''Phytophthora infestans'' is an
oomycete or
water mold, a fungus-like
microorganism that causes the serious
potato and
tomato disease known as late blight or potato blight.
Early blight
''Alternaria solani'' is a fungal pathogen that produces a disease in tomato and potato plants called early blight. The pathogen produces distinctive "bullseye" patterned leaf spots and can also cause stem lesions and fruit rot on tomato and tube ...
, caused by ''
Alternaria solani'', is also often called "potato blight". Late blight was a major culprit in the
1840s European, the
1845–1852 Irish, and the
1846 Highland potato
famine
A famine is a widespread scarcity of food, caused by several factors including war, natural disasters, crop failure, Demographic trap, population imbalance, widespread poverty, an Financial crisis, economic catastrophe or government policies. Th ...
s. The organism can also infect some other members of the
Solanaceae
The Solanaceae , or nightshades, are a family of flowering plants that ranges from annual and perennial herbs to vines, lianas, epiphytes, shrubs, and trees, and includes a number of agricultural crops, medicinal plants, spices, weeds, and orn ...
.
The pathogen is favored by moist, cool environments: sporulation is optimal at in water-saturated or nearly saturated environments, and
zoospore production is favored at temperatures below . Lesion growth rates are typically optimal at a slightly warmer temperature range of .
Etymology
The genus name ''Phytophthora'' comes from the Greek –(), meaning : "plant" – plus the Greek (), meaning : "decay, ruin, perish". The species name ''infestans'' is the present participle of the Latin verb , meaning : "attacking, destroying", from which we get the word "to infest". The name ''Phytophthora infestans'' was coined in 1876 by the German mycologist
Heinrich Anton de Bary (1831–1888).
Life cycle, signs and symptoms
The asexual life cycle of ''Phytophthora infestans'' is characterized by alternating phases of
hypha
A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium.
Structure
A hypha consists of one or ...
l growth, sporulation, sporangia germination (either through
zoospore release or direct germination, i.e. germ tube emergence from the
sporangium
A sporangium (; from Late Latin, ) is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. Virtually all plants, fungi, and many other lineages form sporangia at some point in their life cy ...
), and the re-establishment of hyphal growth.
There is also a sexual cycle, which occurs when isolates of opposite mating type (A1 and A2, see
Mating types below) meet. Hormonal communication triggers the formation of the sexual
spore
In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...
s, 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
A host is a person responsible for guests at an event or for providing hospitality during it.
Host may also refer to:
Places
* Host, Pennsylvania, a village in Berks County
People
*Jim Host (born 1937), American businessman
* Michel 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.
People can observe ''Phytophthora infestans'' produce dark green, then brown then black spots on the surface of potato leaves and stems, often near the tips or edges, where water or dew collects.
The sporangia and