Disease Triangle
Host, environment, pathogen + time
Biotrophs/obligate parasites
parasites that are so dependent upon their hosts that they cannot survive without them
parasites
depends on an organism for its nutrition
obligate parasite (biotroph)
organism that can grow only as a parasite in association with its host plant, cannot be grown in culture media. (plant biotrophs: nematodes, viruses, downy mildews etc.)
saprophytes (necrotroph)
obtain nutrients from dead organic matter
facultative saprophyte
better adapted to living as parasites but can live as a saprophyte
facultative parasite
primarily saprophytes but can live as parasites
obligate saprophytes
live only on dead matter
plant disease
sustained physiological and structural damage caused by living agents
causal agent
organism that incites and causes plant disease
kochs's postulates
1. constant association
2. isolated
3. inoculated
4. re-isolation
symtom
indication of disease by reaction of host. *however, symptoms alone are not enough for accurate diagnosis
signs
indication of disease from direct observation of a pathogen or its parts. (these are indications of the presence of a disease causing organism -eg. bacterial cells, fungus spores)
Do not produce signs, only symptoms
Abiotic disorders
disease cycle
the succession of all events and interactions among the host pathogen and environment that occur during the development of disease
monocyclic disease
one disease cycle per growing season. primary inoculum is the only inoculum for the season
polycyclic disease
having many disease cycles in one growing season. (usually cause explosive epidemics)
produce secondary inoculation throughout growing season
Mycology
the study of fungi
fungus
a eukaryotic, spore-baring achlorophyllus organism that reproduces sexually and asexually, and whose usually filamentous, branched structures are typically surrounded by cell walls composed of chitin.
true fungi
#NAME?
hyphae
long-branching filamentous structure. main mode of vegetative growth, collectively called mycelium
mycelium
a large amount of hyphae
fungi use absorptive nutrition
secrete enzymes that partially digest their food, then absorb the simple nutrients through holes in their cell membranes
haustorium
portion of a parasite fungus or of the root of a parasite plant that penetrates the host's tissue and draws nutrients from it.
intracellular hyphae
hyphae enter into cells, haustoria produced in cells
intercellular hyphae
hyphae remain between cells
structures that bear asexual spores:
conidia, psychidium, acervulas, spordochium
conidia
produced on conidiaphores alone (stalk that holds conidia)
psychidium
flask shaped
acervulas
saucer shaped
spordochium
cushion-like structure
telemorph stage
sexual reproduction occurs through meiosis, involves fertilization
dikaryotic
2 nuclei in one cell. In ascomycota, these are 2 haploid nuclei in one cell. (n+n)
dikaryon
has 2 compatible nuclei that cohabit the cells of the hyphae.
karyogamy
the fusion of nuclei. after karyogamy the cell is diploid
Ascomycetes are characterized by
their sexual spores (ascospores) found in a sac called an ascus
structures that bear sexual asci
1. no ascoma (naked asci) 2. chasmothecia 3. parithecia 4. apothecia 5. pseudothecia
Naked Asci
#NAME?
Taphrina deformans
#NAME?
Chasmothecia
-asci are encased in an ascoma
-chasmothecia: recently introduced term to distinguish powdery mildew ascoma from true cleistothecia
=vertical chasm formed during ascospore discharge
Powdery mildew
#NAME?
two types of spores:
1)asexual spores- conidia, found on conidiaphores
2) sexual spores - ascospores formed in chasmothecia
Shape of appendages of chasmothecium
1) spear-like with inflated base
2) w/curled tips
3) w/dichotomously branched tips
Control of powdery mildew
get resistant plants or dont plant in shade.
prune overcrowded branches to increase air circulation
remove amd destroy infected plant parts
fugicides when necessary and asap
parathecia
#NAME?
parathcial ascomycota: clariceps purpurea
ergot of rye.
eating grains that contain survival structures of this disease schlerotia causes muscle spasms visions etc
Glomeralla
causes bitter rot on apple and its anamorph causes anthracnose of many fruit and veggie crops
chestnut blight
produces bothe conidia and ascospores(sexual/asexual)
-pycnidia break through the lenticels and produce conidia
Apothecia
often called cup fungi, others may be flat disk shaped or stalked.
-ranges in size from microscopic to mushrooms
-most produced above ground, some below
-actively discharges ascospores distances of 2-30cm; discharge during wind currents can carry ascospor
lettuce drop
schlerotinia sclerotiorum
to manage:
fumigate soils, rotate crops, deep plowing, improve soil drainage, spray preventative fungicides
botrytis cinerea
example of asexual ascomycete in apothecia. produces only asexual spores: conidia; NO APOTHICIUM
molinia fructicola
brown rot on stone fruit.
causes blight of blossoms and twigs and soft decay of fruits.
to control: destroy mummies, prune infected stems, keep flowers and fruit dry, spray preventative fungicides in spring as blossoms open.
incubation period
the time after pathogen penetration but before symptoms appear
biotic agent
a living organism that is the cause of damage
What is plant pathology?
The study of plant diseases