Plant Physiol. (1993) 103: 267-272
Chemical Signals from Avocado Surface Wax Trigger
Germination and Appressorium Formation in
Gopi Krishna Podila*, linda M. Rogers, and Pappachan E. Kolattukudy*
Biotechnology Center, The Ohio State University, Columbus, Ohio 4321 O
berry and Blakeman, 1978). There is also evidence to suggest that cuticular components are involved in the control of
funga1 differentiation on leaf surfaces (Macko, 1981; Trione, 1981).
Colletotrichum gloeosporioides Penz. is the causal agent of
anthracnose disease on fruit crops (Verhoeff, 1974; Brown,
1975; Muirhead, 1981; Daykin, 1984) such as avocado (Persea
americana) fruit (Binyamini and Schiffmann-Nadel, 1972). It
was observed that on avocado fruits germination and appressorium formation of C. gloeosporioides spores may be triggered by chemical signals from the surface wax (Prusky
and Saka, 1989; Prusky et al., 1991). In this paper, we confirm the reports that appressorium formation by the avocado
pathogen C. gloeosporioides is induced by surface wax from
avocado fruits. We also demonstrate that appressorium formation by this pathogen is induced by the host wax but not by surface wax from other plants and that avocado wax does
not induce appressorium formation in the spores of Colletotrichum sp. that attack many other hosts. The very long-chain alcohol fraction of the wax was identified as the major
chemical signal that induces appressorium formation.
l h e surface wax of the host, avocado (Persea americana) fruit, induced germination and appressoriumformation in the spores of Colletotrichum gloeosporioides. Waxes from nonhost plants did not induce appressorium formation in this fungus, and avocado wax did not induce appressoriumformation in most Colletotrichum species that infect other hosts. Bioassays of the thin-layer chromatographic fractions of the avocado wax showed that the fatty alcohol fraction was the main appressorium-inducingcomponent. Testing of authentic n-C, to n-Cs2fatty alcohols revealed that C,, and longer-chain alcohols induced appressorium formation. Casliquid chromatographylmass spectrometry analysis of free fatty alcohols revealed that avocado wax containsa high content of very long chains. Waxes from nonhost plants containing an even higher content of the very long-chain alcohols did not induce appressorium formation. Waxes from nonhost plants strongly inhibited appressoriuminduction by avocado wax. Thus, a favorable balance between appressorium-inducingvery iong-chain fatty alcohols and the absence of inhibitors allows the fungus to use the host surface wax to trigger germination and differentiation of infection structures in the pathogen.
MATERIALS A N D METHODS
Funga1 spores use physical or chemical signals from the
plant surface to trigger germination and differentiation into appressoria, which are necessary for successful infection of the host (Emmet and Parberry, 1975; Aist, 1976; Staples and
Hoch, 1987). In anthracnose fungi belonging to the genus
Colletotrichum, severa1 species are thought to produce appressoria in response to specific physical signals and topography of leaf surface (Staples and Macko, 1980). These include Colletotrichum capsici (Parberry, 1963), Colletotrichum trifolii (Miehle and Lukezic, 1972), Colletotrichum lindemuthianum (Mercer et al., 1975), Colletotrichum truncatum (Staples et al., 1976), Colletotrichum graminicola (Lapp and Skoropad, 1978), and Colletotrichum lagenarium (Suzuki et al., 1982). In others, appressorium formation was suggested to
involve chemical signals from the plant, such as Suc in
Colletotrichum piperatum (Grover, 1971), chlorogenic acid in Colletotrichum musae (Swinburne, 1976; Harper and Swinbume, 1979), and phenolics in Colletotrichum acutatum (Par-
Avocados (Persea americana Miller var Haas) were supplied
by Mission Produce (Oxnard, CA). Surface waxes were isolated by dipping intact fruit in...
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