Claviceps

Ergot (ˈɜrgət ) or ergot fungi refers to a group of fungi of the genus Claviceps. The most prominent member of this group is Claviceps purpurea ("rye ergot fungus"). This fungus grows on rye and related plants, and produces alkaloids that can cause ergotism in humans and other mammals who consume grains contaminated with its fruiting structure (called ergot sclerotium). Claviceps includes about 50 known species, mostly in the tropical regions. Economically significant species include C. purpurea (parasitic on grasses and cereals), C. fusiformis (on pearl millet, buffel grass), C. paspali (on dallis grass), C. africana (on sorghum), and C. lutea (on paspalum). C. purpurea most commonly affects outcrossing species such as rye (its most common host), as well as triticale, wheat, and barley. It affects oats only rarely. C. purpurea has at least three races or varieties, which differ in their host specificity: G1 — land grasses of open meadows and fields; G2 — grasses from moist, forest, and mountain habitats; G3 (C. purpurea var. spartinae) — salt marsh grasses (Spartina, Distichlis). An ergot kernel, called a sclerotium, develops when a spore of fungal species of the genus Claviceps infects a floret of flowering grass or cereal. The infection process mimics a pollen grain growing into an ovary during fertilization. Infection requires that the fungal spore have access to the stigma; consequently, plants infected by Claviceps are mainly outcrossing species with open flowers, such as rye (Secale cereale) and ryegrasses (genus Lolium). The proliferating fungal mycelium then destroys the plant ovary and connects with the vascular bundle originally intended for seed nutrition. The first stage of ergot infection manifests itself as a white soft tissue (known as sphacelia) producing sugary honeydew, which often drops out of the infected grass florets. This honeydew contains millions of asexual spores (conidia), which insects disperse to other florets. Later, the sphacelia convert into a hard dry sclerotium inside the husk of the floret.