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58 Cards in this Set
- Front
- Back
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Plant diseases: A parasite is... |
...an organism that lives on or in another organism and obtains its food from it. The association is beneficial to the parasite, but NOT the host. |
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Plant diseases: An obligate parasite, or biotroph,... |
...only live on a living host and cannot lead an independent non-parasitic existence. It does NOT grow in artificial culture medium. |
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Plant diseases: A non-obligate parasite (facultative), or necrotroph,... |
...is an organism that may lead an independent existence or live as a parasite, and can live on either a living or non-living host. |
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Plant diseases: A saprophyte is... |
...an organism that lives on dead organic matter. |
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Biotroph (obligate) have... |
...a narrow host range, cannot grow as saprophytes, attack healty host tissue at any stage, kill host cells slowly, penetrate directly or via natural openings. |
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Examples of biotrophs include... |
...nematodes, phyoplasma, viruses, downy mildew, powdery mildew, rusts, etc. |
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Necrotroph (facultative) have... |
...a wide host range, attack young/weak/senescent tissue, kill host tissue rapidly by producing toxins or enzymes, penetrate through wounds or natural openings. |
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Examples of necrotrophs include... |
...anthracnoses, cankers, fruit rot, leaf spots, blights, root rot, vascular wilt, etc. |
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The term pathogen comes from pathos and gen, meaning... |
...suffering and origin. |
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Parasites become pathogens when... |
...cause harm to the host plant, not merely living off and and obtaining nutrients. These are the disease symptoms. |
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Pathogens are... |
...infectious. |
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Plants ______ an immune system. They produce __________ __________. |
Plants _lack_ an immune system. They are surprisingly resistent to diseases caused by fungi, bacteria, etc. that are present in the environment. They produce _antimicrobial compounds_ and exhibit PCD. |
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PCD stands for... |
...programmed cell death. |
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PCD (programmed cell death) is... |
...the way a plant creates a protective zone of dead cells around the site of a pathogen invasion. The dead plant cells do not support viral growth and lose their interconnectedness, thereby halting the spread of the pathogen. |
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The three points on the Disease Triangle are... |
... the susceptible HOST, the PATHOGEN, and the favorable ENVIRONMENT. |
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Step one in using the Disease Triangle to diagnose is... |
...identify the HOST plant species and cultivar.
Determine what a healthy plant looks like, observe unusual symptoms and disease patterns. |
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Step two in using the Disease Triangle to diagnose is... |
...look for signs of the PATHOGEN.
Look above and below ground. |
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Step three in using the Disease Triangle to diagnose is... |
...assessing the ENVIRONMENT by determining the recent conditions for plant growth.
For example, indoor or outdoor, place (greenhouse, field, etc), fertilizer application, previous plantings, soil characteristics, temperatures, water supply, air-flow, etc. |
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Stages in Disease Development:
1) Inoculation is... |
...the process by which pathogens or their reproductive units are brought into contact with the plant, e.g. contaminated tools. |
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Stages in Disease Development:
2) Penetration is... |
...the entrance of the pathogen into the host, e.g. through wounds. |
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Stages in Disease Development:
3) Infection is... |
...the process by which the pathogen establishes contact with susceptible cells or tissue. |
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Stages in Disease Development:
4) Incubation period is... |
...the time interval between infection of the plant and the appearance of the first disease symptoms. |
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Stages in Disease Development:
5) Invasion is... |
...the later stage of infection in which the pathogen spreads more extensively into the tissue of the host. |
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Stages in Disease Development:
6) Reproduction is... |
...when the pathogen obtains nutrients from the host and increases in size and number quickly. |
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Stages in Disease Development:
7) Dissemination is... |
...the dispersal and spread of the pathogen to other host plants. |
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Stages in Disease Development:
8) Overwintering/oversummering is... |
...when the pathogen goes dormant either in the living host or as spores in the thatch or soil. |
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Pathogens: |
...tiny entities of nucleic acid (either DNA or RNA, not both) with a protein coat.
