An ongoing research since October 2017 until April 2017 is being
conducted in USM main campus and Bukit Dumbar regarding the relationship
between host and parasitic plants. From the research, few parasitic plants were
found comprising of 2 families. They are Cassytha filiformis from
Lauraceae, and a species from Loranthaceae which is Loranthus globossus.
Urban forest is a forest or a large
area of land covered or filled with trees and undergrowth that grow within city
or town. All the trees can be vary in species and each of them play a vital
role in our ecosystem. A lot of species can be found in the forest and they can
be woody plants, shrubs, and many more. Plants also can have some sort of
interactions either it is interaction between animal and plant or the
interaction between plant and plant. An example between plant and plant
interaction is the interaction between host and its parasitic plant.
A parasitic plant is a plant that
living on other plant (host) in order to obtain nutritional requirements and
extract water from the host plant. The special characteristic of parasitic
plant is the haustorium. Haustorium is a parasite-encoded organ or modified
root which helps the parasitic plant to attach and invade the host plant. There
are basically two types of parasites which are holoparasite and hemiparasite.
Holoparasite plants such as Rafflesia, usually depend on the host plant to
survive as they are lacking in chlorophyll content. Hemiparasites on the other
hand, contain chlorophyll which make them able to carry out photosynthesis and
do not depend entirely on the host plant to survive, but somehow can be
dependent to the host plant to some point of degree. Hemiparasites can be
divided into two groups which are obligatory parasite and facultative parasite.
Without the host plant, obligatory parasite could not complete its life cycle
as opposed to facultative parasite as it can complete its life cycle even
without the host plant.
Other than that, there are also some
other types of parasitic plants that can be found such as stem parasite and
root parasite. Stem parasites such as dodder plant (Cuscuta sp.), is a
parasite that attaches to the host’s stem while root parasite mainly target,
attack and attach to the root of the host. About 150 species from the genus Orobanche
are root parasites.
Kuijt (1969) suggested that
haustorium is a special organ that can be found in all parasitic plants. This
organ of plant is important for the parasitic plants as it somehow connects
them to the host plant. Based on Press, 1995; Graves, 1995, haustorium also
helps the plants to penetrate to the stem or root of the host, taking all the
materials needed from the host such as nutrients, and water for survival.
Meanwhile, according to Gaertner, 1950, haustorium has the capability to help
parasitic plants to complete their life cycle through physiological and
The appearance of haustoria are also
differ in each family such as Loranthaceae, Lauraceae, Scrophulariaceae, and
Viscaceae. For example, in Viscaceae, the primary haustorium grows vertically
through the host tissue. Cortical strands develop which are orientated parallel
to the surface. According to Salle, 1978, the cortical strands retain their
mitotic activity throughout the year, as opposed to the primary haustorium. It
is also suggested that the rise of secondary haustoria and aerial shoots are
due to the cortical strands. However, for Cuscuta sp. or also known as
dodder, before the formation of true haustoria, it is suggested that this
species tends to form an ephemeral organ or “prehaustoria”. (Peruse,
19893), but not to Kuijt (1969), as those feature (prehaustoria) may not be a
general feature. Besides that, there will be several changes of the haustorium
as it invades the host body (Thomson, 1925, Bennett, 1944 and Truscott, 1958).
One of the factor that may give an influence to the organization and
differentiation of dodder haustoria is the host species invaded (Kuijt, 1969).
Loranthaceae on the other hand, the secondary
roots or also known as epicortical roots are formed from the base of the plant
or from branches which then producing secondary haustoria at irregular
intervals (Kuijt, 1969). It is suggested that the epicortical roots expression
is affected by the host species. Besides that, the physiological interaction of
the parasitic plants with the host also somehow affect the growth of
epicortical roots can either be promoted or inhibited in Loranthaceae.
The life cycle of
parasitic plants can be divided into 3 stages The first stage is when the
seedlings independently germinates, develops and its attachment to the host
plant happened to occur. Several factors such as temperature, oxygen, light
intensity and water play a key role for the well-growth of the seeds. The
second stage is called intrusive developmental phase. During this stage, the terminal
haustorium at the tip of the radicle develops. Next, the haustorium will invade
the host tissue and conductive connections with the host begins. Finally, the
compatible phase. This phase explained how the haustorium develops based on its
ability to overcome host resistance mechanisms and to compete with host organs for
The growth of parasitic
plants are influenced by the agent that helps in dispersing them. According to
Dawson and Lucas (2005), it shows that some parasitic plants from Loranthaceae
in Australia and Asia are dispersed by birds from the genus Dicaeum. In Africa,
birds from Nectariniidae family are said to be the pollinators for the parasitic
plants. These birds are attracted by the colourful flowers of the parasitic
plants which then happened to initiate the growth of parasitic plants. Other
than that, some of the parasites from Loranthaceae are also dispersed by
insects that live in the aerial root of the plant by attacking or invading the
plant tissue. (Kuijt, 1964).
It is expected that more species of parasites can be found in USM
main campus and Bukit Dumbar. Humidity and light intensity might give impacts
on the growth on parasite on the host plant. The growth of parasitic plant is
related to the agent that helps in dispersing the seed of the parasitic plant.
More parasitic plants can be found and identified in the research
site as they may not be too “selective” in choosing and growing on
any host plant as long as they can survive by robbing all the nutrients that
they need from the host plant. Also, light intensity may be one of the factor
that contributes to the growth of many parasitic plants as they usually are
found on the top layer of tree canopy in order for them to carry out
photosynthesis. An agent like birds help in dispersing the seed of the
parasitic plants. For example, some parasitic plants produce fruits and they
will be eaten by the birds and then it will be released into other places in
the bird’s droppings. Since parasitic plants tend to give few problems to the
forest ecosystem, the growth of these parasites must be controlled so that we
can maintain a good environment for all living organisms. For example, it is
suggested that, by using diesel with DNBP (4,6-dinitro-O-sec-butylphenol), and
PCP (pentachlorophenol) or 2,4-D on certain parasitic plants, the growth of
parasitic plants can be reduced.
As for now, two species of parasitic plants were found and it is
believed that many other species will be found and recorded for this research.
As we know, most of parasitic plants do give an impact to the host plant by
slowly causing the host plant to die. In order to minimize the growth of these
parasitic plants, a lot of efforts need to be done. One of them is by
controlling the growth of the parasitic plants by pruning the infected area
consistently before the condition is getting worse.