Colletotrichum gloeosporioides

Glomerella cingulata is the sexual stage (teleomorph) while the more commonly referred to asexual stage (anamorph) is called Colletotrichum gloeosporioides. For most of this article the pathogen will be referred to as C. gloeosporioides. This pathogen is a significant problem world wide, causing anthracnose and fruit rotting diseases on hundreds of economically important hosts. Laid out here is an overview of some of the most important aspects of this pathogen.

Colletotrichum gloeosporioides has an extremely broad host range, causing anthracnose disease on a variety of crops such as cereals and grasses, legumes, fruits, vegetables, perennial crops, and tree. Although the species is so broad in susceptible hosts, some studies are suggesting Colletotrichum gloeosporioides has sub-populations specific to each host. The symptoms can vary from host to host, but tend to manifest as water soaked, sunken spots on fruit that turn necrotic as the disease progresses, and small dark lesions on leaves.

Using mangos, one of the most economically important hosts, as an example, fruit symptoms manifest late in the season as infected fruit ripens to maturity. At this point fruit develops large, sunken areas of decay that are dark brown to black in color. Occasional fruit cracking can also occur when linear necrotic lesions develop into deep cracks through the epidermis that can extend down into the pulp of the fruit. Because symptoms remain unseen before ripening, plants that appear healthy upon picking can become quickly riddled with disease in storage or transport. Mango leaves exhibit symptoms as small, angular, brown/black lesions that enlarge as the disease progresses. Again, these symptoms vary from host to host, but mangos serve as a decent example for the general symptomatology of this pathogen.

Regardless of host, Colletotrichum gloeosporioides produces several signs useful for diagnosis. When observed under a dissecting microscope acervuli can often be spotted if the diseased tissue has recently been under sporulating conditions. These acervuli will appear orange to pinkish in color, due to the masses of conidia being produced on the surface, and will have black, hair-like, setae spiking out in several directions. Under a compound microscope conidia appear ovoid in shape. On certain hosts the teleomorph of this pathogen, Glomerella cingulata, readily produces perithecia full of asci. When cultured on potato dextrose media, this species can appear gray, orange, or pink in color, and will often exhibit concentric rings of growth radiating from the center. Colletotrichum gloeosporioides can also be identified by PCR if the required resources are available.

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