The vegetable pathology or phytopathology is the science which studies the diseases of the Plante S, especially of the crop plants.

The distinction between a disease and a physiological problem of order is not always easy to make. At the end of this article an enumeration of physiological problems which can is placed be confused with diseases

The diseases of the plants are due at organizations (animal, Bactérie S, Virus, Algue S, Champignon S,…) who are normally present and often in great quantity in their environment, sometimes even of the organizations useful or Symbiote S for the plant.

They become pathogenic only in certain circumstances.
On gathers them under name: organizations phytopathogenes.

Types of diseases

Bacterial diseases

See also: bacterial Disease

Viral diseases

• mosaic Virus
• Phytovirus

Cryptogamic diseases (due to mushrooms)

See also: cryptogamic Disease

The term disease Cryptogamique is used for the parasitic diseases caused by a Champignon S microscopic. This term remained even if certain responsible Micro-organismes are not classified more among mushrooms.

Fight against the diseases

preventive methods

Possible practices in certain cases:

• To avoid the excess of moisture by drainage or an intelligent control of the irrigation

• To eliminate from the sick plants, the remains
• To avoid damaging vegetable fabrics
• To practice long rotation
• To disinfect the seeds (hypochlorite of Na/Ca, Formaldehyde, copper oxychloride, treatment heat)
• To disinfect the material (hypochlorite of Na/Ca, detergents, formol)
• To disinfect the ground by vapor treatment - solarization
• To use resistant varieties

Chemical fights

It is the recourse to fungicides or bactericides (antibiotic). There are for example cupric products such as the ammoniacal copper sulfate or the Oxychlorure of copper, or for example of the Sodium orthophénylphénate, or Foséthyl-aluminum (alliette).

The antibiotics are authorized very little in the majority of the countries for the risks of gene selection of resistance which could pass to the pathogenic bacteria at the man. One finds there products like the Streptomycine, the Terramycine, the Agrimycine, the Kasugamycine.

Biological fights

See also: biological Fight

Alternatives to the chemical treatments are little by little developed and arrive on the market. This category of the elicitor s-phytostimulants brings solutions which already gave results.

One can voluntarily introduce into an infected piece a bacterium or a mushroom inoffensive for the plant but which has antagonisms strong with a bacterium or a particularly pathogenic mushroom. For example one uses Erwinia herbicola against Erwinia will amylovora

Integrated fight

One can of course also combine the various techniques by taking more into account the environmental factor.

See also: integrated Fight

The diseases of the plants are due to two series of factors, which can act jointly:

• of the factors related to the medium in which push or evolve/move the Plante free S and plants (Phytoplancton), which can cause physiological diseases following physical aggressions of factors (acidity, UV, dehydration, radioactivity, Pollution S) or of mineral deficiencies of the ground.
• of the organizations parasite S which can determine parasitic diseases of vegetable origin, cryptogamic, bacterial, viral or animal. In certain cases, more than of disease, they are depredations (example of the animals, bacteria or mushrooms phytophagous). The absence of organizations symbions (Bacterium S, Mushroom S, pollinating.) is also a cause of diseases or of died of the plants.

Physiological problems being able to make think of diseases

They are the physiological dysfunctions of the plant related to factors such those listed hereafter.

Hydrous stress

The lack of water induces a drying, a deceleration, and its excess can cause a radicular Asphyxie. Problems involved in pH of water, its temperature, the Salinity (Salinisation) or on its quality (chemical or organic pollution, for example by Pathovar S of the Bacterium Pseudomonas ).

Chemical composition of the ground

The mineral components necessary to the plants can be in quantity or of insufficient availability at the point to cause true external symptoms and not only one production limited (see: Deficiency).

Principal elements (known as also major)

• NR (nitrogenizes mineral): The lack of nitrogen causes the yellowing of the plant, and its excess can cause in an indirect way a Verse on cereals.
• K (potassium): Potash hunger,
• Mg (magnesium)

Trace elements (known as also minor)

• Fe (iron): An iron deficiency (often not blocking, in calcareous ground) causes Chlorose S
• many other trace elements intervene as well as the natural poisons or Polluant S introduced by the man (Plomb, Arsenic for example…)

Darkness

An abnormally rainy climate at a given season can cause a deficit of light and a deceleration of the growth and/or production. The lack of light as after a strong volcanic eruption covering with dust the atmosphere has the same effects.

Thermo-hygrometrical anomalies

An excess of heat will be identified with a scalding of the plant, insolation often related to a reduction in the hygroscopy causing a double stress for the plant and downtown a reduction in the phenomenon of Rosée.

Freezing has to him also an important effect. It causes rolled edges, a slit of the trunks and barks burst by water. The weight of snow or the white frost causes also the fracture of the branches or the stems. Certain bacteria present on the sheets as Pseudomonas can induce the crystallization of ice on the surface of the plants a little before the 0 °C.

Atmospheric pollution

Fatty dust and substances which clog the sheets, slow down photosynthesis while supporting the colonization of surface by mushrooms or bacteria épiphytes possibly pathogenic. Certain substances conveyed by the atmosphere are very harmful for the plants such as, for example, the Sulfur dioxide and in a general way the acids emitted by the human activity (industry, the combustion of the heatings, exhaust fumes of the vehicles…), the Ozone, the SIDE S, and other oxidants emitted by industry, the heating, the vehicles, acting during the day and/or during the night. One can quote the effect of the transmitting volcanic eruptions of fine ashes: those recover the close plants and if they tired are not washed by rains, those do not have enough any more of light and suffer.

Climatic factors

Are to be taken into account: effects of the wind (breaking, wounds, tensions,…), precipitations (rain, snow, hail), the lightning…

References

Philippe Lepoivre, 2003 PHYTOPATHOLOGY Editions De Boeck & Larcier

Simple: Seedling pathology

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