ABSTRACT
Mistletoes are hemiparasitic plants found on many tree crops of economic importance, and are generally divided into two major families – the Loranthaceae and Viscaceae. The Loranthaceae constitute the largest group with about 950 species divided into 77 genera, and are distributed widely throughout Europe, the America, Africa, Asia and Australasia. Few studies have been conducted on Mistletoes in the past, South-Eastern Nigeria is still lacking in the literature of studies on Mistletoes, and it is not well known how Mistletoes affect the forest ecosystems within this region. This study therefore explored the Phenology, Host Range and Patterns of Infestation of Mistletoes in South-Eastern Nigeria. The study determined host range, phenology as well as severity level of Mistletoe infection on host tree species. Four species of mistletoe, Loranthus micranthus, Tapinanthus bangwensis, Phragmanthera capitata and Viscum triflorum were found across the sites with L. micranthus being the most frequently occurring and most abundant species. Host infestation ranged from 13.33% - 66.66%. The Phenology of two of the parasites was studied from flower formation through to fruiting. A disease severity index was developed and used to evaluate the severity of infection of hosts across the sites.
Results of this study revealed that Mistletoes could parasitize a variety of tree species with few of them having host-specificity. Flowering of Mistletoes occur in both rainy and dry seasons with peaks around May.
The severity indices recorded were 19.8%, 9.6% and 9.2% for Abia State, Imo State and Ebonyi State respectively, indicating most severity levels in Abia State. Majority of the infections were recent thus supporting the observation that infection rates across the study area are progressive.
Further studies that will enable a better understanding of the ecology, biology and damages caused on the host by these parasitic plants in order to reduce the severity of infestation on forest ecosystems in South-Eastern Nigeria are recommended.
TABLE OF CONTENTS
Cover Page i
Title Page ii
Declaration iii
Dedication iv
Certification v
Acknowledgement vi
Table
of Contents vii
List
of Tables
List
of Plates
List
of Figures
Abstract
CHAPTER ONE
1.0 INTRODUCTION 1
1.1 Background of the study 1
1.2 Statement of Problems 5
1.3 Objectives 5
1.4 Justification 6
CHAPTER
TWO
2.0 LITERATURE REVIEW 7
2.1 Classification, Composition and
Distribution 7
2.2 Life History 9
2.3 Spread, Pollination and Germination of
Mistletoes 9
2.4 Relationship with the Host Plants 11
2.5 Host Range of Mistletoes 12
2.6 Phenology of mistletoes 13
2.7 Morpho-Physiological effects on Host Plants 13
2.8 Ecological and Economic Importance of
Mistletoes 15
2.8.1 Mistletoes as Wildlife Habitat 16
2.8.2 Mistletoes as Medicinal Plants 17
2.8.3 Mistletoes as food 18
CHAPTER
THREE
3.0 MATERIALS AND METHODS 19
3.1 Study Area 19
3.2 Population of the study and Sampling
procedure 20
3.3 Method of field investigation 21
3.4 Data Analysis 22
CHAPTER
FOUR
4.0 RESULTS AND DISCUSSION 23
4.1 Host Range 23
4.2 Phenology in relation to seasons of the
year 33
4.2.1 Flower Opening 34
4.3 Severity of Infestation on Hosts 46
CHAPTER
FIVE
5.1 CONCLUSION
AND RECOMMENDATIONS 51
5.2 Conclusion 51
5.3 Recommendations 52
LIST OF TABLES
Table
1 Description of the population of
the study 20
Table
2 Families of Mistletoe found
across the sites 24
Table 3 List
of Plant species encountered at the Moist
Forest Research Station,
Umuahia. 26
Table 4 List
of Plant species encountered at the Imo State
Polytechnic Botanical
Garden. 28
Table 5 List
of Plant species encountered at the Federal College
of Agriculture, Ishiagu. 29
Table
6 Summary of observations on host
range across the study sites. 33
Table
7 Summary of observations on
mistletoe phenology. 45
Table
8 Class of infection across study
sites. 46
Table 9 Percentage
incidence and severity index of mistletoe
infestation across the study sites. 50
LIST OF PLATES
Plate
1: Citrus tangerina with P.
capitata infection 31
Plate 2: Corolla tube splitting during flower opening in P. capitata 35
Plate 3: Fully opened
flowers in P.
