Introduction to Fungi, Third Edition

OTHER MEMBERS OF THE PUCCINIACEAE
631
have been mentioned at the beginning of this
chapter.
Uromyces appendiculatus is a macrocyclic autoecious
rust on French bean (Phaseolus vulgaris) and
many other leguminous plants. Several varieties
have been distinguished. The fungus survives the
winter as teliospores on plant debris or, in milder
conditions, as urediniospores (McMillan et al.,
2003). As one would expect of a situation in which
a rust fungus undergoing sexual reproduction is
being controlled by the breeding of resistant
cultivars, numerous (more than 200) physiological
races of U. appendiculatus are known. Control is
by means of resistant cultivars or, if these fail,
with protectant fungicides (maneb and chlorothalonil).
Strobilurin-type compounds are also
now used against U. appendiculatus. Since beans
are a higher-value crop than cereals, fungicide
applications are generally more profitable.
Uromyces viciae-fabae has a similar life cycle to
that of U. appendiculatus, but it infects broad bean
(Vicia faba) and numerous other plants. It is a
cosmopolitan species but seems to cause lesser
damage than U. appendiculatus.
Uromyces pisi is heteroecious, producing spermogonia
and aecia on Euphorbia cyparissias and
uredinia and telia on various leguminous hosts,
especially pea (Pisum sativum). Infections on the
alternate host are of biological interest because
the fungus infects systemically and causes its
alternate host to produce pseudoflowers, at the
expense of its real flowers (Pfunder & Roy, 2000).
The name U. pisi is now known to cover a
complex of several biologically distinct species
which are united by their alternate host but
infect different members of the Fabaceae as
principal hosts (Pfunder et al., 2001).
22.6 Other members of the
Pucciniaceae
22.6.1 Phragmidium
All Phragmidium spp. are autoecious and confined
to the Rosaceae. The two best-known species,
both extremely common in Europe, are P. violaceum
on leaves of the Rubus fruticosus species
aggregate (bramble or blackberry; Plate 12c) and
P. mucronatum on roses. Both are macrocyclic. The
uredinial and telial stages are readily recognized
from above as chlorotic or purple lesions, and
the spores are formed on the underside of the
host leaves. They are yellowish-orange (urediniospores)
or violet to black (teliospores). The
teliospores contain mostly 4 (P. violaceum) or
6 8 (P. mucronatum) cells with very dark and
rough walls, and are borne on a long stalk
(pedicel) which becomes easily detached from the
lesions. When teliospores are mounted in water,
the base of the pedicel breaks and exudes a large
amount of mucilage (Figs. 22.13c,d). In nature,
this may facilitate the attachment of the teliospore
to adjacent surfaces during overwintering
(Ingold et al., 1981). The teliospores of P. mucronatum
were among the first fungus spores illustrated
by Robert Hooke in 1667 soon after the
invention of the microscope (see Large, 1940).
Phragmidium violaceum shows promise as a
biocontrol agent against the spread of brambles
which were introduced into Australia and are
spreading there in their typically uncontrollable
manner (Mahr & Bruzzese, 1998). Phragmidium
mucronatum is not tolerated by rose breeders or
hobby gardeners; it is controlled by fungicide
applications. Removal of fallen leaves in autumn
can also help to control the disease.
22.6.2 Gymnosporangium
There are about 60 species of Gymnosporangium
which produce their spermogonia and aecia
on members of the Rosaceae, and telia on
Cupressaceae. Uredinia are not normally
formed. One of the most commonly encountered
species is G. fuscum (¼ G. sabinae), the pear trellis
rust, which alternates between Juniperus spp. of
the sabina group (principal host) and pear trees.
The dikaryotic mycelium can survive for many
years in the principal host, and repeated production
of telia is associated with a spindle-shaped
swelling or canker of the infected trunk or twig.
Spore-bearing telia are produced in the spring
as horn-like outgrowths which greatly expand
during rainfall due to swelling of the long teliospore
stalks (Plate 12d; Fig. 22.13f). Teliospores at
the surface of a swollen telial horn germinate
to release basidiospores at the time of leaf