Early interactions during powdery mildew infection

Within minutes of spore deposition, enzymes including cutinase are released by conidia of Erysiphe graminis; these may prepare the infection court and facilitate subsequent fungal development. Germination follows with emergence of the primary germ tube, which contacts the host leaf. Extracellular material is secreted beneath the primary germ tube, which adheres to the leaf. The primary germ tube forms a penetration peg that breaches the host surface and gains access to host cell components including water. The primary germ tube also recognises factor(s) present in the host surface, and this stimulates elongation of the second-formed germ tube. The elongated second tube in turn responds to host surface factor(s) by differentiating an appressorium. Extracellular material, secreted beneath the growing appressorial germ tube, is laid down thickly around the appressorial lobe. An inner ring of extracellular material can often be seen surrounding penetration pores revealed by the removal of primary germ tubes and appressoria. The chemistry of the extracellular material is unknown, but in addition to adhesive properties recent studies show that a monoclonal antibody that recognises purified cutinase and, possibly, hemicellulases, binds to secretions from conidia, primary germ tubes, and appressoria. External factors can also influence germling development. Although light has little effect on the early stages of germling development, it has a profound effect in delaying the formation of haustoria by apparently mature appressoria. Understanding the control of early pathogen development could indicate avenues for genetic engineering and breeding for disease-resistant plants. Key words: Erysiphe graminis, powdery mildew, primary germ tube (PGT), appressoria, extracellular material.

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Initial events in the establishment of cereal powdery mildew infection

Plant Protection Science ◽

10.17221/10322-pps ◽

2002 ◽

Vol 38 (SI 1 - 6th Conf EFPP 2002) ◽

pp. S65-S68 ◽

Cited By ~ 2

Author(s):

T.L.W. Carver ◽

A.J. Wright ◽

B.J. Thomas

Keyword(s):

Powdery Mildew ◽

Germ Tube ◽

Blumeria Graminis ◽

Extracellular Material ◽

Contact Site ◽

Powdery Mildew Fungus ◽

Wind Speeds ◽

Tube Emergence ◽

Conidial Surface ◽

Powdery Mildew Infection

Like spores of many fungi, conidia of Blumeria graminis, the powdery mildew fungus of cereals, release extracellular material. It is released within seconds where conidial surface projections touch a leaf. This ECM is probably adhesive since centrifugation showed that forces greater than those due to normal wind speeds are needed to displace conidia. Also, ECM release is probably involved in rapid sensing of substratum contact, leading to germ tube emergence close to the contact site. Thus, ECM release apparently confers at least two benefits to pathogen survival.

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Cytological studies of early stages of powdery mildew in barley and wheat. IV. Direct ingress from superficial primary germ tubes and appressoria of Erysiphe graminis hordei on barley leavest

Physiological Plant Pathology ◽

10.1016/0048-4059(78)90049-8 ◽

1978 ◽

Vol 13 (3) ◽

pp. 327-333 ◽

Cited By ~ 37

Author(s):

H. Kunoh ◽

T. Tsuzuxi ◽

H. Ishizaki

Keyword(s):

Powdery Mildew ◽

Erysiphe Graminis ◽

Early Stages ◽

Erysiphe Graminis Hordei ◽

Germ Tubes

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First Report of Powdery Mildew on Lemon Balm (Melissa officinalis) Caused by Golovinomyces biocellatus in Hungary

Plant Disease ◽

10.1094/pdis-94-9-1169a ◽

2010 ◽

Vol 94 (9) ◽

pp. 1169-1169 ◽

Cited By ~ 2

Author(s):

E. Kassai-Jáger ◽

L. Kiss ◽

Z. Váczy ◽

K. Z. Váczy

Keyword(s):

