EPWS 310 - PLANT PATHOLOGY 

FUNGI LECTURE 1

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

B. Growth and Reproduction

B1. Fungal life-cycles

 

 

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.

B. Growth and Reproduction

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

B.1 Fungal life-cycles

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.

T op of Document | Lecture 2 | Index of Lectures