Lesson 3 Disease Causing Organisms Flashcards
Why are fungi most important disease causing organism in forests worldwide
Their ability to use lignin and cellulose as substrate, helps fungi form beneficial relationships with plants called mycorrhizae. the vast majority do not cause disease and are defined as obligate saprophytes or decomposers.
What two types of disease causing organisms are responsible for the majority of forest diseases?
Fungi and Dwarf mistletoe
Describe the features of fungi and how they grow and reproduce.
Fungi are eukaryotic spore producing organisms. The spores are their mode of reproduction and act as a mode of dispersal. Fungi can reproduce sexually or a-sexually. Their physical form is usually as mycelium.
Describe the differences between true and dwarf mistletoes.
Dwarf mistletoes are small, yellow/brown/olive green plants. They have stems that jointed stems that are either simple or branched, and typically less than 10cm long. They occur on coniferous species such as lodgepole pine.
True mistletoe occurs on broadleaved plants, generally speaking. They can be found on forest trees, but also trees such as rubber, citrus, apple, cherry, cacao, and coffee trees. Their height varies from a few cm to 1m, which Is notably bigger than dwarf mistletoe.
Describe the features of bacteria and how they grow and reproduce.
Bacteria are one celled prokaryotic organism, characteristically with no nuclear membranes. They have three common shapes: spiral, round, and rod-shaped. Some bacteria have flagella, which are used for swimming, but bacteria have no specialized structures for dispersion. They rely on passive methods for dispersions such as wind or insect dispersal.
Bacteria Reproduce asexually through a process called Binary fission. This is where a single cell duplicates to form 2 cells that are genetically identical.
What are viruses and viroid and describe how they disperse?
Viruses are infectious nucleoprotein particles contained in a capsid . A viroid differs from a virus as it is a small, naked, and circular RNA strand without a capsid. but can still cause disease. Viruses have 8 methods of dispersal. Parasitic animals, parasitic plants, parasitic fungi, seeds, pollen, grafting, contact, and vegetative propagation.
What are some typical symptoms of virus disease in plants?
Symptoms are most obvious in leaves. Common examples of these are: ring spots and mosaics. A mosaic would be a yellow/olive-green/white area mixed with green spots on a leaf. Additional symptoms are stunting, leaf roll, dwarfing, yellows, pox tumors, streak, pitting, and stem distortions.
What is a phytoplasma? Give an example of a phytoplasma caused tree disease.
Phytoplasmas are prokaryotic organisms with no nucleus or cell wall. The reproduce by binary fission or budding and have no flagella. They are typically transmitted by sucking insects. Elm phloem necrosis is caused by phytoplasmas, where leafhoppers transmit the pathogen to the elm and it causes leaves to droop, curl, turn yellow, brown, and finally fall.
What special feature does a plant pathogenic nematode possess and describe the typical symptoms produced by nematodes.
Plant pathogenic nematodes have a hollow stylet used to puncture plant cells.
In roots, they symptoms produced are root knots/galls, root lesions, excessive branching, and injured root tips. Some of the above ground symptoms include yellowing, wilting, stunting, and reduced yields.
Describe how you would tell fungi in the phyla Zygomycota, Ascomycota, and Basidiomycota apart?
Zygomycota have mycelia without septa, multinuclear mycelium, spores are dispersed by animals or airborne, sexual reproduction is by zygospores, asexual repordution by conidia, anthrosproes and chlamydospores.
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