Plant breeding aims to improve crop yields, quality, and resistance to diseases and pests. It involves creating genetic variation through techniques like hybridization and mutation. Varieties are selected and evaluated, then multiplied and distributed. Key activities include generating variability, selection, evaluation, and conservation of germplasm. Mechanisms for both self- and cross-pollination are important. Techniques like hybridization, backcrossing, and male sterility systems are used to develop new varieties with desired traits.

1. Plant improvement
Prepared by: Mary Rose P. Escotido
Instructor I.

2. Plant breeding – science, art and business of crop
improvement for human benefit

3. Goals and objectives of plant breeding – higher yields, improved
quality, disease and insect resistance, change in maturity duration, agronomic
characteristics, photo insensitivity, synchronous maturity, no shattering
characteristics, determinate growth, dormancy, abiotic stress tolerance, etc.
Higher yields
Improve quality
Disease and insect
resistance
day-length sensitive, meaning
that it won't flower and fruit unless
nights and days are of
similar length.
no shattering characteristics
shattering
Low abiotic stress tolerance
and pest resistance

4. Activities in plant breeding:
1. creation of variation – generation of variability:
domestication, germplasm collection, introduction,
hybridization, mutation, genetic engineering
2. selection
3. evaluation
4. multiplication
5. distribution
6. conservation of germplasm

5. Naturally existing variability
1. domestication – process of bringing wild species under human
management (Neolithic period)
2. germplasm collection – collection of a large number of genotypes of
a crop species and its wild relatives it can be seeds or tissues.
3. introduction – taking a genotype or a group of genotypes of plants
into new environments where they were not being grown before
Generation of variability

6. Generation of variability
 Creation of new variability
1. hybridization – crossing genetically dissimilar individuals; produces a hybrid
2. inbreeding – mating of individuals related by ancestry; leads to production of
homozygous individuals
1. Inbred – product of inbreeding hence consequently a homozygous individual

8. 1. selfing – mating with oneself; most intense form of
inbreeding hence approach to homozygosity is
fastest
2. full sibbing – crossing between members of
selected pairs of plants; full sibs have both parents
in common
3. half sibbing – crossing one individual with several
identified ones; half sibs have one common parent
or pollen source
Parent 1 Parent 2
Product
of full
sibbing
SF1

9. 3. Topcross – cross between an inbred and an open-pollinated
variety, This scheme is also known as inbred-variety cross, (Inbred x
Variety), i.e., inbred line is crossed with an open pollinated variety.
Also the cross between a single cross and with another inbred is
known as double top cross.
Inbred
Open pollinated
variety
Topcross F1
Inbred
Double top
cross

10. 4. testcross – cross between a plant or line and a tester
(tester may be an inbred, hybrid, synthetic or open-
pollinated variety). The purpose of the test cross is
to determine the genetic makeup of the dominant organism.
Mm mm
Mm mm
HOMOZYGOUS DOMINANT- TT - tall
HOMOZYGOUS RECESSIVE – tt - infertile
HETEROZYGOUS - fertile
M m
m
m

11. 5. Backcross – a cross between a hybrid and one of its parents;
also a breeding method based on repeated backcrossing of the F1
(first generation offspring of a cross) and the subsequent
generations to the recurrent parent usually to transfer a major trait
controlled by one or a few genes from the donor (as the non-
recurrent parent) and the recipient (as the recurrent parent).
Inbred A Inbred B
F1
F1 Inbred A or B
BC1 hybrid

12. 6. Polycross – open pollination in isolation among a
number of selected genotypes arranged in a manner
that promotes random mating.
7. Reciprocal cross – mating of two individuals in which each is used
as the male parent in one cross and as the female parent in the other
Male parent can be
(receptor or donor)
tall
female parent can be
(Donor or receptor)
short
Reciprocal crossF1

14. 8. Intraspecific cross – crossing individuals
belonging to the same species, ( variety x
variety) cross
sweetcorn glutinous
Sweet glutinous
corn

15. 9. Wide or distant cross – crossing distantly related individuals
1. Interspecific – crossing individuals belonging to different
species
2. Intergeneric – crossing individuals belonging to different
genera
10. Introgressive hybridization – repeatedly backcrossing
interspecific hybrids to one of the parental species leading to
the transfer of some genes from one species to another

16. Heterosis or hybrid vigor; superiority of the F1 hybrid over
its parents; maybe positive or negative; ex. positive
heterosis for yield and negative heterosis for days to
maturity.
1. mid-parent heterosis – increase or decrease in
performance of the hybrid in comparison with the
average performance of the two parents.
2. heterobeltiosis – the increase or decrease in the
performance of the hybrid in comparison with the
better parent of the cross combination of two
parents. (When offspring shows superior or inferiority
traits than dominant parents traits.)
3. standard heterosis – the increase or decrease in the
performance of a hybrid in comparison with the
standard check variety of the region; type of heterosis
practically important to breeders.

