2. CERTIFICATE
This is to certify that this project is bonafide work
done by master/kumari of class
XII bearing HALL TICKET NO:
During the academic year 2019-2020 for the fulfilment
of AISSCE-2020 BIOLOGY PRACTICALS in
JAWAHAR NAVODAYA
VIDYALAYA,MAMNOOR,WARANGAL(D),
TELANGANA.
Signature of the student
Signature of Internal Examiner
Signature of External Examiner
Signature of the Principal
B.POORNIMA
3. ACKNOWLEDGEMENT
At the outset I express my indebtness to the authorities of NVS for
providing me the opportunities for studying in JAWAHAR
NAVODAYA VIDYALAYA, MAMNOOR,
WARANGAL,TELANGANA.
I am very much delighted and feel privileged to place on my
sincere gratefulness to Principal Smt.B.POORNIMA of our
vidyalaya for providing facilities and extending help concerned to
this project work.
I take this opportunity to express my deep sense of gratitude to
Shri.NARSAIYYA(SIR) ,PGT-BIOLOGY of suggesting the
project,valuable guidance and constant encouragement to carry out
this project work.
I also thank Shri.M.V.SHIVA REDDY,PGT-IT &
MD.ESA,FCSA of our vidyalaya for me in completion of the
project.
I also thank MOGILI, lab attendant of our vidyalaya.
Signature of the Student
4. 1. Introduction:
Traditional Plant Breeding procedures are based on manipulation of genes and
chromosomes through sexual reproduction in whole plants. The breeding procedures evolve from
the principle of Mendalian genetics. There has been significant improvement in production and
productivity of important cereal crops globally as a consequence of the “Green Revolution” and
other initiatives. However, today the stage has reached that the available traditional methods of
crop improvement are not sufficient to provide enough and staple food grains to the constantly
growing world population. This situation is projected to be worse by the year 2050 especially in
context of climate change. In other words, the conventional plant breeding practices may not able
to achieve the sustainability in today’s agriculture. Recent advances made in the area of
molecular biology and bioinformatics offer substantial opportunities for enhancing the
effectiveness of classical plant breeding programs. The following are the Advance plant breeding
techniques used in crop improvements:
2. MOLECULAR BREEDING (MARKER ASSISTED SELECTION, MAS)
The term ‘molecular breeding’ is used to describe plant breeding programmes that are supported
by the use of DNA-based markers. Marker assisted selection(MAS) is the breeding strategy in
which selection for a gene is based on molecular markers closely linked to the gene of interest
rather than the gene itself, and the markers are used to monitor the incorporation of the desirable
genes from the donor source. In this technique, linkages are sought between DNA markers and
agronomically important traits such as resistance to Pathogens, Insects and nematodes, tolerance
to abiotic stresses, quality parameters and quantitave traits. Instead for selection of the trait, the
breeder can select for a marker that can be detached very easily in the selection scheme. The
molecular breeding requires the following technologies; genetic maps, molecular marker linked
to agronomical traits, high throughput, automated diagnostic techniques and a modification in the
breeding practices. The essential requirements for marker assisted selection in a plant breeding
program are:
Marker(s) should co-segregate or be closely linked (1cM or less is probably sufficient for
MAS) with the desired traits.
An efficient means of screening large population for the molecular marker(s) should be
available. At present this means relatively easy analysis based on PCR technology.
The screening technique should have high reproducibility across laboratories
It should be economic to use and be user friendly.
Several strategies have been developed that allow on to screen a large number of random,
unmapped molecular markers in relatively short times and to select just those few markers that
resides in the vicinity of the target gene. These high volume marker technologies that have
shown efficacy are RAPD, AFLP, RFLP, Microsatellites, SNPS, etc. These methods rely on two
principles:
5. i. To generate hundreds or even thousands of potentially polymorphic DNA segments
and rapidly visualize from single preparation of DNA; and
ii. Use of Genetic stocks to identify among these thousands of DNA fragments, those
few derived from a region adjacent to the target genes.
In the past few years, by using one or more of these high volume marker technologies,
thousands of loci scattered throughout the have been assayed in a matter of weeks or months.
