Development and Pathogenicity of the Fungus Crinipellis perniciosa
on Interaction with Cacao Leaves
Aruna Kilaru and Karl H. Hasenstein
Department of Biology, University of Louisiana, Lafayette 70504.
Accepted for publication 28 September 2004.
Kilaru, A., and Hasenstein, K. H. 2005. Development and pathogenicity
of the fungus Crinipellisperniciosa on interaction with cacao leaves.
We investigated developmental changes in the primary mycelium of
Crinipellis perniciosa upon its interaction with immature and mature
leaves of Theobroma cacao. On nutritive medium, the primary mycelium
grew significantly slower in the presence of host tissue than without host
tissue. In the absence of the cacao leaves,incomplete phase transition
occurred after 5 days, wherein older hyphae progressed to the dikaryotic
state and growing tips remained monokaryotic. Phase transition occurred
between 3 and 5 days on mature leaves, 10 and 12 days on meristematic
Crinipellis perniciosa, the causative agent of the witches’
broom disease in Theobroma cacao (4), is responsible for major
crop losses in South Americanand Caribbean cocoa plantations.
In 1989 the witches’ broom disease of cocoa was identified in
Bahia, the leading cocoa-growing region in Brazil. In less than
10 years, production shrank from 383,000 tons in 1987–88 to
150,000 tons estimated for 2002–03. Consequently, Brazil slipped
from being the third to the fifth largest cocoa-producing country
in the world (14). Various control methodsused, including sanitary cultural practices, have not been effective in minimizing
damage and incurred high economic costs. The scientific investigations of witches’ broom of cacao began in the 1890s and developed considerable knowledge of the biology and epidemiology of
the disease (26). However, the mechanisms of host–parasite interaction and the subsequent developmental changes have not beenstudied.
The pathogen is a hemibiotrophic basidiomycete with two distinguishable phases in its life cycle. The primary, monokaryotic
and biotrophic phase is followed by a secondary, dikaryotic but
saprophytic stage (25). In suitable environments, the uninucleate
basidiospores germinate and develop into relatively wide (5 to
20 µm), convoluted, primary hyphae that invade T. cacao. Incursion byprimary hyphae incites major morphological changes in
the host tissue, such as stem enlargement, shoot formation, and
loss of apical dominance, that gives rise to the characteristic
broom appearance and enhanced flowering and fruiting. Subsequent to infection, the tissue becomes necrotic and the primary
hyphae undergo phase transition and form thinner (1.5 to 3.0 µm),
hyaline, binucleatesecondary hyphae with clamp connections that
colonize the plant tissues intra- and intercellularly. The saprophytic hyphae eventually produce pink-colored, wide-gilled
basidiocarps ≈2 cm in diameter on dead broom tissues that release
Corresponding author: K. H. Hasenstein; E-mail address: email@example.com
© 2005 The American Phytopathological Society
leaves,and required 2 weeks on T. cacao callus tissue. The biotrophic
mycelia were able to invade immature and mature cacao leaves without
open wounds or stomata. Club-shaped hyphal tips and the formation of
adhesive structures were induced by cuticle extracts and suggest host
recognition. The initial cuticular disintegration at the site of penetration
was followed by blister formation and completedigestion of leaves by the
primary mycelium. The data suggest specific interactions between host
and pathogen that control the onset of the necrotrophic phase of the
fungus. The data further indicate that primary mycelium rather than
spores can be used to study C. perniciosa pathogenicity.
Additional keywords: host–pathogen interaction.
basidiospores, thus completing the life cycle...