Uredinales: Life Cycle, Heteroecism & Biological Specializations



Describe the uredinal and pycnial stages of Puccinia graminis-tritici.


Disease: Rust.

Pathogen: Puccinia graminis-tritici.

Host: Wheat.


Alternate host: To complete life cycle, two hosts are needed.

Collateral host: If a fungus can grow on many hosts.


Life cycle of Puccinia graminis-tritici.


Fungi belonging to the order Uredinales commonly are referred to as rust fungi. Economically speaking, these are amongst the most important of all Basidiomycota species.

  • All are parasitic on plants.
  • Most rust fungi exhibit complicated life cycles that typically involve two taxonomically unrelated host plants and the production of as many as three different types of spores in addition to basidiospores.
  • In primary mycelium, the hyphal compartment is monokaryotic and in secondary mycelium, the compartment is dikaryotic. The secondary mycelium produced following the fusion of two sexually compatible structure.
  • Dikaryotic spores are produced from secondary mycelium which upon dispersion produce dikaryotic phase in another host.
  • They are obligate biotrophs that are incapable of surviving saprobically.
  • Unlike most other basidiomyecetes, the rust fungi produce no basidiocarps.
  • Karyogamy takes place in a special spore known as teliospore which is a part of the basidium.
  • Upon germination, the teliospore gives rise to a typical short germ tube of determinate growth known as promycelium.



Life cycle pattern

Rust fungi may produce as many as five different stages in their life cycles:


StagesDifferent structures with poidy level
0Spermogonia bearing spermatia (n) and receptive hyphae (n).


IAecia bearing aeciospores (n+n).
IIUredinia bearing urediniospores (n+n).
IIITelia bearing teliospores (n+n = 2n)
IVBasidia bearing basidiospores (n)


Stages 0 and I are seen in Barberry plants (Berberris vulgaris). And stages II, III and IV are in wheat.


Based on life cycle patterns, species of Uredinales may be divided into three categories.

  1. Macrocyclic forms
  • Typically exhibit all five reproductive stages.
  1. Demicyclic forms
  • Lack a uredinial stage.
  1. Microcyclic forms
  • Both aeciospores and urediniospores are absent.
  • The teliospore is the only binucleate spore produced.



Smut fungi

  • The mycelia of this fungi are not very prominent.
  • Sexual reproduction by somatogamy.
  • They produce intercellular mycelia but there are some intra-cellular.
  • Few species how clamp connection.
  • Mitric system absent.
    Mycelia dikaryotic.
  • Basidiocarp absent i.e. fruit body absent.
  • In some areas, intracellular mycelia often act as haustoria.
  • Altogether smut organisms are plant pathogens.


Manner of infecting hosts

  1. Externally seed borne
  2. Internally seed borne
  3. Air borne infection by basidiospore through actively growing meristem
  4. Soil borne infections
  5. Method of transmission is unknown.

About Abulais Shomrat

Abulais Shomrat
Currently in 4th year (Hons) in Department of Botany, University of Dhaka. Planning to have multiple careers one by one but promised to be with 'Plantlet' as long as it's primary stage remains unfinished.

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