Peculiar ultrastructural characteristics of fungal cells and of other elements apposed to and in vessel walls in plants of a susceptible carnation cultivar, infected with Fusarium oxysporum f.sp. dianthi race 2

Abstract Ultrastructural characteristics and cytochemical reactions of unusual, irregular elements (IE) in vessel elements in susceptible carnation plants infected with Fusarium oxysporum are reported. As revealed by labelling for chitin, fungal cells in contact with host cell walls or content had altered or defective lucent layers, and labelling was frequently associated with their outer, opaque layer or matter located outside the cells. Coating matter on vessel walls occurred at all stages of infection, and IEs only in later stages. IEs were delineated by opaque, often folded bands, some contouring pit borders, and contained membranous and vesicular structures mixed with other fine components. Only then, IEs were strongly but not uniformly labelled for chitin. Coating, IE-delineating bands, and the opaque outer layer of typical fungal cells were texturally similar, not labelled for chitin or cellulose, except where they impinged upon host walls. Both probes for chitin and cellulose strongly attached to vessel secondary walls. IEs were often confluent with coating, and with fungal cells connected to them by means of microfilamentous structures. Similar microfilamentous structures and opaque bands connected to IEs, the coating, and the microhyphae, or protruding from fungal cells reached into host walls, associated with alterations of these walls. The possible malleable IEs might be a counterpart of the coating, and although they do not occur in the initial stages of the disease, they could play an important role in the final stages of tissue degradation.

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Penetration and colonization of resistant and susceptible Apium graveolens by Fusarium oxysporum f.sp. apii race 2: callose as a structural response

Canadian Journal of Botany ◽

10.1139/b88-324 ◽

1988 ◽

Vol 66 (12) ◽

pp. 2385-2391 ◽

Cited By ~ 7

Author(s):

C. M. Jordan ◽

R. M. Endo ◽

L. S. Jordan

Keyword(s):

Fusarium Oxysporum ◽

Host Cell ◽

Cell Walls ◽

Vascular Tissue ◽

Periodic Acid ◽

Light And Electron Microscopy ◽

Structural Response ◽

Aniline Blue ◽

Apium Graveolens ◽

Race 2

Root apices of Apium graveolens L. resistant and susceptible to race 2 of Fusarium oxysporum f.sp. apii (R. Nels. & Sherb.) were studied at various times after inoculation, using light and electron microscopy to determine structural response(s) of the hosts during penetration and colonization by the pathogen. Penetration was intercellular and intracellular and involved mechanical and enzymatic mechanisms. At the onset of penetration, the host cell walls manifested fluorescence, induced with either aniline blue or sirofluor, at the point of penetration. The fluorescent area was more intense and larger in the resistant host. Fluorescence disappeared with time. After incubation with β-1,3 glucanase fluorescence disappeared, indicating β-1,3 polysaccharide (probably callose) presence. Callose deposits were 2 and 3 times greater in the epidermis and 4 and 9 times greater in the cortex of the resistant than in two susceptible hosts, respectively. Hyphal counts in the cortex of the resistant host were 50% fewer than in the susceptible hosts. Increased callose deposition on host cell walls was associated with reduced colonization. Callose formed in vascular tissue as the fungus colonized it. Callose detection with sirofluor was more sensitive; background fluorescence common with aniline blue without periodic acid – Schiff's reagent pretreatment was absent.

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Treatment with the Mycoparasite Pythium oligandrum Triggers Induction of Defense-Related Reactions in Tomato Roots When Challenged with Fusarium oxysporum f. sp. radicis-lycopersici

Phytopathology ◽

10.1094/phyto.1997.87.1.108 ◽

1997 ◽

Vol 87 (1) ◽

pp. 108-122 ◽

Cited By ~ 108

Author(s):

Nicole Benhamou ◽

Patrice Rey ◽

Mohamed Chérif ◽

John Hockenhull ◽

Yves Tirilly

Keyword(s):

