Chapter 28, pages 573-588
Basic Botany-2 20:16-31:38
Five Kingdoms-3 11:25-15:12
Life Cycle of Puccinia (Wheat Rust)
Summary
1. Contains two different hosts and four kinds of spores
2. The two hosts are:
a. Wheat plant
3. The four spores are:
a. Teliospores - black, 2-celled, winters in wheat stubble, dikaryon
b.
Basidiospores
- black, germinates from
teliospores,
single-celled,
haploid,
blows to
and
infects
the
barberry
in the spring
c.
Aeciospores
- single-celled,
dikaryon,
develops on
barberry
and blows to and
infects
the
wheat
in the spring,
initial
infectors
of wheat plants in the
spring
d.
Uredospores
- red, single-celled,
dikaryon,
develops on the wheat, blows to and
infects
other wheat plants,
secondary
infectors
of
wheat
plants
Events of the Life Cycle
1. Teliospores
a.
Dormant
through the winter while lying on the ground at the base of the dead
wheat
plant
b. Spores are black in color
c. Each spore contains two cells
d. Each cell of the spore is dikaryon
e. Teliospores germinate in the spring by the following process
(1) Each of the two cells forms a diploid nucleus from the two dikaryon nuclei
(2)
Meiosis
occurs on each of the two diploid nuclei to form four
haploid
nuclei in
each of the two cells
(3) Each
of the four nuclei takes some of the
cytoplasm
to produce two 4-celled
basidia
(4) A
sterigma
is pushed out of each cell by the
nucleus
to form a
basidiospore
at
the top of each
sterigma
(5) The
result is that each cell of the
teliospore
produces four
basidiospores
for a
total of eight basidiospores
(6) Of the eight basidiospores, four will be + basidiospores and four will be -
2. Basidiospores
a. These spores are black and are blown about by the wind
b. Some of the basidiospores will land on barberry bushes
c. When some moisture is
present on the surface of the barberry leaf, the basidiospore
will
germinate
d. The
hypha
from the basidiospore
penetrates
the
cuticle
and pushes its way into the
midst of the
mesophyll
but does not go into the inside of the cells of the mesophyll
3. Spermagonia or pycnia
a. The
haploid
hyphae
that came from the
basidiospores
form a
spermagonium
on the
upper surface
of the
barberry
leaf
b. Spermagonia are pear-shaped
c. Small pore at the top end of the "pear"
d. Each spermagonium contains:
(1) Receptive hyphae that fill the inside and extend out through the pore
(2)
Spermatia
- small
spherical
structures that are
interspersed
between the
receptive
hyphae inside the
spermagonium
e. Because both plus and
minus
basidiospores
germinate
on the leaf surface, then both
plus and minus
spermagonia
are scattered over the surface of the leaf
f. Conjugation of spermatia and receptive hyphae:
(1)
Spermatia of both plus and minus spermagonia ooze out of the
pore
at the top of
the spermagonium
(2) Spermatia migrate over the surface of the leaf
(3) When
plus
spermatia
come in contact with minus
receptive
hyphae or visa versa,
plasmogamy
occurs to form a
dikaryon
cell
(4) The dikaryon cell divides by mitosis to form a filament of dikaryon cells
g. The dikaryon filament
grows downward into the
spongy
parenchyma where it
produces an
aecium
4. Aeciospores
a. Aeciospores are produced
in the
aecia.
[The aecia are sometimes called
cluster
cups.]
b. Single-celled spore
c. Dikaryon
d. When the spores are mature, they are blown about by the wind
e. If the
aeciospores
lands on a
wheat
plant the spore enters the leaf through the
stoma
and there
germinates
into a
hypha
- primary infection of the wheat
f. The hyphae
penetrate
individual cells with their
haustoria
and obtain nourishment
directly out of the
cell
5. Uredospores
a. About 10 days after the
infection
of the
wheat
by the
aeciospores,
pustules
(uredinia)
begin to appear on the surface of the wheat plant leaves just under the
epidermis
b. The uredospores that the pustule releases are red (rust colored, thus wheat rust)
c. Spores are single-celled
d. Spores are dikaryon
e. These spores blow about in the wind as the pustules open
f. Uredospores that
land on other wheat plants they infect those plants (secondary
infection)
in the same manner as the aeciospores do to from more
uredinia.
g. The uredospores as they
are produced continue to infect wheat plants while they are
growing and
maturing
6. Teliospores
a. The
wheat
rust
mycelium
in the wheat leaf, shifts from the production of
uredospores
to the production
of
teliospores,
as the wheat begins to mature and turn from
green to yellow
b. Thus it is possible to find both uredospores and teliospores in the same pustule
c. Spores are two-celled
d. Each cell is dikaryon
e. The spores are black
f. When the spores
are released they fall down on the ground in the
stubble
of the
wheat where
the spores spend the winter
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