''Alternaria solani'' is a

fungal A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from th ...

pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...

that produces a disease in

tomato The tomato is the edible berry of the plant ''Solanum lycopersicum'', commonly known as the tomato plant. The species originated in western South America, Mexico, and Central America. The Mexican Nahuatl word gave rise to the Spanish word ...

and

potato The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern Unit ...

plants called early blight. The pathogen produces distinctive "bullseye" patterned leaf spots and can also cause stem lesions and fruit rot on tomato and tuber blight on potato. Despite the name "early," foliar symptoms usually occur on older leaves.
If uncontrolled, early blight can cause significant yield reductions. Primary methods of controlling this disease include preventing long periods of wetness on leaf surfaces and applying

fungicides Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...

.
Early blight can also be caused by ''Alternaria tomatophila'', which is more virulent on stems and leaves of tomato plants than ''Alternaria solani''. Geographically, ''A. solani'' is problematic in tomato production areas east of the

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico in ...

and in the midwest, however, ''A. solani'' is generally not an issue in the less humid Pacific or inter-mountain regions. ''A. solani'' is also present in most potato production regions every year but has a significant effect on yield only when frequent wetting of foliage favors symptom development. Alternaria solani on Solanum lycopersicum

Alternaria solani on Solanum lycopersicum

Hosts and symptoms

''Alternaria solani'' infects stems, leaves and fruits of

(''Solanum lycopersicum'' L.),

(''S. tuberosum''),

eggplant Eggplant ( US, Canada), aubergine ( UK, Ireland) or brinjal (Indian subcontinent, Singapore, Malaysia, South Africa) is a plant species in the nightshade family Solanaceae. ''Solanum melongena'' is grown worldwide for its edible fruit. Mos ...

(''S. melongena'' L.),

bell pepper The bell pepper (also known as paprika, sweet pepper, pepper, or capsicum ) is the fruit of plants in the Grossum Group of the species ''Capsicum annuum''. Cultivars of the plant produce fruits in different colors, including red, yellow, orange ...

and

hot pepper Chili peppers (also chile, chile pepper, chilli pepper, or chilli), from Nahuatl '' chīlli'' (), are varieties of the berry-fruit of plants from the genus ''Capsicum'', which are members of the nightshade family Solanaceae, cultivated for t ...

(''

Capsicum ''Capsicum'' () is a genus of flowering plants in the Solanum, nightshade family Solanaceae, native to Americas, the Americas, cultivated worldwide for their chili pepper or bell pepper fruit. Etymology and names The generic name may come f ...

'' spp.), and other members of the family

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 ...

. Distinguishing symptoms of ''A. solani'' include

leaf spot A leaf spot is a limited, discoloured, diseased area of a leaf that is caused by fungal, bacterial or viral plant diseases, or by injuries from nematodes, insects, environmental factors, toxicity or herbicides. These discoloured spots or lesions ...

an
defoliation
which are most pronounced in the lower canopy. In some cases, ''A. solani'' may also cause

damping off Damping off (or damping-off) is a horticultural disease or condition, caused by several different pathogens that kill or weaken seeds or seedlings before or after they germinate. It is most prevalent in wet and cool conditions. Symptoms There ar ...

On tomatoes

On tomato, foliar symptoms of ''A. solani'' generally occur on the oldest leaves and start as small lesions that are brown to black in color. These leaf spots resemble

concentric In geometry, two or more objects are said to be concentric, coaxal, or coaxial when they share the same center or axis. Circles, regular polygons and regular polyhedra, and spheres may be concentric to one another (sharing the same center point ...

rings - a distinguishing characteristic of the pathogen - and measure up to 1.3 cm (0.51 inches) in diameter. Both the area around the leaf spot and the entire leaf may become yellow or

chlorotic In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green color of leaves, chlorotic leaves are pale, yellow, or yellow-white. The affected plant has little or no ability to ...

. Under favorable conditions (e.g., warm weather with short or abundant dews), significant defoliation of lower leaves may occur, leading t
sunscald
of the fruit. As the disease progresses, symptoms may migrate to the plant stem and fruit. Stem lesions are dark, slightly sunken and concentric in shape. Seedlings can develop small, dark, partially sunken lesions which grow and elongate into circular or oblong lesions. Basal girdling and death of seedlings may occur, a symptom known as collar rot. In fruit, ''A. solani'' invades at the point of attachment to the stem as well as through growth cracks and wounds made by insects, infecting large areas of the fruit Fruit spots are similar in appearance to those on leaves – brown with dark concentric circles. Mature lesions are typically covered by a black, velvety mass of fungal spores that may be visible under proper light conditions. Alternaria solani - stem lesions

