''Glomerella graminicola'' is an economically important crop parasite affecting both

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 ...

and

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 ...

where it causes the plant disease Anthracnose Leaf Blight.

Host and symptoms

''G. graminicola'' is an

anamorphic Anamorphic format is the cinematography technique of shooting a widescreen picture on standard 35 mm film or other visual recording media with a non-widescreen native aspect ratio. It also refers to the projection format in which a distorted ...

fungus which is identified as ''Colletotrichum graminicola'' in the teleomorphic phase. It is the anamorphic phase that causes

anthracnose A plant canker is a small area of dead tissue, which grows slowly, often over years. Some cankers are of only minor consequence, but others are ultimately lethal and therefore can have major economic implications for agriculture and horticultur ...

in many

cereal A cereal is any Poaceae, grass cultivated for the edible components of its grain (botanically, a type of fruit called a caryopsis), composed of the endosperm, Cereal germ, germ, and bran. Cereal Grain, grain crops are grown in greater quantit ...

species. While the main host of this disease is

, it can also affect other cereals and grasses, such as

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 ...

ryegrass ''Lolium'' is a genus of tufted grasses in the bluegrass subfamily (Pooideae). It is often called ryegrass, but this term is sometimes used to refer to grasses in other genera. They are characterized by bunch-like growth habits. ''Lolium'' is ...

, bluegrass,

barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley pr ...

, and some cultivars of fescue where the production of fruiting bodies cause symptoms to appear in the host plant. Corn anthracnose leaf blight is the most common stalk disease in maize and occurs most frequently in reduced-till or

no-till No-till farming (also known as zero tillage or direct drilling) is an agricultural technique for growing crops or pasture without disturbing the soil through tillage. No-till farming decreases the amount of soil erosion tillage causes in certai ...

fields.

Symptoms can vary depending on which part of the growing season the corn is in. Early in the growing season, the main symptom is foliar leaf blight. This often appears as long and wide oval or spindle-shaped water-soaked

lesion A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals. Types There is no designated classifi ...

s on the lower leaves of the plant. This tissue can become necrotic and has the potential to spread throughout the entire leaf, causing it to yellow and die. They are light brown in color, with margins that appear dark brown or purple. If this persists, black fruiting bodies will appear in the center of the lesion. The mid-season symptoms appear several weeks after corn produces tassels, when there will be a top die-back if the infection has spread throughout many parts of the plant. In this dieback, the entire plant will become necrotic and die, beginning at the tassel and working its way down the entire stalk to the lowest leaves. Late in the growing season, another major symptom of this disease appears:

stalk rot Stalk or stalking may refer to: Behaviour * Stalk, the stealthy approach (phase) of a predator towards its prey * Stalking, an act of intrusive behaviour or unwanted attention towards a person * Deer stalking, the pursuit of deer for sport Biolog ...

. It can first be seen as a reflective black stripe on the internodes of the stalk, and can make the stalk soft, causing the plants to easily lodge in heavy precipitation or a wind event.

Morphology

Stromata

* 70-300 μm in diameter * Bear prominent, dark, septate spines (setae) up to 100 μm long.

Conidia

* Developing at the base of the spines * Hyaline to pale yellow, unicellular, sickle-shaped, falcate to fusiform, tapered toward both ends * 3-5 x 19-29 μm.

Phialides

* Unicellular, hylanine and cylindrical, * 4-8 x 8-20 μm.

Growth on PDA

Growth on

potato dextrose agar Potato dextrose agar (BAM Media M127
from the U.S.

is: * Gray and feltlike *

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 ...

and

appressoria An appressorium is a specialized cell typical of many fungal plant pathogens that is used to infect host plants. It is a flattened, hyphal "pressing" organ, from which a minute infection peg grows and enters the host, using turgor pressure capable ...

are numerous when culture are well aerated, and

sclerotia A sclerotium (; (), is a compact mass of hardened fungal mycelium containing food reserves. One role of sclerotia is to survive environmental extremes. In some higher fungi such as ergot, sclerotia become detached and remain dormant until favor ...

sometimes occur. * Appressoria are diagnostic: they are tawny brown, irregular-shaped in edge, prominent, and terminal on thickened

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 ...

