''Curvularia pallescens'' is a

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...

fungus, that commonly grows on crops found in tropical regions. The

conidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to the ...

of the fungus are distinguishable from those of related species due to their lack of curvature. ''C. pallescens'' has been reported to cause infection in plants, and in

immunocompetent In immunology, immunocompetence is the ability of the body to produce a normal immune response following exposure to an antigen. Immunocompetence is the opposite of immunodeficiency (also known as ''immuno-incompetence'' or being ''immuno-comprom ...

individuals. This species is the

anamorph In mycology, the terms teleomorph, anamorph, and holomorph apply to portions of the life cycles of fungi in the phyla Ascomycota and Basidiomycota: *Teleomorph: the sexual reproductive stage (morph), typically a fruiting body. *Anamorph: an ase ...

of ''

Cochliobolus The fungal genus ''Cochliobolus'' includes 55 species, including the following plant pathogenic species: '' C. carbonum'', '' C. heterostrophus'', '' C. miyabeanus'', '' C. sativus'' and '' C. lunatus''. Heterothallism and homothallism Those ...

pallescens''.

Morphology

The colonies of ''C. pallescens'' differ in morphology depending on the growth medium used. On Czapek Yeast Extract Agar (CYA), colonies of ''C. pallescens'' are 50-65mm in diameter. On Malt Extract Agar (MEA), the colonies are fuzzy in texture, and pale grey to grey in colour. On the reverse side, they appear brown to dark brown. The colonies rapidly cover the entire

Petri dish A Petri dish (alternatively known as a Petri plate or cell-culture dish) is a shallow transparent lidded dish that biologists use to hold growth medium in which cells can be cultured,R. C. Dubey (2014): ''A Textbook Of Biotechnology For Class- ...

. On G25N, the colonies of ''C. pallescens'' are 3–6 mm in diameter, and appear grey and brown in colour. On Dichloran Chloramphenicol Malt Agar (DCMA), the colonies are 50–65 mm in diameter, and pale brownish-grey in colour. Lastly, colonies of ''C. pallescens'' grown on Phenylethyl Alcohol Agar (PEA) appear woolly at the centre. The

conidiophore A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an Asexual reproduction, asexual, non-motility, motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are al ...

s of ''C. pallescens'' are rarely branched, and are brown in colour. They can appear slightly bent at the apices, but otherwise they are predominately straight. The dimensions of the conidiophore vary, especially concerning its length. They can be up to 6μm wide. The

of ''C. pallescens'' are rugby or gridiron football- to

bean A bean is the seed of several plants in the family Fabaceae, which are used as vegetables for human or animal food. They can be cooked in many different ways, including boiling, frying, and baking, and are used in many traditional dishes th ...

-shaped, and are less curved than those of related species. They appear smooth in texture, and pale-brown to brown in colour. The three

septa The Southeastern Pennsylvania Transportation Authority (SEPTA) is a regional public transportation authority that operates bus, rapid transit, commuter rail, light rail, and electric trolleybus services for nearly 4 million people in five coun ...

within each conidium give rise to four cells. The third cell from the base appears swollen in comparison to the surrounding cells. The dimensions of the conidia are 18-25 x 9-12 μm. ''

pallescens'' is the

teleomorph In mycology, the terms teleomorph, anamorph, and holomorph apply to portions of the life cycles of fungi in the phyla Ascomycota and Basidiomycota: *Teleomorph: the sexual reproductive stage (morph), typically a fruiting body. *Anamorph: an ase ...

ic form of ''Curvularia pallescens''. It produces spherical

ascoma An ascocarp, or ascoma (), is the fruiting body ( sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores. Ascocarps are mo ...

ta that are black in colour. On the surface of the ascomata, there are protruding colourless necks from which the ascospores emerge.

Ascospore An ascus (; ) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some genera or s ...

s are produced within cylindrical

asci ASCI or Asci may refer to: * Advertising Standards Council of India * Asci, the plural of ascus, in fungal anatomy * Accelerated Strategic Computing Initiative * American Society for Clinical Investigation * Argus Sour Crude Index * Association of ...

. The ascospores are colourless, and are either straight or slightly curved. Each ascospore contains 6-13 septa.

Ecology and growth

''Curvularia pallescens'' is commonly found in tropical regions, such as

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

. They usually grow on unharvested crops (i.e., crops that have not been dried or stored), such as

grass Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns an ...

rice Rice is the seed of the grass species ''Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima ''Oryza glaberrima'', commonly known as African rice, is one of the two domesticated rice species. It was first domesticated and grown i ...

wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...

maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. Th ...

