Grade
Lab Lab counts for 145 points of the total 700 points possible 100 points from weekly quizzes 45 points from 3 disease profiles
3 diseases collected and identified We help with diagnosis After identified prepare 1-2 page disease profile
Lab Objective
To familiarize yourself with the terminology that we use as plant pathologists, particularly that involving the symptoms of disease To understand what affects disease has on plants
Plant Disease
- Condition detrimental to plants
- abnormal
- growth, development, reproduction - any plant part on roots, stems, leaves, fruit
- Continuous irritation
- occurs over time (disease is a dynamic process)
- Primary causal agent
- biotic (living, infectious/contagious) - fungi, nematodes, bacteria, viruses, etc. - abiotic (non-living, non-infectious) - air pollution
- Production of symptoms
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Symptoms and Signs of Plant Diseases
Symptom - visible expression of a disease by a host plant
Examples of Symptoms of Plant Disease
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Necrosis -- browning (death) of host tissues, part or all of the plant.
Lesion - a discrete or localized necrotic area.
Canker -- localized death of woody plant tissue usually resulting in a collapse of the bark.
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Cankers can be formed from callus tissue, e. g., the concentric ridges on the tree above, but in many cases the plant does not form callus tissue, as seen on this redbud.
Vascular discoloration - necrosis of the vascular tissue caused by vascular pathogens or wood rotters
Blight -
rapid necrosis of a plant or plant part. The blackened tissues develop in a short period of time.
Late blight of potato
Fire blight of pear
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Additional examples of blights
Petal blight Rhizoctonia blight (brown patch)
Dieback -
necrosis of terminal portions of the crown that proceeds downward.
Necrosis of plant cells (xylem) involved in water transport, resulting in loss of turgor pressure.
Wilting -
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tissues due to a loss of chlorophyll
Chlorosis -- yellowing of - plant
Mosaic alternating patterns of
light and dark green tissue
Hypertrophy - abnormal increase
in cell size
Hyperplasia - abnormal increase
in cell numbers.
These conditions frequently occur together and cannot be distinguished without a microscope. Both conditions cause overgrowths on plants.
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Examples of overgrowths
Gall or burl
Blister
Examples of overgrowths
Corn smut
Root knot
Crown gall
Stunting reduction in size and vigor of plants caused by many root pathogens
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Signs of Plant Disease
Sign - part of the pathogen visible on host tissue. Usually refers only to macroscopic structures such as the mycelium growing from infected plant.
Hyphae of some fungi are visible on diseased tissue
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Sclerotia - (a compact mass of hyphae surrounded by a darkened rind) are produced by numerous fungi.
Rhizomorphs - specialized
hyphae that look like black shoestring like structures.
Most signs of fungi are reproductive structures such as these Basidiocarps (mushrooms) of a wood decay fungus
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The dark spores (teliospores) of the corn smut fungus become visible when old galls rupture
Additional types of basidiocarps (conks and brackets) of wood decay fungi.
Masses of spores and hyphae are often visible on diseased tissue, e. g. on this moldy corn
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White spores and hyphae on a plant infected by a powdery mildew disease
Apothecia - (reproductive structures of a certain class of fungi) growing on a larch twig.
Spore masses of a fungus growing on an infected leaf.
Elm
Peanut stem
Perithecia (a type of reproductive
structure) on an elm leaf (left) and on a peanut stem.
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Spore tendrils - of a fungus growing on red cedar needle gall.
Spore (telial) horns of a fungus
on red cedar.
Spore-bearing structures (aecia) of a rust fungus on pine.
Spores of the uredial stage of a rust fungus on raspberry and fescue
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The greenish-yellow structures growing on this oak are shoots of the parasitic higher plant true mistletoe.
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