Ultrastructure of conidia, conidium germination, and appressorium development in the plant pathogenic fungus Colletotrichum truncatum

1991 ◽  
Vol 69 (11) ◽  
pp. 2455-2467 ◽  
Author(s):  
C. Gerald Van Dyke ◽  
Charles W. Mims
Keyword(s):  
Germ Tube ◽  
Pathogenic Fungus ◽  
Freeze Substitution ◽  
Colletotrichum Truncatum ◽  
Dialysis Membrane ◽  
The Matrix ◽  
Single Nucleus ◽  
Conidium Germination ◽  
Matrix Spread ◽  
Germ Tubes

Nongerminating conidia of Colletotrichum truncatum were coated with copious amounts of a finely fibrillar extracellular matrix. This matrix spread out onto the dialysis membrane used as a substrate in this study. Each thin-walled conidium contained a single nucleus that underwent mitosis 1–2 h following placement of aqueous suspensions of conidia on membranes. A septum subsequently developed near the middle of the conidium, creating two uninucleate cells. Just prior to or during septum development a germ tube emerged laterally, usually near one end of the conidium. The nucleus moved into the germ tube and underwent mitosis. One daughter nucleus remained in the germ tube, the other moved back into the conidium. Developing germ tubes appeared to produce large amounts of electron-dense, fibrillar material that coated their surfaces. This material blended into the remnants of the matrix initially coating conidia and could not be clearly differentiated from the latter material. Germ tubes grew to various lengths before forming appressoria. Appressorium differentiation began shortly after the germ-tube tip curved sharply. A septum developed to delimit the tip that differentiated into a swollen appressorium. By 6 h following initial hydration of conidia, appressoria were melanized and the surrounding extracellular material had condensed onto their surfaces, forming an electron-dense coating that appeared to stick appressoria to dialysis membranes. A tiny penetration peg developed from an apparently wall-less region on the underside of the mature appressorium and, in some instances, grew a short distance into the dialysis membrane. Key words: electron microscopy, freeze substitution, conidia, appressoria.

Ultrastructure of conidia and conidium germination in the plant pathogenic fungus Alternaria cassiae

1997 ◽  
Vol 75 (2) ◽  
pp. 252-260 ◽  
Author(s):  
C. W. Mims ◽  
M. A. Rogers ◽  
C. G. Van Dyke
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Germ Tube ◽  
Pathogenic Fungus ◽  
Freeze Substitution ◽  
Dialysis Membrane ◽  
Common Mode ◽  
Plant Pathogenic Fungus ◽  
Transmission Electron ◽  
Germ Tubes

Transmission electron microscopy of plunge-frozen and freeze-substituted samples was used to examine germinating conidia of Alternaria cassiae, a plant pathogenic fungus used as a biological control agent for sicklepod (Cassia obtusifolia). Hydrated conidia on small pieces of dialysis membrane were incubated for 1, 2, or 3 h on the surface of corn meal agar prior to fixation. Conidia were large, darkly pigmented, and surrounded by a thick, two-layered wall. Each conidium was divided by transverse and longitudinal septa into multiple cells, a few of which sometimes appeared necrotic. Each septum tapered to a small central pore region with which Woronin bodies were associated. Each healthy cell of a conidium contained a typical complement of cellular organelles including multiple nuclei. With the exception of lipid bodies, all the various organelles were well preserved by plunge freezing and freeze substitution. Evidence of germ tube development was visible by 2 h post-incubation and well-developed germ tubes were present by 3 h. Two modes of germ tube development were observed. In the less common mode germ tubes developed inside conidia and grew internally through one or more adjacent cells before emerging from the conidium surface. Cells penetrated by internal germ tubes appeared necrotic. In the more common mode of germination, germ tubes developed directly from the conidium surface. Multiple germ tubes usually arose from each conidium and grew out in all directions. Germ tubes that contacted the underlying dialysis membrane continued to grow along its surface. Extracellular material was produced in association with developing germ tubes and coated the sides of germinated conidia and covered germ tubes growing along membranes. Key words: transmission electron microscopy, cryofixation, freeze substitution, germ tube development.

