ABSTRACT
This study investigated the mutagenic effect of x-ray on growth of pepper (Capsicum annum) of three different varieties of pepper- Langa langa, (World bitter and California wonder). The experiment was carried out in the screen house of Michael Okpara University of Agriculture, Umudike, Umuahia, Abia State, Nigeria, and in the research field of National Plant, Soil and Water Laboratory, Umudike. The experiment was carried out using seeds collected from National Agricultural Seed Council (NASC), Umudike. The experiment was laid out as Randomised Complete Block Design (RCBD) replicated three times. Parameters evaluated include root length, shoot height, number of leaves, germination percentage, leaf area and plant girth. The x-ray irradiation doses used were 1 Mgy, 2 Mgy, 4 Mgy, 6 Mgy and 8 Mgy. From the result, it was observed that World bitter produced its highest germination percentage (59%), highest number of leaves (3.4 mean value), highest plant girth (1.9 mm) and highest root length (2.4 mm) all at 6 Mgy x-ray radiation dose while Langa langa produced the highest number of leaves at 1 Mgy (3.4 mean value) and 4 Mgy x-ray radiation dose (at 2.7 mean value). Valencia sweet pepper produced the least percentage germination, least number of leaves and least root length. This evaluation suggests that the breeders could use these observations in their breeding selection.
TABLE OF CONTENTS
Title page
i
Declaration ii
Certification iii
Dedication iv
Acknowledgements v
Table of Contents vi
List of Tables viii
List of Figures ix
List of Plates x
Abstract xi
CHAPTER
ONE: INTRODUCTION
1.1 Background of the Study 1
1.2
Justification of the Study 4
1.3 Aim
of the Study 4
1.4
Objectives of the Study 4
CHAPTER TWO: LITERATURE REVIEW
2.1 Mutation 5
2.1.1 Types of Mutation 5
2.1.2 Induced Mutation 6
2.1.3 Physical Mutagens 6
2.2 X-rays 7
2.3 Radiation Units 8
2.4 Chemical Mutagens 8
2.4.1 Spontaneous Mutation 9
2.4.2 Mutation Rate 9
2.4.3 Effect of Mutation on the Phenotype 10
2.4.4 How Does a Mutation Act? 11
2.4.5 Significance of Mutation 11
2.4.5.1 Application in Plant
Breeding 11
2.4.5.2 Mutation Breeding of Pepper 12
2.4.5.3 Uses of Pepper 13
2.4.5.4 Medicinal Uses of Pepper 13
2.4.5.5 Role in Evolution 14
CHAPTER THREE: MATERIALS AND METHODS
3.1 Study Area 15
3.2 Design of the Experiment 15
3.3 Collection of Samples 15
3.4 Seed Treatment 16
3.5 Dosimetry 16
3.6 Treatment 16
3.7 Measurement Parameters 16
3.7.1 Germination Percentage 17
3.7.2 Plant Height
17
3.7.3 Root Length
17
3.8 Statistical Analysis 17
CHAPTER FOUR: RESULTS 18
CHAPTER FIVE
5.1 Discussion 29
5.2 Discussion 30
References 31
LIST OF TABLES
Table 4.1: Effect of genotype and x-ray doses on
the plant girth
of
pepper at 2, 4 and weeks after
planting
25
Table 4.2: Effect of genotype and x-ray doses on the
plant girth
of pepper at 8 and 10 weeks after planting 26
Table 4.3: Effect of genotype and x-ray doses on the
leaf area of
pepper at 2, 4 and 6 weeks after planting 27
Table 4.4: Effect of genotype and x-ray doses on the
leaf area of
pepper at 8 and 10 weeks after planting 28
LIST OF FIGURES
Figure 4.1: Graphical representation of effect of
genotype and x-ray
doses
on percentage germination at 2 WAP 21
Figure 4.2: Graphical representation of effect of
genotype and x-ray
doses
on number of leaves at 2 WAP 22
Figure 4.3 Graph representing effect of genotype and
x-ray doses
on root length
at 23
Figure 4.4: Graph representing effect of genotype and
x-ray doses
on plant girth at 2
WAP
24
LIST OF PLATES
Plate 4.1: Pepper seedlings in the green house at
2 WAP 18
Plate 4.2: Pepper seedlings in the field at 4
WAP 19
Plate 4.3: Pepper seedlings in the field at 6
WAP 19
Plate 4.4: Pepper seedlings in the field at 10 WAP 20
CHAPTER
ONE
INTRODUCTION
1.1
Background
of the Study
A gene mutation is abrupt inheritable
qualitative or quantitative change in the genetic material of an organism
(Vermaet al., 2009). Since in most
organisms, genes are segment of DNA molecules, so a mutation can be regarded as
a change in DNA sequence of corresponding RNA or protein molecule. Most
mutation occur spontaneously by the environmental effect, however they can be
induced in the laboratory either by radiation caused by mutagenic agents such
as X-rays, gamma rays , beta rays, neutrons, chemicals, high temperature and
low pH (Sen and Kar, 2009). Mutations in germ-line tissue are of enormous
biological importance because they provide raw materials from which natural
selection produces evolutionary changes and origin of species (Garrett and
Grisham, 2013, Vermaet al., 2009).
