Interactions between parasitic fungi and mosses: pegged and swollen-tipped rhizoids inFunariaandBryum

Abstract

Two kinds of parasitic fungal infections are described in the rhizoidal systems of both wild and cultured materials of Funaria hygrometrica, Bryum capillare and B. pseudotriquetrum. Protonemal and rhizoidal cells of Funaria produce pegs of host wall material around sites of hyphal penetration. Similar structures appear to be much more widespread in hepatics and in Monoclea have been misinterpreted as rudimentary pegs, the characteristic feature of pegged rhizoids.Swollen side branch initials and the tip cells of major rhizoidal axes contain a single rozellopsidalean (Oomycota formerly Chytridiomycota) zoosporangium in Bryum pseudotriquetrum and up to three similar structures in B. capillare. Each zoosporangium produces a single exit tube. Whereas the infected cells die the subapical cells remain alive and, after zoospore discharge, produce side branches whose tip cells also become infected. Restriction of the parasites to side branch initials and rhizoid tip cells is perhaps because these are the only cells that the zoospores are able to penetrate. Nutrients translocated along rhizoids to sustain tip growth are diverted to nurture the fungi in infected plants. Differences between the number of zoosporangia per host cell and the number of exit tubes between different mosses suggest that more than one species of rozellopsidalean fungus may form rhizoid galls in mosses and not just Pleotrachelus wildemani described previously. Rhizoid galls appear to be genuinely uncommon in mosses but, following clarification of the differences between these and rhizoidal tubers, further discoveries may be anticipated.

New national and regional bryophyte records, 26

“…A recent overview of Pleotrachelus wildemanii is given by Martínez-Abaigar et al (2005). This states that Pleotrachelus wildemanii belongs to Correspondence to: S Nour-El-Deen, Bryology Research Lab., Botany Department, Faculty of Science, Ain Shams University, Cairo, Egypt.…”

“…Similar in-growths were also observed here in rhizoidal cells of Fissidens (Figure 1(H)). Martínez-Abaigar et al (2005) suggested that variations in the number of zoosporangia formed per rhizoid cell, the number of exit tubes produced in each zoosporangium, and the extension of these exit tubes between different hosts suggest that rostellopsid fungi other than Pleotrachelus wildemanii might also induce gall formation in moss rhizoids (see Table 1). Whether this rostellopsid fungus infects a wide range of hosts or is a species-specific parasite now invites experimental studies.…”

“…Email: samarnour11@hotmail.com the Rozellopsidales (Division: Oomycota), an order containing highly specialized parasites including those that infect moss rhizoids inducing them to form galls. Although the fungus that produces galls in mosses was previously identified as Pleotrachelus wildemanii, Martínez-Abaigar et al (2005) stated that differences between the number of zoosporangia per host cell and the number of exit tubes between different mosses, suggest that more than one species of rozellopsidalean fungus may form rhizoid galls in mosses and not just P. wildemanii.…”

Fungal symbioses in bryophytes: New insights in the Twenty First Century

“…In striking contrast we must underline that, despite a huge number of reports of fungal fruiting bodies growing on mosses (Dobbeler 1997), many of which are species-specific, a symbiotic relationship has yet to be demonstrated. Apart from specialized rostellopsid (chytrid) parasites that colonize the rhizoid apical cells in a handful of mosses (Martinez-Abaigar et al 2005) all other fungal structures reported on mosses are confined to dead or dying host cells; we know not a single electron micrograph illustrating a healthy hypha in a healthy moss cell.…”

Defence responses ofAphanoregma patens(Hedw.) Lindb. to inoculation withPythium aphanidermatum

“…The majority of fungi that infect the leaves and stems of mosses are specialized ascomycetes (Dö bbeler, 1997) though some cosmopolitan, parasitic, and saprotrophic fungi have also been found in association with bryophytes (Davey et al, 2010). It appears that mosses may possess resistance to a variety of microbial pathogens, similar to those in higher plants (Ponce de Leó n & Montesano, 2013) and that the defensive responses of mosses to pathogenic fungi may differ between the filamentous (rhizoids and protonemata) and gametophore (especially on leaf surfaces) stages (Hoshino et al, 1999;Tsuneda et al, 2000Tsuneda et al, , 2001aDö bbeler, 2003;Davey et al, 2009;Martínez-Abaigar et al, 2005;Oliver et al, 2009;Tojo & Newsham, 2012). Thus, a detailed analysis of each stage is crucial to understand bryophyte pathology (i.e.…”