Molecular Plant Pathology - Pathogen Profiles
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Molecular, ecological and evolutionary approaches to
understanding Alternaria diseases of citrus
Kazuya Akimitsu1,, Tobin L. Peever2 and L. W. Timmer3
1 Laboratory of Plant Pathology, Department of Life Sciences,
Faculty of Agriculture, Kagawa University, Miki, Kagawa 761-0795, Japan
2 Department of Plant Pathology, Washington State University,
Pullman, WA 99164-6430, USA
3 Institute of Food and Agricultural Sciences, Citrus Research and
Education Center, Department of Plant Pathology, University of Florida, Lake
Alfred, FL 33850, USA
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| Summary: |
Alternaria fungi cause four
different diseases of citrus: Alternaria brown spot of tangerines,
Alternaria leaf spot of rough lemon, Alternaria black rot of several
citrus fruits and Mancha foliar of Mexican lime. The first three
diseases are caused by the small-spored species, Alternaria alternata
and the causal agents can only be differentiated using pathogenicity
tests, toxin assays or genetic markers. Mancha foliar is caused by
the morphologically distinct, large-spored species A. limicola.
Substantial progress has been made in understanding the biology, ecology,
population biology, systematics, molecular biology and biochemistry of the
interactions between these pathogens and citrus. Epidemiological studies
have focused on brown spot of tangerines and their hybrids and have
contributed to the development of a model of disease development which has
improved control and reduced fungicide use. Studies of the population
genetics, host specificity and ecology of A. alternata from
different ecological niches on citrus have revealed host specific forms of
the pathogen which cause disease on different citrus species, the
existence of three phylogenetic lineages of the fungus which cause brown
spot world-wide, and closely related non-pathogenic isolates which
colonize healthy citrus tissue. The role of host-specific toxins in
Alternaria diseases of citrus has been extensively studied for over 20
years, and these pathosystems have become model systems for host-pathogen
interactions. Recent molecular research has started to unravel the genetic
basis of toxin production and the host susceptibility to toxin, and the
role of extracellular, degradative enzymes in disease. |
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