TYPE 1: USTILAGO (Smut) Occurrence
Usti.ago is parasite on the grasses like wheat. It is commonly called smut. It attacks on the ovaries of grasses. Sometimes, it completely destoy the whole ears (wheat) and produces black powdery mass of spores. Ustilago tritici is common in Pakistan. It attacks on wheat. Usti’ago avenae attacks on oat. Ustilago nada attacks Or barely. UstPago zeae attacks on maize.
Mycelium of Ustilago is composed of monokaryotic and dikaryotic hyphae. The hyphae are septate. The primary mycelium is monokaryotic. It is short lived and does not grow much. Secondary mycelium is dikaryotic. It develops chlamydospores. Mycelium is intracellular or extracellular. It may develop haustoria.
Fig: Life cycle of Ustilago
The life cycle of Ustilogo wake patses through following stages:
- Attack of chlamydospores or Teleutospores: Ustilago attacks on nature wheat plant in spring. ‘Hie ears (inflorescence) of wheat are rovered by black powdery mass. This powdery mass is composed of large number of chlamydospores. Each spore is unicellular and binticleate. It has a thick sail.
- Formation of promycelium (primary my –:elium):
Chkunydospores are dispersed by wind. They fall on the ears of heal iv plants. They germinate on the ear. Their nuclei fuse to form dipinid zygote nucleus. The zygote nucleus undergoes meiosis. The spore produces a short germ tube or promycelium. Transve.se septa are produced in promycelium. It divides promycelium into four cells. Each cell contains single nucleus.
- Basidiospore formation: Each cell of promycelium produces a sterigma. Basidiospores or sporidia are produced on this sterigma.
- Formation of secondary mycelium: The basidiospore germinates to form new mycelium. It becomes dikaryotic by conjugation between hyphae or basidiospores.
The cells of promycelium germinate to produce hyphae directly in Ust logo tilted. These hyphae undergo conjugation to produces dikaryotic hypha. They do not produce basidiospores.
The dikaryotic hyphae infect the ovaries of hosts. Their growth is intracellular. These reach the embryo. These does not cause disease in embryo and become dormant in it.
- Formation of chlamydospores: The infected seeds are sown next season. Dormant hyphae become active. It grows in the apical meristem of host. Host plant develops ears. Mycelium of Ustilogo ente:s in the flower and reaches the ovaries of the young flowers. It forms a mass of hyphae. This mass of hyphae consists of short binecleate cells. Each cell secretes a thick wall around it. It is transformed into chlamydospores. Chlainydospores are produced in largi, number. It changes the ear into black dusty mass.