PLPA 3004 Lecture Notes - Lecture 3: Silvering, Heart Rot, Hypertrophy

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PLPA 3004/BIOL 3004 Unit 1 Review
Birth of plant pathology: Late blight of potato p 19-20, 421-426
P 19-20
Potato introduced from South Central America to Europe 1570 and well established crop in Ireland
Farmers used to pay rent, farmers dependent for sustenance and survival with potato
Potato favored by cool, wet climate
Stored tubers for winter in shallow ditches, then grew well for years
1840 crops began to fail
1845 favorable weather, then Europe and Ireland cloudy, wetter, and cooler for weeks
Crops showed blighted leaves and shoots, then whole plants died
Next winter tubers in ground rotten, masses of rotting tubers in ditches, nothing else to eat
Death of Irish by starvation
1846, corn imported from US, 1 ½ million Irish died from hunger, many left Ireland to US
Theory of spontaneous generation doctors suggested as mildew fungus growth affected leaves, stems, tubers
Dr. J Lindley, proposed incorrectly that plants over absorbed water from rains and tissue would swell and rot
Dr. Miles Berkeley noticed mold covering plants and labeled fungus (oomycete)
1861 Anton deBary , proved potato blight was caused by fungus by fungus with 2 sets of healthy potatoes
Dusted spores with one, healthy tubers dusted became blighted and died
Fungus oomycete named phytophthora infestans (infectious plant destroyer) was the cause
Phyto=plant Phthora = destruction infestans = infectious
deBary also showed fungus survived winter in infected potato tubers in field or storage
deBary disproved theory of spontaneous generation – microorganisms are produced spontaneously by dying and dead
plants and animals ushered in the germ theory of disease – the proposal that infectious and contagious diseases are
caused by germs (microorganisms).
Honor of proof for Louis Pasteur who proved the theories and published his work with potato blight fungus in 1861-1863
P 421-426
Late blight disease the most devastating disease of potatoes in world in areas cool, moist weather: norther US, east
coast of Canada, western Europe, central and southern China, southeastern Brazil, and tropical highlands
Also destructs tomatoes and other members of family Solanaceaea.
First water-soaked spots at edges of lower leaves, enlarge rapidly form brown, blighted areas with indefinite borders.
Zone of white, downy mildew growth 3-5 millimeters wide at border of lesion underside leaves. Entire leaves infect, die
and become limp. Continuously wet conditions, aboveground parts blight and rot away and give off odor. Entire plants
and fields become blighted and die in few days or weeks.
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In dry weather activities of the pathogen are slowed or stopped. Existing lesions stop enlarging, turn black, curl, wither
and no oomycete appears on underside of leaf. Weather moist again, oomycete resumes and disease develops rapidly.
Affected tubers purplish or brownish blotches of water soaked, dark reddish brown tissue and extends 5-15 mL into
flesh of tuber. Areas become firm, dry and sunken. Infected tubers covered with sporangiophores and spores of the
pathogen or invaded by secondary fungi and bacteria, causing soft rots with putrid odor
Signs: phytophthora infestans
Mycelium produces branched sporangiophores, produce lemon-shaped sporangia at tips. When sporangia are
produced, sporangiophores form swellings, a characteristic for oomycete. Sporangia germinate by releasing 3-8
zoospores below 15 deg C but above 15 deg C sporangia may germinate directly by producing a germ tube
Oomycete requires 2 mating types for sexual reproduction. New strains are more aggressive than old ones. When 2
mating types grow adjacently, female hypha grows through the young antheridium. The antheridium then fertilizes the
oogonium and develops into a thick walled and hardy oospore. Oospores germinate by means of a germ tube that
produces a sporangium.
Antheridium – male reproductive cell
Oogonium – female reproductive cell
Development of disease
Pathogen strains until 1980 belonged to mating type A1 and reproduced in absence of mating type A2 (asexually) they
did not produce oospores and overwintered only as mycelium in tubers. Spread of A2 from Mexico made possible the
sexual reproduction of the pathogen, resulted in production of oospores aboveground and belowground potato plant
tissue. Oospores survive in soil for 3-4 years. Oospores make possible the production of new strains through genetice
recombination of pathogenic characteristics of the mating strains.
Mycelium from infected tubers or from germinating oospores and zoospores spreads into shoots produced from
infected or healthy tubers, causing discoloration and collapse of the cells. Mycelium reaches aerial parts of plant,
produces sporangiophores, emerge through the stomata and produce sporangia. Sporangia ripen, detach and carried
off by wind or dispersed by rain. Germ tube penetrates directly or enters through a stoma. Mycelium grows between
cells, sens long curled haustoria into cells. Mycelium spreads into fresh tissue. New sporangia form within 4 days.
Disease develops, establishes lesions enlarge and new ones develop, kills foliage, reduces yields
Can be controlled by a combination of sanitary measures, resistant varieties, chemical sprays. Only disease free
potatoes should be used for seed. All volunteer potato plants should be destroyed. Can be a source of infection. Most
popular commercial potato varieties susceptible to late blight. New varieties, crosses with wild potato species have one
or more genes for resistance. They were attacked by other races. Even resistant varieties should be sprayed regularly
with fungicides. New strains of two mating types are resistant to metalaxyl.
Lecture 1
Biotic diseases
Kingdom Eubacteria – Bacteria
Kingdom Chromolveolata – Oomycetes
Kingdom Protozoa
Kingdom fungi
Kingdom Animalia – Nematodes
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Kingdom plantae
Fungal infection after Joplin tornado Dec 2012 – Zygomycosis – Mucormycosis
Foodborne illnesses – Dole greens Listeriosis
Frogs – killer fungus – Batrachochyytrium salamandrivoras
Livestock – Fescue toxicosis – decrease weight, necrosis (death) of tissue in feet, tail and ears
White-nose syndrome in bats at Arkansas caverns
Medical uses: Penicillin Hallucinogenic fungi
Food uses – Agaricus bisporus and Lentinula edodes – Shittake
Plant – eukaryotic tissues, grown and development, movement of gases, water and nutrients
Alteration in the normal structure of function of a plant results from causal agent
Any malfunctioning of host cells and tissues from casual pathogenic agents leads to development of symptoms, either
abiotic and biotic factors
Roots – water comes up through xylem
Microsporangium and connective is in the anther of the stamen
Ovule is in the ovary
Perianth consists of Petal (Corolla), sepal (calyx)
Totipotent every cell able to produce new organism
Water movement – Transporation through leaf, Cohesion through xylem, Absorption from roots
Photosynthesis – conversion of light energy into chemical energy CO2 + H20 with light and chlorophyll through
chloroplast = C6H12O6 + O2
Gas exchange through guard cell of stomata where some pathogens go through to get into plant
Cell to cell movement of materials go through plasmodesmata – pathogens are smart
Auxin – apical dominance, dell elongation, tropism
Cytokinins – cell division, fruit and embryo development, prevents senescense
Gibberellin – stem elongation, converts between juvenile and adult development, involved in flowering, break seed and
bud dormancy
Abscisic acid – stress resistance, initiation of dormancy, stimulation of growth
Ethylene – fruit ripening
Brought to US 1825 by Joel Robert Poinsette
1923 – Paul Ecke selected a shorter stature
1945 – improved albert ecke-free branching
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