interactions. Especially, although the morphology and anatomy of Cuscuta spp. are
well-studied, the cellular mechanisms of the interactions between parasitic plants and
their susceptible hosts are not well understood.
Cuscuta can serve as a key model plant for deciphering the mechanism of
parasitism as well as for examining host plant-parasite plant interactions [9]. Most
studies used isotope labels and observed carbon or nitrogen flux between Cuscuta
and the host plant [10, 11]. Some studies compared metabolites (e.g., plant hormones) in Cuscuta seedlings (haustorium-induced and/or non-induced seedlings)
with Cuscuta attached to host plants [12, 13]. Documented host plant responses to
attack by Cuscuta spp. include a hypersensitive-like response (HLR) and phytoalexin production by a non-host tropical liana in response to C. reflexa [14] and the
expression of a PR gene by Cuscuta-infested alfalfa [15]. Best studied among host
plant defenses against Cuscuta spp. are the responses of resistant tomato varieties to
C. reflexa, in which elongation of hypodermal host cells, a subsequent HLR, and
accumulation of phenolics and peroxidases at the attachment site create a mechanical
barrier that can block haustorial formation [16, 17].
Effective field dodder control is extremely difficult to achieve due to the nature of
attachment and close association between the host and the parasite, which requires a
highly effective and selective herbicide to destroy the parasite without damaging its
host. To establish strategies to control parasite growth and restrict the spread of field
dodder in crop fields, it is important to learn more about this pest, studying its life
cycle, development, and parasitic-host interactions.
2
Biology and Ecology Characters of Field Dodder
Autotrophic flowering plants constitute the predominant group among weed species,
but weeds also include some semiparasitic and parasitic flowering plants. The parasitic
plants are represented by approximately 4200 species classified in 274 genera, which
makes a little more than 1% of all flowering plants. Only some 11% of all genera
include species that may be considered as parasites of cultivated plants. The worst
economic damage in important host crops is caused by species from only four genera:
Cuscuta, Arceuthobium, Orobanche, and Striga [18]. The genus Cuscuta L. (dodders)
is one the most diverse and challenging groups of parasitic plants with more than
200 species and over 70 varieties [19–21]. The stem of a field dodder plant is threadlike
and twining, and it is either leafless or the leaves are reduced to hardly visible scales.
Fully matured field dodder seeds fall off and accumulate on the ground. They may then
either germinate during the following season if a suitable host plant is growing in the
vicinity or may stay dormant until such conditions have occurred [22]. These stem
parasites attach to the host by haustoria and depend entirely (or nearly so) on their hosts
for the necessary water and nutrient supplies [2, 23]. At an appropriate moment of
maturation, a field dodder plant forms inflorescences with abounding hermaphrodite
and actinomorphic flowers. The flowers are hermaphroditic, tiny, mostly white,
reddish, or yellow. Petals are either individual or coalescent. The corona is bellshaped or round, mostly with four or five petals (Picture 1a, b). The flower has
five stamens. The fruit is a pod containing one to four seeds. The seed is tiny,
5 Field Dodder: Life Cycle and Interaction with Host Plants
103
well-studied, the cellular mechanisms of the interactions between parasitic plants and
their susceptible hosts are not well understood.
Cuscuta can serve as a key model plant for deciphering the mechanism of
parasitism as well as for examining host plant-parasite plant interactions [9]. Most
studies used isotope labels and observed carbon or nitrogen flux between Cuscuta
and the host plant [10, 11]. Some studies compared metabolites (e.g., plant hormones) in Cuscuta seedlings (haustorium-induced and/or non-induced seedlings)
with Cuscuta attached to host plants [12, 13]. Documented host plant responses to
attack by Cuscuta spp. include a hypersensitive-like response (HLR) and phytoalexin production by a non-host tropical liana in response to C. reflexa [14] and the
expression of a PR gene by Cuscuta-infested alfalfa [15]. Best studied among host
plant defenses against Cuscuta spp. are the responses of resistant tomato varieties to
C. reflexa, in which elongation of hypodermal host cells, a subsequent HLR, and
accumulation of phenolics and peroxidases at the attachment site create a mechanical
barrier that can block haustorial formation [16, 17].
Effective field dodder control is extremely difficult to achieve due to the nature of
attachment and close association between the host and the parasite, which requires a
highly effective and selective herbicide to destroy the parasite without damaging its
host. To establish strategies to control parasite growth and restrict the spread of field
dodder in crop fields, it is important to learn more about this pest, studying its life
cycle, development, and parasitic-host interactions.
2
Biology and Ecology Characters of Field Dodder
Autotrophic flowering plants constitute the predominant group among weed species,
but weeds also include some semiparasitic and parasitic flowering plants. The parasitic
plants are represented by approximately 4200 species classified in 274 genera, which
makes a little more than 1% of all flowering plants. Only some 11% of all genera
include species that may be considered as parasites of cultivated plants. The worst
economic damage in important host crops is caused by species from only four genera:
Cuscuta, Arceuthobium, Orobanche, and Striga [18]. The genus Cuscuta L. (dodders)
is one the most diverse and challenging groups of parasitic plants with more than
200 species and over 70 varieties [19–21]. The stem of a field dodder plant is threadlike
and twining, and it is either leafless or the leaves are reduced to hardly visible scales.
Fully matured field dodder seeds fall off and accumulate on the ground. They may then
either germinate during the following season if a suitable host plant is growing in the
vicinity or may stay dormant until such conditions have occurred [22]. These stem
parasites attach to the host by haustoria and depend entirely (or nearly so) on their hosts
for the necessary water and nutrient supplies [2, 23]. At an appropriate moment of
maturation, a field dodder plant forms inflorescences with abounding hermaphrodite
and actinomorphic flowers. The flowers are hermaphroditic, tiny, mostly white,
reddish, or yellow. Petals are either individual or coalescent. The corona is bellshaped or round, mostly with four or five petals (Picture 1a, b). The flower has
five stamens. The fruit is a pod containing one to four seeds. The seed is tiny,
5 Field Dodder: Life Cycle and Interaction with Host Plants
103