Phytophthora infestans is an oomycete or water mold, a microorganism which causes the serious potato and tomato disease known as late blight or potato blight. (Early blight, caused by Alternaria solani, is also often called "potato blight".) Late blight was a major culprit in the 1840s European, the 1845 Irish, and the 1846 Highland potato famines. The organism can also infect some other members of the Solanaceae. The pathogen is favored by moist, cool environments: sporulation is optimal at 12–18°C in water-saturated or nearly saturated environments, and zoospore production is favored at temperatures below 15° C. Lesion growth rates are typically optimal at a slightly warmer temperature range of 20 to 24° C
Scientific classification
Domain: Eukaryota
(unranked): SAR
Superphylum: Heterokonta
Class: Oomycota
Order: Peronosporales
Family: Pythiaceae
Genus: Phytophthora
Species: P.infestans
Binomial name
Phytophthora infestans
(Mont.) de Bary
ETYMOLOGY
The genus name Phytophthora comes from the Greek φυτό-(phyto), meaning : "plant" - plus the Greek φθορά (phthora), meaning : "decay, ruin, perish". The species name infestans is the present participle of the Latin verb infestare, meaning : "attacking, destroying", from which we get the word "to infest".
LIFE CYCLE AND SYNONYMS
The asexual life cycle of Phytophthora infestans is characterized by alternating phases of hyphal growth, sporulation, sporangia germination (either through zoospore release or direct germination, i.e. germ tube emergence from the sporangium), and the re-establishment of hyphal growth. There is also a sexual cycle, which occurs when isolates of opposite mating type (A1 and A2) meet. Hormonal communication triggers the formation of the sexual spores, called oospores. The different types of spores play major roles in the dissemination and survival of P. infestans. Sporangia are spread by wind or water and enable the movement of P. infestans between different host plants. The zoospores released from sporangia are biflagellated and chemotactic, allowing further movement of P. infestans on water films found on leaves or soils. Both sporangia and zoospores are short-lived, in contrast to oospores which can persist in a viable form for many years.
The color of potato sign is white. People can observe phytophthora infestans produces sporangia and sporangiophores on the surface of potato stems and leaves. These sporangia and sporangiophores are always appear on the lower surface of the foliage. As for tuber blight, the white mycelium often on the tubers surface.
Under ideal conditions, the life cycle can be completed on potato or tomato foliage in about five days.[5 Sporangia develop on the leaves, spreading through the crop when temperatures are above 10 °C (50 °F) and humidity is over 75–80% for 2 days or more. Rain can wash spores into the soil where they infect young tubers, and the spores can also travel long distances on the wind. The early stages of blight are easily missed. Symptoms include the appearance of dark blotches on leaf tips and plant stems. White mold will appear under the leaves in humid conditions and the whole plant may quickly collapse. Infected tubers develop grey or dark patches that are reddish brown beneath the skin, and quickly decay to a foul-smelling mush caused by the infestation of secondary soft bacterial rots. Seemingly healthy tubers may rot later when in store.
P. infestans survives poorly in nature apart from its plant hosts. Under most conditions, the hyphae and asexual sporangia can survive for only brief periods in plant debris or soil, and are generally killed off during frosts or very warm weather. The exceptions involve oospores, and hyphae present within tubers. The persistence of viable pathogen within tubers, such as those that are left in the ground after the previous year's harvest or left in cull piles is a major problem in disease management. In particular, volunteer plants sprouting from infected tubers are thought to be a major source of inoculum at the start of a growing season.[9] This can have devastating effects by destroying entire crops.
In the past, copper sulfate solution (called 'bluestone') was used to combat potato blight. Copper pesticides remain in use on organic crops, both in the form of copper hydroxide and copper sulfate. Given the dangers of copper toxicity, other organic control options that have been shown to be effective include horticultural oils, phosphorous acids, and rhamnolipid biosurfactants, while sprays containing "beneficial" microbes such as Bacillus subtilis or compounds that encourage the plant to produce defensive chemicals (such as knotweed extract) have not performed as well.[56]
Control of tuber blight Edit
Ridging is often used to reduce tuber contamination by blight. This normally involves piling soil or mulch around the stems of the potato blight meaning the pathogen has farther to travel to get to the tuber. Another approach is to destroy the canopy around five weeks before harvest, using a contact herbicide or sulfuric acid to burn off the foliage. Eliminating infected foliage reduces the likelihood of tuber infection.
