Alternaria spp.: from general saprophyte to
Bart P. H. J. Thomma
Centre of Microbial and Plant Genetics (CMPG), Katholieke Universiteit
Leuven, Kasteelpark Arenberg 20, B-3001 Heverlee-Leuven, Belgium
||Alternaria species are
mainly saprophytic fungi. However, some species have acquired pathogenic
capacities collectively causing disease over a broad host range. This
review summarizes the knowledge on pathogenic strategies employed by the
fungus to plunder the host. Furthermore, strategies employed by potential
host plants in order to ward off an attack are discussed.
||Alternaria spp. kingdom
Fungi, subkingdom Eumycotera, phylum Fungi Imperfecti (a
non-phylogenetic or artificial phylum of fungi without known sexual stages
whose members may or may not be related; taxonomy does not reflect
relationships), form class Hypomycetes, Form order Moniliales, form family
Dematiaceae, genus Alternaria. Some species of Alternaria
are the asexual anamorph of the ascomycete Pleospora while others
are speculated to be anamorphs of Leptosphaeria.
||Most Alternaria species are
common saprophytes that derive energy as a result of cellulytic activity
and are found in a variety of habitats as ubiquitous agents of decay. Some
species are plant pathogens that cause a range of economically important
diseases like stem cancer, leaf blight or leaf spot on a large variety of
crops. Latent infections can occur and result in post-harvest diseases or
damping-off in case of infected seed.
Symptoms caused by, and appearance of Alternaria
spp. (A) Stand of A. alternata conidiophores with chains of conidia
(picture kindly provided by G. Barron). (B) Germinating conidia of A.
alternata f.sp. citri, the causal agent of brown spot,
infecting a citrus leaf (SEM picture kindly provided by A. Bhatia and P.
Timmer). (C) Black spot on potato caused by A. solani (picture
kindly provided by Carlos A. Lopes). (D) Typical ‘target spot’ symptom
of Alternaria: a series of concentric rings at the site of attack.
(E) A. brassicicola on a susceptible Arabidopsis leaf. (F)
developing chains of A. brassicicola conidia on the surface of an
inoculated Arabidopsis leaf. (G) A. brassicicola conidia
with longitudinal as well as transverse septa (phaeodictyospores).
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