Plp 120 Lab Practical 1

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Koch's Postulates

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1. The suspected pathogen is constantly associated with the disease
2. The suspected pathogen is isolated in pure culture and identified
3. healthy hosts are inoculated with the pure cultures and the disease is reproduced with he same symptoms
4. The suspected pathogen is reisolated in pure culture and shown to be identical with the culture in step 2

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Thallus

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Vegetative body of a fungi that consists of many hyphae

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Hyphae

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contain all the organelles that are known in higher plants

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Mycelium

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Hyphae in mass

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Spores

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how fungi reproduce and there are many specialized kinds

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Sexual Reproduction

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involves meiosis

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Asecual reproduction

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only involves mitosis

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Bacterial Streaming from infected leaf tissue with vascular wilt disease

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Bacterial canker in tomato stem

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Bacterial canker foliage symptoms on tomato

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Bacterial Speck casual agent

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Pseudomonas syringae pv. tomato

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Bacterial Speck symptoms

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Difficult to distinguish from bacterial spot, but early symptoms are small greasy lesions often with chlorotic haloes. Can cause severe disease in CA under cool and wet conditions

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Pseudomonas

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Colonies are generally white. When grown on a medium of low iron content produce a yellow-green diffusible, fluorescent pigment.

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Bacterial canker of tomato casual agent

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Clavibacter michiganensis subsp. Michiganensis

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Bacterial canker of tomato symptoms

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Result from bacterial colonization of surgace tissue (birds-eye spots). Systemic symptoms result from invasion of the vascular tissue (stem cankers)

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Disease Cycle of bacterial canker of tomatoes

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Contaminated seeds are one of the most important primary sources of inoculum. Secondary infections occur most easily through root or shoot wounds make during transplanting. Also via rain splash or soil water are of minor importance in CA.

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Control of bacterial canker

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seed selection, inspection, and certification, seed disinfestation, cultural practices, clean seed bed, rotation, and direct seeding

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Fire Blight causal agent

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Erwinia amylovora: a short, rod-shaped organism with peritrichous flagella.

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Fire blight symptoms

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Kills flowers and twigs, may also girdle trunks. Bacterial ooze, blighted fruit, and stem canker

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Fire blight control

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careful pruning of cankers, copper sprays, antibiotics, and biological control.

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Black Rot of Crucifers Causal agent

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Xanthomonas campestris pv. campestris (Xcc)

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Black rot of crucifers symptoms

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Large V shaped chlorotic blotches or lesions that appear at the margins of leaves. Initially infected tissues turn black. Infected leaves fall off, the stem and stalks of infected plants may turn black or brown.

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Black rot of crucifers disease cycle

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bacteria overwinter in debris and in seeds. Splashed onto leaves and infect through tomates, hydathodes, or wounds. Bacteria can spread systemically. Disintegration of the xylem occurs.

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Bacterial blights of bean causal agent

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Pseudomonas syringae pv. phaseolicola (halo blight)
Xanthomonas (axonopodis) campestris pv. phaseoli (common blight)

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Bacterial blights of bean symptoms

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Initial symptoms are small translucent watersoaked spots on undersurface of leaves. Spots enlarge and become dead tissue.

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Halo blight symptoms

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Distinct chlorotic rings or halos that surround the lesions on leaves. Due to a toxin (phaseolotoxin). New growth appear light green to yellow.
Not a problem in CA unless sprinklers are used

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KOH positive

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Gram negative (Pst, Pseudomonas aeruginosa)
Has threads

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KOH negative

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Gram positive (Cmm)

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Positive Immunostrip test (lateral flow)

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Crown Gall Causal Agent

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Agrobacterium tumefaciens

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Pectobacterium carotovorum (note how cells look)

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Crown gall on tomato hypertrophy and hyperplasia

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Soft rot on Potato causal agent

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Pectobacterium carotovorum

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Crown Gall

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A cancerous growth composed of disorganized proliferating plant cells. It affects woody and herbaceous plants, mostly on pome and stone fruit trees.

