agr 154 chapter 4 - fungi
TRANSCRIPT
Chapter Overview
Explain the major characteristics of fungi
Identify the modification of hypae
Give explanation of the types of fungi
Discuss the reproduction of fungi
Clarify classification of fungi
Characteristics of Plant Pathogenic Fungi
Small - Usually filamentous and branched
Lack chlorophyll
Microscopic
Have cell wall - that contain glucan & chitin but no cellulose
Eukaryotic
The MorphologyThe body of the fungus is called mycelium
The individual branches of mycelium are called hyphaeMycelium (a mass of hyphae)
Each hyphae or mycelium is generally uniform in thickness (0.5 m in diameter)The mycelium consists of many cells containing one or more nuclei per cell
The mycelium may be either have a:1. Septa (higher fungi) - Septate hyphae2. No septa (lower fungi)- Aseptate hyphae
Somatic Structure-Modification of Hyphae
A. Rhizoids A short, thin hyphae growing in a root like fashion towards the substrateArise from the node of stolon Absorb water and nourishment from substrate
B. Stolon The hyphae that grow horizontally above substrum and then bend down into the substrum
C. Rhizomorphs Root-like structures, thicker than mycelium
A thick strands of hyphae
Extend from the mycelium through the substrate
They help in spreading the fungus from one root system to another root system.
D. Haustorium (absorptive organs)The lateral branches of hyphae that penetrate into the host cells
And enlarge in the form of knob-like
Obtain nourishment from the protoplasts of the host cells.
Originate on the hyphae of obligate parasites
E. Appressorium
The small swelling formed at the tip of hyphae
Allowed the germ tube to penetrate into the host epidermis
Germ tube – The early growth of mycelium produced by a germinating fungus spores.
F. Chlamydospores
Larger than the standard spores
Formed from the dense of cytoplasm at certain portion of hyphae
Have thick wall
It is the life-stage which survives in unfavourable conditions
G. Sclerotia It is a dark, hard and irregular structure
It is the resting bodies formed from the hyphal aggregation
It is a fungal “survival structure” Formed under unfavorable conditions
Saprophyte
Live on the dead organic matterHelp decomposeMost of 100,000 species.Obligate saprophyte – only can live as saprophyteFacultative saprophyte – lives as parasite but in certain condition can live as saprophyte
Parasite
Live in the living host
Obligate parasite – only live in the living host/ organism
Facultative parasite – lives as saprophyte but in certain condition can live as parasite.
Symbion
Live with other living organism and both give the advantage to one another Not important in causing disease in plant
Eg: Mycorrhizae – the relationship of fungi and roots will enhance the absorbent of nutrients
Mycorrhizae (fungus-root)
Some Mycorrhizae colonize roots intercellularly (ectomycorrhizae)Some of them colonize roots intracellularly (endomycorrhizae)The mycorrhizae mycelium is much more smaller than the plant roots.Help the plant to absorb nutrients and water from soilAt the same time the mycorrhizae also get the nutrients directly from the plant.
Reproduction of Fungi
Three (3) types of reproduction:
Asexual reproduction
Sexual reproduction
Parasexual reproduction
1. Asexual Reproduction
Formation of spores without involving the fusion of nuclei or sex cells.
The most important way of reproduction - produce a lot of sporesCan be group into 4 categories:
Fragmentation
Fission
Budding
Spore Formation
1. Fragmentation - A part of the vegetative hypha separated and develops into a new individual mycelium
2. Fission - The somatic cells splitting to produce two cells
3. Budding - A small bud is produced from the parent cell. Then, the young bud will separated from the parent cell and become a new individual
4. Spore Formation - The spores also have many shape, size, colour, arrangement and way of their formation. Structure responsible for spore
production is called sporophore
Asexual SporesAsexual spores are either:
1. In sporangia / sporangium
The terminal end of sporophore will develop containers (sporangia)
The container will hold asexual spores
The asexual spores are call sporangiospores (non motile spores)
A motile and flagelleted spores are known as zoospore
Sporangia containing zoospore is called zoosporangium
2. Exposed directly to the atmosphere (Conidia and conidiophore)In some fungi, the spores are not contained within membranes, they are borne free.This sporophore is called conidiophore and the spores are conidiaConidiophore may be unbranched or branched andMay or may not contain a vesicle at the end
2. Sexual Reproduction
Involves the fusion of two nuclei
The spore is called sexual spore and the fusing cells are called gametes
3 Phases of Sexual Reproduction
Plasmogamy – fusion of 2 protoplasts of 2 gametes or (fusion of hyphae)
Karyogamy – fusion of 2 nuclei from the fusing gametes to form a diploid zygotic nucleus
Meiosis – formation of 4 haploid spores
Fungal Sex Organs- Gametangia
1. Isogametangia – morphologically similar gametangia
the gametes are very similar and cannot be classified into "male" or "female”
2. Heterogametangia – morphologically different gametangia
Antheridium - male gametangium & contains antherozoids Oogonium - female gamentangium & contains female gamete
Fungal Sexual Cell- Gametes
3 types of gametes :
1. Isogamous – an equal sizes of gametes (cannot be distinguish)
2. Anisogamous – 2 unequal sizes of gametes (the shape is same but the size is different)
3. Heterogamous – 2 different gametes (male is motile , female is non motile)