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These are the factors for the establishment of plant diseases.
- Pathogen properties.
- Properties of the host.
- Presence/absence of nutritional component.
- Properties of environment.
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A) Pathogen properties
1. Level of virulence:
Pathogen’s ability to infect/damage the host or to infect a resistant gene.
The ability of a microbe to grow according to environmental conditions.
3. Dispersal efficiency:
Efficient spore dispersal by pathogen or pathogen itself dispersed, by water, air or vector.
4. Survival efficiency:
In plants, there is environmental stress for microbe and also competition with the beneficial microbe, so microbial survival is important for the disease to develop.
5. Reproduction fitness:
Microbes reproduction should fast so that microbes adapt to the environment quickly.
B) Properties of host
The host is susceptible in case of immunity. If host immunity is low then it is easy for the pathogen to attack.
2. Growth and stage form
Different microbes attack on plants on different stages, which are germination, growth, reproduction, spreading seed. Pseudomonas aeruginosa attacks the germination stage of Arabidopsis thaliana and stops germination, the seed becomes dormant.
3. Population density
Some plants are densely populated in areas and diseases are easily spread.
4. General health
Sometime infect with the primary disease may susceptible to other diseases.
C) Nutrient component
Plant fertilized heavily with nitrogen are attacked more severely by some microbe.An example is Puccinia (Rust) on wheat. N2 deficiency causes weaken or slower growth, faster aging and pathogen are more prone to attack slow-growing, for example, fusarium on tomato.
Increased phosphorus either improves nutrient balance in the plant but if too much increase it attracts the more microbe towards plant and causes disease.
Excess potassium increases the severity of some diseases
Example; rice blast.
D) Environmental factor
Environmental factors determine whether the disease occurs or not.
If the plant and microbe have an optimum temperature, pathogen gets the upper hand.
If the temperature is optimum for the plant, not for pathogen then disease progresses slowly or even not happen.
Temperature also effects on incubation period/latent period, generation time and infection period.
In summer: Leaf roll symptom is common.
In spring: Ring spot symptom is common.
Fungi are mainly infecting plants which are grown mostly during the presence of high moisture. At high moisture spore germination of fungi is also maximum and activation of bacteria is also high.it also increases the succulence of the plant. Soil pathogen is often more virulent when soil increases the salutation point.
3. Effect of wind
The wind is important in the dispersal of a pathogen which are spread directly with wind or by the vector, that can be carried along with long distances by wind.
Damage by wind (by direct damage, windblown sand, plant rubbing) make susceptible the host for the microbe, it can also cause the release of spore and bacterial form from infected tissues.
4. Effect of light
Sunlight is important to the plant health, plant that does not receive the required amount of light to meet the culture requirement become stressed. This may make them susceptible to infection, low light usually favors susceptible to viral infection.
5. Effect of soil pH
Soil pH mostly affects pathogen then plant, the pathogen is sensitive to pH.
Plasmodiophora brassicae (clubroot) optimum at pH 5.7 but inhibited at pH 7.8.
Streptomyces scabies (potato Scab) optimum pH 5.2 to 8 and inhibited below 5.2
pH causes nutrient imbalance and weakened the plant.