Introduction to Fungi, Third Edition

TAPHRINALES
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9.2 Taphrinales
The Taphrinales are ecologically biotrophic parasites
mainly of flowering plants, causing a wide
variety of disorders which often lead to strikingly
abnormal development of the infected host
tissue to form witches’ brooms, galls or leaf
curls. About six genera are known of which
Protomyces (10 species) and Taphrina (95 species)
are the most important. Both Protomyces and
Taphrina can be isolated from their hosts as
ascospores, and these germinate in pure culture
by budding to form saprotrophic haploid yeast
cells. In the host plant, however, a mycelium
of intercellular septate hyphae is produced. In
Protomyces, hyphae are diploid, whereas they are
dikaryotic in Taphrina. Dikaryotic hyphae are
most unusual among ascomycetes but are typical
of basidiomycetes. Biotrophic infection of the
host plant culminates in individual hyphal tips
undergoing meiosis (preceded by karyogamy
in Taphrina), producing usually eight haploid
ascospores which are discharged violently. We
will discuss only Taphrina here; for Protomyces and
related genera, species descriptions are given
by Reddy and Kramer (1975).
9.2.1 Taphrina
Species of Taphrina are mostly parasitic on
Fagaceae and Rosaceae (Mix, 1949), causing
diseases of three main kinds. (1) Leaf curl or
blister diseases, e.g. Taphrina deformans, the cause
of peach leaf curl (Fig. 9.1; Plate 4a); T. tosquinetii,
the cause of leaf blister of alder; and T. populina,
the cause of yellow leaf blister of poplar. (2)
Diseases of above-ground plant organs in which
the infected twig undergoes repeated branching
to form dense tufts of twigs called witches’
brooms. Examples are T. betulina, causing
witches’ brooms of birch (Plate 4b), T. insititiae
causes witches’ brooms of plum and damson,
and T. wiesneri causes witches’ brooms and leaf
curl of cherry. However, not all witches’ brooms
are caused by Taphrina, and similar twig proliferation
is also associated with infection by mites.
(3) Diseases of fruits, e.g. T. pruni, which causes
the condition known as pocket plums in which
the fruit is wrinkled and shrivelled and has a
cavity in the centre in place of the stone. Taphrina
amentorum causes conspicuous tongue-like
outgrowths on female catkins of alder, Alnus
glutinosa (Plate 4c).
Taphrina deformans
Peach leaf curl is common on leaves and twigs
on peach and almond, especially after a cool and
moist spring. Towards the end of May, infected
peach leaves show raised reddish puckered
blisters which eventually acquire a waxy bloom
(Fig. 9.1). Sections of leaves in this condition
show an extensive septate mycelium growing
between cells of the mesophyll and between the
cuticle and epidermis, where the hyphae end in
Fig 9.1 Taphrina deformans. Peach leaf
showing leaf curl.