Transcript 幻灯片 1

Horticultural Plant
Disease
Chapter 4 Occurrence
and Developmentment of
Plant Disease
Section 1 Pathogenicity
of Plant Pathogens and
Resistance of Host Plants
Section one- Parasitism of plant pathogen
1. Interrelation of plant and microbe
1.1 Mutualistic symbiosis（共生）
 Two organisms can not live separately.
One is beneficial to the other, they keep
alive by living together.
1.2 Commensalism(共栖，或偏利共生）
Two organisms can live separately. When
they live together, one can acquire more
benefits, while another benefits less or none.
1.3 Parasitism（寄生）
One organism lives on another organism,
requiring another one to afford the nutrients.
The organism which afford nutrients names as
host; and another one that acquires nutrients
is called parasite.
2. Parasitism and pathogenicity
2.1 Parasitism
The ability which pathogen gains the
nutrients from alive host plant.
2.2 Pathogenicity
The competence that pathogen destroys the
host plant and brings forth the disease.
Nourishing manner:
Biotrophy(活体营养）
The parasites obtain the nutrients from
alive host, and do not kill the host cells and
tissues immediately. These parasites are called
obligate parasites.
Necrotrophy（死体营养）
The parasites firstly kill the host cells and
tissues, and then acquire the nutrients from
the dead cells and tissues. These parasites are
celled necrotrophic parasites.
3. Pathogenic mechanism of plant pathogen
Pathogenic microbes not only snatch the
nutrients and water from host plant, but also
inflict the mechanical pressure on host and
produce the harmful metabolic products to affect
host normal physiological activities. For example,
enzyme, toxin, growth regulating substances
produced by pathogens can induce a series of
pathological changes to host plants .
3.1 Snatching the nutrients and water from host
plant
 Various pathogens have parasitism, and can
gain the necessary
living substances from host.
 Parasites deplete（消耗） the nutrients of host
plant, causing malnutrition, yellowing, stunting,
even necrosis.
 Hemiparasites mainly despoil(掠夺) the water
from host, causing mild harm to host.
 Holoparasites bring forth tremendous damage
to host , causing yellowing and necrosis promptly.
3.2 Mechanical pressure
 Firstly hypha of fungi (germ tube) and
radicel(胚根) of higher parasitic plants touch the
host plant and attach to the surface of plant; in
succession, the top of the hypha swells to form
appressorium, and the appressorium produces
infection pegs to penetrate cuticle(角质层) and
cell wall, or excretes(分泌) the enzymes to
decompose cuticle and cell wall .
Nematode penetrates the plant cuticular
cell wall by stylet and the head or the
whole body enters plant cell.
 Some pathogenic fungi form the
fruiting body(子实体）under plant cuticle,
and impose the strong mechanical
pressure on plant cuticle, causing the
cuticle to expand, plump up and rupture ,
eventually resulting in the fruiting body
basseting.
3.3 Enzyme
 The pathogen produces many enzymes related to
pathogenicity, mainly including cutinolytic
enzyme(角质水解酶), cytolytic enzyme(细胞降解
酶), protease, amylase(淀粉酶), lipase(脂肪酶), etc.
 Many pathogenic fungi can produce a series of
enzymes to catabolize the cuticle and cell wall.
3.4 Toxin
Toxin is a kind of poisonous compound
which produces in metabolic process. It can
disturb the normal physiological function of
host plant in lower concentration.
Toxin is a kind of pathogenic substance
with high efficiency. In lower concentration,
it can induce the host to produce disease
symptom.
3.5 Growth regulating substances
 Many pathogens can the analogs of plant growth
regulating substances to disturb the normal
physiological activity of plant, inducing plants to
produce many pathological changes in conformation,
e.g. excessive growth(徒长), stunting, malformation,
defoliation(落叶), inhibiting apical dominance(顶端抑制),
root top inactivity(根尖钝化), etc.
 Pathogen also can affect the normal function of
plant growth regulating system to bring forth
pathological changes.
Section 2 Plant disease resistance
1.Conception and types of plant disease
resistance
Plant disease resistance---The traits
which the host plant avoid, cease, or
counteract the invasion and expansion of
pathogen to alleviate disease outbreak
and loss degree.
Differentiation according to race specialization
Race specific resistance: host disease
resistance only aims at several specific races;
host varieties have specific interactions with
pathogen races.
Race non-specific resistance: the plant
disease resistance controls by minor genes,
aiming at the whole group of pathogen; the
host varieties have no specific interaction with
pathogen races.
Differentiation according to resistance
mechanism of host plant:
 Passive resistance: Before touching with
pathogen, the host plant has already had some
characters to resist the invasion of pathogen.
 Active resistance: Pathogen invasion
induces the host to generate defense reaction.
2. Plant resistance mechanism
 According to the character of resistant
factors, the resistant factors can be divided
into morphological and structural resistance,
i.e. physical defense; physiological and
biochemical resistant factors, i.e. chemical
defense.
2.1 Passive resistant factors
 Inherent morphological and structural characters
of host plant. The host resists the invasion and
expansion in virtue of mechanical tenacity and
stability to the enzyme produced by pathogen
 Most plants have chemical passive resistance.
Resistant plants may contain natural antimicrobial
substances or inhibitors to enzyme produced by
pathogen. Another possibility is that the resistant
plants lack the required contents which pathogen
parasitizes in host or causes disease.
2.2 Physical active resistant factors
Invasion of pathogen induces the metabolic
changes of plant, causing morphological and
structural changes of plant in subcellular,
cellular, or textural level. Physical resistant
factors can limit invasion of pathogen in cell
wall, single cell, or part tissues.
Invasion and damage of pathogen can bring
forth lignification(木质化) and suberization(木
栓化) of plant cell wall, and deposition of
phenol and calcium ion.
2.3 Chemical active resistant factors
Chemical active resistant factors include
hypersensitive necrotic reaction,
phytoalexin(植物保卫素) synthesis, toxin
decomposition.
2.3.1 Hypersensitive necrotic reaction
The host plant is highly sensitive to invasion
of non-compatible pathogen. The infected
cells and adjacent cells become necrotic
rapidly; the pathogens are restrained , killed
or limited in the necrotic tissues.
2.3.2 Phytoalexin
 A kind of low molecular weight , antimicrobial,
secondary metabolites which produce or accumulate after
infected by pathogen or stimulated by physiological and
physical factors.
 Phytoalexin is the induced product. Besides fungi,
bacteria, virus, nematode, metallic ion, sodium azide(叠氮
化钠), cycloheximide(放线菌酮), mechanical stimulation
also can activate the plant to produce phytoalexin. Lately
the cell wall components of fungi, e.g. dextran(葡聚糖),
glycoprotein(糖蛋白), or cell wall segments of hypha are
discovered to have the activated effect.
3.Plant Induced resistance and resistant mechanism
Induced resistance--- acquired resistance, advanced
inoculation or disposal by chemical or physical factors
can bring the disease resistance to plant.
Cross-protection--- host plant firstly inoculates the
weak pathogenic strains, and then inoculates the
strong pathogenic strains. The host can resist the
strong strains and alleviate the symptom.