The red portion in the stem of cane is due to a fungal disease called red-rot caused by the organism Glomerella tucumanensis. The organism attacks during the conidial stage (imperfect stage) when it is known as Colletotrichum falcatum.
The pathogen infects the host mainly through the leaf scars at abscission or immediately thereafter, enters the parenchyma, grows intracellularly in the early stages, and forms an intercellular mycelium in the later stages. The fungal hyphae penetrate the host’s cell wall during the progressive stage of the disease forming minute penetration pegs. These pegs expand to the normal hyphal diameter immediately after reaching the other side of the cell wall. This mechanical pressure causes the dissolution of the tissue. Thus the tissue dissolution is not due to enzyme action, but due to mechanical pressure.
But hydrolyzing enzymes are produced at a later stage when the tissues begin to die and the pathogen grows on the dead cells of the host, that is, in the saprophytic phase of the fungus. Only at this time reddening of the stem vascular tissue occurs followed by the formation of lysigenic cavities. At this stage when the affected canes are split open, the tissues of the internodes which are normally white or yellow-white will become red in one or more internodes usually near the base.
The reddening is conspicuous in the vascular bundles and progresses towards the pith. When such diseased shoots appear in the field, secondary infection is caused by conidia which are produced in aierouli (asexual reproductive bodies) and transmitted through insects, wind and water.