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Rosellinia buxi Fabre.
Stromata densely gregarious, uniperitheciate, black, subglobose with a constricted base and a conical
apex, 1-1.4mm high x 1.1-1.2 mm diam; ectostroma hard, carbonaceous, smooth
to roughened; subiculum brown to purplish brown, abundant,
woolly, persistent at the base of mature stromata, long adhering to side walls,
usually conspicuous
between the stromata, mixed with synnematous structures up to 1mm high bearing the anamorph.
Ostioles papillate, minutely to broadly conical.
Asci cylindrical, with apical apparatus inverted hat-shaped, amyloid,
4-5.5 µm high x 3.5-4 µm broad.
Ascospores 20-28 x 6-7.5 µm, narrowly ellipsoid-inequilateral with
narrowly rounded ends, brown to dark brown, with a straight
to slightly oblique germ slit 12-15 µm long on the flattened side; slimy
sheath or appendages absent.
Anamorph in nature: Dematophora, visible as grey to pinkish
brown tufts
on erect synnemata mixed with the subiculum.
Specimens examined. FRANCE:
Ariège (09):
Coume de Roux, vicinity St Girons, 12 Apr. 1992, JFM-9334, on Buxus, leg N. de Munnik;
Rimont, Las Muros, 02 Jun. 2000, JF-00058, on Buxus sempervirens;
Rimont, Las Muros, 27 Nov. 2001, JF-01264, on Buxus sempervirens;
Haute Garonne (31):
Toulouse, CRS park, 25 Mar. 1994, JFM-9455, on Buxus;
Toulouse, CRS park, 22 Feb. 1995, JFM-9522, on Buxus. Tarn
(81): Escoussens, La Blancariée, 07 Feb. 2002, JF-02025, on Buxus sempervirens.
Notes: Rosellinia buxi is very similar to R. necatrix
in having large and carbonaceous stromata embedded in a persistent subiculum,
a synnematous anamorph referrable to Dematophora, narrowly ellipsoid
ascospores with a short germ slit on the flattened side and in causing root
rot disease. Rosellinia buxi is readily separated from R. necatrix
by its host-specificity for Buxus and its shorter ascospores lacking
a slimy sheath.
Rosellinia buxi was first described by Fabre (1878) from southern
France and reported as apparently rare. Aside a few collections reported from
Great Britain (Petrini, 1993), R. buxi is still considered a rare species
and is not yet reported outside Europe. Rosellinia buxi
has recently been re-typified from material collected in Ariège (Petrini &
Candoussau, 1993)
In our experience, it is rarely absent from any Buxus grove in
nature, but remains very inconspicuous as it grows mainly on roots and at the
base of dying or dead stems, usually within the leaf litter. We had the opportunity
to observe in a Buxus grove close to our house the very long development
of R. buxi, extending over several years from the first signs of dying
associated to the growth of the anamorph, until fertile stromata appear and
continue to develop long after. The appearance of R. buxi is very likely
linked to drought stress, as it is more frequent on karstic soil. This observation
agrees with the opinion of Whalley (1996), Rogers (2000) and others about
those xylariaceous fungi considered as latent pathogens.
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