Dodders (Cuscuta spp.) are holo-parasites, usually annuals, or perennials under certain conditions.
They are members of the morning glory family (Convolvulaceae) in old references that include
Cuscuta, Convolvulus and Ipomoea and of dodder family (Cuscutaceae) in the more recent
publications.
Cuscuta is a yellow or orange plant, twinged with purple or red color sometimes but generally
white. The stems can be very thin and thread like or relatively stout. However, all Cuscuta species
are herbaceous vines with twining, slender, pale stems, with reduced, scale-like leaves, and have
no roots. Plants have no or merely low amounts of chlorophyll, and usually do not have a
photosynthetic activity (Hibberd et al., 1998; Garcia et al., 2014) or may be placed as intermediate
between hemi- and holoparastic conditions (Nickrent and Muselman, 2004) hence some species
show residual photosynthesis (Dawson et al., 1994; Hibberd at al., 1998) and have thus been
designated as cryptically photosynthetic (Funk et al., 2007; McNeal et al., 2007a, b). All Cuscuta
species are fully dependent on host plants to complete their life cycle, and therefore regarded as
obligate holoparasites.
Cuscuta spp. are the most problematic parasitic weeds in agriculture in the semi-humid and semiarid areas of Africa and Asia (Sauberborn, 1994). They are nearly cosmopolitan, occurring in a
wide range of habitats and hosts with a high number of species in the Americas (Yuncker, 1932;
Hunziker, 1950; Mabberley, 1997; Stefanović et al., 2007). Their wide geographical distribution
and host range make them among the most damaging parasitic weeds worldover (Ashton and
Santana, 1976; Holm et al., 1997). Damage can ultimately lead to total destruction and death of
the host plants.
The genus Cuscuta comprises some 200 species (Costea, 2007), usually grouped in three
subgenera; Monogyna, Cuscuta and Grammica. Molecular studies on subgenera Grammica and
Cuscuta, delimit major clades within these groups. Differences in seed morphology between these
subgenera were reported. Seed exostructure features supported the subgeneric classification based
on exosomorpholigical (vague term) characters (Kim et al., 2000). However, the sequences used
were unalienable among subgenera, preventing the phylogenetic comparison across the genus
(García et al., 2014). A new phylogenetic classification proposed by Costea et al. (2015) placed
194 accepted species of Cuscuta into four subgenera and 18 sections. While only 10–15 of these
species are considered economically important pests (Parker and Riches, 1993; Costea, 2007),
their broad geographical distribution and host ranges contribute to impacts on a wide range of
agricultural cropping systems (Dawson et al. 1994; Costea and Tardif, 2006).
Cuscuta spp. are not host-specific, although they show a wide variation in their host ranges. Severe
infestations can stunt, smother and kill host plants, cause severe yield and stand reductions. The
worldwide plant species that are commonly parasitized by certain parasitic genera, including
Cuscuta spp. were thoroughly reviewed and documented (Qasem, 2006). Cuscuta spp. parasitize
many wild and cultivated plant species. They are destructive to certain high-value crops and
particularly troublesome where alfalfa, clover, and onion are grown for seeds (Ristau, 2001; Swift,
2001). Some species can parasitize a wide range of host of herbaceous and woody plants, while
others may be more host restricted (Qasem, 2006).
Cuscuta’s successful parasitism depends critically on efficient host-location mechanisms, as the
free-living seedlings of these vine-growing species (Lyshede, 1985; Koch et al.,2004; Furuhashi et
al., 2011) and, being obligate parasites, must rapidly make an attachment to a susceptible host
before exhausting their limited stored food (Lanini and Kogan, 2005; Costea and Tardif, 2006).Lyshede (1985) indicated that host plants less than about three weeks old seem not to be attacked
by Cuscuta seedlings.