borne state on microthreads constructed from safety-line threads produced by orb--weaving spiders (Araneus diadematus), and conidia inoculated onto glass, agar, or living or dead barley coleoptile epidermes. Suspended conidia germinated but generally produced only multiple short germ tubes. Conidia on living or dead coleoptiles, bathed from beneath with 0.01 Ca(NO₃)₂ solution, generally produced one short germ tube and a second germ tube which elongated and formed a normal appressorium. On glass and agar, multiple short germ tubes were sometimes formed but long germ tubes were formed less frequently than on host epidermis. When conidia with short germ tubes were transferred from microthreads to coleoptiles, they produced a long germ tube which differentiated an appressorium. Conidia with a single short germ tube were also transferred from microthreads so that only the tip of the short germ tube was in contact with a leaf epidermal strip layed on agar, whilst the conidium rested on the agar. Long germ tubes were formed more frequently by such conidia than by controls which had no contact with the leaf epidermis. This suggested that a stimulus causing elongation of the second tube was perceived through the short germ tube in contact with the epidermal strip. Where long germ tubes made contact with the epidermal strip, normal appressoria were formed more frequently than where the long tube made contact with the agar surface alone. The results indicate that germlings develop through distinct stages in response to particular stimuli.     

疏水表面诱导橡胶树炭疽菌侵染结构的发育分化过程

为了解橡胶树2种炭疽病菌的侵染结构发育分化过程,采用平板菌落生长速率法测定了3株胶孢炭疽菌Colletotrichum gloeosporioides和3株尖孢炭疽菌C.acutatum的菌丝生长速率,测量其分生孢子大小,显微观察2种炭疽菌在疏水表面诱导下侵染结构的发育分化过程。结果表明,胶孢炭疽菌菌丝生长速率为0.96~1.36 cm/d,显著高于尖孢炭疽菌的菌丝生长速率0.72~0.89 cm/d,但二者分生孢子大小无显著差异。在疏水表面诱导下,2种炭疽菌分生孢子在接种2~6 h后开始萌发,12 h孢子萌发率为71.70%~88.05%,13~16 h开始分化附着胞,24 h附着胞形成率为48.99%~70.74%,36 h菌丝诱发形成大量附着枝,48 h后分生孢子产生的次生菌丝也可诱发形成附着枝,附着枝呈圆形、姜瓣形、梨形或不规则形。分生孢子极易产生,可在菌丝顶端成簇或菌丝侧面排列产生,也可由分生孢子形成的芽管产生,或在芽管分化附着胞过程分枝形成分生孢子;附着胞多着生于芽管顶端,少数附着胞顶端可继续萌发类似短芽管结构,再次分化形成可黑色化的次级附着胞。表明橡胶树2种炭疽菌不同菌株间分生孢子萌发时间、孢子萌发率、附着胞形成时间和形成率有一定差异,但种间无明显差异;橡胶树炭疽菌分生孢子极易形成,在疏水表面容易分化形成附着胞和附着枝,说明具有极强的适生性。     

苹果炭疽叶枯病病原Glomerella cingulata及其侵染过程

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.     

Light and Scanning Electron Microscopy Studies on the Infection of Oriental Lily Leaves By Botrytis Elliptica

Light, scanning electron and fluorescent microscopy were used to observe the infection process of Botrytis elliptica on leaves of oriental lily (cv. Star Gazer). At 20 °C and 100% relative humidity, conidia germinated on both adaxial and abaxial foliar surfaces, but germ tubes failed to invade epidermal cells on the adaxial surface. On abaxial surfaces, short (< 20 m) swollen germ tube appressoria penetrated through stomatal openings (19%), through the epidermis near guard cells (52%), or directly through epidermal cells (29%). Esterase activity was detected on germ tubes and conidia after 6 h of incubation, and deformation of the cuticle on abaxial surfaces of lily was observed surrounding infection sites. By 3 h after inoculation, almost 70% of the conidia had germinated, but no penetration was observed. At 6 h after inoculation, almost one-third of germinated conidia had penetrated epidermal cells, and water-soaked lesions were associated with 20% of the penetrations. By 9 h after inoculation, approximately 60% of the germinated conidia had penetrated plant tissues, and water-soaked lesions were associated with 60% of the infections. Fluorescent microscopy with a specific fungal stain allowed assessment of successful infection and visualization of sub-epidermal hyphae. We conclude that penetration of abaxial foliar surfaces of oriental lilies by B. elliptica occurs via short swollen germ tube appressoria mostly near stomata.     