X-ray is an electromagnetic wave of
high energy and very short wavelength, which is able to pass through materials
opaque to light. It can be measured in rad, miligrays, or other equivalent
units. It is being absorbed to different degrees by different materials
(Ababio, 2000, Okekeet al., 2008,
Anyakoha, 2006). There are ionizing radiations and non-ionizing radiations
(Garrett and Grisham, 2013). Ionizing radiation has such high energy that it
can knock an atom’s electron out of their orbit. It can go on to cause lots of
problems, such as breaking covalent bonds in other molecules (Okekeet al.,2008, Anyakoha, 2006, Ababio,
2000). DNA of an organism is held together by covalent bond (Raven et al., 2002). The backbones of the two
DNA strands are made of nucleotides linked together by covalent bonds
(Ramalingam, 2004, Garrett and Grisham,2013).
Therefore when seeds are exposedto
ionizing radiations such as X-rays, it breaks these bonds and the DNA will be
chopped up into tiny pieces. The cell will try to repair these DNA breaks, but
it is very difficult for the cell to correctly put all these DNA pieces back
together again. Inevitably, some mistakes may be made and these mistakes are
mutations because they change DNA sequence sequences of the organism. This
means that ionizing radiations can cause mutations in cells. Because mutations
can occur randomly anywhere in cell’s DNA, mutations are often detrimental. The
effects of detrimental mutations may be minor or catastrophic depending on the
functions of the altered gene. Ionizing radiations is not always bad; it can
sometimes be of advantage. For instance noxious plants can be mutated and they
become edible. Morphological mutation can change the height of a plant or
change it from soft to smooth seed. These radiations can also be referred to as
pollutants which cause mutations by irradiation while other chemical pollutants
capable of causing mutations are known as chemical mutagens (Garrett and
Grisham, 2013, Vermaet al., 2009).
Plants sometimes transmit somatic
mutations to their descendants asexually or sexually (a case when flower buds
in somatically mutated part of plant). Mutations create a variation in the gene
pool by the natural selection, while more favorable (beneficial or
advantageous) ones tend to accumulate, resulting in evolutionary change
(Broertjes, 1976).
Pepper (Capsicum annum) is an important spice crop grown in tropical, sub
tropical as well as temperate regions. Evidence supports Mexican origin of
domesticated Capsicum annum while
other domesticated species arose in South America (Mcleadet al., 1982). The genus Capsicum comprises of many cultivated
spices, of which few are worldwide in distribution and approximately twenty
wild species (Pickersyll, 1971). In Nigeria the genus are represented by two
cultivated species: CapsicumannumL. and
CapsicumfrutescensL.(Mcleadet al.,1982).Pepper is rich in vitamin
C, some quantities of vitamin A, B1, B2 and phosphorus
hence form an important ingredient in Nigeria diet. The economic importance of
pepper as well asproduction is increasing globally. In Nigeria, however, pepper
production has been challenged by many biotic and abiotic factors which include
susceptibility to pests and diseases, low yield and late maturity among others
(Ado and Asiribo, 1989). Some of these problems are addressed through
conventional crossbreeding without much achievement. However with the use of
mutation breeding techniques for improvement of pepper plant, remarkable
progress has been achieved (FAO/IAEA, 1977; Daskalov, 1986).
There is a growing interest in taking
advantage of induced mutation for the improvement of pepper production
(Daskalov, 1972, 1977, 1986; Parenet al.,
2007). Mutagenesis in crop plant significantly influences the morphological and
physiological parameters which in turn enhances yield, days to maturity and
resistance to pests and diseases (Gopalakrishnan and Selvanarayanan, 2009;
Tomlecova, 2010). The use of mutagenic agents to induce variability in
morphological traits has been identified as a practical tool especially where
natural variability is not available. Venkata and Raghauan(1940) reported the identification
of several types of plants affecting size of plants, branching chlorophyll
content, size of leaf and fruits by exposing dry seeds of Capsicumspp to X-rays. Daskalov (1974) obtained several useful
mutants by exposing pepper plant to gamma rays, X-rays and EMS. These include
male sterile mutants, anthocyanin less mutants, gene markers, mutant with
changed fruit form, colour and dwarf plants which were used directly in
crossbreeding programs. Daskalov and Mihailov (1988) reported the recovery of (3)
male sterile mutants from a female parent obtained from a gamma induced pepper
mutants useful for the development of hybrid cultivars. They proposed the use
of female sterile line as pollenizer in hybrid seed production. Recently
several mutants of pepper have been reported among which are mutation induced
change in shoot architecture (Paranet al.,
2007). Honda et al., (2006) reported
the development of some induced mutants of sweet pepper (C. annum .L.) while Tomlecovaet al., (2009) developed orange mature
pepper fruit with increased beta carotene (Pro vitamin) which is currently used
for molecular marker assisted selection.
Normally, during reproduction genes
are transmitted unchanged from generation to generation. But on certain cases,
genetically heritable changes (mutation) occur and result in altered forms due
to radiations such as X-rays. Together with recombination, mutation provides
for genetic variability within species and ultimately, the evolution of new
species.
1.2
Justification
of the Study
The process of developing new crop
varieties can take almost 25 years. Now, however biotechnology through mutation
breeding has shortened the time for new crop varieties to be brought to market.
Exposing pepper seed to x-ray radiation doses creates mutants with traits
(desirable or non-desirable) which may be selected for specific purpose in
plant breeding.
1.3 Aim
of the Study
The aim of this study is to determine
the mutagenic potential of different X-ray doses on the growth of three
varieties of pepper.
1.4 Objectives of the Study
1. Determine
the optimal dose of X-ray for mutation of Capsicumannum.
2. Determine
the effects of X-rays on the morphological characters of the 3 varieties of Capsicumannum.
3. Determine
the effects of X-rays on the growth parameters of (3) varieties of Capsicumannum.
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