Class: Teliomycetes
This group comprises two distantly
related orders, Uredinales and Ustilaginales,
which produce no basidiomata, merely forming pustules on their living hosts.
And the basidia develop directly from a specialized resting spore called a
teliospore.
Order:
Uredinales
The rust
fungi are all obligately biotrophic on vascular plants, and often have very
narrow host ranges, reduce yields of our domesticated plants, particularly the
cereals on which we are so dependent. The rust fungi produce basidia from
overwintering spores (teliospores), so they don t form basidiomata. But they do produce no fewer
than five different kinds of spore, each specialized for a particular step or
phase in the life cycle. And they often alternate between two hosts, which are
often from taxonomically distant groups. our efforts to control many diseases
of our food crops depend on our knowledge of the life history of the pathogens.
In any case, these most complex of all fungal cycles are intrinsically
fascinating.
Puccinia
graminis:
causing black stem rust of wheat, produc five spore forms
and moving back and forward between two different hosts, The five stages produced
are:
Stage 0:Spermagonium , Stage I:
Aecium , Stage II: Uredium, Stage III: Telium , Stage IV:
Basidium
Basidiospores land on a young leaf
of barberry (Berberis) in spring, and initiate localized infections.
Intercellular hyphae send haustoria into host cells to absorb food.
monokaryotic mycelia develop tiny flask-shaped
spermagonia (stage 0) in the upper layers of the leaf. Each spermagonium forms
tiny spermatiawhich ooze out in a sweet-smelling nectar. attracted Insect that fly from one
spermagonium to another, transferring spermatia of each mating type to initiate
the dikaryophasewhich spreads to the lower surface of the barberry leaf,
where the fungus has already produced the
primordia of cup-like structures called aecia (stage I). The flower-like aecia liberate
dikaryotic aeciospores can t
infect the barberry. Only if they land on a wheat plant (Triticum) establish new dikaryotic
infections.