Disease cycle

In the spring, fruiting structures (

acervuli An acervulus (pl. acervuli) is a small asexual fruiting body that erupts through the epidermis of host plants parasitised by mitosporic fungi of the form order Melanconiales ( Deuteromycota, Coelomycetes). It has the form of a small cushion at th ...

) form from corn residue and produce banana-shaped spores (conidia) that are dispersed by wind blown raindrops and splashing. Conidial spores infect young plants through the epidermis or stomata. Anthracnose develops rapidly in cloudy, overcast conditions with high temperatures and humidity. In optimal environmental conditions, conidia can germinate in as little as 6–8 hours in 100% humidity. Initial necrotic spots or lesions can be seen within 72 hours after infection by conidia. Lower leaves that develop lesions provide conidial spores and cause secondary infections on the upper leaves and stalk. Vascular infections primarily occur from wounds caused by stalk-boring insects, such as the larvae of the

European corn borer The European corn borer (''Ostrinia nubilalis''), also known as the European corn worm or European high-flyer, is a moth of the family Crambidae which includes other grass moths. It is a pest of grain, particularly maize (''Zea mays''). The in ...

, allowing for conidia to infect and colonize the

xylem Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from ...

. From this, anthracnose top die back (vascular wilt) or stalk rot can occur. In the fall, ''C. graminicola'' survives as a saprophyte on corn leaf residue. The pathogen can also overwinter on corn stalks as conidia in an extracellular secretion. The secretion prevents conidia from desiccating and protects them from unfavorable environmental conditions. Overwintering on corn residue serves as a vital source of primary

inoculum In biology, inoculum refers to the source material used for inoculation. ''Inoculum'' may refer to: * In medicine, material that is the source of the inoculation in a vaccine * In microbiology, propagules: cells, tissue, or viruses that are used t ...

for the leaf blight phase in the spring. The cycle will start all over again when

susceptible Susceptibility may refer to: Physics and engineering In physics the susceptibility is a quantification for the change of an extensive property under variation of an intensive property. The word may refer to: * In physics, the susceptibility of a ...

corn seedlings emerge from the ground in the spring.

Environment

There are several conditions that favor the infection and persistence of anthracnose leaf blight. When high temperatures and long periods of wet weather or high humidity occur, these are the most ideal conditions for its spread and survival. A specific temperature range is required in order for the pathogen to successfully infect the host plant, between . Two other things, those being prolonged periods of low sunlight due to overcast conditions, or an already weakened host due to the infection of other diseases or pests will also favor infection of the host plant. In addition to this, there are two cultural practices that will also favor the disease. Continuous plantings of the same host without introducing

crop rotation Crop rotation is the practice of growing a series of different types of crops in the same area across a sequence of growing seasons. It reduces reliance on one set of nutrients, pest and weed pressure, and the probability of developing resistant ...

and no-till fields will favor persistence of the pathogen between

growing season A season is a division of the year marked by changes in weather, ecology, and the amount of daylight. The growing season is that portion of the year in which local conditions (i.e. rainfall, temperature, daylight) permit normal plant growth. Whil ...

Disease management

Since ''C. graminicola'' is found to survive on corn residue, specifically on the soil surface, one of the most effective methods of control is a one-year minimum of crop rotation to reduce anthracnose leaf blight. A study in 2009 showed more severe symptoms of leaf blight due to ''C. graminicola'' when grown on fields previously used for corn in comparison to fields previously used for soybean. There are cultural practices that can be taken to disrupt the primary inoculum phase and conidial spore infection of the host plant, and these include using hybrid cultivars resistant to the pathogen and keeping the host plants healthy and controlling other pests to keep them resilient to infection. While there are hybrids resistant to the leaf blight, these same hybrids are often not resistant to the stalk rot that occurs later in the growing season. There is also a cultural practice that disrupts the saprophytic stage of the pathogen, and this involves plowing the leftover corn residue deep into the soil and then using a one-year crop rotation away from the same host plant that was just used in that field. These methods move the saprophytic stage into the soil, where it is out-competed by other organisms, and does not survive.