Plant Defense ◽

Fusarium Oxysporum ◽

Host Cell ◽

Cell Walls ◽

Pythium Oligandrum ◽

Tomato Plants ◽

Host Cytoplasm ◽

Defense Reactions ◽

Tomato Roots ◽

Root Tissues

The influence exerted by the mycoparasite Pythium oligandrum in triggering plant defense reactions was investigated using an experimental system in which tomato plants were infected with the crown and root rot pathogen Fusarium oxysporum f. sp. radicis-lycopersici. To assess the antagonistic potential of P. oligandrum against F. oxysporum f. sp. radicis-lycopersici, the interaction between the two fungi was studied by scanning and transmission electron microscopy (SEM and TEM, respectively). SEM investigations of the interaction region between the fungi demonstrated that collapse and loss of turgor of F. oxysporum f. sp. radicis-lycopersici hyphae began soon after close contact was established with P. oligandrum. Ultrastructural observations confirmed that intimate contact between hyphae of P. oligandrum and cells of the pathogen resulted in a series of disturbances, including generalized disorganization of the host cytoplasm, retraction of the plasmalemma, and, finally, complete loss of the protoplasm. Cytochemical labeling of chitin with wheat germ agglutinin (WGA)/ovomucoid-gold complex showed that, except in the area of hyphal penetration, the chitin component of the host cell walls was structurally preserved at a time when the host cytoplasm had undergone complete disorganization. Interestingly, the same antagonistic process was observed in planta. The specific labeling patterns obtained with the exoglucanase-gold and WGA-ovomucoid-gold complexes confirmed that P. oligandrum successfully penetrated invading cells of the pathogen without causing substantial cell wall alterations, shown by the intense labeling of chitin. Cytological investigations of samples from P. oligandrum-inoculated tomato roots revealed that the fungus was able to colonize root tissues without inducing extensive cell damage. However, there was a novel finding concerning the structural alteration of the invading hyphae, evidenced by the frequent occurrence of empty fungal shells in root tissues. Pythium ingress in root tissues was associated with host metabolic changes, culminating in the elaboration of structural barriers at sites of potential fungal penetration. Striking differences in the extent of F. oxysporum f. sp. radicis-lycopersici colonization were observed between P. oligandrum-inoculated and control tomato plants. In control roots, the pathogen multiplied abundantly through much of the tissues, whereas in P. oligandrum-colonized roots pathogen growth was restricted to the outermost root tissues. This restricted pattern of pathogen colonization was accompanied by deposition of newly formed barriers beyond the infection sites. These host reactions appeared to be amplified compared to those seen in nonchallenged P. oligandrum-infected plants. Most hyphae of the pathogen that penetrated the epidermis exhibited considerable changes. Wall appositions contained large amounts of callose, in addition to be infiltrated with phenolic compounds. The labeling pattern obtained with gold-complexed laccase showed that phenolics were widely distributed in Fusarium-challenged P. oligandrum-inoculated tomato roots. Such compounds accumulated in the host cell walls and intercellular spaces. The wall-bound chitin component in Fusarium hyphae colonizing P. oligandrum-inoculated roots was preserved at a time when hyphae had undergone substantial degradation. These observations provide the first convincing evidence that P. oligandrum has the potential to induce plant defense reactions in addition to acting as a mycoparasite.

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Fine structural observations on substances attributable to Ceratocystis ulmi in American elm and aspects of host cell disturbances

Canadian Journal of Botany ◽

10.1139/b78-309 ◽

1978 ◽

Vol 56 (20) ◽

pp. 2550-2566 ◽

Cited By ~ 14

Author(s):

G. B. Ouellette

Keyword(s):