The next problem is to determine which of the amplified loci near the targeted gene. Two
strategies have proved effective:
1. Nearly isogenic line (NIL) strategy:
Breeders have developed NIL genetic stocks and have been maintaining these inbreds lines that
differ at the targeted locus. Nearly isogenic lines are created when a donor line (P1) is crossed
to a recipient line (P2). The resulting F1 hybrid is then back crossed to the P2 recipient to
produce the backcross 1 generation (BC1). From BC1, a single individual containing the
dominant alleles of the target genes from P1 is selected. Selection for the target gene is normally
made on the basis of phenotype. This BC1 individual is again backcrossed to P2, and the cycle of
backcross selection is repeated for a number of generations. In the BC7 generation, most if not
all of the genome wiil be derived from P2, except for a small chromosomal segment containing
the selected dominant allele, which is derived from P1. Line homozygous for the target gene can
be selected from the BC7F2 is said to be nearly isogenic with the recipient parent, P2.
2. Bulk segregent analysis (BSA): This method is more generally applicable, and relies on the
use of segregating populations (Michelmore et al., 1991). It requires the generation of
populations of bulked segregates (bulks). When P1 and P2 are hybridized, the F2 generation
derived from the cross will segregate for alleles from both parents at all loci throughout the
genome. If the F2 population is divided into two pools of contrasting individuals on the basis of
screenings at a single target locus, these two pools (Bulk 1 and Bulk 2) will differ in their allelic
content only at loci contained in the chromosomal region close to the target gene. Bulk 1
individuals selected for recessive phenotype will contains only P2 alleles near the target, while
Bulk 2 plants selected for dominants phenotypes will contains alleles from both P1 and P2 at loci
unlinked to the target.
Marker assisted selection has become a promising and potent approach for integrating
biotechnology with conventional and traditional breeding. The plant breeder interest on
molecular markers revolves around certain basic issues which have been illustrated below:
1. Resistance breeding: At present breeding for disease and pest resistance is conducted on the
segregating populations derived from crosses of susceptible cultivars with resistant donors.
These Populations are then selected either under natural disease or pest hot spots or under
artificially created conditions. Although these procedures have given excellent results, they are
time consuming. Besides, there are always susceptible plants that escape attack. Screening of
6. plants with several different pathogens and their pathotypes or pests and their biotypes
simultaneously or even sequentially is difficult, if not possible. Availability of tightly linked
genetic markers for resistance genes will help in identifying plants carrying these genes without
subjecting them to pathogen or insect attack in early generation. The breeder will require a low
amount of DNA from each individual plant to be tested without destroying the plants, and see the
presence or absence of the product of PCR reaction (marker band) on the gel. Only materials in
the advanced generations would be required to be tested in disease and insect nurseries. Thus,
with MAS it is now possible for the breeder to many rounds of selection in the year without
depending on the natural occurance of the pest or pathogen as well.
2. Pyramiding of major/minor genes into cultivars for development of durable
resistance/multiple resistance: Pathogens and insects are known to overcome resistance
provided by single genes. Single gene resistances are fragile and often broken down easily.
Therefore breeder intended to accumulate several major and minor resistance genes into one
cultivar in order to achieve durable resistance. Durability of resistance has been increased by
developing multiline and by pyramiding of resistance genes.MAS for resistance genes can be
useful in these approaches. Pyramiding of bacterial blight resistance genes Xa1, Xa2, Xa3,
Xa4, Xa5 and Xa10 in different combination using molecular markers has been reported in
rice (Yoshimura et al., 1995).
3. Improvement of qualitative character: RFLP markers have been linked to the linolenic
acid content Fan locus in soybean (Brummer et al., 1995). Not only this, RAPD markers that
control somatic embryogenesis in alfalfa have been identified (Yu and Pauls, 1993).
4. Molecular Markers for hybrid vigor: Hybrids in crops such as maize, sorghum, rice
pearl millet, cotton and several vegetable crops have contributed greatly towards increasing
the yield potential of these crops. Using the molecular marker on a set of diallel crosses
among eight elite parental lines widely used in Chinese hybrid rice production programme,
high correlation was found between specific heterozygosity and mid parent heterosis.