Domain: Eukaryota
(unranked): SAR
Superphylum: Heterokonta
Class: Oomycota
Order: Peronosporales
Family: Pythiaceae
Genus: Phytophthora
Species: P.infestans
Binomial name
Phytophthora infestans
(Mont.) de Bary
ETYMOLOGY
The genus name Phytophthora comes from the Greek φυτό-(phyto), meaning : "plant" - plus the Greek φθορά (phthora), meaning : "decay, ruin, perish". The species name infestans is the present participle of the Latin verb infestare, meaning : "attacking, destroying", from which we get the word "to infest".
LIFE CYCLE AND SYNONYMS
The color of potato sign is white. People can observe phytophthora infestans produces sporangia and sporangiophores on the surface of potato stems and leaves. These sporangia and sporangiophores are always appear on the lower surface of the foliage. As for tuber blight, the white mycelium often on the tubers surface.
Under ideal conditions, the life cycle can be completed on potato or tomato foliage in about five days.[5 Sporangia develop on the leaves, spreading through the crop when temperatures are above 10 °C (50 °F) and humidity is over 75–80% for 2 days or more. Rain can wash spores into the soil where they infect young tubers, and the spores can also travel long distances on the wind. The early stages of blight are easily missed. Symptoms include the appearance of dark blotches on leaf tips and plant stems. White mold will appear under the leaves in humid conditions and the whole plant may quickly collapse. Infected tubers develop grey or dark patches that are reddish brown beneath the skin, and quickly decay to a foul-smelling mush caused by the infestation of secondary soft bacterial rots. Seemingly healthy tubers may rot later when in store.
P. infestans survives poorly in nature apart from its plant hosts. Under most conditions, the hyphae and asexual sporangia can survive for only brief periods in plant debris or soil, and are generally killed off during frosts or very warm weather. The exceptions involve oospores, and hyphae present within tubers. The persistence of viable pathogen within tubers, such as those that are left in the ground after the previous year's harvest or left in cull piles is a major problem in disease management. In particular, volunteer plants sprouting from infected tubers are thought to be a major source of inoculum at the start of a growing season.[9] This can have devastating effects by destroying entire crops.
DAMAGE OF LATE BLIGHT OF POTATO
Late blight (Phytophthora infestans) is the most destructive fungal disease of potato, reducing yields considerably. For example: it is best known as the cause of the Irish potato famine of the 1840s, which resulted in the death or emigration of over 2 million people from Ireland.[10] In 1995, there was a 4-6% lower yield of potatoes from the Columbia River drainage basin because of late blight[11], which cost around 1.3 million to control the late blight (Tai,1998). There is another reason why the late blight could cause a large damage is that late blight has a wide geographic range
DISEASES MANAGEMENT
Fungicides for the control of potato blight are normally only used in a preventative manner, optionally in conjunction with disease forecasting. In susceptible varieties, sometimes fungicide applications may be needed weekly. An early spray is most effective. The choice of fungicide can depend on the nature of local strains of P. infestans. Metalaxyl is a fungicide that was marketed for use against P. infestans, but suffered serious resistance issues when used on its own. In some regions of the world during the 1980s and 1990s, most strains of P. infestans became resistant to metalaxyl, but in subsequent years many populations shifted back to sensitivity. To reduce the occurrence of resistance, it is strongly advised to use single-target fungicides such as metalaxyl along with carbamate compounds. A combination of other compounds are recommended for managing metalaxyl-resistant strains. These include mandipropamid, chlorothalonil, fluazinam, triphenytin, mancozeb and others. In the United States, the Environmental Protection Agency has approved oxathiapiprolin for use against late blight.
 |
| Fertilizer use |
Control of tuber blight Edit
Ridging is often used to reduce tuber contamination by blight. This normally involves piling soil or mulch around the stems of the potato blight meaning the pathogen has farther to travel to get to the tuber. Another approach is to destroy the canopy around five weeks before harvest, using a contact herbicide or sulfuric acid to burn off the foliage. Eliminating infected foliage reduces the likelihood of tuber infection.