Powdery Mildew ◽

Plant Species ◽

Its Sequences ◽

Lemon Balm ◽

Powdery Mildews ◽

Leaf Surfaces ◽

Pathogenicity Tests ◽

Pathogen Dna ◽

Germ Tubes ◽

Powdery Mildew Infection

Lemon balm is a well-known perennial, medicinal and culinary herb, and also a melliferous plant that is grown commercially in many parts of the world including Hungary. In October 2009, symptoms of powdery mildew infection were observed on lemon balm plants grown in several gardens in Budapest, Maklár, and Eger, Hungary, as well as in Ghenci, Romania. Abundant mycelium and conidial sporulation was observed on both leaf surfaces and stems. Conidia were produced in chains and were ellipsoid-ovoid to subcylindrical, measured 29 to 44 × 15 to 18 μm, and germinated with germ tubes produced apically or subapically on conidia. The basal septa of the conidiophores were sometimes displaced from the point of branching. The width of their foot cells increased from base to top and sometimes enlarged considerably at a particular point. Hyphal appressoria were nipple shaped. On the basis of these characteristics, the pathogen was identified as an Oidium sp. belonging to the subgenus Reticuloidium. The teleomorph stage was not found. To precisely identify the pathogen, DNA was extracted from mycelia collected from single leaves collected in Budapest and Ghenci with a Qiagen (Valencia, CA) DNeasy Plant Kit. The internal transcribed spacer (ITS) sequences of the nrDNA were amplified and sequenced as described in Jankovics et al. (3). The two ITS sequences, deposited in GenBank under Accession Nos. HM156493 and HM156494, were identical to several ITS sequences of Golovinomyces biocellatus, such as AB307675, AF011291, and EU035602. Thus, the pathogen was identified as G. biocellatus based on the host plant species, anamorph morphology, and ITS sequence. It was clearly distinguished from Neoerysiphe galeopsidis, another powdery mildew species known to infect lemon balm in Europe (1). Specimens were deposited under Accession Nos. HAL 2369F and HAL 2370F at the Herbarium of Martin Luther University, Halle, Germany. Pathogenicity tests were carried out in cabinets within a controlled environment as described for other powdery mildews in Jankovics et al. (3) using five potted healthy lemon balm plants bought from a nursery. The first powdery mildew colonies appeared 7 to 10 days after inoculation, and 2 to 3 weeks later, nearly all the leaves and stems of the three inoculated plants became covered with powdery mildew mycelium. Light microscopy confirmed that the pathogen was the anamorph of G. biocellatus. The two noninoculated plants remained healthy. This confirmed the pathogenicity of the fungus collected from the field to lemon balm. G. biocellatus has long been known to infect lemon balm in some European countries and elsewhere (1), but was not listed as a pathogen of this plant species in Hungary (4). However, it was reported from Romania, a neighboring country, more than 30 years ago (2). This suggests that G. biocellatus might have occurred in Hungary on lemon balm during the past decades without being reported in the literature. References: (1) U. Braun. Beih. Nova Hedwigia 89:1, 1987. (2) O. Constantinescu and G. Negrean. Sydowia 29:75, 1976-77. (3) T. Jankovics et al. Phytopathology 98:529, 2008. (4) Sz. Nagy and L. Kiss. Acta Phytopathol. Entomol. Hung. 41:79, 2006.

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Morphogenesis of Powdery Mildew Fungi in Water (3) Decrease of the Formation and Penetration Frequency of Short Germ Tubes from Water-Immersed Conidia of Erysiphe graminis.

Japanese Journal of Phytopathology ◽

10.3186/jjphytopath.60.636 ◽

1994 ◽

Vol 60 (5) ◽

pp. 636-639 ◽

Cited By ~ 2

Author(s):

Naoto YAMAOKA ◽

Yoshimi MARUYAMA ◽

Issei KOBAYASHI ◽

Hitoshi KUNOH

Keyword(s):

Powdery Mildew ◽

Erysiphe Graminis ◽

Powdery Mildew Fungi ◽

Germ Tubes

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The surface of Erysiphe graminis and the production of extracellular material at the fungus – host interface during germling and colony development

Canadian Journal of Botany ◽

10.1139/b95-030 ◽

1995 ◽

Vol 73 (2) ◽

pp. 272-287 ◽

Cited By ~ 34

Author(s):

T. L. W. Carver ◽

B. J. Thomas ◽

S. M. Ingerson-Morris

Keyword(s):

Electron Microscopy ◽

Scanning Electron Microscopy ◽

Low Temperature ◽

Erysiphe Graminis ◽

Colony Development ◽

Extracellular Material ◽

Fungal Enzymes ◽

Temperature Scanning ◽

Germ Tubes ◽

Scanning Electron

Low temperature scanning electron microscopy was used to study the development of Erysiphe graminis DC f.sp. avenae Marchal from germination through infection to sporulation of the fungal colony. To clarify resolution of the fungus–host interface and facilitate interpretation of fungal surface structures, epicuticular waxes were removed from host leaves before inoculation. Whereas conidia were covered in spinelike protrusions or globular bodies, young germ tubes, appressoria, and hyphae were initially smooth walled, but by 15 h after inoculation, wartlike bodies, resembling globular bodies on conidia, were present on first appressorial lobes; these increased in number, eventually covering the appressorium surface and appearing on contiguous hyphae. Wartlike bodies also appeared at junctions of hyphal branches, on hyphal appressoria, and on conidiophore basal cells. Their function, if any, is unknown. The meristematic zone, at the apex of the conidiophore basal cell, remained smooth walled, but globular bodies appeared on the wall of young conidia as soon as the limiting septum had formed. Observations with the fungus in situ revealed the presence of amorphous extracellular material around primary germ tubes and appressorial lobes. Extracellular material was also present beneath appressorial germ tubes and hyphae but it was hidden unless the fungus was displaced. It could not be seen beneath conidia. The extracellular material appeared to be adhesive, sticking the fungus firmly to the host surface. Removal of the fungus showed that the extracellular material was deposited close to the tip of developing germ tubes and hyphae. It was particularly thick around primary germ tubes and appressorial lobes, and a discrete ring of extracellular material was often visible around penetration pores (holes in the leaf surface seen beneath primary germ tubes and appressorial lobes). In addition to its adhesive properties, the extracellular material may act as a matrix in which fungal enzymes are sited and focused for attack on the host. Key words: Erysiphe graminis, low temperature scanning electron microscopy, extracellular material, fungal adhesion, fungal surface morphology.