Biological control Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also invo ...

may also be possible, though the large-scale implementation of this method has not been studied. This is done by applying yeasts to the leaf surfaces that are showing symptoms of the leaf blight.

Importance

Corn anthracnose caused by ''C. graminicola'' is a disease present worldwide. This disease can affect all parts of the plant and can develop at any time during the growing season. This disease is typically seen in

leaf blight Blight refers to a specific symptom affecting plants in response to infection by a pathogenic organism. Description Blight is a rapid and complete chlorosis, browning, then death of plant tissues such as leaves, branches, twigs, or floral org ...

or stalk rot form. Before the 1970s, Anthracnose was not an issue in North America. In the early 1970s, north-central and eastern U.S was hit with severe epidemics. Within 2 years of ''C. graminicola''s appearance in Western-Indiana,

sweet corn Sweet corn (''Zea mays'' convar. ''saccharata'' var. ''rugosa''), also called sugar corn and pole corn, is a variety of maize grown for human consumption with a high sugar content. Sweet corn is the result of a naturally occurring recessive muta ...

production for

canning Canning is a method of food preservation in which food is processed and sealed in an airtight container (jars like Mason jars, and steel and tin cans). Canning provides a shelf life that typically ranges from one to five years, although u ...

companies were nearly wiped out and production no longer exists there today. Anthracnose stalk rot was seen in many U.S corn fields in the 1980s and 1990s. A survey conducted in Illinois in 1982 and 1983 found that 34 to 46% of rotted corn stalks contained ''C. graminicola.'' Estimates on yield grain losses from anthracnose leaf blight and stalk rot range from zero to over 40%. This is dependent on hybrid, environment, timing of infection, and other stresses.

Pathogenesis

Once conidia germinate on corn leaves, a germ tube differentiates and develops into an appresoria and allows ''C. graminicola'' to penetrate epidermal cells. Germination and appressorium formation occur best in the temperature range ) Penetration occurs in a much narrower temperature range . In order to penetrate the cell wall, the fungus first pumps

melanin Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...

into the walls of the appressorium to create

turgor pressure Turgor pressure is the force within the cell that pushes the plasma membrane against the cell wall. It is also called ''hydrostatic pressure'', and is defined as the pressure in a fluid measured at a certain point within itself when at equilibri ...

in the appressorium. The melanin allows water into the appressorium cell but nothing out. This builds up an incredible amount of turgor pressure which the fungus then uses to push a hyphae through the corn cell wall. This is called the penetration peg. The penetration peg then grows, extends through the cell extracting nutrients and the host cell wall dies. Hyphae migrate from epidermal cells to

mesophyll A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...

cells. As a defense response, the cells produce

papilla Papilla (Latin, 'nipple') or papillae may refer to: In animals * Papilla (fish anatomy), in the mouth of fish * Basilar papilla, a sensory organ of lizards, amphibians and fish * Dental papilla, in a developing tooth * Dermal papillae, part of ...

e to prevent cell entry but is typically not seen successful. It is believed ''C. graminicola'' has a

biotrophic Symbiosis (from Ancient Greek, Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different Organism, biological organisms, be it Mutualism (biolog ...

phase because the plasma membrane of the epidermal cells is not immediately penetrated after invasion into the epidermal cell wall. Between 48–72 hours after infection, ''C. graminicola'' shifted from biotrophic growth to nectrotrophy (lesions appear). This is when secondary hyphae invade cell walls and intercellular spaces.

References

External links

Index Fungorum

USDA ARS Fungal Database

Colletotrichum dot org

fungi.ensembl.org
{{Taxonbar, from=Q5571229 Colletotrichum Fungal plant pathogens and diseases Cereal diseases Maize diseases Wheat diseases Fungi described in 1952