Host Cell ◽

Cell Walls ◽

Parenchyma Cell ◽

Dutch Elm Disease ◽

Similar Material ◽

Fungal Cell ◽

Fibrillar Material ◽

American Elm ◽

Vessel Walls ◽

Parenchyma Cell Walls

Plugging of certain vessels may occur in elm shortly after inoculation with the Dutch elm disease pathogen, Ceratocystis ulmi (Buism.) C. Moreau. Plugging components include fibrillar material of varying density and fungal cells traceable mostly to inoculated spores. Some material is similar to fungal cell contents, and indications of extrusion of the latter through ruptured or unruptured walls were obtained. Other material is also attributable to disintegrating fungal walls. Radioautographs obtained from samples treated with [6-3H]thymidine indicate significant labeling of fungal cell contents and of similar material, free.Similar fibrillar material, some labeled, is present within pit membranes, in adjacent parenchyma cell walls, and in periplasmic areas associated with retraction of the plasmalemma and with other cytoplasmic disturbances. Host vessel walls are also altered in the presence of some fibrillar material but apparently release only limited amounts of disintegration products into vessels.The possible implications of these observations are discussed in relation to current hypotheses on wilt diseases.

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Ultrastructural and cytochemical study of colonization of xylem vessel elements of susceptible and resistant Dianthus caryophyllus by Fusarium oxysporum f.sp. dianthi

Canadian Journal of Botany ◽

10.1139/b99-033 ◽

1999 ◽

Vol 77 (5) ◽

pp. 644-663 ◽

Cited By ~ 10

Author(s):

G B Ouellette ◽

R P Baayen ◽

M Simard ◽

D Rioux

Keyword(s):

Cell Wall ◽

Fusarium Oxysporum ◽

Host Cell ◽

Parenchyma Cell ◽

Dianthus Caryophyllus ◽

Vessel Element ◽

Cytochemical Study ◽

Secondary Invasion ◽

Vessel Elements ◽

Parenchyma Cells

The colonization processes of the xylem in the susceptible carnation cv. Early Sam and the resistant cv. Novada were studied ultrastructurally following inoculation with Fusarium oxysporum f.sp. dianthi. Samples from 1 to 3 cm above the incision were collected over 5 weeks and processed following conventional procedures as well as with probes for cellulose, N-acetyl-glucosamine, and pectin. The fungus grew profusely in the vessel lumina of the susceptible cultivar. Some of the colonized vessels were lined with coating material connected to the fungal cell wall and extending into the host cell wall through microfilamentous-like structures. Coatings did not label for pectin or cellulose. The pathogen crossed from one vessel element to another (and at times to parenchyma cells) usually directly through pit membranes; often the invading structures of the fungus appeared to be either only membrane-bound or formed solely of microfilamentous-like entities. The fungus subsequently invaded extensively, generally by means of microhyphae, the vessel intercalary walls from the pit membranes and vessel wall junctures. Microhyphae had thin or imperceptible walls and contained only some of the normal cytoplasmic components. Initially, the invading hyphae dislocated the host cell walls, apparently mechanically more than by lysis; however, more pronounced lysis occurred following general tissue invasion. Host parenchyma cells seemed relatively unaffected, even after the surrounding walls had undergone severe degradation. Colonization of resistant plants was restricted. Degradation of tissues did not occur and microhyphae were not observed. Inoculated vessel elements in the 'Novada' plants contained numerous fungal cells and little occluding material, whereas the surrounding vessels were almost completely occluded. The initially invaded xylem became tangentially compartmentalized by parenchyma cell wall thickenings and by hyperplastic parenchyma. Occasionally, hyperplastic tissues were slightly re-invaded, forming secondary invasion pockets. Vessel-occluding material varied in structure and opacity, not only from vessel to vessel but also within the same vessel, and contained microfilamentous-like structures and other types of fine fibrillar material. Some vessel elements in or near the secondary invasion pockets contained only the finer fibrils that reacted strongly with an antibody specific for pectin. Vessel elements rarely contained tyloses.Key words: cellulose, chitin, Dianthus caryophyllus, Fusarium wilt, gels and gums, host wall degradation, microhyphae, pectin, tyloses.

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Effects of air discharge on surface charges and cell walls of Fusarium oxysporum

International Microbiology ◽

10.1007/s10123-020-00157-7 ◽

2021 ◽

Author(s):

Mengdie Liu ◽

Hui Tang ◽

Huiwen Jiang ◽

Jie Li ◽

Shoulei Yan ◽

...

