Biology Reference
In-Depth Information
The summer spores appear about 10 days after
infection. This stage can be repeated, the spores
reinfecting wheat, and, since they are carried by
wind from one plant to another, one state to
another, even to hundreds of miles, they account
for large outbreaks of disease. In Mexico and
southern Texas this II stage continues through
the winter and causes spring infection without
the intervention of barberry. Waves of uredio-
spores coming up from the South may start north-
ern infection.
Normally in the North, spring infection starts
on barberry from sporidia (basidiospores) pro-
duced on a promycelium put forth by
a teliospore wintered on a wheat stem. Two
sexes occur in this rust,
designated + and - rather than male and female.
A young teliospore contains two nuclei, one +
and the other -; as the spore matures, these fuse to
a single nucleus, which divides twice in the pro-
duction of the four-celled basidium
(promycelium). Each cell produces a sporidium;
two of these are + and two -. A sporidium falling
on a barberry leaf germinates, sends in an infec-
tion thread, and develops a mononucleate (hap-
loid) feeding mycelium and finally a flask-shaped
pycnium containing pycniospores, which corre-
spond to the sex of the sporidium starting infec-
tion. The pycnia are in reddish lesions on the
upper leaf surface. Hyphal threads, receptive
hyphae, extend through the mouth of the
pycnium. Aided by insects, which are attracted
by a sweet nectar, pycniospores (spermatia) of
one sex are brought into contact with receptive
hyphae of the opposite sex, and sexual union
takes place, without which there is no further
development of the rust.
The dicaryotic or binucleate mycelium formed
from the fertilized hypha grows through the cells
of the barberry leaf and masses together on the
underside to produce aecia filled with a yellowish
waxy layer of aeciospores in cluster-cup forma-
tion. These spores, unable to reinfect barberry or
mahonia are wind-borne to the cereal or grass
host, the subsequent mycelium continuing binu-
cleate until the fusion in the teliospore. New
crops of urediospores can be produced every 10
to 14 days.
Control
Resistant varieties are of primary
importance, but they are difficult to maintain
because the sexual process in rusts allows the
continuous development of new strains.
More than 200 strains are known, but only
a dozen or so are important in any one year.
Race 15B is prevalent most years and can attack
all varieties of wheat grown in this country. Erad-
ication of the barberry eliminates the alternate
host and also the breeding place of new rust
varieties. Most barberry and mahonia species
are under quarantine, but some have been desig-
nated rust-resistant by the U.S. Department
of Agriculture and may be shipped interstate
under permit.
Puccinia helianthi
Sunflower Rust
. 0, I, II, III
general on sunflower, Jerusalem artichoke, and
heliopsis. Numerous brownish pustules in which
repeating spores are formed develop on underside
of leaves, which may dry and drop.
Puccinia heterospora III on abutilon, holly-
hock, mallow, and malvaviscus.
Puccinia heucherae III on coral bells, wood-
land star, saxifrage, bishops-cap, and foam-
flower.
Puccinia hieracii 0, I, II, III widespread on
endive and hawksbeard. Endive leaves are spot-
ted and blighted with dusty spore pustules. The
crop is occasionally lost, but no control has
seemed practical.
Puccinia horiana
White Rust
. III, IV on chry-
santhemum; no alternate host known. First
reported in England in 1964; became widespread
there in 1976. Found in amateur chrysanthemum
plantings in New Jersey and Pennsylvania in
1977.
Puccinia iridis
Iris Rust
. 0, I, II, III on bulbous
iris, serious in the Southeast, uncommon in
Northwest. Small, oblong to oval, red or dark
brown powdery spots, often surrounded by
a yellow margin, are present on leaves and
stems, which may die prematurely. In inoculation
tests with Dutch iris, varieties Early Blue, Gold
and Silver, Golden West, Imperator, Lemon
Queen, and Texas Gold were resistant.
Puccinia
jaceae
var.
diffusa
Rust
on
Centaurea
.
Puccinia lagenophorae On English daisy.
