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.

Histopathology of Fusarium wilt of staghorn sumac (Rhus typhina) caused by Fusarium oxysporum f. sp. callistephi race 3. II. Characteristics of opaque matter associated with extensive host cell and cell wall alterations

“…The present observations reinforce the hypothesis, as already expressed for other systems and supported by similar observations (Ouellette and Baayen 2000;Ouellette and Rioux 1993;Ouellette et al 1995Ouellette et al , 1999aOuellette et al , 2004aOuellette et al , 2004bOuellette et al , 2004cOuellette et al , 2004d, that the OM occurrence primarily relates to the pathogen, as: 1) OM, including that of the VWLM, was also connected to fungal cells, and often by means of microfilaments (see also Atstatt 2003, showing some endophyte-like fungal cells with their walls pervaded by similar filamenatous structures); and 2) close similarities noted between OM present in host walls or in periplasmic areas, that of the VWLM, and content of some fungal cells and elements (compare Figs. 6d,7d,8c and element in Fig.…”

Tissue invasion and alteration in eggplant infected with Verticillium dahliae: A light and transmission electron microscopy study

“…Examples of links of this material with OM pervading middle lamellae and with that present in host cell periplasmic spaces have also been provided. These observations corroborate the majority of similar ones that we have made concerning other wilt diseases affecting tomato, carnation, and staghorn sumac (Ouellette et al 2004b(Ouellette et al , 2004c(Ouellette et al , 2004e, 2005b. The matter deposited on vessel walls in plants infected with Verticillium and other fungal wilt pathogens has been defined as coating by other authors Cooper 1983, 1984;Gold et al 1996;Pegg and Brady 2002;Pegg et al 1976;Robb et al 1979aRobb et al , 1979bRobb et al , 1987Robb 2000).…”

“…These were characterized by three demarcated layers: a shredded one, unlabelled for cellulose, a more compact and opaque cellulose-labelled layer, and the unlabelled VWLM layer. This type of alteration mirrored that of pit membranes of half-bordered pits in the metaxylem in DED affected elms and Fusariuminfected carnations (Ouellette 1978a(Ouellette , 1978bOuellette et al 1999Ouellette et al , 2004bOuellette et al , 2004cOuellette and Rioux 1993) and often of intertracheary pit membranes in staghorn sumac (Ouellette et al 2005a). In all instances, the term "swelling of pit membranes" should not apply, in our opinion, when it is primarily attributed to covering layers of extraneous matter, likely of a pathogen origin in most cases.…”

“…The main cumulative ultrastructural and cytochemical evidence for a pathogen origin of the components becoming apposed to vessel walls in this and the other wilt diseases considered (Ouellette et al 2004b(Ouellette et al , 2004c, and unpublished observations) may be summarized as follows: connections of the vessel wall lining matter with the pathogen elements; its relation with host wall penetration and alterations; labelling, in carnation, for chitin and in staghorn sumac for DNA; and connections with similar opaque matter present in host walls and in cell periplasmic areas. Undoubtedly, the use of other specific probes at the TEM level would help to unravel other features of this matter and confirm its nature and role in disease development, particularly if it represents a cause rather than an effect.…”

“…We have already described particular modes of pathogen development, of tissue alterations, of host cell reactions and related aspects concerning Dutch elm disease and Fusarium wilts of carnation, tomato and staghorn sumac (Charest et al 2004;Ouellette 1978b;Ouellette et al 1995Ouellette et al , 1999Ouellette et al , 2004aOuellette et al , 2004bOuellette et al , 2004cOuellette et al , 2004dOuellette et al , 2004e, 2005aOuellette et al , 2005b. These works present peculiar characteristics of pathogen structures, of host cell wall and content alterations related to extensive tissue invasion by opaque matter, not ascribable to a host origin, of various host cell reactions and so on, and more than circumstantial evidence was presented to show that most of the material lining vessel walls did not always correspond to the notions of coating as supported by others.…”