5. MAS for trait difficult to evaluate: The MAS is especially useful for the traits that are
ardous and/or expensive to evaluate such as male fertility restorer genes for cytoplasmic male
sterility in which the presence of the fertility restorer genes (Frs) in the breeding lines can’t
easily be detached by conventionally breeding technique as they involve careful and
extensive evaluation and analysis of innumerable segregants.
6. Molecular Marker and abiotic resistance: In rice and maize, QTL for root traits have
been identified and are being used to breed high yielding drought resistance Rice and Maize
genotypes. MAS have helped to improve the yield performance under drought in beans,
soybean and peas.
7. 3. Micro-Propagation:
Clonal Propagation in vitro is called Micro-propagation. The word clone was first used by
Webber for apply to cultivated plants that were propagated vegetatively. It signifies that plants
grown from such vegetative parts are not individuals in the ordinary sense, but are simply
transplanted parts of the same individual and such plants are identical. Thus, clonal propagation
is the multiplication of the genetically identical individuals by asexual reproduction while clone
is a plant population derived from a single individual by asexual individuals. The significant
advantage offered by the aseptic method of clonal propagation (Micropropagaion) over the
Conventional methods is that in a relatively short span of time and space, a large number of
plants can be produced starting from a single individuals. Some potential uses of clonal
propagation in agronomical crops are:
Large scale increase of a heterozygous genotypes
Increase of self incompatible genotypes
Increase of a male sterile parent in a hybrid seed program
Production of a disease free rootstock, and
Preservation and international exchange of germplasm.
Advantages of Micropropagation:
In vitro micro-propagation techniques are now often preferred to conventional practices of
asexual propagation because of following advantages:
A small amount of plant tissue is needed as the initial explant for regeneration of millions
of clonal plants in one year.
The invitro stocks can be quickly proliferated at any time of the year.
The invitro technique provides a method for speedly international exchange of plant
materials.
Production of disease free plants.
Germplasm storage: Plant breeding programme rely heavily on the germplasm.
Preservation of the germplasm is a mean to assure the availability of genetic materials as
the need arises.
Seed Production: For Seed production in some of the crops, a major limiting factor is the
high degree of genetic conservation required. In such cases micropropagation can be
used.
8. 4. Double Haploid Production:
In the double haploid procedure, haploid plants are generated from anther of F1 plants, or by
other means, and the chromosomes of the haploid plants are doubled with colchicines treatment
to produce diploid plants. An example of the double haploid procedure using anther culture
follows:
Crossing generation: Crossing cultivar A and Cultivar B
F1 Generation: Culture Anther to produce 2000 t0 3000 haploid plants.
F2 Generation: Double chromosome of the haploid plants and harvest seeds from double haploid
plants produced.
F3 Generation: Grow progeny rows from double haploid plants and harvest seeds from superior
rows.
F4 Generation: Grow progeny rows in the field and select superior rows.
F5 Generation: Grow Preliminary Yield Trial.
F6 to F8 Generation: Continues yield trials.
F9 and F10 Generation: Increase and distribute superior lines as a new cultivars.
Double haploid plants are normally homozygous at all loci and it is unnecessary to grow
segregating generation. Lines generated by the double-haploid procedures may reach preliminary
yield trials two to three generation earlier than with the pedigree- selection or Bulk selection
procedures. Like the single seed descent procedure, early generations are not exposed to
environmental stresses in the field, and attrition of lines is greater in initial field evaluation trials
than with pedigree selection or bulk population procedures, in which early generations are field
grown. The double haploid plants should be vigorous, stable, free from tissue culture induced
variations, and represents a random selection of F1 pollen gametes.
