PhD

Hemiparasitic plants belonging to the family Loranthaceae are major tree
parasites. Dendrophthoe falcata, Helicanthus elastica, Macrosolen capitellatus are
major hemiparasites infecting perennial crops of the tropics. Helixanthera
wallichiana and Taxillus tomentosus are two important hemiparasites infecting the
fruit and timber trees of the high ranges. Apart from being a troublesome parasite
they also serve as a linchpin reservoir supporting an extensive ecosystem. The
prevailing investigation namely “Physiological and molecular studies on genera of
Loranthaceae and their management” was carried out at Department of Plant
Physiology, College of Agriculture, Vellanikkara, Thrissur, during the period from
2015 to 2020.
Morphological characters of representative species viz., Dendrophthoe falcata,
Helicanthus elastica, Macrosolen capitellatus, Helixanthera wallichiana and Taxillus
tomentosus from five selected. Samples of these were collected from various
locations from the plains and highranges of Thrissur. In all the selected species,
leaves were oppositely arranged, D. falcata and H. elastica had oblong shaped leaves,
leaves of M. capitellatus was lanceolate in shape, and H. wallichiana and T.
tomentosus had narrow ovate shaped leaves. Fruit was berry in all the genera.
Hemiparasites possess a physiological structure called haustoria through which they
abstract water and minerals from the host. Haustorial branching pattern in all the
genera was found to be basal epicortical root (ber). Haustorial portions of the
collected samples were treated and prepared to permanent slides. Anatomical sections
of the haustoria of the five selected genera of Loranthaceae revealed that there exists
a transition zone between the host- parasite interphase region. This was observed as
undifferentiated parenchymatous cells which aid in translocation of molecules.
Presence of xylem elements were observed at the haustorial region. Haustorial
anatomy of M. capitellatus was unique as there was complete merging of cells of host
and parasite at the interphase region.
The lineage of five selected genera belonging to Loranthaceae family were
studied by molecular assay. The results from the ISSR assay revealed that, T.
tomentosus and M. capitellatus had maximum similarity compared to all the other
genera, since it formed a separate cluster. Morphological characterization indicated
similarity between the two genera in the haustorial attachment pattern. Both the
species have a single point of attachment to the host. H. wallichiana was observed to
be more similar to the first cluster. D. falcata formed another branch close to H.
wallichiana, where all these four genera formed the main group. H. elastica formed a
separate lone group, which indicated genetical variance from other genera studied.
Morphological observations supporting such a uniqueness in this parasite was noted
in haustorial branching type, where basal epicortical root with lateral tendril like
structures from nodes and internodes were observed. The parasite also showed other
phylogenetically advanced characters according to Angiosperm Phylogeny Group
(APG system) of classification like fused corolla and calyx.
To study the host parasite interaction, root feeding studies with labelled 32P
were undertaken. Cocoa plants infected with both parasites D. falcata and H. elastica
was selected for the study. 32P in carrier solution of 1000ppm orthophosphoric acid @
2 mCi per plant was fed to the surface running roots of cocoa. Leaf samples of the
host and parasite were collected at 7 and 14 days after treatment and assayed for radio
activity. To understand the translocation from parasite to host, leaves of the parasitic
species both D. falcate and H. elastica were also smeared with labelled 32P and leaf
samples were analysed from different parts of both the host and the parasite. These
experiments were done on different trees. Leaf samples of the host and parasite were
collected at 2, 7 and 14 DAT and assayed for radio activity. Results from the radio
assay indicated that there is bidirectional movement of nutrients from host to parasite
and parasite to host. There exists a prioritized partitioning pattern for nutrient
transport (phosphorous) based on demand by the sink, regardless of the parent plant.
The host and parasite were found to act as a single system indicating their coexistence.
Physiological parameters of the host and parasites were also observed using InfraRed Gas Analyser (IRGA) for a period of six months. It was observed that stomatal
conductivity of D. falcata and H. elastica was significantly higher than the host
cocoa. Even though there was no much variation in the photosynthetically active
radiation (PAR) received by the host and parasite during the period of observation, D.
falcata and H. elastica had significantly higher rate of photosynthesis than cocoa.
Transpiration rate of both parasites were significantly higher than their host.
Carboxylation efficiency and light use efficiency of H. elastica were observed to be
significantly higher than the host, cocoa.
Field experiment was conducted to improve the management strategy and control
the spread of the parasite. Use of surfactant was found to improve the efficacy of
ethephon in controlling the regrowth of parasite on host plant. Non- ionic surfactants
viz., Nonyl phenol ethoxylate (NPE) and Organosilicone (OS) were selected for the
study. A combination of OS (0.5 ml/L) surfactant with ethephon (25ml/L) was
successful in suppressing the regrowth of both D. falcata and H. elastica.