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 species of cultivated plants. These organisms attack crops in tropical and subtropical regions, producing multimillion-dollar losses to agro-industry.
Fungi of the genus Colletotrichum are responsible for fruit rot after being harvested, anthracnose and blight on commercially important plants, including bananas, papayas, cassava, sorghum, coffee, beans, tomatoes, peppers and many others.
The taxonomic classification of the species of Colletotrichum it is controversial and is currently under review. Some morphological characteristics are useful to differentiate groups of species but are not useful in other cases.
It has been suggested that the genus Colletotrichum contains complexes of cryptic species that are closely related to each other, with similar colonization and infection behavior.
The Colletotrichum they are part of the group of ascomycete fungi. These organisms are characterized by presenting a reproductive structure in the form of a sac. Its mycelium is formed by septate hyphae.
Among other characteristics of ascomycetes in general, and of the Colletotrichum in particular they are:
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 living plant cells by breaking down 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..
The gender Colletotrichum, was erected by Corda in the year 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.
Identification based on morphological characteristics of fungi Colletotrichum it is possible in some species based on the host to which they are associated, mycelial growth, sporulation capacity and particular characteristics of conidia, appressoria and sclerotia.
For this, it is necessary to carry out artificial cultures of the fungus and observe the germination of the conidia..
Morphological characteristics and host range have traditionally been used to define fungal species. The excessive and inappropriate use of the type of host for the determination of species caused 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 species of Colletotrichum 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 to differentiate species of Colletotrichum.
The multi-locus phylogeny has been widely applied to identify species of this genus. Using this methodology it has been suggested that C. gloeosporioides it is actually a complex consisting of 23 taxa. At least 19 new species have also been described based on the multiple locus phylogeny..
Other suggested tools to help elucidate the identity of species of Colletotrichum have been the biochemical and physiological analyzes.
When Corda, in 1831, described the first species of the genus Colletotrichum (C. lineola), 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 subspatulate setae 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.
This condition, also known as black spot disease on leaves, is caused 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 it is very common in nursery plants and in many crops. This disease can affect leaves, branches, flowers and fruits. The main species of Collecotrichum 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 present as leaf blights, stains on stems, branches or flowers, cankers on the stem and branches, or fruit rot. Symptom expression is highly dependent on the infected plant species.
The economic damage caused by Colletotrichum in plants, it is generally the result of losses due to fruit rot 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.