Conidial germination, infection structure formation, and early colony development of powdery mildew on poinsettia

ABSTRACT Powdery mildew disease on poinsettias (Euphorbia pulcherrima) growing in commercial greenhouses was first observed in the United States in 1990 and has become an economically significant problem for poinsettia growers in the Midwest and northern United States since 1992. The temporal development of infection structures produced by conidial germ tubes of the pathogen (Oidium sp.) and the effect of high temperature on their development were investigated using poinsettia leaf disks placed in humidity chambers. Observations were made using light microscopy and scanning electron microscopy. At 20 degrees C (85% relative humidity), conidia germinated and formed an appressorium within 6 h of inoculation. Germination over time followed a monomolecular curve (r(2) = 0.77, P 相似文献   

Germination of Alternaria linicola conidia on linseed: effects of temperature, incubation time, leaf wetness and light regime

Conidia of Alternaria linicola germinated on both water agar and linseed leaves (detached or attached) over a wide range of temperatures (5–25°C) by producing one to several germ tubes. At temperatures between 10°C and 25°C and under continuous wetness in darkness, germination started within 2 h after inoculation and reached a maximum (100%) by 8 to 24 h, depending on temperature. At 5°C, the onset of germination was later and the rate of germ tube elongation was slower than that at 10–25°C. During germination, conidia of A. linicola were sensitive to dry interruptions of wet periods and to light. Short (2 h) or long (12 h) dry interruptions occurring at any time between 2 and 6 h after inoculation stopped conidial germination and germ tube elongation. With continuous wetness, light periods 2 to 12 h long immediately after inoculation inhibited conidial germination, which was resumed only when a dark period followed subsequently. However, germination and germ tube elongation of A. linicola conidia stopped and the viability of the conidia was lost during exposure to dry light periods immediately after inoculation with spore suspensions. Penetration of leaves by A. linicola was evident after 12 h and occurred mainly through epidermal cells (direct) with or without the formation of appressoria.     

Effects of temperature on ascospore germination and penetration of oilseed rape (Brassica napus) leaves by A- or B-group Leptosphaeria maculans (phoma stem canker)

Ascospores of both A-group and B-group Leptosphaeria maculans germinated at temperatures from 5 to 20°C on leaves of oilseed rape. Germination of ascospores of both groups started 2 h after inoculation and percentage germination reached its maximum about 14 h after inoculation at all temperatures. Both the percentage of A-/B-group ascospores that had germinated after 24 h incubation and germ tube length increased with increasing temperature from 5 to 20°C. Germ tubes from B-group ascospores were longer than those from A-group ascospores at all temperatures, with the greatest difference at 20°C. Hyphae from ascospores of both groups penetrated the leaves predominantly through stomata, at temperatures from 5 to 20°C. A-group ascospores produced highly branched hyphae that grew tortuously, whereas B-group ascospores produced long, straight hyphae. The percentage of germinated ascospores that penetrated stomata increased with increasing temperature from 5 to 20°C and was greater for A-group than for B-group L. maculans after 40 h incubation.     

The influence of the primary germ tube on infection of barley by Erysiphe graminis f. sp. hordei

In each of three separate genotype combinations of Erysiphe graminis f. sp. hordei and barley the probability of infection success by an appressorium was reduced by close proximity to a primary germ tube interacting with the same host cell, whether this germ tube was produced by the same or another conidium. Infection success of appressoria was unaffected by events in an adjacent cell, whether associated with other conidia or with the primary germ tube of the same conidium. This interaction between germ tubes and underlying host cells should be considered when mechanisms of resistance to E. graminis f. sp. hordei are investigated.     