, and

sorghum ''Sorghum'' () is a genus of about 25 species of flowering plants in the grass family (Poaceae). Some of these species are grown as cereals for human consumption and some in pastures for animals. One species is grown for grain, while many othe ...

. Optimal growth occurs at 25-30 °C, and at an a_w of 0.976. The minimum a_w for growth is 0.89. Germination occurs at 0.855 a_w but does not result in the establishment of colonies.

Sulphur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...

and

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 ...

are

macronutrients A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...

involved in the production of DNA,

RNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...

and

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

s in fungal species. It has been reported that ''C. pallescens'' is able to grow and sporulate in the absence of both. Magnesium sulphide and

tripotassium phosphate Tripotassium phosphate, also called tribasic potassium phosphate is a water-soluble salt with the chemical formula K3PO4.(H2O)x (x = 0, 3, 7, 9). Tripotassium phosphate is basic. Production Tripotassium phosphate is produced by the neutralizati ...

support the growth and sporulation of ''C. pallescens'' whereas,

ammonium sulphate Ammonium sulfate (American English and international scientific usage; ammonium sulphate in British English); (NH4)2SO4, is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen a ...

and

ammonium phosphate Ammonium phosphate is the inorganic compound with the formula (NH4)3PO4. It is the ammonium salt of orthophosphoric acid. A related "double salt", (NH4)3PO4.(NH4)2HPO4 is also recognized but is impractical use. Both triammonium salts evolve ammoni ...

do not.

Physiology

''Curvularia pallescens'' acts as a biological

reducing agent In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are commonly reducing agents include the Earth meta ...

of AgNO₃, resulting in the production of silver

nanoparticles A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 1 ...

(Ag NPs). This is considered a

green Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 Nanometre, nm. In subtractive color systems, used in painting and color printing, it is created by ...

method of Ag NP synthesis, unlike other methods that use chemical agents. Silver nanoparticles have widespread applications in industries such as healthcare, environmental health and drug-gene delivery. ''Curvularia pallescens'' has been reported to produce several

secondary metabolites Secondary metabolites, also called specialised metabolites, toxins, secondary products, or natural products, are organic compounds produced by any lifeform, e.g. bacteria, fungi, animals, or plants, which are not directly involved in the nor ...

—particularly, isolates from spirostaphylotrichines and curvupallides. These two groups of secondary metabolites are structurally similar. Isolates of spirostaphylotrichines (i.e., C and D) were found to be

phytotoxins Phytotoxins are substances that are poisonous or toxic to the growth of plants. Phytotoxic substances may result from human activity, as with herbicides, or they may be produced by plants, by microorganisms, or by naturally occurring chemical react ...

whereas, the curvupallide isolates showed no phytotoxic activity. Despite the limited genome sequencing of this fungus, ''C. pallescens'' has been found to produce several

enzymes Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...

with differing immunological and physiological functions in humans. These enzymes include BRN-1,

vacuolar A vacuole () is a membrane-bound organelle which is present in Plant cell, plant and Fungus, fungal Cell (biology), cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water ...

protease A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the ...

fructose-bisphosphate aldolase Fructose-bisphosphate aldolase (), often just aldolase, is an enzyme catalyzing a reversible reaction that splits the aldol, fructose 1,6-bisphosphate, into the triose phosphates dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate ( ...

, mannitol-1-phosphate 5-dehydrogenase,

formate dehydrogenase Formate dehydrogenases are a set of enzymes that catalyse the oxidation of formate to carbon dioxide, donating the electrons to a second substrate, such as NAD+ in formate:NAD+ oxidoreductase () or to a cytochrome in formate:ferricytochrome-b1 o ...

pyruvate decarboxylase Pyruvate decarboxylase is an enzyme () that catalyses the decarboxylation of pyruvic acid to acetaldehyde. It is also called 2-oxo-acid carboxylase, alpha-ketoacid carboxylase, and pyruvic decarboxylase. In anaerobic conditions, this enzyme is ...

transketolase Transketolase (abbreviated as TK) is an enzyme that is encoded by the TKT gene. It participates in both the pentose phosphate pathway in all organisms and the Calvin cycle of photosynthesis. Transketolase catalyzes two important reactions, which ...

peroxidase Peroxidases or peroxide reductases ( EC numberbr>1.11.1.x are a large group of enzymes which play a role in various biological processes. They are named after the fact that they commonly break up peroxides. Functionality Peroxidases typically ca ...