capitata 37
Plate 4: Flowering in
L. micranthus 38
Plate 5: Flowering in
T. bangwensis 39
Plate 6: T. bangwensis showing a dead flower and
black ants 41
Plate 7: P. capitata
showing styles, filaments and anthers. 43
Plate 8: Cluster
of fruits in T. bangwensis 44
Plate 9: T. bangwensis infection on T. ivorensis with reduced host branches 47
Plate 10a: Withered
branches of Citrus spp 48
Plate 10b: Defoliated
branches of T. grandis with L. micranthus
infection 49
LIST OF FIGURES
Figure 1: Map of Nigeria
showing Eco-climatic zones of Nigeria and study areas 19
CHAPTER 1
INTRODUCTION
1.1
BACKGROUND
OF THE STUDY
Forest
trees in various ecological locations occasionally experience certain stress
factors in their growth and establishment. One of such stresses stem from the
fact that parasites find forest trees as potent and viable hosts for their
parasitic activities which in addition to their impacts on the host have
notable effects on the ecosystems in which they are found. Taxonomically, these
parasitic plants are a diverse group of flowering plants found in major biomes
and are represented by almost 4000 species (Gareth, 2005). The angiosperms
became parasitic by losing their autotrophism during their evolution
(Raynal-Roques & Pare, 1998; Salle et al; 1998. These parasitic angiosperms find their way
into the tissues of their host through penetration (Noutcheu et al; 2013) and
interfere with the tree’s normal development and existence (Smith, 1970; Berner
et al., 1994; Boyle, 1994). Smith
(1970) classified these stress factors into those that cause injury and those
that cause diseases. Generally, abiotic stress factors are those that cause
injury, while biotic stress factors are those that cause diseases.
A
parasitic plant is described by a free encyclopedia, Wikipedia as one that
derives some or all of its nutritional requirements from another living plant.
There are modified organs in all parasitic plants, named sucker or haustoria
(one: haustorium) that represent a permanent structural and physiological
bridge that connect them to the xylem, the phloem or both by penetrating the
host plants. With this ability, water and nutrients are extracted from the
host. Parasitic plants can be grouped into 3000 species belonging to 18
families (Atsatt, 1983) are characterized as follows:
i) Obligate
parasites – these are parasites that do not complete their life cycle without a
host.
ii) Facultative
parasites – these parasites can complete their life cycle without depending on a
host.
iii) Stem/Epiphytic
parasites – as the name implies, the host stem is where these parasites are
attached.
iv) Root/Epirhizal
parasites – these are attached to the roots of the host.
v) Hemi-parasite
– these are parasites that, to some extent, are photosynthetic but parasitic
under certain natural conditions/factors. Water and mineral nutrients are
usually extracted from the host plant by these hemi-parasites. However, some
parts or fraction of the organic nutrients required by the parasites are as
well obtained from the host.
vi) Holo-parasite
– all of the fixed carbon required are obtained from the host by these
parasites.
According
to Visser (1981), the parasitic epiphytes and epirhizes are classified
according to their level of fixation while the hemi-parasites and
holo-parasites are based on the nutritive exigencies of the parasites (Noutcheu
et al; 2013). Raynal-Roques and Pare (1998) reported that about 64% of
parasitic species are epirhizes and only 36% are epiphytes.
Pennings
and Callaway (2002), asserted that host performance is often reduced severely
due to parasitism, and this results in variations in competitive interactions
between non-host plants and host, and diverse effects on the structure of the
community, species diversity, cycling of vegetation and zonation. Mistletoes
are therefore, obligate epiphytic hemi-parasites. Mistletoes, with such common
names as – devil’s fuge ,bird lime, all heal, , Iscador, from the above
represent a general term for woody-shoot parasites in different plant families,
particularly Loranthaceae and Viscaceae (Parker and Riches, 1993;
Polhill and Wiens, 1998); and majority of the genera of African mistletoes are
found in the family – Loranthaceae (Polhill and Wiens, 1998).
Nickrent (2001) described mistletoes as polyphyletic group of angiosperms made
of over 1,300 species from different habitats across all the continents in the
world. Similarly, Gill (1953) described the mistletoes as the most widespread
and most destructive woody, chlorophyllous, epiphytic hemi-parasites in the
tropical regions of the world. They are evergreen flowering (angiosperm)
plants, parasitic only on perennial spermatophytes (seed plants) i.e. they
occur on gymnosperms (Baker et al.,
1992) and angiosperms alike.
The
mistletoes are generally divided into two major families. These are the Loranthaceae and Viscaceae (Kuijt, 1969; Parker and Riches, 1993).
The
Loranthaceae and Viscaceae are vastly studied and enjoy a worldwide distribution,
comprising most (>98%) of mistletoe species:
with an estimation of 940 and 350 species respectively (Watson and
Dallwitz, 1992; Nickrent, 2001). Supporting this view, Engone and Salle, (2006)
reported that the Loranthaceae constitute the largest group with about 950
species divided into 77 genera. Barlow (1996) described Loranthaceae and Viscaceae
as being presently distributed widely, ranging from boreal climates to
tropical, temperate, and arid zones throughout Africa, Asia, Europe, the
Americas, and Australasia (but not found in Tasmania), They are not found in
extremely dry or cold regions. However, certain Loranthaceae reduce to a large
extent, the yield of the host plants. Also affected is the quality of harvest
in ornamental plants, orchards, plantations, and natural forests across the
world (Sonke et al., 2000).