橡胶树白粉病菌分生孢子在不同介质的萌发过程及其内容物的变化

 本研究采用不同的染色方法和显微技术观察橡胶树白粉病菌(Oidium heveae)分生孢子的超微结构,分生孢子在不同介质表面及不同介质溶液中的萌发情况,以及孢子萌发过程中孢内主要物质的变化,以明确O. heveae分生孢子在不同介质萌发的形态变化及萌发所需能量来源。结果表明：O. heveae 分生孢子表面具有较浅的花纹结构,呈椭圆形或者卵圆形,大小为26.1~45.1μm×13.5~21.9μm。O. heveae 分生孢子在亲水和疏水介质上均能萌发产生芽管和附着胞,在葡萄糖水中的萌发率略高于清水中,但萌发率无显著性差异 (P>0.05),芽管和附着胞形成与形态无明显差别。分生孢子萌发过程中,几个液泡会融合形成一个,最终消散而呈不明显可见的泡囊结构。孢子内的糖原、脂质及分裂后的核仁等可通过芽管向附着胞输送,表明O. heveae 分生孢子萌发所需能量物质主要来源于自身能量贮备。     

Influence of Nutrient and Environmental Factors on Conidial Germination of Potebniamyces pyri

ABSTRACT Potebniamyces pyri is the causal agent of Phacidiopycnis rot, a postharvest disease of pears. Infection of fruit occurs in the orchard, and symptoms develop during storage. Conidial germination of P. pyri in response to nutrient, temperature, wetness duration, relative humidity (RH), and pH was determined in vitro. Conidia germinated by either budding or developing germ tubes in various concentrations of pear juice solutions. The mode of conidial germination was nutrient-dependent. Low nutrient levels favored budding, whereas high nutrient levels favored germ tube development. Conidia germinated at 0 to 30 degrees C but not at 35 degrees C, with optimum temperature between 20 and 25 degrees C. Wetness durations of 4 to 5 h and 6 to 8 h at optimum temperature were required for budding and developing germ tubes, respectively, and 20 to 24 h of wetness was required to reach germination peaks. Regardless of temperature, conidia germinated primarily by budding in 10% pear juice. Secondary conidia, produced by budding of conidia, initially increased their dimensions and later germinated at 0 to 25 degrees C in the same manner as mother conidia. No germination of secondary conidia occurred at 30 degrees C. Germ tubes from conidia elongated at 0 to 25 degrees C but not at 30 degrees C. No germination occurred at 相似文献   

Infection efficiency of Phaeoisariopsis personata and the influence of different wetness patterns on germ-tube growth of the pathogen

Controlled environment studies with Phaeoisariopsis personata , the causal agent of late leaf spot disease of groundnut ( Arachis hypogaea ), have shown that infection is enhanced if leaves are exposed to alternate wet and dry periods (intermittent wetness) compared with continuous wetness. Detailed investigations to elucidate this phenomenon revealed more germ tubes per conidium and more branching of germ tubes with intermittent wetness than with continuous wetness. With intermittent wetness there was clear evidence of tropic growth of germ tubes and branches towards stomata and subsequent penetration. With continuous wetness, germ tube growth did not appear to be directional and germ tubes commonly passed over the stomatal guard cells, therefore leading to relatively few stomatal penetrations. For both wetness regimes, stomatal penetrations continued to increase with increased leaf wetness for at least 6 days after inoculation and there was a linear relationship between the number of stomatal penetrations and the number of resultant lesions. Infection efficiency was markedly increased when the spore load was reduced to 0.1 conidia per cm² (about one spore per leaflet).     

Subcuticular-Intracellular Hemibiotrophic and Intercellular Necrotrophic Development of Colletotrichum acutatum on Almond

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.     