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Gall of Grape Causal agent

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Agrobacterium tumefaciens

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Olive Knot causal agent

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Pseudomonas savastonoi pv. savastonoi (causes olive knot)
pv. nerii (causes oleander knot)

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Agrobacterium tumefaciens media plate

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Clavibacter michiganensis ssp. michiganensis media plate

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Pathogen dissemination of crown gall

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Nursery stock, irrigation water, contaminated soil and tools

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Pathogen dissemination of olive knot

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Splash water, irrigation water, insects, contaminated tools

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Pathogen dissemination of soft rot

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Human (storage, transit), insects, and contaminated soil

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Oxidase Test

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Selective media

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Allows microbes of interest to grow while inhibiting the growth of other microbes. Eg. PARP for Phytophthora capsici

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Differential media

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Used to distinguish microbes from each other based on growing characteristics such as colony morphology, color, and how the colony is interacting with the media.
Eg. CVP media for Pectobacterium carotovorum

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The hypersensitive response (HR) test

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Brown rot blossom blight and fruit rot of stone fruit causal agent

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Monilinia functicola

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Brown rot blossom blight and fruit rot of stone fruit characteristics

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This disease is widespread and destructive on stone fruits. Both flowers, fruits in the orchard, and in storage may be affected, cankers may form. Mummies serve as survival structures of the pathogen

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Mummies and saucer-shaped fruiting bodies are:

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apothecia

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Apothecia

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Sexual fruiting bodies that release ascospores in the spring

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Blossom blight and fruit blight symptoms

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infected blossoms become necrotic and die. Young blossom spurs and associated leaves collapse to form shoot blight. Gum exudes at base of infected flowers. Cankers and gray brown spore masses form

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Fruit rot signs

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Gray brown spore masses are formed on mature fruit, in the orchard and in storage

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Peach leaf curl causal agent

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Tephrina deformans

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Peach leaf curl characteristics

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Common and potentially destructive disease of peach and allies, but is easily controlled by a single fungicide spray in late fall or early spring.

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Peach leaf curl symptoms

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Spectacular malformations of the leaves. Thinkened, curled and tinted yellowish or reddish. Fruit symptoms include irregular reddish lesions sometimes develop on the fruit.

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Asci form on the leaf surface and produce inoculum

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Apple Scab causal agents

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Venturia inaequalis
(sexual state: Spilocaea pomi)

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Apple Scab characteristics

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The principle effect on host is the disfiguring of the fruit, resulting in loss of quality. The disease can affect fruit size or cause premature drop and defoliation

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Apple scab fruit and foliar sysptoms

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Fruit develop circular lesions, velvety and olive-green at first then becoming dark, often with scabby texture. Leaves develop similar lesions

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Fruiting body with asci of apple scab

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Conidial Chains

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Apothecium of brown rot of stone fruits

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Layer of asci on infected leaf of peach leaf curl

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Powdery Mildew of cereals and grasses causal agent

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Blumeria graminis

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Powdery mildew symptoms

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Note the white, later gray-tan, mildew colonies. The underlying host tissue remains green for a short period and then becomes chlorotic.

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Powdery mildew of cereals and grasses disease cycle

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The fungus oversummers as chasmothecia on residues of barley or weed hosts. In the fall or winter, rain and cool temperatures stimulate the chasmothecia to release ascospores. Secondary infection by conidia permits the fungus to spread from weed to barley.

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Powdery Mildew of Grape causal agents

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Erysiphe necator

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Powdery mildew of grape symptom

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Initial signs include white, webby mycelium that later takes on a white powdery appearance

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Powdery mildew of grape signs

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Cleistothecia with hooked appendages, transparent conidia formed in chains

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Powdery Mildew of Roses causal agent

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Sphaerotheca pannosa f. sp. rosae

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Powdery mildew of roses symptoms

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On older leaves, large white patches of fungus growth appear, may cause necrosis. White patches of fungal growth also appear on young, green shoots, may coalesce and cover the entire terminal portions of the growing shoots

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Erysiphe cichoracearum on salvi sp.

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Erysiphe cichoracearum on Taraxacum sp. (Dandelion)

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Erysiphe polygoni on Escholzia sp. (Poppy)

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Erysiphe altoides on Quercus sp. (Oak)

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Powdery mildew haustoria

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Chasmothecia

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