Substrate surface influences upon germination of Colletotrichum truncatum conidia

1994 ◽  
Vol 72 (12) ◽  
pp. 1758-1765 ◽  
Author(s):  
G. H. Egley
Keyword(s):  
Germ Tube ◽  
Substrate Surface ◽  
Cellulose Nitrate ◽  
Colletotrichum Truncatum ◽  
Glass Cover ◽  
Solid Substrates ◽  
Appressoria Formation ◽  
Germ Tubes ◽  
Cellulose Nitrate Filter ◽  
Good Germination

Substrates influenced germination of conidia of the mycoherbicide, Colletotrichum truncatum. Very few (< 10%) conidia germinated when incubated while suspended in water or when incubated on or in partially liquefied agar. Many (> 70%) were induced to germinate when incubated on firm agar. The percentage of germinated conidia increased as agar firmness increased. Not all solid substrates equally influenced germination. Over 50% of the conidia germinated on chromatography paper, cellulose acetate filter, or on hard (plastic cover slip) substrates. In contrast, germination was relatively poor on cellulose nitrate filter and glass cover slips. Some natural substrates of dissimilar texture (wood, live plant leaf) produced good germination. Lower O2 levels or limited gas exchange for submerged conidia did not prevent germination because many conidia germinated while submerged on or between firm substrates. Subjecting conidia to motion during incubation between glass cover slips favored germ tube production rather than appressoria formation. Evidence suggests a positive germination response of C. truncatum conidia to solid substrates that occurs prior to the well-documented thigmotropic response of germ tubes of germinated conidia. Key words: Colletotrichum truncatum, conidia germination, thigmotropism, substrate.

scholarly journals Pecan Scab Fungus Lacks Substrate Specificity for Early Infection Stages

1996 ◽  
Vol 121 (5) ◽  
pp. 948-953 ◽  
Author(s):  
I.E. Yates ◽  
K.M.T. Cason ◽  
Darrell Sparks
Keyword(s):  
Substrate Specificity ◽  
Surface Hardness ◽  
Deionized Water ◽  
Dialysis Membrane ◽  
Appressorium Formation ◽  
Pecan Scab ◽  
Stomatal Guard Cells ◽  
Conidium Germination ◽  
Chemical Stimuli ◽  
Germ Tubes

Leaves and callus of pecan [Carya illinoinensis (Wangenh.) K. Koch], and glass, dialysis membrane, and agar were examined for capacity to support two of the earliest infection stages—conidium (spore) germination and appressorium formation—of Cladosporium caryigenum (Ellis & Langl.) Gottwald, the fungus causing pecan scab. Light and temperature effects on formation of germ tubes and appressoria were examined for conidia suspended in distilled-deionized water. Conidia formed germ tubes on all substrates and in distilled-deionized water; hence, conidia possessed endogenous materials required for germination and are independent of specific topographic or chemical stimuli. All substrates, except 2% water agar and water, sustained appressoria development, thus implicating regulation by surface hardness. More appressoria formed on leaf discs than on other substrates. Additionally, conidia formed appressoria with short germ tubes when near a leaf structural feature, such as stomatal guard cells. Thus, the pecan scab fungal isolate used in these experiments appeared to lack substrate specificity for forming germ tubes, but not appressoria, during the prepenetration stages of development. Conidium germination was maximized at about 25 °C and germination did not respond to light.

scholarly journals APPRESSORIUM FORMATION IN THE PECAN SCAB FUNGUS

HortScience ◽  
1992 ◽  
Vol 27 (6) ◽  
pp. 627f-627
Author(s):  
K.M.T. Cason ◽  
I.E. Yates
Keyword(s):  
Germ Tube ◽  
Light And Electron Microscopy ◽  
Preliminary Evidence ◽  
Tube Length ◽  
Dialysis Membrane ◽  
Appressorium Formation ◽  
Pecan Scab ◽  
Germ Tubes

Pecan scab, caused by the fungus Cladosporium caryigenum (Ell. et Lant) Gottwald, produces more damage to pecan than all other diseases and insects combined. Early events during infection are critical to disease establishment and to expression of host resistance, but have not been examined previously. Objectives of this research were to determine if there is regulation of appressorial formation and if it is related to resistance. Pre-infectional host-pathogen interactions were studied in vivo (on leaves) and in vitro (on callus, dialysis membrane, and agar) with light and electron microscopy. Leaves, callus tissue, dialysis membranes, and agar were inoculated with scab conidia and were incubated under conditions optimum for germination. Conidia germinate and produce a germ tube on agar and dialysis membrane, but appressoria are not formed. Appressoria form on pecan callus, but germ tubes are long. Long germ tubes are often associated with resistant disease reactions. In vivo, appressoria form readily, but germ tube length varies depending on the location of the spore on the leaf surface. Preliminary evidence indicates that surface topography affects induction of appressorium formation in the scab fungus.