17. theories to support heterosis:
1. dominance hypothesis – that heterosis is
due to the accumulation of favorable
dominant genes from the two parents in
the hybrid
2. overdominance hypothesis – that
heterozygotes are more vigorous and
productive than either homozygotes
“heterosis is expected to be high when inbreds used in
producing the hybrids and with high combining abilities.”

18. Combining ability – the ability of a genotype (inbred, pureline, or synthetic) to
transfer its desirable traits to its progeny
1. general combining ability (GCA) – average performance of a strain in a series of
crosses; estimated using testers of broad genetic base and identifies mainly additive
genetic effects. (GCA of gametes to develop during crosses)
2. specific combining ability (SCA) – deviation from performance predicted on the basis
of general combining ability of parental lines; estimated by using testers of narrow
genetic base and identifies both additive and non-additive gene action
Inbreeding depression – loss in vigor due to inbreeding

19. Mechanisms promoting self pollination
Cleistogamy – flowers do not open at all ensuring complete
self-pollination
Chasmogamy – flowers open but only
after pollination has taken place
stigmas closely surrounded by anthers
flowers open but stamen and stigma are
hidden by other floral organs
stigma when receptive elongate through
staminal columns

20. Mechanisms promoting cross pollination
Dicliny or unisexuality – flowers are either
staminate (male) or pistillate (female)
 monoecy – staminate and pistillate flowers occur
in the same plant either in the same or in
different inflorescences

21. Dioecy – male and female flowers are present on
different plants, the plants in such species are either
male or female
FEMALE MALE

22. Mechanisms promoting cross pollination
 Dichogamy – stamens and pistils of hermaphrodite (perfect,
bisexual) flowers may mature at different times facilitating cross
pollination
 protogyny – pistils mature before stamens
 protandry – stamens mature before pistils
 stigmas are covered with waxy film
 self-incompatibility
 male sterility

23. Systems of pollen control
emasculation – removal of immature anthers (or
androecium) from a hermaphrodite flower using
clip, hot water or suction/vacuum methods

24. Systems of pollen control
male sterility systems – male gametes nonfunctional but female gametes are
fertile, male sterility is caused by a recessive gene (ms). When both parents
carry the recessive gene then the pollen is not viable. If you cross a genetically
male sterile plant (ms) with a male heterozygous fertile plant (Ms), the F1
offspring will only carry one copy of the ms gene (Msms) and will be fertile.
1. Cytoplasmic male sterility (CMS) – genes for male sterility residing in the
cytoplasm particularly in the mitochondrion

25. 2. Genetic male sterility – sterility controlled by a
nuclear gene, usually recessive

26. 3. Cytoplasmic-genetic male sterility – controlled by interaction
between genetic factors present in the cytoplasm and nucleus;
presence of a male sterility gene in the cytoplasm and a restorer
gene in the nucleus results in the latter overcoming the effect of
the former to restore fertility
4. environment-sensitive genetic male sterility (EGMS) – genetic
male sterility system conditioned by environmental factors

27. 5. Photoperiod sensitive genic male sterility (PGMS) – responds
to photoperiod or duration of daylength for expression of pollen
sterility and fertility (day length exposure)
6. Thermosensitive genic male sterility (TGMS) – male
sterility/fertility alteration conditioned by different temperature
regimes. (sudden Changes in temperature)
7. Photothermosensitive genic male sterility (PTGMS) –
conditioned by both photoperiod and temperature (day length
and temperature)
8. chemically induced male sterility – use of chemical hybridizing
agents or gametocides like ethrel, monosodium methyl
arsenate and sodium methyl arsenate. (chemical application)

28. Self-incompatibility systems – failure of pollen from a flower to
fertilize the same flower or other flowers on the same plant.
1. heteromorphic system – flowers of different incompatibility
groups are different in morphology, ex. Pin and thrum
flowers in Primula
2. homomorphic system – incompatibility is not associated with
morphological differences among flowers; incompatibility
reaction of pollen may be controlled by the genotype of the
plant on which it is produced.