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Cytological studies of early stages of powdery mildew in barley and wheat leaves: (II) significance of the primary germ tube of Erysiphe graminis on barley leaves

Physiological Plant Pathology ◽

10.1016/0048-4059(77)90022-4 ◽

1977 ◽

Vol 10 (2) ◽

pp. 191-199 ◽

Cited By ~ 44

Author(s):

Hitoshi Kunoh ◽

Hiroshi Ishizaki ◽

Kyoko Nakaya

Keyword(s):

Powdery Mildew ◽

Germ Tube ◽

Erysiphe Graminis ◽

Early Stages ◽

Barley Leaves ◽

Wheat Leaves

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Effect of temperature, relative humidity and light on conidial germination of oak powdery mildew (Microsphaera alphitoides Griff. et Maubl.) under controlled conditions

Archives of Biological Sciences ◽

10.2298/abs1303069p ◽

2013 ◽

Vol 65 (3) ◽

pp. 1069-1077 ◽

Cited By ~ 6

Author(s):

P. Pap ◽

B. Rankovic ◽

S. Masirevic

Keyword(s):

Relative Humidity ◽

Powdery Mildew ◽

Germ Tube ◽

Inhibitory Effect ◽

Conidial Germination ◽

Effect Of Temperature ◽

Tube Length ◽

Controlled Conditions ◽

Germ Tube Length ◽

Germ Tubes

The influence of temperature, humidity and light on the conidial germination and germ tube elongation of oak powdery mildew (Microsphaera alphitoides Griff. et Maubl.) was studied in controlled conditions. The maximal germ tube length was attained at 25?C, whereas at lower and higher than optimal temperatures, germ tube growth was significantly lower. Germ tubes begin to develop at all values of relative humidity (10-100%), reaching the maximum length at 90%. The development of germ tubes was the most intense in full light and the lowest in total darkness. The artificial infection of floating leaves showed that an increasing age had an inhibitory effect on the mycelium development and spore formation. Since conidia play a crucial role in powdery mildew epidemiology, it is of particular importance to elucidate the influence of environmental factors in the complex relations that exist between the plant and its pathogen.

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Evidence that the cAMP Pathway Controls Emergence of Both Primary and Appressorial Germ Tubes of Barley Powdery Mildew

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi.2000.13.5.494 ◽

2000 ◽

Vol 13 (5) ◽

pp. 494-502 ◽

Cited By ~ 32

Author(s):

Julia Kinane ◽

Sussie Dalvin ◽

Lene Bindslev ◽

Alison Hall ◽

Sarah Gurr ◽

...

Keyword(s):

Powdery Mildew ◽

Cholera Toxin ◽

Germ Tube ◽

Cellulose Membrane ◽

Dependent Manner ◽

Biphasic Pattern ◽

Camp Pathway ◽

Barley Powdery Mildew ◽

Camp Levels ◽

Germ Tubes

Development of conidia of barley powdery mildew involves the formation of a primary germ tube (PGT), an appressorial germ tube (AGT), and an appressorium. Previously, it was found that cyclic AMP (cAMP) was involved in these developmental processes. Comparison of development on the host surface with two types of cellulose membrane revealed that frequency of PGT emergence was surface independent. On one type of cellulose, where the frequencies of both AGT and appressorial differentiation were similar to that on the host surface, cAMP levels and protein kinase A (PKA) activities had a biphasic pattern with peaks at 15 min and 4 h after inoculation (prior to PGT and AGT emergence, respectively). The effect of manipulating cAMP levels was tested on another type of cellulose membrane, which stimulated a lower degree of AGT and appressorial formation than the host surface. Cholera toxin and forskolin, activators of adenylyl cyclase, significantly increased PGT emergence, but cAMP did not. Cholera toxin, forskolin, and cAMP increased the frequency of AGT and appressorial formation, but in a time-dependent manner.

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