5. Somaclonal Variation
Genetic Variability is the essential component of any breeding program designed to improve the
characterstics of crop plants. The variability generated by the use of a tissue culture cycle has
been termed somaclonal variation by Larkin and Scowcroft (1981). They defined a tissue culture
cycle as a process that involves the establishment of a dedifferentiated cell or tissue culture under
different conditions, proliferation for a number of generations and the subsequent regeneration of
plants. In other words one imposes a period of callus proliferation between an explants and the
regeneration of plants. The initiating explants for a tissue culture cycle may come virtually from
any plant organ or cell type including embryos, microspores, roots, leaves and protoplasts.
Historically, it became accepted dictum that all plants arising from tissue culture should be exact
9. copies of the parental plants. However phenotypic variants were frequently observed amongst
regenerated plants. These were usually dismissed earlier as tissue culture artifact due to the
recent exposure of exogenous phytoharmone, and sometimes they were labeled as epigenetic
events. However, evidence has now shown that these variants are not artifacts but variation
arising due to culture of cells and this has been termed as somaclonal variation. The cause of
variation is attributed to change in the chromosomal number and structure. Two schemes, with
and without in vitro selection, have been generally followed for getting somaclonal variation in
crop plants.
Explant
Explant derived callus
Shoot regeneration
Plant
Transfer to the field
Screening for disease traits
Agronomical traits
Fig : A flow diagram for generation of Somaclonal variation without in-vitro selection.
Genetic variation in Somatic cell cultures includes a wide mutation spectrum such as point
mutations, Chromosomal rearrangements, inversion, duplications, polyploidy, aneuploidy and
deletion. Either qualitatively or quantitatively inherited characters may be affected by the tissue
culture- induced mutation.
10. 6. Mutation Breeding:
Mutation is the sudden heritable change in a characteristic of organisms. Clearly, a mutation may
be the result of a change in gene ,a change in chromosome(s) that involves several genes or
change in plasma gene(genes present in cytoplasm, e.g. chloroplast, mitochondria etc which have
circular DNA , as chromosome).Mutation produced by change in the base sequence of gene (as a
result of base pair transition or transversion , deletion, duplication or inversion ,etc) are known
as gene or point mutation. Some mutation can be produced by change in chromosome structure,
or even in chromosome number: they are termed as chromosomal mutations.
Mutation occurs in a natural population at low rate; these are known as spontaneous mutations.
The frequency of spontaneous mutation is generally is one in 10 lacks i.e.10-6 but different genes
shows different mutation rates .for example R locus in maize mutates at a frequency of 4.92×10-
4
, Su 2.4×10-6,while Wx appears to be highly stable. Mutation can be artificially induced by
treating with a certain physical or chemical agents; such mutations are known as induced
mutation, and the agents used for producing mutation are termed as mutagens. The utilization of
induced mutation for crop improvement is known as mutation breeding.
Application of mutation breeding
Mutation breeding has been used for improving both the oligogenic as well as polygenic
character. It has been used to improve both the morphological as well as the physiological
characters, disease resistance and quantitative character including yielding ability. The various
applications of mutation breeding can be summarized as follows;
1.Induction of desirable mutation alleles, which may not be present in the germplasm or which
may be present ,but may not be available to the breeder due to political and geophysical reasons.
2. It is useful in improving specific characteristics of a well adapted high yielding variety. This is
particularly so in case of clonal crops due to their highly homozygous nature.
3. Mutagenesis is very useful in improving various quantative characters including the yield.
Several varieties have been developed using this technique.
4. F1 hybrids from the intervarietal crosses may be treated with the mutagens in order to improve
genetic variability by inducing mutations and by facilitating recombination among linked genes.
5. Irridation of interspecific hybrids has been done to produce translocations. This is done to
transfer a chromosome segment carrying a desirable gene from the alien chromosome to the
chromosome of cultivated species.
11. 7. Gene Pyramiding:
The development of molecular genetics and associated technology like MAS has led to the
emergence of a new field in plant breeding-Gene pyramiding. Pyramiding involves stacking
multiple genes leading to the simultaneous expression of more than one gene in a variety to
develop durable resistance expression. Introgression of multiple QTLs/genes for a solitary trait
or multiple traits into a cultivar that is deficient for these traits is known as ‘‘gene pyramiding’’.
