Penetration and early colonization in basidiospore-derived infection ofMelampsora pulcherrima(Bub.) Maire onMercurialis annuaL.

Abstract

SUMMARY -The early phases of basidiospore-derived infection of Me/ampsora pulcherrima (Bub.) Maire on the leaves of Mercurialis annua L. were studied by light microscopy, SEM and TEM. The fine morphology of the basidiospore germling penetration and intraepidermal infection structures is discussed in comparison with that of other rusts recently described. The direct penetration through the epidermal cell wall, characteristic of the rust basidiospore-derived germlings, is confirmed. The absence of an extrahyphal matrix around the intraepidermal vesicle and the presence of a collar around the vesicle neck are pointed out.

Host surface tissues and basidiospore-derived infection strategies of some rust fungi

“…Consequently, in order to fit themselves onto a substratum with the above characteristics, it would be necessary for the basidiospore germlings to modify their way of penetration from the direct one, which is typical of the rust monokaryotic phase, to that of the indirect type. Notwithstanding, Longo et al (2000) observed that the morpho-functional characteristics of the penetration structures of C.flaccidum remained those of a monokaryotic phase, even if this indirect penetration recalled the mode of penetration (through the stomatal aperture) of a dikaryon.…”

“…One other case of indirect basidiospore-derived penetration on gymnosperms was proposed by Ragazzi et al (1987) and Ragazzi and Dellavalle Fedi (1992) Longo et al (2000) demonstrated that the basidiospore-derived penetration of C. flaccidum on Pinus pinea was effectively indirect through the stomata, giving rise to a substomatal infection structure on all types of host needles.…”

“…In point of fact, Longo et al (1994), in their studies on the monokaryotic phase of Melampsora pulcherrima (Bub.) Maire on Mercurialis annua L., reported a direct basidiospore-derived penetration on the leaves of this angiosperm.…”

“…on pine secondary needles, and by Crysomyxa abietis on Picea abies growing needles. Hence, Longo et al (2000) supposed that the reason for the dynamics of indirect penetration carried out by some rust fungi in the monokaryotic phase could be as follows. The rust fungi which evolved to infect "in nature" organs with some surface cyto-histological characteristics, such as the heavily cutinized and thick walled epidermal cells of the secondary needles of Pinus spp., could be prevented from exercising a suitable mechanical and/or enzymatic action.…”

Penetration and early colonization in basidiosporederived infection on needles of Pinus pinea L. by Cronartium flaccidum (Alb. et Schw.) Wint.

“…However, subsequent studies on the penetration of the basidiospore germ tubes of sev eral rust fungi on their hosts (MILLER et al 1980;GRAY et al 1983;GOLD andMENDGEN 1984, 1991;HOPKIN et al 1988; LONGO et al 1988LONGO et al , 1991LONGO et al , 1994LONGO et al , 1997MORIN et al 1992) confirmed direct penetration for these spores and consid ered the indirect penetration of (i) C.ribicola on P.strobus (PATTON and JOHNSON 1970) and (ii) Cronartium comandrae Pk. on Pinus banksiana Lamb.…”