|
Ergot (pron. ) 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'').〔(ergot ), online medical dictionary〕〔(ergot ), Dorland's Medical Dictionary〕 ''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:〔(【引用サイトリンク】 Intraspecific variability of ''C. purpurea'' )〕 *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''). == Life cycle == 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. At this stage, alkaloids and lipids accumulate in the sclerotium. ''Claviceps '' species from tropic and subtropic regions produce macro- and microconidia in their honeydew. Macroconidia differ in shape and size between the species, whereas microconidia are rather uniform, oval to globose (5x3μm). Macroconidia are able to produce secondary conidia. A germ tube emerges from a macroconidium through the surface of a honeydew drop and a secondary conidium of an oval to pearlike shape is formed, to which the contents of the original macroconidium migrates. Secondary conidia form a white, frost-like surface on honeydew drops and spread via the wind. No such process occurs in ''Claviceps purpurea'', ''Claviceps grohii'', ''Claviceps nigricans'', and ''Claviceps zizaniae'', all from northern temperate regions. When a mature sclerotium drops to the ground, the fungus remains dormant until proper conditions (such as the onset of spring or a rain period) trigger its fruiting phase . It germinates, forming one or several fruiting bodies with heads and stipes, variously coloured (resembling a tiny mushroom). In the head, threadlike sexual spores form, which are ejected simultaneously when suitable grass hosts are flowering. Ergot infection causes a reduction in the yield and quality of grain and hay, and if livestock eat infected grain or hay it may cause a disease called ergotism. Black and protruding sclerotia of ''C. purpurea'' are well known. However, many tropical ergots have brown or greyish sclerotia, mimicking the shape of the host seed. For this reason, the infection is often overlooked. Insects, including flies and moths, carry conidia of ''Claviceps'' species, but it is unknown whether insects play a role in spreading the fungus from infected to healthy plants. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ergot」の詳細全文を読む スポンサード リンク
|