One of the most important uses of gene pyramiding is the transfer of multiple disease resistance
genes for imparting durable disease .Pyramiding of genes for certain traits (such as for disease
resistance) following conventional backcrossing is tedious, time-consuming and difficult,
although successful pyramiding of resistance against all the three rusts [leaf (LR), stem (SR), and
yellow (YR) rusts] in wheat was achieved in India through conventional backcrossing technique
by B. P. Pal and coworkers as early as the 1950s (Gupta, 2007). With the availability of
molecular markers, it has now become much easier for breeders to combine desirable alleles at a
number of loci in a relatively short period of time .MAS has been successfully utilized in several
major crops to pyramid a number of targeted genes .In wheat, gene pyramiding using MAS has
been achieved for resistance against leaf rust (Cox et al., 1994; Gupta et al.2005; Singh et
al.2004; Nocente et al.,2007), powdery mildew (Liu et al.,2000; Wang et al.,2001). The success
of gene pyramiding depends upon several critical factors, including the number of genes to be
transferred, the distance between the target genes and flanking markers, the number of genotype
selected in each breeding generation, the nature of germplasm etc. Innovative tools such as DNA
chips, micro arrays, SNPs are making rapid steps, aiming towards assessing the gene functions
through genome wide experimental approaches.
8. Genetic Engineering:
Plant Genetic engineering refers to the transfer of foreign DNA which codes for specific genetic
information, from a donor species into a recipient plant species by means of a bacterial plasmid,
virus, or the vector. The procedure is also referred to as transformation. For the plant breeder,
plant genetic engineering has the potential for transferring a desirable foreign gene from a wide
range of source, including non- plant genetic material, into an economic crop species without
sexual hybridization. In many respects, plant genetic engineering (transformation) is comparable
to the back cross method of breeding in which desirable genes are transferred to recipient
genotypes by a succession of crosses. The molecular biologist inserts a segment of DNA that
code for desirable traits into the plant genotype where it replicates and is expressed in the new
plant genotypes. The crop species that have been genetically transformed with foreign DNA
includes corn, alfa alfa, potato, cauliflower, soybean, lettuce, sunflower, carrot, canola, cotton,
tomato etc.
12. Genetic Transformation: The transfer of the gene is mediated with the bacterial pathogen
Agrobacterium tumefaciens which is able to transfer a piece of its DNA (T-DNA) into DNA of
the plant resulting in the new, genetically transferred plant cell. Agrobacterium tumefaciens
infect plants by transferring T- DNA of the Ti- plasmid into plant cells and the t-DNA becomes
incorporated into the plant DNA’s , hence causing the crown gall disease.The gall of the tumour
are developed because the T-DNA from the bacteria has genes which regulates the biosynthesis
of the plant harmone IAA and Cytokinin. After plant become infected with A.tumefaciens,
abnormal level of IAA and cytokinin causes’ anomalous growth and tumer formation. Mutants of
A.tumefaciens have been developed in which the T-DNA doesnot produce IAA or cytokinin.
Foreign DNA is incorporated in to these non harmone producing A.tumefaciens strains as part of
the T-DNA. As, a result the modified A.tumefaciens as a vehicle to introduce the foreign genes
into the plants. This process now makes it possible to genetically engineered specific crop plants.
Steps, involving transformation:
Identification Isolation Introduction
(gene) (gene) (host)
Transmission Regeneration Selection & Integration
(Progeny) Expression genome
8. Genomic Selection:
It has been predicted for over two decades that molecular marker technology would reshape
breeding programs and facilitate rapid gains from selection. Currently, however, marker-assisted
selection (MAS) has failed to significantly improve polygenic traits. While MAS has been
effective for the manipulation of large effect alleles with known association to a marker, it has
been at an impasse when many alleles of small effect segregate and no substantial, reliable effects
can beidentified.