Keyword(s):

Fusarium Oxysporum ◽

Cell Walls ◽

Surface Charges ◽

Air Discharge

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Marker Development for Differentiation of Fusarium oxysporum f. sp. Niveum Race 3 from Races 1 and 2

International Journal of Molecular Sciences ◽

10.3390/ijms22020822 ◽

2021 ◽

Vol 22 (2) ◽

pp. 822

Author(s):

Owen Hudson ◽

Sumyya Waliullah ◽

James C. Fulton ◽

Pingsheng Ji ◽

Nicholas S. Dufault ◽

...

Keyword(s):

South Carolina ◽

Fusarium Oxysporum ◽

Fusarium Wilt ◽

Conventional Polymerase Chain Reaction ◽

Detection Methods ◽

Limiting Factors ◽

Pcr Marker ◽

Primer Sets ◽

Race Differentiation ◽

Race 2

Fusarium wilt of watermelon, caused by Fusarium oxysporum f. sp. niveum (FON), is pathogenic only to watermelon and has become one of the main limiting factors in watermelon production internationally. Detection methods for this pathogen are limited, with few published molecular assays available to differentiate FON from other formae speciales of F. oxysporum. FON has four known races that vary in virulence but are difficult and costly to differentiate using traditional inoculation methods and only race 2 can be differentiated molecularly. In this study, genomic and chromosomal comparisons facilitated the development of a conventional polymerase chain reaction (PCR) assay that could differentiate race 3 from races 1 and 2, and by using two other published PCR markers in unison with the new marker, the three races could be differentiated. The new PCR marker, FNR3-F/FNR3-R, amplified a 511 bp region on the “pathogenicity chromosome” of the FON genome that is absent in race 3. FNR3-F/FNR3-R detected genomic DNA down to 2.0 pg/µL. This marker, along with two previously published FON markers, was successfully applied to test over 160 pathogenic FON isolates from Florida, Georgia, and South Carolina. Together, these three FON primer sets worked well for differentiating races 1, 2, and 3 of FON. For each marker, a greater proportion (60 to 90%) of molecular results agreed with the traditional bioassay method of race differentiation compared to those that did not. The new PCR marker should be useful to differentiate FON races and improve Fusarium wilt research.

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Review — The Orientation of Cellulose Microfibrils in the cell walls of Tracheids in Conifers

IAWA Journal ◽

10.1163/22941932-90000108 ◽

2005 ◽

Vol 26 (2) ◽

pp. 161-174 ◽

Cited By ~ 40

Author(s):

Hisashi Abe ◽

Ryo Funada

Keyword(s):

Electron Microscopy ◽

Scanning Electron Microscopy ◽

Outer Layer ◽

Cell Walls ◽

Secondary Wall ◽

Middle Layer ◽

Cellulose Microfibrils ◽

Conifer Species ◽

Predominant Orientation ◽

Scanning Electron

We examined the orientation of cellulose microfibrils (Mfs) in the cell walls of tracheids in some conifer species by field emission-scanning electron microscopy (FE-SEM) and developed a model on the basis of our observations. Mfs depositing on the primary walls in differentiating tracheids were not well-ordered. The predominant orientation of the Mfs changed from longitudinal to transverse, as the differentiation of tracheids proceeded. The first Mfs to be deposited in the outer layer of the secondary wall (S1 layer) were arranged as an S-helix. Then the orientation of Mfs changed gradually, with rotation in the clockwise direction as viewed from the lumen side of tracheids, from the outermost to the innermost S1 layer. Mfs in the middle layer of the secondary wall (S2 layer) were oriented in a steep Z-helix with a deviation of less than 15° within the layer. The orientation of Mfs in the inner layer of the secondary wall (S3 layer) changed, with rotation in a counterclockwise direction as viewed from the lumen side, from the outermost to the innermost S3 layer. The angle of orientation of Mfs that were deposited on the innermost S3 layer varied among tracheids from 40° in a Z-helix to 20° in an S-helix.

