Cuscuta japonica (Japanese dodder)

in the family Convolvulaceae, the CAB Thesaurus continues to use the Cronquist system which places it under Cuscutaceae.    Cuscuta japonica, with a single style falls in section Monogyna of the genus, which also includes the weedy species C. reflexa, C. monogyna and C. lupuliformis (Yuncker, 1932).

Flora of China (2009) lists two varieties var. formosana (Hayata) Yuncker, and var. japonica. It also refers to some possible confusion with C. engelmannii Krock in some localities in China. Otherwise C. japonica appears to be a well-recognised and well-defined species, free of nomenclatural uncertainties.

Cuscuta species have no specialized dispersal mechanism and movement is assumed to occur by wind and water.

The main biotic dispersal agent of C. japonica, both locally and internationally, is man, as seeds and vines are transported for use in medicinal herb products.

At the local level there may be accidental movement as a result of soil movement, and disposal of garden waste. At the international level, it has been suggested that some of the introductions to USA may have resulted from contamination of kudzu vine (Pueraria lobata) (Yuncker, 1965; O’Driscoll, 2003).

While some introductions into USA may have arisen from deliberate introduction of herbal products accidentally contaminated with whole viable seeds, most are thought to be the result of deliberate smuggling of vegetative material for medicinal purposes (Fred Hrusa, California Department of Food and Agriculture, USA, personal communication, 2009).

  Information on chromosome numbers has not been found, although it is probably a multiple of 14. C. lupulina has 2n = 28 (Flora of China, 2009).   Two varieties - var. formosana and var. japonica - are recognised in China and in Taiwan (Guo and Li, 2000a; Liao et al., 2000; Flora of China, 2009). Guo and Li (2000b) refer to ‘rich genetic variation’ in C. japonica in China. Hybrids are apparently rare or non-existent.  

  C. japonica reproduces both by seed and vegetatively. The flowering of Cuscuta species has been linked in different studies either to the flowering of the host, or, in C. reflexa particularly, to short days. In China, flowering occurs in August and fruiting in September, while in California it occurs very late in the season in the north of the state, suggesting that it is reacting to the shorter days of the autumn, but no specific study has been reported. Fortunately whether because of the late flowering or for lack of fertilization, seed set has not so far occurred in California (Tidwell, 2008). It has been confirmed that C. japonica is self-sterile (Tidwell, 2008) and the populations in California may be largely clonal. The presence of extra floral nectarines supports the assumption of insect pollination (Schaffner, 1980). Seed set does apparently occur in Texas and there is comment that a single plant can yield over 2000 seeds (Texas Invasives, 2007) with viability for 20 years (GBEP, 2006).   Vegetative spread occurs via the stems either naturally or deliberately by transfer of lengths of detached stem.   C. japonica can behave as an annual or, at least in California, as a perennial, readily surviving mild winters.  

  Cuscuta species are obligate parasites with negligible chlorophyll, totally dependent on attachment to a host plant within a short period after germination. Germination does not depend on the presence of host plants but occurs over a prolonged period as a proportion of hard-coated seeds gradually become permeable and allow absorption of water. This ensures that not too many seeds germinate at one time in the possible absence of a potential host plant. In many species, there is also an innate dormancy which is broken by chilling over the winter. There is a scarcity of information on the germination behaviour of C. japonica, but Lee (2007b) in his studies of the ultra-structure and development of the seedlings, used the standard procedure, for Cuscuta spp., of scarification by concentrated sulphuric acid to obtain germination for his studies, and it is assumed it is similar in its behaviour to other Cuscuta spp. On germination a very short root is formed which provides anchorage only, while the plumule elongates rapidly and, in the light, circumnutates widely anticlockwise until contact is made with a stem or other solid object. The length of the seedling rarely exceeds 10 cm and if a host is not located, the seedling dies. In most species the seedlings are not expected to survive more than a few days, but according to Camilli (2003) seedlings of C. japonica may survive for several weeks in the absence of a host. Once contact with a stem or other object is made, the shoot will twine around it, whether living or inanimate and the root and shoot base below this point will soon die. The anticlockwise coiling action requires blue or far-red light (Furuhashi et al., 1995) and is suppressed under red light or darkness. If a suitable host stem is found, several coils will develop, with pre-haustorial swellings on the inner face of the coiled stem, from which full haustoria develop in the presence of cytokinins, which derive partly from the parasite and partly from the host. Haustorial initiation may also involve calmodulin (Huang and Li, 1991). It also depends on blue or far-red light, with far-red being the much more effective (Furuhashi et al., 1995, 1997; Tada et al., 1996). Intrusive organs develop from the haustorium and searching hyphae penetrate the host tissues by a combination of separation and penetration of cells (these processes reviewed by Parker and Riches, 1993). Connections are then formed by a bridge of tracheids with the host xylem, while connection with the phloem via plasmodesmata between searching hyphae and host parenchyma cells has also been confirmed in C. odorata by Dorr (1987). Development of the tracheids and sieve tubes in C. japonica is described by Huang and Li (1987).Structure and development of the upper haustorium of C. japonica are also described by Lee (2007c). Once the haustorial connection is complete, new shoot buds develop close by, leading to the outgrowth of shoots which can elongate at a rate of 15 cm per day.   Although C. japonica stems normally show little sign of green-ness, there are well-developed chloroplasts: Lee KyuBae (2007d) and van der Kooij et al. (2005) have shown that there is a significant level of photosynthesis, comparable to, or greater than, that of C. reflexa. Chlorophyll content and photosynthetic activity are greatest in starved plants, e.g. in seedlings before attachment to the host, although the green colour is generally masked by the high levels of yellow carotenoids. This photosynthetic capacity clearly contributes to the unusual ability of seedlings (and stem fragments) of this species to survive for several weeks before attaching to a host.   Vegetative growth may continue for some time before any flowers are formed, or flowering may occur very rapidly. Flowering is thought by some authors to be linked to the flowering of the host plant but this is not apparently consistent.