The weaknesses of traditional MAS come from the way MAS splits the task into two
components, first identifying QTL and then estimating their effects. QTL identification
methods can make MAS poorly suited to crop improvement: (i) Biparental populations may be
used that are not representative and in any event do not have the same level of allelic diversity
and phase as the breeding program as a whole (ii) the necessity of generating such populations is
costly such that the populations may be small and therefore underpowered; (iii) validation of
discoveries is then warranted, requiring additional effort; (iv) the separation of QTL identification
from estimation means that estimated effects will be biased, and small-effect QTL will be missed
entirely as a result of using stringent significance thresholds. Association mapping (AM)
13. applied directly to breeding populations has been proposed to mitigate the lack of relevance
of biparental populations in QTL identification and QTL have been mapped in this way.
This practice nevertheless retains the disadvantage of biased effect estimates and therefore poor
prediction of line performance.
GS emerged out of a desire to exploit high density parallel genotyping technologies. At such
high densities, it was assumed that linkage phase between markers or haplotype blocks of
markers and casual polymorphism would be consistent across families so that population-wide
estimates of marker effects would be meaningful. GS uses a ‘training population’ of individuals
that have been both genotyped and phenotyped to develop a model that takes genotypic data
from a ‘candidate population’ of untested individuals and produces genomic estimated breeding
values (GEBVs). These GEBVs say nothing of the function of the underlying genes but they
are the ideal selection criterion in the plant breeding context, untested individuals would belong
to a broader population defined as a crop market class or the breeding program as a whole. In
simulation studies, GEBVs based solely on individuals’ genotype have been remarkably accurate.
These accuracies have held up in empirical studies of dairy cattle, mice and in biparental
populations of maize, barley and Arabidopsis.GS is revolutionizing both animal and plant
breeding.
9. Quantitative Trait Loci (QTL) Mapping:
A quantitative trait is governed by polygenes and is markedly affected by the environment. As a
result, it shows a continuous variation as opposed to the discrete variation that is characterstics of
qualitative traits. Polygenes are those genes that have small and cumulative effect on the
concerned traits, and several polygenes affect a single trait. Quantitative trait loci (QTL) are a
position in a chromosome that contains one or more polygenes involved in the determination of a
quantitative traits.
QTL mapping involves testing DNA markers throughout the genome for the likelihood that they
are associated with a QTL. Individuals in a suitable mapping population are analyzed in terms of
DNA marker genotypes and the phenotypes of interest. For each DNA marker, individuals are
split into classes according to marker genotype. A significant difference between the DNA
marker and the trait of interest indicates a linkage between the DNA marker and the traits of
interest i.e., the DNA marker is probably linked to a QTL controlling the phenotypes of interest.
The mapping of the QTL is done using the markers restriction fragment length polymorphism
(RFLP), randomly amplified polymorphic DNA (RAPD), microsatellite or simple sequence
repeat (SSR), amplified fragment length polymorphism (AFLP), single nucleotide polymorphism
(SNP) markers have been developed in a range of crops.
The mapping population must be relatively large in order to detect QTLs having minor effects,
and the biological relevance of the uncovered QTLs depends on the cut-off chosen for the
statistical significance. In QTL mapping, environmental factor and genetics background have a
marked impact on the results; some QTLs may be detectable in some but not in other
environment. One of the most powerful applications of QTL mapping is to analyze gene ×gene
and gene×environment interaction.
14. 10. Polyploidy Breeding:
Ploidy refers to the number of copies of the entire chromosome set in a cell of an individual. The
complete chromosome set is characteristic of, or basic to, a species. A set of chromosomes (the
genome) is designated by “x”. Furthermore, the basic set is called the monoploid set. The
haploid number (n) is the number of chromosomes that occurs in gametes. This represents half
the chromosome number in somatic cells, which is designated 2n. A diploid species, such as corn, has
n =10 and 2n=20. Also, a diploid species has 2n =2x in its somatic cells, and n =x in its gametes.
Polyploidy is the heritable condition of possessing more than two complete sets of chromosomes.
Most polyploids have an even number of sets of chromosomes, with four being the most
common (tetraploidy).
Fig. | Evolutionary alternation of diploidy and polyploidy.
