EPWS 310 - PLANT PATHOLOGY
INTRODUCTION
TO FUNGI AND FUNGI-LIKE ORGANISMS
&
NATURE OF FUNGAL PLANT PATHOGENS
Readings:
Pages 386 - 403.
(In)
Famous fungal epiphytotics
Potato
Late blight; Grape Downy mildew; Bunt or stinking smut of wheat; Rust of wheat
(since 1BC); Club root of crucifers; Dutch elm disease; Chestnut Blight; Oak
Wilt; Boxwood Canker; Coffee Rust; southern corn leaf blight.
Contents
of Lecture
A. Nature of fungi and fungi-like organisms
l Fungi and fungi-like organisms are classified into
three different kingdoms, reflecting their true genetic diversity. Yet they are
considered together in this course because many aspects of their life cycles,
nutrition and pathology are similar.
l All true fungi and fungi-like organisms are eukaryotic
(mitochondria and membrane-bound nucleus and organelles) varying from a few
microns to several kilometers in size.
l They reproduce by spores and usually
exist in thread-like chains of cells known as hyphae, or as single cells as in yeast.
l They are almost always heterotrophic,
but some are autotrophic and can fix carbon dioxide using
energy from the oxidation of (amino organic) nitrogen.
l Nevertheless all fungi are able to obtain food from
other organisms either living or dead.
l The origin of fungi is still controversial but they
are about 1 billion years old and derived from ancient algal or
protozoan line (main fungal line) and more recently from the siphonaceous
crysophyte algae (yellow-green or golden algae) (Oomycetes).
l Fungi are distinct from higher plants and animals:
they have polysaccharide fibrillar cell walls, they can
synthesize the benzene ring, and have biosynthetic pathways
for lysine, ethylene and hundreds of other
molecules.
l The vegetative body (soma or thallus)
usually consists of thread-like hyphae to form a mycelium.
l Some fungi also grow as yeasts and
reproduce by budding.
l Fungi usually grow from a spore which germinates to
form a germ tube or by budding.
l Mycelial growth is always at the tip and at branch points
l Temperature affects fungal growth and reproduction.
Psychrophiles
Mesophiles
Thermophiles.
l Light often affects spoulation and
secondary metabolite production.
« Water availability is critical to
fungi
l Oxygen and Carbon dioxide
affects growth and reproduction
l Fungi have a pleomorphic life cycle
- alternation of generations
l Fungi have both sexual and asexual reproductive
cycles
l Generalized life cycle of fungi
l Fungi maybe either homothallic
or
heterothallic.
If heterothallic usually with 2 sexes.
l Fungi differ from all
other eukaryotes in the separation of two things:
Plasmogamy is separated from Karyogamy and
Mitosis is separated from Cytokinesis.
l Fungi are usually haploid,
maybe dikaryotic, heterokaryotic
or homokaryotic.