Ultrastructure of conidium germination of Cochliobolus carbonus

1974 ◽  
Vol 52 (11) ◽  
pp. 2335-2340 ◽  
Author(s):  
Gordon M. Murray ◽  
Douglas P. Maxwell
Keyword(s):  
Germ Tube ◽  
Tube Wall ◽  
Outer Electron ◽  
Spherical Form ◽  
Innermost Layer ◽  
Apical Vesicles ◽  
Conidium Germination ◽  
Central Pore ◽  
Septal Pores ◽  
Germ Tubes

Multiseptate conidia of Cochliobolus carbonus germinate in water by one or two polar germ tubes. The septa between cells within a conidium contain a central pore, which is plugged before germination but open during germination, so that all cells are interconnected. During germination, vacuoles enlarge, endoplasmic reticulum profiles increase in number, and mitochondria change from a spherical form with loosely arranged cristae to an elongated form with closely packed cristae. The conidium wall consists of an inner electron-translucent layer and an outer electron-opaque layer. The germ tube wall is continuous with the innermost layer of the conidium wall. Shortly after germination, a septum with a central pore forms in the germ tube by invagination where it emerges from the conidium. The germ tube wall is surrounded by a fibrillar sheath. The presence of apical vesicles in the germ tube tip is confirmed. The associations of Woronin bodies with septal pores and microbodies, of lipids with vacuoles, and of microbodies with lipids and vacuoles are discussed.

Ultrastructure and lipid identification during conidium germination of Stemphylium sarcinaeforme

1976 ◽  
Vol 22 (1) ◽  
pp. 92-100 ◽  
Author(s):  
Gordon M. Murray ◽  
Douglas P. Maxwell
Keyword(s):  
Endoplasmic Reticulum ◽  
Acid Phosphatase ◽  
Total Lipid ◽  
Germ Tube ◽  
Tube Wall ◽  
Dry Weight ◽  
Lipid Bodies ◽  
Conidium Germination ◽  
Germ Tubes ◽  
Qualitative Changes

Multicelled conidia of Stemphylium sarcinaeforme germinate in water forming several germ tubes. Individual cells within conidia are connected by pores which are plugged in ungerminated conidia and open in germinated ones. During germination, vacuoles enlarge, endoplasmic reticulum profiles increase in number, and mitochondria change from spherical to elongate. The germ tube wall is laid down at the site of emergence from the conidium. Shortly after germination, a septum with a central pore forms where the germ tube emerged. The germ tube wall is surrounded by a fibrillar sheath. Lipid bodies are closely associated with vacuoles during germination. The ultrastructural location of lipid was found by extraction of conidia with lipid solvents. Total lipid decreases from 14.4% of the dry weight of ungerminated conidia to 13.4% of the dry weight of conidia germinated for 10 h. No qualitative changes occurred in the major lipid classes of conidia during germination. The activities of lipase and acid phosphatase were detected in ungerminated and germinated conidia.

High-pressure freezing and freeze substitution of teliospores of the rust fungus Gymnosporangium clavipes

1990 ◽  
Vol 48 (3) ◽  
pp. 692-693
Author(s):  
Robert W. Roberson
Keyword(s):  
High Pressure ◽  
Room Temperature ◽  
Pathogenic Fungus ◽  
Rust Fungus ◽  
Freeze Substitution ◽  
Ice Crystals ◽  
High Pressure Freezing ◽  
Thin Walled Structures ◽  
Cytological Changes ◽  
Dextran Solution

The use of cryo-techniques for the preparation of biological specimens in electron microscopy has led to superior preservation of ultrastructural detail. Although these techniques have obvious advantages, a critical limitation is that only 10-40 μm thick cells and tissue layers can be frozen without the formation of distorting ice crystals. However, thicker samples (600 μm) may be frozen well by rapid freezing under high-pressure (2,100 bar). To date, most work using cryo-techniques on fungi have been confined to examining small, thin-walled structures. High-pressure freezing and freeze substitution are used here to analysis pre-germination stages of specialized, sexual spores (teliospores) of the plant pathogenic fungus Gymnosporangium clavipes C & P.Dormant teliospores were incubated in drops of water at room temperature (25°C) to break dormancy and stimulate germination. Spores were collected at approximately 30 min intervals after hydration so that early cytological changes associated with spore germination could be monitored. Prior to high-pressure freezing, the samples were incubated for 5-10 min in a 20% dextran solution for added cryoprotection during freezing. Forty to 50 spores were placed in specimen cups and holders and immediately frozen at high pressure using the Balzers HPM 010 apparatus.

