Introduction to Fungi, Third Edition

668 BASIDIOMYCETE YEASTS
Fig 24.5 Sporobolomycesroseus.(a c)
Various stages in the budding of cells.
(d) Cell bearing a sterigma and a
ballistoconidium. (e) Cell with two
sterigmata. (f) Cell with three sterigmata.
van der Walt (1970) on Sporidiobolus, the diploid
yeast cells of R. toruloides do not develop into
teliospores directly, but first produce a mycelium
which in turn forms teliospores. Conjugation
between haploid cells of compatible mating
type is mediated by peptide hormones. One of
them, rhodotorucine A, has been identified as
an undecapeptide with a farnesyl side chain
(Kamiya et al., 1979).
Some species of Rhodosporidium and Sporidiobolus
are entirely homothallic, and here all yeast
cells seem to be diploid (Fell & Statzell-Tallman,
1998; Statzell-Tallman & Fell, 1998). Meiosis
in a diploid yeast cell establishes a clamped
dikaryotic mycelium which produces teliospores.
Germinating teliospores give rise to metabasidia
which produce diploid basidiospores.
Ecology
Sporobolomyces, Rhodotorula and other yeasts
belonging to the Urediniomycetes are found in
diverse habitats such as the soil (Sláviková &
Vadkertiová, 2003) and the sea, including deep
sea locations (Nagahama et al., 2001). However,
their most prominent habitat is healthy and
moribund vegetation (Nakase, 2000) from which
they can be isolated throughout the year.
Together with the black yeast Aureobasidium
(Ascomycota; see p. 484), they form a major
component of the phylloplane yeast population.
Breeze and Dix (1981) have estimated that
yeasts (including ascomycetes) produce up to
50 times more biomass than hyphal fungi
on Acer leaves throughout the growing season.
Sporobolomyces roseus is the most abundant phylloplane
yeast, comprising for example 76% of the
yeast population on grapes (de la Torre et al.,
1999). Scanning electron microscopy studies have
shown that cells of S. roseus may form sheets
of mucilage by which they adhere to the leaf
surface. There is no evidence that the growth of
the yeasts causes corrosion of the cuticle (Bashi &
Fokkema, 1976). There is interest in the suggestion
that Sporobolomyces or Rhodotorula on leaf
surfaces may compete with foliar pathogens,
and that biological control of the pathogens
might be possible (Fokkema & van der Meulen,
1976). Such an approach is especially promising
in the control of post-harvest diseases
because the incubation conditions can be more
precisely controlled (Janisiewicz & Bors, 1995;
Janisiewicz & Korsten, 2002). Many Sporobolomyces