Angiospermic parasites

Dendrophthoe falcata (mistletoe)

Distribution

Dendrophthoe falcata (L.f.) Ettingsh (= Loranthus falcatus L.f.) is commonly known as Indian mistletoe, Giant Mistletoe, Honey Suckle Mistletoe and Showy Mistletoe. It belongs to the family Loranthaceae. The plant is indigenous to the tropical regions of the world including, India, Sri Lanka, Bangladesh, Malaysia, Myanmar, Thailand, China, Australia, New Zealand, South America and Africa.
Dendrophthoe falcata
Dendrophthoe falcata growing on mango tree. Pointed leaves are of mango tree serving as host whereas, ovate leaves and inflorescence are of mistletoe growing on host.

Dendrophthoe comprises of about 30 species, of which, about 7 species are reported from Indian subcontinent. In Indian Ayurvedic System of Medicine, Dendrophthoe falcata is mentioned as “Vanda”.


Habit and habitat

Dendrophthoe falcata is partial stem-parasite (=hemiparasite) growing on the on wide host range of angiosperms as well as gymnosperms including mango, guava, neem, teak, arjun, fig, Indian bael, etc. The plant body is bushy shrub with woody dichotomously branched stem. Stem is glabrous with grey-smooth bark. Leaves are thick, opposite, ovate to oblanceolate, entire with prominent midrib. Young leaves are violet to pink colored.

Flowers

Flowers are born in axillary to supra-axillary, unilateral spikes. Depending upon the variety, flowers are whitish-yellow, yellowish-red, pink, orange or orange-red colored. In Indian subcontinent, Dendrophthoe falcata var. falcata (honeysuckle mistletoe) bear white flowers, whereas, Dendrophthoe falcata var. coccinea (red honeysuckle mistletoe) bears red flowers.


Host-parasite interaction

Dendrophthoe falcata is an obligate (dependent throughout the life cycle) hemi-parasite of xylem only. The plant is photsynthetic and produce their own photosynthates. It is dependent upon the host plants for the water and nutrients, which is abosrobed by the haustoria, which unites the xylem of both the host and parasite in the wounded regions.
Plants parasitized by few number of mistletoes are less likely to be affected. However, the tree carrying the Dendrophthoe falcata in large number show reduced growth of the branches. In severe cases it can kill the host plant in a decades or more.

Sources

  • Subhashini K, Kumar PKR and Gaddeyya G (2019) A comprehensive review on Dendrophthoe falcata (L.f.) Ettingsh. (Loranthaceae). Tropical Plant Research 6(3): 514–520. (https://doi.org/10.22271/tpr.2019.v6.i3.064).



Cuscuta reflexa (Amarbel)

Distribution

Cuscuta (dodder) commonly known as, Amarbel, Akashbel, Amarvalli, Swarnlata in India. Dodders are comprising of about 180 species (Sharma and Kapoor, 2014) and are distributed throughout the temperate to the tropical regions of the world.  Cuscuta reflexa is of common occurrence in India. It parasitizes a number of host plants including Anacardium occidentale, Bougainvillea spectabilis, Brassica campestris, Camellia sinensis, Casuarina equisetifolia, Cleodendrum inerme, Dolichos lablab, Litchi sinensis, Medicago sativa, Tabebuia argentea, Thevetia peruviana, Ziziphus mauritiana, etc. It is an obligate stem holoparasite, belonging to family Cuscutaceae.

Biology

Cuscuta
Cuscuta reflexa (Amarbel)

Dodders are rootless, leafless, annual or perennial plant. Cuscuta probably produces roots followed by seed germination. If finds a host, it parasitizes, otherwise, become dead. Dodder is non-host specific and grows twining over other plants. Dodder is touch-sensitive, which does not discriminate between living plant stems and non-living sticks. Dodder penetrates the host through the haustoria, become associated to the vascular bundle. As haustoria are developed inside the host plants roots are degenerated. The haustoria are extracellular and draw water and carbon and other nutrients from the host throughout its life cycle. Sometimes, viruses are transferred from the host plants through these haustoria (Sharma and Kapoor, 2014).
Dodder flowers in early summer. The flowers are bisexual, self-fertile, white, yellow to cream color. Flowers are pollinated by insects. Water, animals and man help in seed dispersal over longer distances.

The chlorophyllous nature of Cuscuta is the subject of debate. The plants lack chlorophyll, or found only in a reduced amount and are not usually photosynthetically active (Kaiser et al., 2015). In yellow-green appearing parts carotenoids are dominating the chlorophyll (Sharma and Kapoor, 2014).

Annual loss

The infestation of crops by dodder resulted in 23-100 % loss in total yield. In sever infection host are killed.

Control measures

As none of the methods can totally control the infection, prevention is the only effective measure to get rid of dodder up to some extent.
  • Crop rotation with non-host plant reduces the infection.
  • Delaying in planting until fall control the infection.
  • Use of resistant varieties is also recommended.
  • Application of herbicides is also effective.

References:

  • Kaiser, B., Vogg, G., F├╝rst, U.B. and Albert, M., 2015. Parasitic plants of the genus Cuscuta and their interaction with susceptible and resistant host plants. Frontiers in plant science6, p.45.
  • Sharma, Y.P. and Kapoor, V., Parasitic angiosperms and biology of Cuscuta species–an overview.



Orobanche (Broomrape)

Orobanche (broom-rape) is achlorophyllous total root-parasite. It absorbs nutrition from the host roots by means of haustoria. Orobanche is a flowering plant with about 200 species belonging to dicot family Orobanchaceae. Different species of Orobanche parasitize tobacco, tomato, eggplant, potato, cabbage, coleus, bell pepper, sunflower, celery, beans and mustard. It is commonly known as 'Tokra' in north India, 'vakumba' in Gujarat, 'bambaku' in Maharashtra, 'pokayilaikalan' in Tamil Nadu, 'bodu' or 'malle' in Andhra Pradesh. In the district Maharajganj of Uttar Pradesh, it exclusively parasitizes  mustard plants, which can easily be seen during the winters season (Rabi crop). Infection of Orobanche causes moderate loss in annual yield, but continuous infection in the suitable host makes the soil sick.

Orobanche
Orobanche a total parasite growing on the root of mustard.

Control measures

  • Infection can be managed by removal of vegetative plants before seed setting occurs for 2 to 3  consecutive years.
  • Infection of Orobanche can be reduced by crop rotation. Orobanche never parasitizes the plants like wheat and coriander. Crop rotation with these non-host plants for 2 to 3 seasons is best measure to get rid of Orobanche (personal observation during 2015-20).