Biology Reference
In-Depth Information
burned areas. Infected roots are matted together
with whitemycelium. More or less resinous annual
fructifications are formed on the ground. They are
irregular, an undulating brown upper surface with
narrowwhite margin, 2 to 3 inches across. There is
no control, but the disease is minor.
Rhizoctonia
Deuteromycetes, Hyphomycetes
Sclerotial form of
Pellicularia, Corticium,
Macrophomina, and Helicobasidium
. Young
mycelium colorless; branches constricted at
points of origin from main axis; older mycelium
colored, wefts of brownish yellow to brown
strands, organized into dense groups of hyphae,
sclerotia, made up of short, irregular, angular or
somewhat barrel-shaped cells (see
Fig. 8
).
Rhizoctonia sp.
Postharvest Decay
on leather-
leaf fern.
Rhizoctonia
Fig. 7 Pythium
Blackleg on Geranium
bataticola
Charcoal
Rot
.
Macrophomina phaseoli
Rhizoctonia
▶
and temperature. Exact determination is not
always practical. Nematode wounds often dis-
pose plants to rot. Diseases include African-
violet rot, aloe root rot, black rot of orchids,
begonia root rot, coleus black leg, geranium cut-
ting rot (see
Fig. 7
), bean and parsley root rot,
rhubarb crown rot, mottle necrosis of sweet
potato, and other rots. Some plants can be treated
with hot water, 115
F for 30 min. Sterilize soil
before use; avoid excessive watering. See
▶
crocorum
Violet
Root
Rot
.
Helicobasidium purpureum
.
Rhizoctonia solani
Black Scurf
of potatoes,
Brown Patch
of turf.
▶
Pellicularia filamentosa
Root Rot
and
Crown Rot
of clovers.
Rhizoctonia solani
Root and Stem Rot
of poin-
settia and other ornamental plants, including basil,
begonia, camellia, calla, carnation, chrysanthe-
mum, coleus, cornflower, geranium, gloxinia,
impatiens, lily, pansy, pothos, peperomia, prim-
rose, ragweed, rosemary, caper spurge, and sain-
foin (crown rot). Although
Pythium
flourishes best
in the low oxygen content of poorly drained soils,
Rhizoctonia
, causing similar root rots, is serious in
well-drained soils. On poinsettia, dark brown
lesions at or above soil level are often covered
with brown mycelium; the leaves turn yellow and
drop, the roots rot, and the plant dies.
Web Blight
and
Stem Canker
on alfalfa.
Damping-off
and
Bottom Rot
on Cichorum (endive, escarole and
witloof chicory) and Nicotiana.
Rhizoctonia tuliparum
Gray Bulb Rot
of tulips,
in northeastern and Pacific states. The most con-
spicuous sign of this disease is a bare patch in
▶
Damping-Off
,
for seedling rots.
Rhizina
Ascomycetes, Pezizales
Cup-shaped apothecia with rhizoids underneath;
asci operculate, opening with a lid, eight-spored;
spores fusoid, spindle-shaped, paraphyses present.
Rhizina undulata
Seedling Root Rot
,
Damping-Off
. Coniferous seedlings in the Pacific
Northwest are sometimes killed in isolated circular
patches 2 to 4 feet in diameter, particularly in
