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The below mentioned article provides short note on colletotrichum.
Mycelium of Colletotrichum:
It is internal, septate and branched. The slender hyphae are both intercellular and intracellular. They are usually hyaline when young. With age the hyphal wall becomes darker and thicker and the cytoplasm, which contains droplets of oil, becomes denser.
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The thick-walled hypha finally collect, intertwine and become compacted to form small usually black stromata beneath the cuticle or epidermis (Fig. 16.13A).
The acervulus consisting of a dense, palisade-like layer of short, hyaline comdiophores, is formed on the stromatic surface (A). The conidiophores are unseptate and usually unbra rarely branched (B).
The conidia are abstricted singly, sometimes in chains at the tips of conidiophores acrogenously. As the conidia mature the overlying cuticle or epidermis ruptures.
The conidia are usually hyaline to slightly ochreoous, continuous (non-septate or one-celled), oblong to fusoid usually with a large oil globule in the centre, somewhat curved with rounded ends or pointed at one end.
The acervuli (A) are characterised by the presence of long, rigid, dark brown bristles or setoe which either form a fringe around the acervulus or are intermixed with the conidiophores.
The setae are septate and attenuated towards their upper lightly coloured ends. Moist weather is essential for conidia formation. They are dispersed by wind, spattering rain or irrigated water.
The conidia are short-lived and thus germinate readily under suitable conditions of moisture and temperature by one or more germ tubes (D) to form the mycelium.
More often an appresonum is formed when the germ tube comes in contact with the host surface. Penetration through the host cuticle occurs by means of a slender infection tube or peg which arises from the side of appresorium in contact with the host.
Terminal or intercalary thick-walled chlamydospores are formed by the septation of hyphae. They persist in the soil for a long time.
The form-genus includes a number of species which cause serious diseases to economically important plants.
The common examples are:
1. Colletotrichum falcatum incitant of red rot of sugarcane (Saccharum officinarum).
2. C. capsici incitant of ripe fruit rot and the back of chillies (Capsicum amum).
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3. C. gloeosporioides incitant of mango anthracnose. The disease aspect is considered in the last chapter.