The physiological effects of C. japonica on its hosts are discussed under Impacts.

  Most of the concern over this species as an invasive weed arises from its economic value as a herbal medicine and the deliberate introduction and propagation that this has encouraged in USA. Several Cuscuta species are used in Chinese herbal remedies under the term ‘Semen Cuscutae’ (or ‘tu si zi’ in Chinese). Li et al. (2000) state that Semen Cuscutae is originally specified as the dry ripe seed of C. chinensis in China Pharmacopoeia. However, a survey of the herb market showed that C. australis was the main source and C. japonica was also a source in some areas. Their paper further shows that the content of sesamin (a lignan with dietary fat-reduction potential) is highest in C. chinensis and not detectable in C. japonica. Content of sesamin was higher in stems than in seeds, and it appears that stems are frequently used as a source material as well as seeds. According to Du et al. (1998), the preferred species is C. chinensis but C. australis and C. japonica are now often used because of the ‘decline in the production capacity of C. chinensis’. Ye Min et al. (2002) however show that C. australis has a much higher flavonoid content than either C. chinensis or C. japonica and comment that ‘the quality of Semen Cuscutae can be evaluated according to the content of flavonoids’. The properties attributed to these ingredients include ‘replenishing the kidney essence or ‘jing’ in order to support healthy sexual and reproductive functioning’; ‘nourishing the liver and brightening the eyes’; indications include ‘Impotence, seminal emission, dripping of urine after urination, enuresis, frequent urination, aching and weakness of the loins and knees, blurred vision and tinnitus; threatened abortion due to deficiency of the kidney; diarrhea due to hypofunction of the spleen and the kidney; external use for vitiligo’. There is evidence to support claims for some of these effects. Qin et al. (2000) confirm that extracts from seeds of C. chinensis ‘invigorate the reproductive system and reproductive endocrine function in male rats’. Oh Hyuncheol et al. (2002) confirm that derivatives of a caffeoylquinic acid from C. japonica have activity in keeping with reputed antihypertensive action of ‘Cuscuta Semen’. Yang et al. (2006) show that an extract of C. japonica can significantly protect the human sperm from damage caused by reactive oxygen species. Many other studies involve treatment with a combination of Cuscuta extracts with other herbs, making it difficult to judge the value of the Cuscuta itself.   Extracts of C. japonica have shown anti-fungal activity against Alternaria mali (Kim et al., 1993).

C. japonica is widely valued in Asia for its medicinal benefits, and is likewise valued by some communities of Asian extraction in USA.           

It is doubtful that C. japonica can be said to provide any environmental service.

 

  Many countries include all Cuscuta species in their official lists of prohibited, quarantine species. Holm et al. (1997) indicate that 25 countries have declared Cuscuta spp. as noxious, and that the movement of Cuscuta-infested material is prohibited in every state of the USA.   Dry heat at 100°C for 15 minutes has been shown to selectively kill seeds of Cuscuta spp. in nigerseed (Guizotia abyssinica) (Strasser, 1988) providing a means of de-contaminating contaminated imports but this has not had to be applied to the problem of C. japonica.  

Successful eradication of C. japonica has been reported from some sites in USA. It is recorded that C. japonica was identified on the Clemson University site in South Carolina in 1971 (Invasive Plants of the Eastern United States, 2003). In 1991 it was decided to eradicate the infestation starting with removal of all C. japonica mats, then using herbicides glyphosate and dacthal to kill all host and parasitic vegetation within the infested site, followed by a controlled burn to fully destroy the vegetation and any seeds on the soil surface, fumigation with methyl bromide and sterilization with Vapam and Basamid granules.

 

  Methods for Cuscuta spp. in general include the use of clean seed.  

  Control of an established Cuscuta infestation may start with manual removal of the vegetative mass of the parasite from a woody host plant, or by mowing where it occurs on a herbaceous host. This may be followed by fire, before or after use of a herbicide. If there is evidence of germination from seed, the seedlings my need to be destroyed by repeated tillage.  

  Movement of Cuscuta material must be minimized by cleaning equipment leaving an infested site and by controlling the movement of domestic animals.  

 Melanagromyza cuscutae and the gall-forming weevils Smicronyx spp. have been tested for control of other Cuscuta spp. Similarly the fungi Alternaria cuscutacidae and Colletotrichum gloeosporioides have shown promise in some situations but none have proved reliable enough for use in practice. On C. japonica, a number of fungi have been studied for their potential as biocontrol agents, including Fusarium solani, F. semitectum, Pestalotiopsis guepini [Pestalotia guepinii] and Alternaria tenuis, but they have not yet been fully developed for use (Guo et al., 1998; Guo and Li, 2000).  

  Literature on C. japonica in USA refers to the use of pre- and post-emergence herbicides but few specific compounds are named. In the case of pre-emergence herbicides, trifluralin is mentioned by GBEP (2006) and others could include pendimethalin which is used successfully in legume crops for control of other Cuscuta spp. including C. campestris; and perhaps imidazolinone herbicides including imazaquin. Post-emergence, glyphosate, glufosinate and dacthal have all been used effectively. Herbicides may also be injected into the trunks of infested trees, to kill both parasite and host to prevent spread when trees are felled and utilized (Texas Invasives, 2007).  

  There is no evidence for host varietal resistance to C. japonica.  

Detection of C. japonica in USA has involved visual inspection of imported herbal products and germination studies to check for viable seed. In the field it has been detected by surveys of residential neighbourhoods, concentrating on those known to have Asian immigrant populations. Aerial surveys are being considered (Tidwell, 2008).