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Histological studies on the development of Phoma root rot of alfalfa

The Journal of Agriculture of the University of Puerto Rico ◽

10.46429/jaupr.v89i3-4.1046 ◽

1969 ◽

Vol 89 (3-4) ◽

pp. 251-262

Author(s):

Rocío del P. Rodríguez

Keyword(s):

Root Rot ◽

Cell Walls ◽

Enzymatic Degradation ◽

Cortical Cell ◽

Host Responses ◽

Histological Studies ◽

Tissue Degradation ◽

Electron And Light Microscopy ◽

Xylem Elements ◽

Scanning Electron

Several stages of the disease cycle of root rot of alfalfa caused by Phoma medicaginis var. medicaginis were studied by using scanning electron and light microscopy. First activity of the pathogen was the external colonization of the root. The pathogen penetrated directly causing discoloration and tissue disintegration. Inter- and intracellular penetration facilitated by enzymatic degradation was likely the mechanism involved in breaching the barrier of the epidermal cells. Colonization of the cortex was intercellular. Radial access to the xylem elements was achieved through the cortex. Host responses to invasion by the pathogen were suberization of cortical cell walls and occlusion of vessels with pectic substances and wound gum. Cavities in the cortex resulting from tissue degradation were associated with later stages of infection. Intracellular hyphae were observed in dead cells of the cortex and in the xylem.

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Multiple Evolutionary Trajectories Have Led to the Emergence of Races in Fusarium oxysporum f. sp. lycopersici

Applied and Environmental Microbiology ◽

10.1128/aem.02548-16 ◽

2016 ◽

Vol 83 (4) ◽

Cited By ~ 15

Author(s):

V. Chellappan Biju ◽

Like Fokkens ◽

Petra M. Houterman ◽

Martijn Rep ◽

Ben J. C. Cornelissen

Keyword(s):

Transposable Elements ◽

Fusarium Oxysporum ◽

Resistance Genes ◽

Pcr Analysis ◽

Genomic Fragment ◽

Avirulence Genes ◽

Content Type ◽

Race 1 ◽

Tomato Cultivars ◽

Race 2

ABSTRACT Race 1 isolates of Fusarium oxysporum f. sp. lycopersici (FOL) are characterized by the presence of AVR1 in their genomes. The product of this gene, Avr1, triggers resistance in tomato cultivars carrying resistance gene I. In FOL race 2 and race 3 isolates, AVR1 is absent, and hence they are virulent on tomato cultivars carrying I. In this study, we analyzed an approximately 100-kb genomic fragment containing the AVR1 locus of FOL race 1 isolate 004 (FOL004) and compared it to the sequenced genome of FOL race 2 isolate 4287 (FOL4287). A genomic fragment of 31 kb containing AVR1 was found to be missing in FOL4287. Further analysis suggests that race 2 evolved from race 1 by deletion of this 31-kb fragment due to a recombination event between two transposable elements bordering the fragment. A worldwide collection of 71 FOL isolates representing races 1, 2, and 3, all known vegetative compatibility groups (VCGs), and five continents was subjected to PCR analysis of the AVR1 locus, including the two bordering transposable elements. Based on phylogenetic analysis using the EF1-α gene, five evolutionary lineages for FOL that correlate well with VCGs were identified. More importantly, we show that FOL races evolved in a stepwise manner within each VCG by the loss of function of avirulence genes in a number of alternative ways. IMPORTANCE Plant-pathogenic microorganisms frequently mutate to overcome disease resistance genes that have been introduced in crops. For the fungus Fusarium oxysporum f. sp. lycopersici, the causal agent of Fusarium wilt in tomato, we have identified the nature of the mutations that have led to the overcoming of the I and I-2 resistance genes in all five known clonal lineages, which include a newly discovered lineage. Five different deletion events, at least several of which are caused by recombination between transposable elements, have led to loss of AVR1 and overcoming of I. Two new events affecting AVR2 that led to overcoming of I-2 have been identified. We propose a reconstruction of the evolution of races in FOL, in which the same mutations in AVR2 and AVR3 have occurred in different lineages and the FOL pathogenicity chromosome has been transferred to new lineages several times.

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