According
to Burkill (1985), mistletoe is the group term used for all the species in the
seven genera of the family Loranthaceae (Phragmanthera, Tapinanthus, Globimetula, ,
Berhautia, Agelanthus, Helixanthera
and Englerina) and dozens of other species that are recognized in West
Africa.
Similarly,
Omolaya and Famaye (1998) stated that six genera of the family Loranthaceae are known to occur and they
include: Tapinanthus, Loranthus,
Agelanthus, Globimetula, Phragmanthera and Englerina. Tapinanthus is the most investigated genus of all
Mistletoes in Nigeria and Ghana compared to the others (Wood, 1975). This is
probably because the genus appears to be the commonest occurring Mistletoe in
these two countries.
Diverse
tree crops of high economic importance like the citrus species, particularly
sweet orange (Citrus sinensis), and
Citrus grape fruit (Citrus paradisi),
shea butter tree (Vitellaria paradoxa),
cocoa (Theobroma cacao), the neem tree (Azadirachta indica L.), and rubber play host to mistletoes (Hevea brasiliensis Muell Arg.) (Bright
and Okusanya, 1998; Overfield et al.,
1998; Gill and Onyibe, 1990; Begho et al.,
2007) in West Africa. Different species of mistletoes have also been observed
growing on medicinal and cultivated trees like the Kola-nut tree (Cola nitida Vent. Schot and Endl.).
Also, forest trees such as the sand paper tree (Ficus exasperata Vahl), teak (Tectona
grandis L.f) and Terminalia species
are not left out in mistletoe infestation.
In
any ecosystem or community, the flowering and fruiting periods are determined
by the phenology of trees and this is indirectly dependent on the variations in
environmental factors. (Rivera et al., 2002; Hamann, 2004; Zhang et al., 2006).
Therefore, the understanding of mistletoe phenology would aid in clarifying the
period of their fruit and seed availability, which is a useful information in
managing mistletoe populations (Noutcheu et al., 2013).
1.2
STATEMENT
OF PROBLEM
Mistletoes
are hemi-parasitic plants that are diverse and are distributed worldwide.
Infestation of trees by parasitic plants costs more, because parasites normally
decrease growth, fruit production as well as increase tree mortality. The
hemi-parasitic plants of which Mistletoe is one do not enjoy wide research
interest like other parasitic forms and hence there is near paucity of
documented research on the biology of the above parasite especially taxonomy,
host/plant relationship, and physiological characteristics (Simeon et al., 2013).
Vast
majority of studies have included Mistletoes to be important in the structure
and functioning of forest and woodland communities. Given that a few studies
might have been carried out on Mistletoes in the past, South-East Nigeria is
still lacking in the literature of studies on mistletoes. Tropical regions,
especially the Afro-tropics are particularly not well represented in the
literature of Mistletoes. It is not certain if Mistletoe will be essential in
structuring these highly diverse ecosystems as in less diverse temperate areas.
Again, it is not well known how Mistletoes affect diversity patterns of
different groups within the same habitat (Watson, 2001).
1.3
OBJECTIVES
OF THE STUDY
The
major objective of this study was to explore the phenology, host range and
patterns of infestation of Mistletoes in South - Eastern Nigeria through the
following specific objectives:
i) to determine the host range of the various
species of Mistletoe that occur in the study area;
ii) to
describe the phenology of the parasite in relation to seasons of the year;
iii) to estimate
the severity of infestation of hosts by the parasite
1.4
JUSTIFICATION
The
protection of essential biological resource, provision of new and improved
genome, biotechnological improvement of agricultural and forestry sub-sectors
could depend to an extent on research into some neglected species which have
alternative development significance. Large-scale protection of landscapes from
adverse parasitic influences would only be possible if the relationship between
a host and a given parasite is studied and understood. This could translate
into saving of important resource as well as guarantee sustained forest
services and livelihood improvement to populations. It is hoped, therefore,
that information from this study will provide a very good kowledge of the
phenology, host range and patterns of infestation of Mistletoe and how it
affects the ecosystem in the rainforest area of South-East Nigeria, while
adding to the few existing Mistletoe literature of tropical regions and at the
same time forming a foundation for conducting more Afro-centric research on
Mistletoe.
Research
groups, scientists and several other stakeholders in ecological and biological
researches will be aided with the output of this research which will provide
not only information on mode of interactions but accentuate on African and
tropical resources of biological/ecological significance.
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