PLANT DISEASE CYCLE Flashcards
Disease development occurs over a period as a series of events. This series of events is called the_____
disease cycle
The basic steps in most disease cycles are as follows:
Inoculation
Penetration
Infection
Growth and Reproduction
Dissemination
Survival
These three often survive in crop residue or in the soil.
Fungi, bacteria, and nematodes
These two often survive in insect vectors.
Viruses and bacteria
These three can be dispersed by insects.
Fungi, bacteria, and viruses
Only these two are dispersed by rain or wind.
fungi and bacteria
The type of disease which produces only one infection cycle per host cycle is called _____?
monocyclic
Three types of plant diseases that tend to produce only one
infection cycle per host cycle (monocyclic):
(1) postharvest diseases,
(2) diseases caused by soil-borne plant pathogens, and
(3) rusts without a urediniospore stage.
4 stages of MONOCYCLIC DISEASE
Primary Inoculum
Dissemination
Primary Infection
Overwintering
It is considered such if there are repeated complete infection cycles, that is, infection followed by pathogen development, new inoculum production, dispersal to new susceptible sites, and new infections, all within a single
crop cycle.
polycyclic
This describes the introduction/contact of the plant pathogen to the host.
INOCULATION
? – arrival of the pathogen to the host
Inoculation
? – the pathogen(s) that land on the host
- Any part of the pathogen that can initiate infection
Inoculum
TYPES OF INOCULUM
? – asexual or sexual spores, mycelia fragments, sclerotial
bodies, rhizomorphs, and dormant mycelia in seeds
Fungi
TYPES OF INOCULUM
? – eggs, larvae, and adults
Nematodes
TYPES OF INOCULUM
? – phytoplasma cells, protozoan cells, bacterial cells
Bacteria
SOURCES OF INOCULUM (6)
infected living plants
Plant debris
Infested soil
Infected seed and vegetative propagating materials
Contaminated containers, storage areas and equipment
Insects, nematodes and other living agents that carry inocula
An example of active penetration of the pathogen is?
Direct penetration
An example of passive penetration of the pathogen is?
Penetration through natural openings and wounds
This is the most common type of penetration by fungi and nematodes and the only type by parasitic plants.
Fungi use a fine hyphae produced by a spore mycelium or penetration peg produced by an appressorium.
- This is formed at the point of contact with the host
- It can be through mechanical force and softening of the cell walls by an enzyme.
DIRECT PENETRATION
PENETRATION THROUGH NATURAL OPENINGS
- also called a stomate is a pore, found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange.
Stomata
- A ______ is a type of pore, commonly found in
angiosperms, that secretes water through pores in the epidermis or leaf margin, typically at the tip of a marginal tooth or serration.
Hydathodes
- one of many raised pores in the stem of a woody plant that allows gas exchange between the atmosphere and the internal tissues.
Lenticels
- A pore, in the base of a flower, through which nectar is secreted.
Nectarthode
This occurs when the pathogen invades the plant tissue and
establishes a parasitic relationship between itself and the plant.
INFECTION
Examples of NATURAL OPENINGS (4)
Stomata
Hydathodes
Lenticels
Nectarthode
These 2 organisms and phytoplasmas are not able to actively penetrate or enter plant host tissues. Therefore, they must rely on other methods to infect plant tissues and cells.
Viruses, bacteria,
When Successful, infection is evident as___?
symptoms
3 different types of Infection:
Local infection
Systemic infection
Latent infection
- This type of infection produces symptoms which are physiological or structural changes within a limited area of host tissue, such as leaf spots, galls, and cankers.
Local infection
- symptoms of this type of infection are those involving the reaction of a greater part or all of the plant, such as wilting, yellowing, and dwarfing.
Systemic infection
This type of infection is where the state in which a host is infected with a pathogen but does not show symptoms. It persists until signs or symptoms are prompted to appear by environmental or nutritional conditions or by the stage of maturity of the host or
pathogen.
Latent infection
Bacterial leaf blight of rice caused by Xanthomonas oryzae pv. oryzae is an example of what type of infection?
LOCAL
Bacterial Wilt of Tomato caused by Ralstonia solanacearum is an example of what type of infection?
SYSTEMIC
Anthracnose of mango caused by
Colletotrichum gloeosporioides is an example of what type of infection?
LATENT
INFECTION PROCESS IS AFFECTED BY VARIOUS
FACTORS
– Resistance & susceptibility of the host
– Aggressiveness & virulence of the pathogen
– Environmental factors
– Host nutrition & pH
– Incubation period (depends upon host-pathogen combination, stage of host and
environment etc.)
What are the two concurrent stages that occur during infection as pathogen invade different cells, grow & multiply?
Invasion and reproduction
REPRODUCTION style of Fungi
Sexual or asexual spores
REPRODUCTION method of bacteria
Binary Fission
REPRODUCTION method of Virus
Replication
REPRODUCTION method of Nematodes
Self-fertilization (Hermaphrodites)
inoculum are disseminated or spread by a variety of factors (5).
Wind
Seed and planting materials
Rain
Man
Insects
Media where organisms can survive
- In infected crop debris
- In seed
- In soil
- On growing plants
- Infected material on host plants
- In propagating material
- Alternate host
- As dormant structures e. g. sclerotia, chlamydospores
