Morphological aspects of early host-parasite interactions in infections ofMelampsora pinitorquaandMelampsora larici-tremulaeonPinus sylvestris.Implications in the taxonomical relationship of the two rust fungi

Abstract

A cyto-histological study was carried out on Pinus sylvestris seedlings artificially infected with basidiospores of Melampsora pinitorqua and Melampsora laricitremulae, in order to differentiate between the two rust fungi and delineate their taxonomical relationships. The general morphology of the early phases of the majority of infections of Melampsora larici-tremulae on P. sylvestris show similar characteristics to those of M. pinitorqua. Moreover, in M. larici-tremulae / P. sylvestris interactions, the following were the specific characteristics: abnormal germlings and secondary basidiospore production, «cell wall-like appositions» encasing the fungal structures in the host, necrosis of the infection structures, necrosis of the host tissue colonized by mycelium from epidermal to parenchymal cells. Such reaction types reveal the coexistence of pre-and posthaustorial defence mechanisms, typical, respectively, of a nonhost and host resistance. This coexistence which is useful in understanding the evolution of this host-rust interaction, was examined. The described defence mechanisms of P. sylvestris vs. M. larici-tremulae could indicate that the two rust fungi are still closely related entities, however diverging, which evolve from «formae speciales» to «species».

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

“…Indeed, owing to the partial overlapping of the host range of M. pinitorqua and M. larici-tremulae described in previous works by Longo et al (1970;1975), a basidiospore-derived direct penetration was shown also in the following cases of inoculations: 1) M. larici-tremulae on growing shoots of P. sylvestris (Longo et al 1997); 2) M. pinitorqua on growing needles from brachiblasts of Larix decidua (Moricca et al 2003); 3) M. larici-tremulae on cotyledons and primary needles of P. pinea (Moricca et al 2003).…”

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.…”

“…appendiculatus by GOLD and MENDGEN (1984), for Puccinia xanthii Schw. by MORIN et al (1992), for Melampsora pulcherrima (Bub) Maire by LONGO et al (1994), for M. pimtorqua and M. larici tremulae by LONGO et al (1997), is made up of a thin neck which de rives from the penetration peg and of a widened portion with a large central vacuole. In accord ance with what has been observed in the substomatal vesicle of C. flaccidum, also in the intraepidermal one there is no septum to separate the infection peg from the vesicle; only in C. quercuum f. sp.…”

“…The Literature considers such behaviour to be typi cal of the monokaryotic infection phase, as re ported for many rusts (GRAY et al 1983;GOLD and MENDGEN 1984;BERGDAHL and FRENCH 1985;HOPKIN et al 1988;LONGO et al 1994LONGO et al , 1997, as well as for C. flaccidum on P. pinaster and P. nigra subsp. laricio (RAGAZZI and DEL-LA VALLE FEDI 1992).…”

“…On the other hand, LONGO et al (1988LONGO et al ( , 1991LONGO et al ( , 1997, studying the basidiospore-derived penetration oiMelampsorapinitorqua (A Br.) Rostr.…”