Microscopical studies of the infection of gerbara flowers byBotrytis cinerea

The formation of lesions on ray florets of gerbera flowers caused by single conidia ofBotrytis cinerea was studied in two cultivars infected by two isolates of the pathogen. No differences in reaction after inoculation with conidia of either isolate were seen on either cultivar. The conidia produced usually one germ tube not longer than 10 m, but conidia with five germ tubes were also seen. Direct penetration of germ tubes through the upper cuticle of ray florets was observed. No appressoria or other specialised structures were observed before penetration, and degradation of the cuticle did not occur. Germination of conidia and subsequent flower infection was dependent on the availability of free water, but not on the addition of external nutrients.Between 18 to 25°C, fungal development usually stopped after cuticle penetration, two to four cells around the site of penetration becoming necrotic. This number did not increase when inoculated flowers were subsequently placed at 4°C, conditions conductive for the formation of spreading lesions. When flowers were incubated constantly at 4°C, lesions became visible 3 days after inoculation as a group of 10 to 14 cells. Initially from a vesicle-like structure, mycelium spread subcuticularly or in the lumen of epidermal cells resulting in the death of 40 to 50 cells at 18 days after inoculation. Ungerminated conidia and conidial germlings which has not yet penetrated the cuticle did not cause any visible symptoms in underlying epidermal cells.     

Light and scanning electron microscopy studies on the infection process of melon leaves by Colletotrichum lagenarium

Colletotrichum lagenarium is the casual agent of anthracnose disease of melons. Light and scanning electron microscopy were used to observe the infection process of C. lagenarium on the leaves of two melon cultivars differing in susceptibility. On both cultivars conidia began germinating 12 h after inoculation (hai), forming appressoria directly or at the tips of germ-tubes. By 48 hai appressoria had melanised and direct penetration of host tissue had begun. On the susceptible cultivar, infection vesicles formed within 72 hai and developed thick, knotted primary hyphae within epidermal cells. By 96 hai C. lagenarium produced highly branched secondary hyphae that invaded underlying mesophyll cells. After 96 hai, light brown lesions appeared on the leaves, coincident with cell necrosis and invasion by secondary hyphae. While appressoria formed more quickly on the resistant cultivar, fewer germinated to develop biotrophic primary or invasive necrotrophic secondary hyphae than on the susceptible cultivar. These results confirm that C. lagenarium is a hemibiotrophic pathogen, and that resistance in melons restricts colonisation by inhibiting the development of necrotrophic secondary hyphae.     

Rapid pregermination and germination responses of <Emphasis Type="Italic">Erysiphe pisi</Emphasis> conidia to contact and light

In darkness, most Erysiphe pisi conidia responded rapidly to contact with a hydrophobic artificial substratum and released extracellular material (ECM) in the same way as on pea cuticle. On this substratum and barley leaf epidermis, conidia then produced a germ tube that emerged close to the substratum, contacted it, and differentiated an appressorium. By contrast, on a hydrophilic substratum, ECM release and germination were delayed and infrequent, and germ tubes often emerged and faced away from the substratum toward vertical light, thereby failing to make contact and form appressoria. This finding supported the hypothesis that ECM release is involved in both triggering germination and sensing substratum contact. Exposure to white light dramatically affected the germ tube emergence site so most emerged from a site in the conidial wall facing the light. Lateral light did not affect the frequency of germ tubes making substratum contact; but when lit from above, most germ tubes emerged up, facing away from the substratum. The germ tubes formed in light were longer than those formed in darkness, but no phototropism was found for the elongating tubes. Examination of Blumeria graminis indicated that its conidia and germ tubes are insensitive to white light.     

The role of primary germ tubes in the life cycle of Blumeria graminis: The primary germ tube is responsible for the suppression of resistance induction of a host plant cell

When the conidia of Blumeria graminis f. sp. hordei (Bgh) are inoculated on barley coleoptile cells they produce short germ tubes called primary germ tubes (PGTs) about 2 h after inoculation. We evaluated the positive role of a PGT in inducing accessibility of the host cell under the germ tube. When an appressorium (APP) penetrated the same cell on which a PGT was present, the ratio of haustorium formation (penetration efficiency) was significantly higher than when an APP penetrated the cell adjacent to the one on which a PGT was present. When an APP penetrated the cell laterally adjacent to the one on which a PGT was present we killed the cell under the PGT by puncturing it with a microneedle and then investigated the penetration efficiency of the cell adjacent to the dead cell. As a control we killed the cell longitudinally adjacent to the one on which a PGT was present and investigated the penetration efficiency of the laterally adjacent cell. The results showed that the penetration efficiency of the former was significantly lower than that of the latter. This suggests that some accessibility factor might transfer from a cell on which a PGT is present to a laterally adjacent cell. The existence of a conidium body but not a PGT was not effective for induced accessibility of the host cell. Moreover, when a Bgh germling was removed 6 h after inoculation and another germling was transferred to the same cell, the penetration efficiency was significantly higher than that of control. As a control, a Bgh germling was transferred to a cell on which no germling was present. These results suggest that the existence of PGT is effective for induced accessibility of a host cell when penetrated by Bgh. However, it is unclear whether or not a PGT secretes some substance(s) which suppresses the resistance induction of a host cell.     

