Biology Reference
In-Depth Information
killed back extensively. Most of the tubers
are small, often with a brown jelly rot at the
stem end.
Under moist conditions a white cobwebby
weft of mycelium is formed at the base of
potato stems, and the basidial stage is pro-
duced as a powdery crust on this weft. The
fungus winters as mycelium or sclerotia in
soil or tubers. The mycelium can grow sapro-
phytically long distances in the soil indepen-
dent of any plant. Infection is favored by cool
temperatures; the disease is most serious in
wet seasons on heavy soils. The average yearly
loss for the country is about 10 million
bushels, 2 to 3 %, but individual losses may
be from 5 to 50 %. For control use healthy
tubers for seed.
Thanatephorus cucumeris (Syn.
Pellicularia
filamentosa
(Anamorph,
Rhizoctonia solani
)).
Brown Patch
of turf,
Root and Leaf Rot
of lawn
grasses, wheat grass, bentgrass, fescues, ryegrass,
Kentucky bluegrass (infrequently on Canada
bluegrass), St. Augustine grass, and Bermuda
grass. Brown or blackish patches on the turf
resemble sunscald or chinch bug injury. The
areas are roughly circular, from an inch to 3 feet
across, sometimes up to 20 feet. The fungus
works outward with a “smoke ring” of grayish
black mycelium at the advancing margin. The
leaves are first water-soaked, black, then col-
lapsed, dry and light brown, but the roots are
seldom killed. The disease develops most rapidly
during warm humid periods and with an excess of
nitrogen.
Thanatephorus cucumeris (Syn.
Pellicularia
filamentosa
(Anamorph,
Rhizoctonia solani
)).
Root and Stem Rot
,
Damping-Off
of ornamen-
tals. In wet weather cobwebby mycelium
develops on lower portions of stems; the
lower leaves rot and upper portions of
plants wilt and die. Seedlings and older plants
so rotted include
Aconitum
, abelia,
Achillea,
Ageratum
, aster, artichoke, begonia, calendula,
campanula, carnation, endive, dahlia, delphin-
ium, geranium, iris, lettuce, lupine, orchids,
platycodon, poinsettia, salsify, sunflower and
tulip. For control avoid excessive use of
manure.
Paecilomyces
Deuteromycetes, Hyphomycetes
Conidiophores and branches more divergent than
in
Penicillium
; conidia (phialospores) in dry
basipetal chains, one-celled, ovoid to fusoid,
hyaline.
Paecilomyces buxi (see
Sesquicillium buxi
).
Root Rot
and
Decline
on boxwood.
Sesquicillium buxi (formerly
Paecilomyces
buxi
).
Root Rot
and
Decline
on boxwood.
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Pellicularia
▶
Blights
.
Thanatephorus cucumeris (Syn.
Pellicularia
filamentosa
) (considered by some
Botryobasidium
).
Rhizoctoniose
,
Black Scurf
of
potatoes, stem canker and soil rot of beans (see
under
Blights
for Web Blight of beans and
other plants); Rhizoctonia Dry Rot Canker of
Beets, Crown and Crater Rot of Carrots; Rhizoc-
tonia Disease of Celery, Crucifers, Cucurbits;
Bottom Rot of Lettuce; Damping-Off of Pepper
and Eggplant; Root Rot of Onion; Root and Basal
Stem Rot of Pea; Crown Rot of Rhubarb. The
sterile state of this fungus,
Rhizoctonia solani
,
was first named in 1858 in a German textbook
and is still the most familiar term for a fungus
with many pathogenic strains causing many types
of diseases.
Any cook has seen signs of the pathogen on
potato tubers - small brown to black hard
flecks, sclerotia, on the skin. They look like
particles of dirt but do not scrub off when
potatoes are washed. There may be only one
or two sclerotia, or they may nearly cover the
whole surface of the tuber. When such potatoes
are planted, the growing point may be killed.
Some sprouts renew growth after being gir-
dled, which may be repeated until they die.
Larger plants have stems decayed just
below the soil line, interrupting the downward
transfer of food and resulting in a cluster of
green or reddish aerial tubers. Roots may be
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