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Pathogen Biology

Colletotrichum cereale overwinters as mycelium (Figure 17) or conidia associated with previously infected plant tissue. The fungus may also survive as darkly pigmented aggregates of hyphal cells (stromata) that are formed on stolons and at the base of tillers (Figure 18). Exposure of the stromata to sunlight and moderate temperatures of 15 to 25ºC (59 to 77ºF) can induce formation of conidia. The conidia may serve as initial inoculum for basal rot anthracnose in the spring or early summer. However, further research is required to determine whether basal rot anthracnose and foliar anthracnose are two distinct diseases caused by different strains of C. cereale or simply phases of a single disease. Conidia are spread to surrounding leaf blades by water, mowing, and other cultural practices that cause physical disruption of the turfgrass sward.

Figure 17

Figure 18

In early to mid-summer during warm, wet periods, conidia may also germinate on plant surfaces to form germ tubes that develop into lobed, melanized appressoria (Figure 19). Appressoria serve to anchor the fungal filaments to the plant surface. A penetration peg emerges from a pore in the appressorium and penetrates plant epidermal cells directly. Penetration of the epidermis is closely followed by production of a single, irregularly-shaped infection hypha. One or more branches from the infection hypha then invade surrounding plant mesophyll cells. From this point, C. cereale behaves as a necrotroph, killing plant tissue with enzymes, and possibly toxins, in advance of mycelium growth. The sexual stage (teleomorph) of C. cereale is the ascomycete Glomerella graminicola. This stage has been observed in laboratory cultures but not on infected turfgrasses.

Figure 19

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