The role of primary germ tubes in the life cycle of Blumeria graminis: The primary germ tube is responsible for the suppression of resistance induction of a host plant cell

When the conidia of Blumeria graminis f. sp. hordei (Bgh) are inoculated on barley coleoptile cells they produce short germ tubes called primary germ tubes (PGTs) about 2 h after inoculation. We evaluated the positive role of a PGT in inducing accessibility of the host cell under the germ tube. When an appressorium (APP) penetrated the same cell on which a PGT was present, the ratio of haustorium formation (penetration efficiency) was significantly higher than when an APP penetrated the cell adjacent to the one on which a PGT was present. When an APP penetrated the cell laterally adjacent to the one on which a PGT was present we killed the cell under the PGT by puncturing it with a microneedle and then investigated the penetration efficiency of the cell adjacent to the dead cell. As a control we killed the cell longitudinally adjacent to the one on which a PGT was present and investigated the penetration efficiency of the laterally adjacent cell. The results showed that the penetration efficiency of the former was significantly lower than that of the latter. This suggests that some accessibility factor might transfer from a cell on which a PGT is present to a laterally adjacent cell. The existence of a conidium body but not a PGT was not effective for induced accessibility of the host cell. Moreover, when a Bgh germling was removed 6 h after inoculation and another germling was transferred to the same cell, the penetration efficiency was significantly higher than that of control. As a control, a Bgh germling was transferred to a cell on which no germling was present. These results suggest that the existence of PGT is effective for induced accessibility of a host cell when penetrated by Bgh. However, it is unclear whether or not a PGT secretes some substance(s) which suppresses the resistance induction of a host cell.     

Effects of ozone exposure and leaf age of wheat on infection processes of Septoria nodorum Berk.

The infection process of Septoria nodorum was studied on the flag and second leaves of wheat plants at the flag-leaf emergence growth stage (GS 39), after pre-inoculative fumigation with different doses of ozone (0, 80, 180 or 240 μg/m³) for 7 h daily over 7 days. On ozone-treated plants, formation of appressoria occurred earlier, leading to a greater number and density of appressoria and faster growth of superficial infection hyphae than on plants grown without ozone amendment. Additionally, on leaves treated with 180 and 240 μg/m³ ozone, the percentage of papillae per appressorium was only half that on control plants. The number of germ tubes per conidium was not significantly affected by any treatment. Effects of increasing leaf age on the infection process were similar to those obtained with ozone. These results provide further evidence for similarities in the physiological effects of ozone and leaf ageing, which support the hypothesis that disease alterations due to ozone are strongly determined by the senescing effects of the pollutant.     

Induction, Regulation, and Role in Pathogenesis of Appressoria in Monilinia fructicola

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.     

荸荠茎点霉秆枯病菌侵染过程的超微观察

<正>荸荠(Eleocharis dulcis),又称马蹄,为莎草科多年生草本植物,是一种具有食用和药用价值的水生蔬菜。近年来,随着荸荠在我国种植面积的不断扩大,病害发生也呈逐年上升趋势。荸荠茎点霉秆枯病是2009年在湖北省荸荠产区发现的一种新病害,由Phoma bellidis侵染引起,该病在湖北省团风地区发生尤为严重,对荸荠的产量和品质造成严重影响;病害一般在8~12月发生,发病初期在荸荠茎秆上产生圆形或梭形红褐色小斑,随后病斑沿茎