Freeze substitution fixation of fungal reproductive structures and spores

1989 ◽  
Vol 47 ◽  
pp. 990-991
Author(s):  
C. W. Mims ◽  
E. A. Richardson
Keyword(s):  
Plant Pathogens ◽  
Freeze Substitution ◽  
Uranyl Acetate ◽  
Chemical Fixation ◽  
Dialysis Membrane ◽  
Razor Blade ◽  
Thin Sections ◽  
Reproductive Structures ◽  
Dry Down ◽  
Diamond Knife

The advantages of freeze substitution fixation over conventional chemical fixation for preservation of ultrastructural details in fungi have been discussed by various authors. As most ascomycetes, basidiomycetes and deuteromycetes do not fix well using conventional chemical fixation protocols, freeze substitution has attracted the attention of many individuals interested in fungal ultrastructure. Thus far most workers using this technique on fungi have concentrated on thin walled somatic hyphae. However, in our laboratory we have experimented with the use of freeze substitution on a variety of fungal reproductive structures and spores with promising results.Here we present data on freeze substituted samples of sporangia of the zygomycete Umbellopsis vinacea, basidia of Exobasidium camelliae var. gracilis, developing teliospores of the smut Sporisorium sorghi, germinating teliospores of the rust Gymnosporangium clavipes, germinating conidia of the deuteromycete Cercosporidium personatum, and developing ascospores of Ascodesmis nigricans.Spores of G. clavipes and C. personatum were deposited on moist pieces of sterile dialysis membrane where they hydrated and germinated. Asci of A. nigricans developed on pieces of dialysis membrane lying on nutrient agar plates. U. vinacea was cultured on small pieces of agar-coated wire. In the plant pathogens E. camelliae var. gracilis and S. sorghi, a razor blade was used to remove smal1 pieces of infected host issue. All samples were plunged directly into liquid propane and processed for study according to Hoch.l Samples on dialysis membrane were flat embedded. Serial thin sections were cut using a diamond knife, collected on slot grids, and allowed to dry down onto Formvar coated aluminum racks. Sections were post stained with uranyl acetate and lead citrate.

scholarly journals Use of seed treatment with fungicide in control of colletotrichum truncatum and physiological quality of soybean seeds glycine max

2013 ◽  
Vol 4 (2) ◽  
pp. 98-106
Author(s):  
Vinícius Almeida Oliveira ◽  
Lorenxo Paradiso Martins ◽  
Rogério Cavalcante Gonçalves ◽  
Luíz Paulo Figueredo Benício ◽  
Daniella Lima da Costa ◽  
...  
Keyword(s):  
Glycine Max ◽  
Seed Treatment ◽  
Pathogenic Fungus ◽  
Dry Weight ◽  
Soybean Seeds ◽  
Colletotrichum Truncatum ◽  
Fresh Weight ◽  
Crop Development ◽  
Physiological Quality

The fungus are the main microorganisms present in seeds, is the main cause of deterioration and loss in production. The anthracnose caused by C. truncatum associated with soybean seeds as has main vehicle for introduction into the planting areas can be detected in all stages of crop development, from the cotyledons to the end of the cycle, being present in the stems, veins, leaflets and pods. Thus aimed to evaluate the influence of using different products fungicides as seed treatment, where the seeds were inoculated with the pathogenic fungus and treated with the chemicals They take Carbedazim + Fludioxonil + metalaxyl-M and carboxin + thiram. For each fungicide product was two tramentos done using the doses recommended by the manufacturer and 75% of dose. We evaluated health, germination and promote plant (Plant growth, fresh weight and dry weight of root and shoot). This work concludes that the use of fungicide controls significantly seeds infected with C. truncatum and presents a significant improvement as the development of structures seedling.

Anastomosis of germ tubes and migration of nuclei in germ tube networks of the soybean rust pathogen, Phakopsora pachyrhizi

2011 ◽  
Vol 132 (2) ◽  
pp. 163-167 ◽  
Author(s):  
R. Vittal ◽  
H. -C. Yang ◽  
G. L. Hartman
Keyword(s):  
Germ Tube ◽  
Soybean Rust ◽  
Phakopsora Pachyrhizi ◽  
Rust Pathogen ◽  
And Migration ◽  
Germ Tubes
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