Plant Diseases Caused By Fungi - Universiti Putra Malaysiavodppl.upm.edu.my/uploads/docs/Lec 2.pdf · Fungi Estimated between 70,000 and 1.5 million species, most yet to be discovered

Plant Diseases Caused By Fungi

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Small, microscopic, eukaryotic

Usually filamentous, branched

Spore-bearing

Lack chlorophyll

Cell wall

Chitin and glucan

No cellulose

Fungi


Fungi

Estimated between 70,000 and 1.5 million species, most yet to be discovered

Some mushroom-producing fungi are the largest living organisms of any kind e.g., Armillaria ostoyae (honey mushroom)

produced mycelia 3.5 miles in diameter

Plays various roles: Edible & medicinal mushrooms (e.g., Lingzhi) Wood rotting & degradation Source for antibiotics (e.g., Penicillium) Pathogenic


Classification of Plant Pathogenic Fungi

Divided into 2 categories1. Fungal-like organisms

Kingdom: Protozoa

Kingdom: Chromista, previously known as lower fungi

2. True fungi

Kingdom: Fungi

References Ainsworth (1973) Agrios (2005), p390-397


Classification of Plant Pathogenic Fungi (cont’)

Phylum : …..mycota

Class : …..mycetes

Order : …..ales

Family : …..aceae

Name : binomial (2 words)

E.g.: Phytophthora palmivora Butl.

Genus name Spesies name



Kingdom Phylum Class

Protozoa Plasmodiophoro-mycota

Plasmodiophoro-mycetes

Chromista Oomycota Oomycetes

Fungi(Lower)

ChytridiomycotaZygomycota

ChytridiomycetesZygomycetes

Source: Agrios (2005)






Kingdom Phylum Class

Fungi

(Higher)

Ascomycota Hemiascomycetes

Plectomycetes

Pyrenomycetes

Loculoascomycetes

Discomycetes

Deuteromycetes

Basidiomycota Teliomycetes

Hymenomycetes

Source: Ainsworth (1973)





Fungal-like Organisms: Morphology

1. Kingdom: Protozoa

2. Kingdom: Chromista


Fungal-like Organisms: Morphology (cont’)

1. Kingdom: Protozoa

Unicellular, amoeboid, multi-nucleate, no definite cell wall

Body: plasmodium

Resting spore = zoospore, 2 flagella

E.g., slime molds





2. Kingdom Chromista

Uni- or multi-cellular, filamentous or colonial, mycelium containing cellulose and glucans but no cross walls

Produce asexual & sexual spores

E.g., Pythium, Phytophthora



True Fungi

Characteristics of plant pathogenic fungi

Morphology

Reproduction

Ecology

Dissemination


True Fungi: Morphology

Mycelium: filamentous

vegetative body branches

out in all directions

Hyphae: individual branches

of mycelium, usually 2-10

µm in diameter

Coenocytic (without cross walls)

Septate

Three types of hyphae. A: Non-septate (coenocytic). B: Septate with uninucleate cells. C: Septate with multinucleate cells.


Fungi reproduce chiefly by means of spores

2 types of reproduction

1. Asexual

2. Sexual

True Fungi: Reproduction


True Fungi: Reproduction (cont’)

1. Asexual reproduction

• Does not involve nucleus fusion or sex organs

• Important means of reproduction

• E.g.: budding, production of sporangiospores, zoospores or conidia

Zoospores in sporangia(Source: JPT)

Budding yeast, Saccharomyces cerevisiae(Source: Webster, 1988)


2. Sexual reproduction• Involve sex organs (gametangia)

• 3 steps:i. Plasmogamy: fusion of 2 haploid hyphal

strands

ii. Karyogamy: fusion of 2 compatible nuclei to form diploid nuclei (zygote)

iii. Meiosis: meiosis of zygote to produce 4 haploid nuclei (each may become a sexual spore)

iv. E.g.: basidiospores










True Fungi: Ecology

Plant pathogenic fungi:

Biotrophs: spend all of their lives on the host (obligate parasites)

Hemibiotrophs: spend part of their lives on the host as parasites and part on dead tissues of the same host on the ground as saprophytes


True Fungi: Dissemination

Fungi are disseminated primarily in the form of spores.

Others means (to a lesser extent): Fragments of hyphae Sclerotia

Dissemination agents: Wind Water Insects Animals Humans


Specialized Structures

Modified hyphae:

Rhizoid

Rhizomorph

Hypopodia

Appressorium

Haustorium

Resting structures:

Chlamydospore

intercalary & terminal

Sclerotium

Aggregation of hyphae to form small dark brown aggregates


Specialized Structures (cont’)

Rhizomorph

Appressorium

Hypopodia

Sources: Rao (1975), Agrios (2005), McGonigle (2005), JPT

Rhizoid

HaustoriumA=Appressorium, PP=Penetration Peg, IM= Intracellular Mycelium


Specialized Structures (cont’)

Sclerotia

Source: Webster (1988), JPT

Clamydospores

Intercalary

Terminal


Quiz

Q1 : Define plant pathology

Q2 : Types of disease

Q3 : Name the first fungicide

Q4 : 3 categories of disease symptom

Q5 : how many steps are there in Koch’s postulates?


Thank You


Quiz

Q1 : Name the categories of plant pathogenic fungi

Q2 : Name 7 levels in fungi classification

Q3 : Name two types of fungal spores

Q4 : how many steps are there in fungal sexual reproduction

Q5 : Name two specialized structures of fungi



Documents

Plant Diseases Caused By Fungi - Universiti Putra Malaysiavodppl.upm.edu.my/uploads/docs/Lec 2.pdf · Fungi Estimated between 70,000 and 1.5 million species, most yet to be discovered