COLLETOTRICHUM: CHARACTERISTICS, TAXONOMY, MORPHOLOGY - BIOLOGY - 2025

Colletotrichum is a genus of sac fungi (Ascomycota) with an extensive number of species. They are globally recognized as pathogens of many wild plants and of most cultivated plant species. These organisms attack crops in tropical and subtropical regions, causing multimillion-dollar losses to agro-industry.

Fungi of the genus Colletotrichum are responsible for post-harvest fruit rots, anthracnose, and blight on commercially important plants, including bananas, papayas, cassava, sorghum, coffee, beans, tomatoes, chili peppers, and many others.

Colletotrichum gloeosporoides. Taken and edited from

The taxonomic classification of Colletotrichum species is controversial and is currently under review. Some morphological characteristics are useful to differentiate groups of species but are not useful in other cases.

The genus Colletotrichum has been suggested to contain complexes of cryptic species that are closely related to each other, with similar colonization and infection behavior.

characteristics

Colletotrichum are part of the group of ascomycete fungi. These organisms are characterized by presenting a reproductive structure in the shape of a sac. Its mycelium is made up of septate hyphae.

Among other characteristics of ascomycetes in general, and of Colletotrichum in particular, are:

Asexual reproduction by conidiospores

Sexual reproduction always involves the production of an ascus with two or more haploid ascospores. They tolerate temperatures between 10 and 40 ° C, but their optimum development temperature is 28 ° C.

During the infection process, the phytopathogenic species of the genus Colletotrichum initially colonize the living cells of the plant, breaking the cell wall, but without penetrating the plasma membrane of these cells (this prevents progressive cell death).

The beginning of the feeding of dead parts of the plant by the fungus is associated with notable morphological, genetic and physiological changes of the latter. These changes in the fungus cause massive cell death and destruction of host tissues.

Anthracnose caused by Colletotricum sp. Taken and edited from

Taxonomy

The genus Colletotrichum, was erected by Corda in 1831, to describe the species C. lineola, based on material collected in Prague (Czech Republic) from the stem of an unidentified herbaceous plant of the Apiaceae family.

At present, although the genus Colletotrichum is considered valid, the definition of the different species is controversial and is subject to revision.

Some species of this genus are confused with species of the genus Gleosporium, however the latter do not produce mushrooms in the acervules.

Taxonomic identification of the species of

Morphological

Identification based on morphological characteristics of Colletotrichum fungi is possible in some species based on the host to which they are associated, mycelial growth, sporulation capacity and particular characteristics of the conidia, appressoria and sclerotia.

For this, it is necessary to carry out artificial cultures of the fungus and observe the germination of the conidia.

Molecular

Morphological characteristics and host range have traditionally been used to define fungal species. The excessive and inappropriate use of host type for species determination led to the proliferation of unnecessary scientific names.

This may be due, in part, to the fact that plant species with a wide spatial distribution can be affected by different species of fungi. Also contributing to this is the fact that some Colletotrichum species may associate with a single plant species, while others may associate with more than one host.

Due to the aforementioned, molecular biology as a tool has provided new knowledge about the systematics of this group of fungi, particularly in the delimitation of species and the definition of inter and intraspecific relationships.

The internal transcribable spacer region of ribosomal RNA (ITS) is the region most commonly used to differentiate fungi. This region has proven to be of little use in differentiating Colletotrichum species.

The multi-locus phylogeny has been widely applied to identify species of this genus. Using this methodology it has been suggested that C. gloeosporioides is actually a complex consisting of 23 taxa. At least 19 new species have also been described based on the multiple locus phylogeny.

Other tools

Other suggested tools to help elucidate the identity of Colletotrichum species have been biochemical and physiological analyzes.

Morphology

When Corda, in 1831, described the first species of the genus Colletotrichum (C. lineola), he mentioned that this species forms linear spindle-shaped acervuli, they present a curved appearance, with hyaline conidia with sharp and brown ends, of opaque tonality, with setae subspatulate and sharp tips.

In general, fungi of the genus Colletotrichum possess closed, setosus, cushion-shaped asexual fruiting bodies, located on or near the epidermis, which open irregularly.

The basal stroma is of variable thickness, dark brown to colorless or nearly colorless. Basal stromal cells are polyhedral, almost the same diameter and without spaces between them.

Cultured colonies of Colletotrichum species on PDA; C. gloeosporioides group 1 (a); group 2 (b); group 3 (c); C. musae (d); C. truncatum (e). Taken and edited from

Anthracnose caused by

This condition, also known as the disease of the black spots on the leaves, is produced by various types of fungi. Sometimes it is difficult to determine the genus and species of the fungus responsible for particular attacks.

Anthracnose caused by Collecotrichum is very common in nursery plants and in many crops. This disease can affect leaves, branches, flowers and fruits. The main Collecotrichum species responsible for anthracnose belong to the complex of species of C. gloeosporioides.

Leaf spots are the most common cause of production losses, due to anthracnose caused by Colletotrichum in nursery plants. The disease can also appear as blight on leaves, spots on stems, branches or flowers, cankers on the stem and branches, or fruit rot. The expression of symptoms is highly dependent on the infected plant species.

The economic damage produced by Colletotrichum in plants is generally the result of losses due to rotting of the fruit in the field or after harvest. This disease has caused losses of 17% of papaya crops, 30% of mango and up to 50% of chili crops.

References

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