Biology Reference
In-Depth Information
Dodder
Dodders are seed plants parasitic on stems and
other parts of cultivated or wild plants. They are
leafless, orange to yellow twining vines, without
chlorophyll and hence incapable of manufactur-
ing their own food. They are called love vine,
strangle weed, gold thread, hairweed, devil's
hair, devil's ringlet, pull down, clover silk, and
hell-bind, the last being most appropriate. There
are about 40 species in the United States, causing
serious agricultural losses in clovers, alfalfa, and
flax, and becoming more and more important in
gardens on ornamentals and sometimes vegeta-
bles. Dodders belong to the single genus Cuscuta ,
family Cuscutaceae, close to the morning-glory
family.
Dodder seed is grayish to reddish brown,
resembling small legume seed but roughened
with three flattened sides. It germinates as ordi-
nary seed but is synchronized to start a little later
than its host seedlings. The parasite is a slender,
yellowish, unbranched thread with the growing
tip circling around in search of support. When it
touches the host it twines like a morning-glory
and puts out little suckers, haustoria, into the
stem of the victim, after which its original
connection with the soil dries up (see Fig. 1 ).
Although seedlings can live for a few weeks
without a susceptible host, they finally die if
a connection is not established. Successful para-
sites continue to twine and to spread orange ten-
drils from one plant to the next, often making
a tangle of matted orange hairs many feet across,
with a black region in the center where plants
have died. Such tangles are conspicuous in
weeds along roadsides.
In ornamental plantings host plants are not
often killed but exhibit stunting and pallor, symp-
toms of starvation. Minute scales or rudimentary
leaves form on the dodder tendrils followed by
dense clusters of beautiful white blossoms (some-
times pale pink or yellow), which ripen seed in
late summer, with as many as 3000 seed being
produced on a single plant.
Cuscuta spp. Much of the dodder infesting
ornamentals is not readily identified as to spe-
cies, but it is widespread on a great many shrubs,
perennials and annuals. It is found very com-
monlyonchrysanthemum,alsostranglingany
other plant in the vicinity. Many hours may be
spent cleaning up ivy and trumpet-vine, petunias
and asters. Dodder is reported on camellias in
the South. It is even a pest of house plants, if
field soil has been used for the potting mixture.
Dodder has, however, one virtue for plant
pathologists. It is used as a bridge between
plants to carry viruses and MLOs in testing
their host range.
Cuscuta americana on citrus C. californica
on beet.
Cuscuta
coryli
Hazel
Dodder .
C.
epithymum. Clover Dodder on legumes.
Cuscuta exaltata on redbud, ilex, and sumac.
Cuscuta gronovii Common Dodder on but-
tonbush, cucumber, raspberry, members of the
potato family, and many garden ornamentals,
including hedge plants.
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