...parasitic and only multiply in living cells. |
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A virion is... |
...a virus outside of a cell in the extra-cellular state. |
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Pathogens: |
...upsetting the metabolism of the plant cell, which in turn cause cells to produce abnormal and injurious substances. |
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Pathogens:
Viruses were first indentified and isolated from... |
...tobacco plants. |
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Pathogens: |
...either abrasions of the cell wall or by plant parasites such as nematodes or aphids. |
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Virus symptoms:
Mottling is... |
...an abnormal coloration, either light or dark. |
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Virus symptoms:
Mosaic is... |
...light in color and creats a mosaic-like pattern. |
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Virus symptoms:
Chlorosis is... |
...lightening of color resultant of a reduced amount of chlorophyll. |
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Virus symptoms:
Vein clearing is... |
...when the veins of the leaves become light and more distinct, tissue surrounding the veins become subject to a localized chlorosis. |
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Virus symptoms:
Leaf spots... |
...include various appearances of spots, lightening, darkening, whorling, PCD, and even the absence of leaf tissue. |
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Other virus symptoms include: |
...leaf rolling and curling, leaf distortion, Rugose rose, enation, stunting, reduced yield, etc
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Pathogens: |
...tiny organisms that contain cytoplasm enclosed by a cell wall, but lack an organized nuclei and do NOT require a living host for reproduction and growth (live as parasites or saprophytes), and do not have a means to enter a plant host. |
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Pathogens:
Fungi are... |
...the largest group of pathogens, lack chlorophyll so sustain life by feeding on living or dead material. They can be single-celled like yeast, or large multi-celled like mushrooms, molds and mildew. |
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Hyphae are... |
...individual fungi threads. |
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Mycelium is... |
...a collective mass of fungus threads (hyphae). |
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Pathogens:
Fungi produce... |
...spores, which are the fungi's product of reproduction. |
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Pathogens:
Fungi reproductive structures are called... |
....fruiting bodies. |
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Fungal groups: |
...produce asexual spores in sporangia (fruiting body) called sporangiospores. e.g. rhizopus (soft-rot on fruits and vegetables), mucor (rhizopus and mucor used to ferment soy beans to make tofu), arbuscular mycorrhizal fungi (absorb phosphorus from trees), etc. |
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Fungal groups:
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...bear sexual spores (ascospores) in groups of eight in an enclosed sac called an ascus, septate hyphae. e.g. bread and beer yeasts, morel mushrooms, and the asexual spores, conidia, cause Dutch elm disease and chestnut blight. |
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Fungal groups: Class Basidiomycetes... |
...bear their sexual spores externally on a basidium (basidiospores). e.g. bracket fungi, mushrooms, puffballs, bird's nest fungi, many wood decay pathogens, etc. |
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Fungal groups: Class Deutermycetes... |
...sexual stage unknown. |
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Fungal groups:
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...are water molds, more closely related to brown algae than true fungi. e.g. pythium, phytophthora, downy mildew, white rust, etc. |
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Fungal groups: Class Chytridiomyctes... |
...have hyphae with no cross -walls, most are saphrophytes. Most primitive group of true fungi. eg. Physoderma (corn brown spot), Synchytrium (potato wart), etc. |
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Most fungi cause... |
...local or generalized symptoms on their host. |
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Common necrotic symptoms include... |
...root rot (disintegration or decay of roots),
...damping off (rapid death of young seedlings). |
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Damping off is... |
...the rapid death of young seedlings. |
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Pathogens:
Nematodes are... |
...small, generally round worm-like animals (aka, eel worms), soil-born and feed on underground plant parts, leaves, or flowers (e.g. chrysanthemum foliar nematode). |
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Endoparasitic nematodes... |
...enter plant parts such as roots, feed, and complete their life cycles there. |
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Ectoparasitic nematodes... |
...feed on the surface cells of roots. |
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Nematodes cause... |
...below ground: root knots, cysts (galls), root lesions, stubby root, and root branching.
...above ground: necrotic spots, rots, and distorted growth. |
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Nematodes can be managed by practicing... |
...crop rotation. |
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Pathogens:
Phytoplasma... |
...microrganisms with membrane-bound cells, but without cell walls, are smaller than bacteria. They live in the vascular systerm of plants and spread by sap-feeding insects (e.g. leafhoppers, planthoppers). Are obligate. |