catalase Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals) which catalyzes the decomposition of hydrogen peroxide to water and oxygen. It is a very important enzyme in protecting t ...

phosphogluconate dehydrogenase 6-Phosphogluconate dehydrogenase (6PGD) is an enzyme in the pentose phosphate pathway. It forms ribulose 5-phosphate from 6-phosphogluconate: :6-phospho-D-gluconate + NAD(P)+ \rightleftharpoons D-Ribulose 5-phosphate + CO2 + NAD(P)H + H+ It i ...

and

14-3-3 protein 14-3-3 proteins are a family of conserved regulatory molecules that are expressed in all eukaryotic cells. 14-3-3 proteins have the ability to bind a multitude of functionally diverse signaling proteins, including kinases, phosphatases, and trans ...

. These proteins give ''C. pallescens'' its allergenic potential in humans. They have also been reported as allergens of other fungal species, and of species outside the kingdom Fungi.

Infection and disease

''Curvularia pallescens'' has been reported to cause subcutaneous,

pulmonary The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of th ...

, and cerebral lesions, in immunocompetent individuals. It is thought that lesions arise as the result of inhalation of soils containing ''C. pallescens''. The human pathogenic potential of ''C. pallescens'' stems from its viability and functionality at the normal human body temperature (37 °C), and its ability to disseminate. In addition to human infection, there have been multiple reported cases of

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 ...

s caused by ''C. pallescens'', in crops. In particular, infections have occurred in

bamboo Bamboos are a diverse group of evergreen perennial flowering plants making up the subfamily Bambusoideae of the grass family Poaceae. Giant bamboos are the largest members of the grass family. The origin of the word "bamboo" is uncertain, bu ...

s (such as ''

Bambusa vulgaris ''Bambusa vulgaris'', common bamboo, is an open-clump type bamboo species. It is native to Indochina and to the province of Yunnan in southern China, but it has been widely cultivated in many other places and has become naturalized in several re ...

'', '' Dendrocalamus longispathus'' and ''

Thyrsostachys ''Thyrsostachys'' is a genus of Chinese and Indochinese bamboo in the grass family. ;Species # ''Thyrsostachys oliveri'' Gamble - edible-seeded bamboo - Yunnan, Myanmar, Laos, Thailand; naturalised in Assam + Bangladesh # ''Thyrsostachys siame ...

oliveri''),

sugarcane Sugarcane or sugar cane is a species of (often hybrid) tall, Perennial plant, perennial grass (in the genus ''Saccharum'', tribe Andropogoneae) that is used for sugar Sugar industry, production. The plants are 2–6 m (6–20 ft) tall with ...

s, and

es (such as ''

Imperata ''Imperata'' is a small but widespread genus of tropical and subtropical grasses, commonly known as satintails. Satintail grass species are perennial rhizomatous herbs with solid, erect stems and silky inflorescences. The best known species is ...

arundinacea'' and ''

Eleusine coracana ''Eleusine coracana'', or finger millet, also known as ragi in India, kodo in Nepal, is an annual herbaceous plant widely grown as a cereal crop in the arid and semiarid areas in Africa and Asia. It is a tetraploid and self-pollinating species p ...

''). The severity of disease and the appearance of the spots differ between species. In ''B. vulgaris'', the leaf spots appear circular or irregular in shape with a greyish-black centre and yellow perimeter. In sugarcane, the leaf spots appear

elliptical Elliptical may mean: * having the shape of an ellipse, or more broadly, any oval shape ** in botany, having an elliptic leaf shape ** of aircraft wings, having an elliptical planform * characterised by ellipsis (the omission of words), or by conc ...

in shape and light brown in colour. In ''I. arundinacea'' and ''E. coracana'', the leaf spots appear irregular in shape and brown to black in colour. ''Curvularia pallescens'' invades the host organism via the

stoma 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 ...

ta or proceeding damage. Infection arises as the result of the propagation 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 ...

e within the host, causing the host cell to rupture. This results in the spotty appearance on the leaf. Over time, the spots combine to form

necrotic Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...

zones at the leaf tips causing dehydration in those areas. The leaf spots can be controlled by

fungicide 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, ...

sprays, such as

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 ...

(0.1%). In addition to leaf spots, infection can result in: the hindrance of germination, inhibited growth of seedlings and mature crops of lesser quality (e.g., fewer grains produced, and the grains that are produced are damaged).

References

{{Taxonbar, from=Q60743548 Pleosporaceae Fungi described in 1933 Taxa named by Karel Bernard Boedijn