Diploid
Speciation
Diploidspecies AA Diploid species BB
2N gamete
2N + 1N gametes
2N gamete
F1 (AB)
2N gamete
Duplicati on
Triploid(A A A )
2N + 2N
Autotetrapol oi d (AAAA ) Allotetrapol oi d (AABB)
Partiall y diploidized tetrapl oi ds
Diploid
15. Autoploids: Autoploids comprise duplicates of the same genome. Autoploids are useful in making
alloploids and wide crosses. Natural autoploids of commercial importancecommercial value
include banana, a triploid, which is seedless (diploid bananas have hard seeds not desirable in
production for food). Other important autoploids are tetraploid crops such as alfalfa, peanut,
potato, and coffee. Spontaneous autoploids are very important in the horticultural industry where
the gigas feature has produced superior varieties of flowering ornamentals of narcissus, tulip,
hyacinth, gladiolus, and dahlia among others.
Alloploids
Allopolyploid comprises of 2 or more distinct genome, generally each genome has two
copies.A number of economically important crops are alloploids. These include food crops
(e.g., wheat, oat), industrial crops (e.g., tobacco, cotton, sugarcane), and fruits crops (e.g.,
strawberry, blueberry). These crops, by definition, contain a combination of different genomes.
Dubbed the triangle of U, it describes the origins of three Brassica species by alloploidy. The
diploid species involved are turnip or Chinese cabbage (B. campestris, n=10), cabbage or kale (B.
oleracea, n=9), and black mustard (B. nigra, n =8). For example, B. napus has 2n =38, being a
natural amphiploid of B. oleracea and B. campestris. In cereal crops, wheat is a widely studied
alloploid that comprises genomes from three species. Cultivated common wheat (Triticum
aestivum) is a hexaploid with 21 pairs of chromosomes and is designated AABBDD. The AA
genome comes from T. monococcum. Tetraploid wheats have the genomic formula AABB.
wheat (T. dicoccum) crossed naturally with Aegilops squarrosa (DD) to form common wheat.
Fig.ThetriangleofUshowingtheoriginsofvariousalloploidsinBrassica. Fig. The evolutionof the HexaploidWheat
(2n 20)
nn(2n
16)
B.
campestri
s
B. nigra
nn
nn
B.
oleracea
(2n
18)
T. aestivum 2n 6x
42 (AABBDD)
Chromosome doubling
T. turgidum T. tauschii 2n 14
(AABB) 28 (DD)
3x 21 (ABD)
Chromosome doubling
BB(2n 2x 14) (Aegilops speltoides?)
(AA)
2n 2x 14
UnknownTriticum monococcum
B.
juncea
(2n
36)
(e.g.,
brown
B. napus
(2n 38)
B. carinata
(2n 34)
16. Conclusion
Conventional breeding methodologies have extensively proven successful in development of
plant cultivars and germplasm. The most renowned examples include the semi-dwarf high-
yielding cultivars of cereals developed during the Green Revolution and the hybrid rice
developed in 1970s. However, conventional breeding is still dependent to a considerable extent
on subjective evaluation and empirical selection. It is tedious, time-consuming and difficult.
Scientific breeding needs less experience and more science, i.e. practical and accurate evaluation,
and effective and efficient selection. Molecular marker-assisted breeding (MAB) has brought
great challenges, opportunities and prospects for conventional breeding. The rapid development
of molecular markers (particularly DNA markers) and continuous improvement of molecular
assays has led to the birth of a new member in the family of plant breeding - molecular marker-
assisted breeding (MAB). The extensive use of molecular markers in various fields of plant
science, e.g. germplasm evaluation, genetic mapping, map-based gene discovery,
characterization of traits and crop improvement, has demonstrated that molecular technology is a
powerful and reliable tool in genetic manipulation of agronomically important traits in crop
plants . The significant advantage offered by the aseptic method of clonal propagation
(Micropropagaion) over the Conventional methods is that in a relatively short span of time and
space, a large number of plants can be produced starting from a single individuals. The genomic
selection , Gene pyramiding, MAS(Marker Assisted Selection), Mapping of the QTL(
Quantitively Trait Loci) are the emerging highly efficient technique which are in use nowadays
for the improvement of the crop species to revolutionize the world.