On potatoes

In potato, primary damage by ''A. solani'' is attributed to premature defoliation of potato plants, which results in tuber yield reduction. Initial infection occurs on older leaves, with concentric dark brown spots developing mainly in the leaf center. The disease progresses during the period of potato vegetation, and infected leaves turn yellow and either dry out or fall off the stem. On stems, spots are gaunt with no clear contours (as compared to leaf spots). Tuber lesions are dry, dark and pressed into the tuber surface, with the underlying flesh turning dry, leathery and brown. During storage, tuber lesions may enlarge and tubers may become shriveled. Disease severity due to ''A. solani'' is highest when potato plants are injured, under stress or lack proper nutrition. High levels of

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

, moderate

potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...

and low

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...

in the soil can reduce susceptibility of infection by the pathogen.

Disease cycle

''Alternaria solani'' is a deuteromycete with a polycyclic life cycle. ''Alternaria solani'' reproduces asexually by means of conidia. ''A.solani'' is generally considered to be a

necrotrophic A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from t ...

pathogen, i.e. it kills the host tissue using cell wall degrading enzymes and toxins and feeds on the dead plant cell material The life cycle starts with the fungus overwintering in crop residues or wild members of the family

, such as

black nightshade Black nightshade is a common name for several plants and may refer to: * '' Solanum americanum'' (American black nightshade) of much of North America * ''Solanum nigrum'' (European black nightshade) of Europe * '' Solanum ptychanthum'' (Eastern bla ...

. In the spring, conidia are produced. Multicellular conidia are splashed by water or by wind onto an uninfected plant. The conidia infect the plant by entering through small wounds,

stomata In botany, a stoma (from Greek ''στόμα'', "mouth", plural "stomata"), also called a stomate (plural "stomates"), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange. The pore is bor ...

, or direct penetration. Infections usually start on older leaves close to the ground. The fungus takes time to grow and eventually forms a lesion. From this lesion, more conidia are created and released. These conidia infect other plants or other parts of the same plant within the same growing season. Every part of the plant can be infected and form lesions. This is especially important when fruit or tubers are infected as they can be used to spread the disease. In general, development of the pathogen can be aggravated by an increase in inoculum from alternative hosts such as weeds or other solanaceous species.Olanya, O.M., et al. (2009) The effect of cropping systems and irrigation management on development of potato early blight. ''J. Gen. Plant Pathol.'': 75, 267-275. Disease severity and prevalence are highest when plants are mature.

Environment

''Alternaria solani'' spores are universally present in fields where host plants have been grown. Free water is required for Alternaria spores to germinate; spores will be unable to infect a perfectly dry leaf. Alternaria spores germinate within 2 hours over a wide range of temperatures but at 26.6-29.4 °C (80-85 °F) may only take 1/2 hour. Another 3 to 12 hours are required for the fungus to penetrate the plant depending on temperature. After penetration, lesions may form within 2–3 days or the infection can remain dormant awaiting proper conditions 5.5 °C (60 °F) and extended periods of wetness Alternaria sporulates best at about 26.6 °C (80 °F) when abundant moisture (as provided by rain, mist, fog, dew, irrigation) is present. Infections are most prevalent on poorly nourished or otherwise stressed plants.

Management

Cultural control

*Clear infected debris from field to reduce inoculum for the next year. *Water plants in the morning so plants are wet for the shortest amount of time. *Use a drip irrigation system to minimize leaf wetness which provides optimal conditions for fungal growth. *Use mulch so spores in soil cannot splash onto leaves from the soil. *Rotate to a non-

Solanaceous 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 orna ...

crop for at least three years. The more potato-free years, the less infection. *If possible control wild population of ''Solanaceae''. This will decrease the amount of inoculum to infect your plants. *Closely monitor field, especially in warm damp weather when it grows fastest, to reduce loss of crop and spray fungicide in time. *Plant resistant cultivars. *Increase air circulation in rows. Damp conditions allow for optimal growth of ''A. Solani'' and the disease spreads more rapidly. This can be achieved by planting farther apart or by trimming leaves.

Chemical control

There are numerous fungicides on the market for controlling early blight. Some of the fungicides on the market are (

azoxystrobin Azoxystrobin is the ISO common name for an organic compound that is used as a fungicide. It is a broad spectrum systemic active ingredient widely used in agriculture to protect crops from fungal diseases. It was first marketed in 1996 using the b ...

pyraclostrobin Pyraclostrobin is a quinone outside inhibitor ( QI)-type fungicide used in agriculture. Among the QIs, it lies within the strobilurin chemical class. Use Pyraclostrobin is used to protect ''Fragaria'', ''Rubus idaeus'', ''Vaccinium corymbosum'', ...

