3. Here are the names of 5 plant diseases that can and have caused significant d

Question

3. Here are the names of 5 plant diseases that can and have caused significant damage: 1. Potato blight 2. Potato scab 3. Lettuce drop 4. Powdery mildew 5. Ergot Pick one of these diseases and provide the following information: a) Tell us what the cause of each disease is and how it manifests. b)Tell us the type of organism responsible for the disease. c) Give an example of the extent of damage caused by the disease. d)Tell us at least one method of control for the disease. 3. Here are the names of 5 plant diseases that can and have caused significant damage: 1. Potato blight 2. Potato scab 3. Lettuce drop 4. Powdery mildew 5. Ergot Pick one of these diseases and provide the following information: a) Tell us what the cause of each disease is and how it manifests. b)Tell us the type of organism responsible for the disease. c) Give an example of the extent of damage caused by the disease. d)Tell us at least one method of control for the disease. 3. Here are the names of 5 plant diseases that can and have caused significant damage: 1. Potato blight 2. Potato scab 3. Lettuce drop 4. Powdery mildew 5. Ergot Pick one of these diseases and provide the following information: a) Tell us what the cause of each disease is and how it manifests. b)Tell us the type of organism responsible for the disease. c) Give an example of the extent of damage caused by the disease. d)Tell us at least one method of control for the disease.

Explanation / Answer

Potato blight

a) Phytophthora infestans is an oomycete that causes the serious potato disease known as late blight or potato blight. (Early blight, caused by Alternaria solani, is also often called "potato blight".) . The organism can also infect tomatoes and some other members of the Solanaceae. At first, the spots are gray-green and water-soaked, but they soon enlarge and turn dark brown and firm, with a rough surface.

b) Phytophthora infestans is an oomycete which is responsible for the disease.

c)

Potato late blight is one of the most devastating plant diseases. The epidemics that destroyed potato crops in Europe in the 1840s led to mass starvation. For example, in the Great Irish Famine of 1845 to 1847, up to one million people died and a similar number of people emigrated to the rest of Europe and the USA. There were, of course, factors that contributed to the starvation, including the land-tenure system in Ireland at that time, and the almost total dependence of the poorer working population on potatoes as their source of food. Nevertheless, potato blight ranks as one of the most devastating diseases in human history. Even today it is one of the major pathogens that chemical companies target in their search for new fungicides.

The disease is caused by a fungus-like organism, Phytophthora infestans, which is a specialised pathogen of potato and, to a lesser extent, tomato (another member of the plant family Solanaceae).

d)

Control of potato blight traditionally relied on copper-based fungicides such as Bordeaux mixture (consisting of copper sulphate and calcium oxide). However, copper is potentially phytotoxic, so disease forecasting was developed to enable growers to predict when the environmental conditions were highly conducive to spread of the pathogen and thus when the growers needed to spray to protect their crops. Forecasting methods for blight epidemics differ in different countries but in Britain they are based on the "temperature-humidity rule" devised by Beaumont (1947). After a certain date (depending on locality) blight was found to develop within 15-22 days following a period when the temperature was not less than 10oC and the relative humidity was over 75% for 2 consecutive days. Radio stations now broadcast warnings of the Beaumont periods or updated versions of these in the early-morning farming programmes.

Copper is a broad-spectrum fungicide which acts as a protectant – it must be applied to prevent disease. It has been superseded by modern systemic fungicides, which move within the plant and can both protect and eradicate existing infections. These fungicides are much more specific in their mode of action. Chief among these for control of potato blight are the acylalanine fungicides such as metalaxyl and furalaxyl. They act specifically on the RNA polymerase of Phytophthora and closely related fungi. However, resistance to them can develop quickly in the pathogen population – it requires only a single gene mutation leading to a minor change in the RNA polymerase molecule. In many parts of the world, P. infestans is now resistant to these fungicides.

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