Red rot of sugarcane is caused by:

Question

Accepted Answer

The correct option is 4: Colletotrichum

Red rot is arguably the most destructive and economically significant disease of sugarcane worldwide, and it is caused by the pathogenic fungus Colletotrichum falcatum (teleomorph: Glomerella tucumanensis). This pathogen primarily infects the stalk, and the disease gets its name from the characteristic symptom: the internal tissues, or pith, of the sugarcane stalk develop a distinct red coloration. A crucial diagnostic feature for this disease is the presence of prominent transverse white patches or spots within the red-colored tissue, which are areas where the fungus has killed the host cells. The fungus penetrates the cane through wounds, especially at the nodes, or through the sett (planting material), leading to the breakdown of cellulose and the accumulation of red-pigmented host defense compounds. The damage causes the cane to become pithy and sour, significantly reducing both the yield and the quality of juice, making Colletotrichum the specific causal agent that sugarcane farmers and plant pathologists are constantly battling.

The incorrect option is 1: Cercospora

The genus Cercospora is a large and important group of fungi known primarily for causing Cercospora leaf spot diseases across a very broad range of plant hosts. These diseases are typified by small, often circular or angular, brown or gray spots on the leaves, usually surrounded by a reddish border. While species of Cercospora can affect many plants, they are not the etiological agent of the red rot of sugarcane. For instance, Cercospora beticola causes the devastating leaf spot of sugar beet, and other species cause leaf blight in maize or leaf spots in banana, demonstrating their preference for foliar, rather than vascular, disease symptoms. Therefore, the pathology caused by Cercospora does not match the description of the internal stalk rot seen in sugarcane.

The incorrect option is 2: Phytophthora

Phytophthora is a genus that belongs to the Oomycetes, often misleadingly called water molds, and are not classified as true fungi, although they cause many plant diseases. These organisms are highly adapted to wet conditions and are famous for causing economically devastating blights, root rots, and fruit rots, particularly in horticultural and vegetable crops. The most historically notable disease is the late blight of potato, caused by Phytophthora infestans. Crucially, Phytophthora species do not cause the Red rot of sugarcane, as their infection mechanisms and host preferences are fundamentally different. They typically cause a soft, water-soaked rot or rapid collapse of plant tissue, unlike the specific vascular reddening caused by the red rot fungus.

The incorrect option is 3: Alternaria

The fungi belonging to the genus Alternaria are common molds that are responsible for a variety of plant diseases collectively termed Alternaria leaf spots, blights, and sometimes post-harvest decays. These pathogens produce mycotoxins and are identified by their dark, multicellular spores. A well-known example of a disease caused by this genus is early blight of potato and tomato, caused by Alternaria solani, where concentric dark rings appear on the leaves. While they are significant plant pathogens, they do not cause the Red rot disease. Their pathology is generally characterized by necrotic spots on leaves and stems, which differs distinctly from the systemic, internal pith reddening that defines the Red rot condition in sugarcane.