The Mechanisms by Which Pathogens Cause Disease

Plant diseases cause a huge loose of fruits, vegetables and crops since long time ago, historically diseases causes huge loose that leads to the dead of millions of peoples on earth. During early peoples, not know the causes of diseases, they were considering the cause of diseases some mysterious agents, much myth related to the causes of diseases.

As science advance the mysterious agents of diseases discovered, peoples come to know the real causes and agents. Scientist observed fungi, bacteria and microorganisms were the causes of different diseases, but another big question arise after the discovery of casual agents, How fungi and microorganisms cause diseases?”

The Mechanisms by Which Pathogens Cause Disease: agrinfobank.com

Previously it became noticeable that fungi and other microorganisms were the causes rather than the results of plant disease, efforts began to understand the mechanisms by which microorganisms cause disease.

The Mechanisms by Which Pathogens Cause Disease: agrinfobank.com

In 1886, deBary, working with the Sclerotinia rot disease of carrots other vegetables, noticed that host cells were killed in advance of the invading fungal hyphae and a juice from rotted tissue released that could able break down healthy host tissue, when juice from rotted tissue boiled and treat healthy tissues, had no effect on healthy tissue. DeBary concluded that the pathogen produces enzymes and toxins that degrade and kill plant cells from which the fungus can then obtain its nutrients.

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After deBary, many attempted to show that most plant diseases, particularly vascular wilts and leaf spots, were caused by toxins secreted by the pathogens, but those claims could not be confirmed. A 1925 suggestion that the bacterium Pseudomonas tabaci, the cause of the wildfire disease of tobacco, produces a toxin that is responsible for the bacteria-free chlorotic zone (“halo”) surrounding the bacteria-containing necrotic leaf spots was confirmed in 1934.

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The wildfire toxin was the first toxin to be isolated in pure form in the early 1950s. In 1947, a species of the fungus Helminthosporium (Bipolaris), which attacked and caused blight only on oats of the variety Victoria and its derivatives, was shown to produce a toxin named victorin. This toxin could induce the symptoms of the disease only on the varieties susceptible to the fungus.

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Many other bacterial and fungal toxins were subsequently detected and identified. The toxins exhibited several distinctive mechanisms of action, each affecting specific sites on mitochondria, chloroplasts, plasma membranes, specific enzymes, or specific cells such as guard cells. In addition, several detailed biochemical studies were carried out to elucidate the mechanisms by which toxins affect or kill plant cells or by which cells of resistant plants avoid or inactivate them.

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Plant Diseases May Cause Financial Losses

In addition to direct losses in yield and quality, financial losses from plant diseases can arise in many ways.Farmers may have to plant varieties or species of plants that are resistant to disease but are less productive, more costly, or commercially less profitable than other varieties. They may have to spray or otherwise control a disease, thus incurring expenses for chemicals, machinery, storage space, and labor. Shippers may have to provide refrigerated warehouses and transportation vehicles, thereby increasing expenses. Plant diseases may limit the time during which products can be kept fresh and healthy, thus forcing growers to sell during a short period of time when products are abundant and prices are low. Healthy and diseased plant products may need to be separated from one another to avoid spreading of the disease, thus increasing handling costs.Plant Diseases May Cause Financial Losses
The cost of controlling plant diseases, as well as lost productivity, is a loss attributable to diseases. Some plant diseases can be controlled almost entirely by one or another method, thus resulting in financial losses only to the amount of the cost of the control. Sometimes, however, this cost may be almost as high as, or even higher than, the return expected from the crop, as in the case of certain diseases of small grains. For other diseases, no effective control measures are yet known, and only a combination of cultural practices and the use of somewhat resistant varieties makes it possible to raise a crop. For most plant diseases, however, as long as we still have chemical pesticides, practical controls are available, although some losses may be incurred, despite the control measures taken. In these cases, the benefits from the control applied are generally much greater than the combined direct losses from the disease and the indirect losses due to expenses for control.
Despite the variety of types and sizes of financial losses that may be caused by plant diseases, wellinformed farmers who use the best combinations of available resistant varieties and proper cultural, biological, and chemical control practices not only manage to produce a good crop in years of severe disease outbreaks, but may also obtain much greater economic benefits from increased prices after other farmers suffer severe crop losses.

Source: Plant Pathology by GEORGE N. AGRIOS