Bacillus subtilis ''Bacillus subtilis'', known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus ''Bacillu ...

chlorothalonil Chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile) is an organic compound mainly used as a broad spectrum, nonsystemic fungicide, with other uses as a wood protectant, pesticide, acaricide, and to control mold, mildew, bacteria, algae. Ch ...

, copper products, hydrogen dioxide (Hydroperoxyl),

mancozeb Mancozeb is a dithiocarbamate non-systemic agricultural fungicide with multi-site, protective action on contact. It is a combination of two other dithiocarbamates: maneb and zineb. The mixture controls many fungal diseases in a wide range of field ...

potassium bicarbonate Potassium bicarbonate (IUPAC name: potassium hydrogencarbonate, also known as potassium acid carbonate) is the inorganic compound with the chemical formula KHCO3. It is a white solid. Production and reactivity It is manufactured by treating an ...

, and

ziram Zinc dimethyldithiocarbamate is a coordination complex of zinc with dimethyldithiocarbamate. It is a pale yellow solid that is used as a fungicide, the sulfur vulcanization of rubber, and other industrial applications. Applications Known as zir ...

. Specific spraying regiments are found on the label. Labels for these products should be read carefully before applying. Quinone outside inhibitor (

QoI Qo inhibitors (QoI), or quinone outside inhibitors, are a group of fungicides used in agriculture. Some of these fungicides are among the most popular in the world. QoI are chemical compounds which act at the quinol ''outer'' binding site of the ...

s) fungicides e.g. azoxystrobin are used due to their broad-spectrum activity. However, decreased fungicide sensitivity has been observed in ''A. solani''due to a F129L (Phenylalanine (F) changed to Leucine at position 129) amino acid substitution. AU - Leiminger, J. H. AU - Adolf, B. AU - Hausladen, H. TI - Occurrence of the F129L mutation in Alternaria solani populations in Germany in response to QoI application, and its effect on sensitivity JO - Plant Pathology JA - Plant Pathol VL - 63 IS - 3 SN - 1365-3059 UR - https://dx.doi.org/10.1111/ppa.12120 DO - 10.1111/ppa.12120 SP - 640 EP - 650

Economic significance

Early blight caused by ''A. solani'' is the most destructive disease of tomatoes in the

tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...

and

subtropical The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Geographical z ...

regions. Each 1% increase in intensity can reduce yield by 1.36%, and complete crop failure can occur when the disease is most severe.Pandey, K.K., et al. (2003). Resistance to early blight of tomato with respect to various parameters of disease epidemics. ''J. Gen. Plant Pathol.'': 69, 364-371. Yield losses of up to 79% have been reported in the U.S., of which 20-40% is due to seedling losses (i.e., collar rot) in the field.Chaerani, R. and R.e. Voorrips. (2006). Tomato early blight (''Alternaria solani''): the pathogen, genetics, and breeding for resistance.. ''J. Gen. Plant Pathol.'': 72, 335-347. ''A. solani'' is also one of the most important foliar pathogens of potato. In the U.S., yield loss estimates attributed to foliar damage, which results in decreased tuber quality and yield reduction, can reach 20-30%. In storage, ''A. solani'' can cause

dry rot Dry rot is wood decay caused by one of several species of fungi that digest parts of the wood which give the wood strength and stiffness. It was previously used to describe any decay of cured wood in ships and buildings by a fungus which resul ...

of tubers and may also reduce storage length, which both of which diminish the quantity and quality of marketable tubers. Because ''A. solani'' is one of numerous tomato/potato pathogens that are typically controlled with the same products, accurately estimating both the total economic loss and the total expenditure on fungicides for control of early blight is difficult. Best estimates suggest that total annual global expenditures on fungicide control of ''A. solani'' is approximately $77 million: $32 million for tomatoes and $45 million for potatoes.

Historical impact

Though the causal pathogen is distributed worldwide and can cause crop yield reductions, early blight has never caused widespread famine or other sudden and major detrimental effects on humanity. The disease is not to be confused with

late blight ''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, caused by ''Alternaria solani'', is also often called "pot ...

, which is caused by the oomycete ''

Phytophthora infestans ''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, caused by ''Alternaria solani'', is also often called "pot ...

.''

Late blight ''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, caused by ''Alternaria solani'', is also often called "pot ...

disease together with the socio-economic situation at the time was responsible for the Great Famine of Ireland in the 1840s.

References

External links

Index Fungorum

USDA ARS Fungal Database

* Resistance to Alternaria solani in Hybrids Between a Solanum tuberosum Haploid and S. raphanifolium. B. Weber and S. H. Jansky. Phytopathology . {{Taxonbar, from=Q2715597 solani Fungal plant pathogens and diseases Potato diseases Tomato diseases Fungi described in 1882