29. Mutation
heritable change in an organism
1. spontaneous – mutations occurring in natural
populations
2. induced – mutations artificially produced by
treatment with certain physical or chemical
agents or mutagens
 physical mutagens – most often result in chromosome
changes and larger DNA deletion while mutagenic
chemicals typically cause point mutations. β rays, α
rays, fast and thermal neutrons, x-rays and γ rays , UV
radiation
 chemical mutagens – alkylating agents, acridine dyes,
base analogues, etc.
 chimera – an individual with one genotype in some of
its parts and another genotype in the other parts
1. periclinal chimera – when the entire outer (outer
periclinal) or inner (inner periclinal) layer of shoot
apical meristem is affected. Outer layer gives rise
to the dermal system and part of mesophyll while
the inner layer produces the rest of the plant.
2. sectorial chimera – only a part of the outer (outer
sectorial) or inner (inner sectorial) layer is
affected

30. Mutation

31. Polyploidization – increasing ploidy level to more than two identical or distinct genomes;
types of polyploids
Euploidy – change in chromosome number involving one or more complete genomes;
chromosome number is an exact multiple of the basic or genomic number, ex.
Triploids, tetraploids, pentaploids, etc.
1. autopolyploid – when all the genomes present in a polyploid species are
identical
2. allopolyploid – two or more distinct genomes are present
3. amphidiploid – an allopolyploid that has two copies of each genome present in
it; have regular meiosis
4. segmental allopolyploid – contains two or more genomes which are identical
with each other, except for some minor differences
Aneuploidy – change in chromosome number involving one or a few chromosomes of the
genome; nullisomics, monosomics, trisomics, etc.
Somaclonal variation – heritable variation for both qualitative and quantitative traits shown
by plants regenerated from tissue and cell cultures
Gametoclonal variation – heritable variation shown by plants regenerated from pollen or
anther culture.

32. Genetic engineering
 production of transgenic plants
 changing the genetic makeup of plants by direct introduction of
genes (transgenes) from microorganisms, animals or other plant
species; done when sexual hybridization between the recipient
and donor is impossible
 steps:
1. identification of genes, construction of vectors
2. in vitro plant regeneration system
3. gene introduction methods
4. molecular analysis
5. gene expression assays
6. stability and transmission analysis

34. Selection
Identification of individuals or lines that are more desirable than others in a heterogeneous
population
1. Natural selection – change in gene frequencies from one generation to another
because of differences in survival and reproductive abilities of parental genotypes in
natural populations. (the process whereby organisms better adapted to their
environment tend to survive and produce more offspring.)

35. 1. Artificial selection – change in gene frequencies brought about
by man as is done in plant breeding where certain individuals
or genotypes are not used as parents of the next generation

36. modes of selection
1. stabilizing or normalizing selection – Natural selection that acts to maintain the
constancy of a species over successive generations. It involves selection against the
extremes of the range of phenotypes for a particular characteristic.
2. directional selection – change towards a particular direction due to changing
environments resulting also in change of genetic constitution of the population;
mode observed when breeders do artificial selection
3. diversifying or disruptive selection – opposite of stabilizing selection; leads to either
formation of subpopulations differing in their characteristics or polymorphism in
which each genotype is represented by a distinct phenotype.

37. 1. Qualitative traits –
monogenic or oligogenic traits;
show discrete or non-
continuous variation,
controlled by one or few
genes, less influenced by
environment
Traits selected for:

38. Traits selected for:
2. Quantitative traits – polygenic, metric or measurable traits;
show continuous variation, controlled by many genes, highly
influenced by environment

39. Bases of selection
1. phenotypic variance – sum of genotypic variance,
environmental variance and GxE variance
2. genotypic variance – sum of additive and non-additive types of
gene action

40. 3. Non-additive gene action – due to intralocus and
interlocus interactions, refers also to the phenomenon in which the
one allele is expressed stronger than the other alleles.
.(Heterozygous)
4. Additive gene action – due to individual effects of genes,
referred to as the phenomenon in which the two alleles contribute
equally to the production of the phenotype or both alleles are
expressed. (Homozygous recessive and Homozygous Dominant)
5. Intralocus interaction –Interactions take place between
the alleles of the same gene i.e., alleles at the same locus is
called intragenic or intralocus gene interaction.
6. Interlocus interaction - take place between the alleles
at different loci i.e between alleles of different genes.

41. 7. Complete dominance – heterozygote is equal to
the dominant homozygote in value
8. Partial dominance – value of the heterozygote is
between the average of the two homozygotes and the value
of the dominant homozygote
9. Over dominance – is a condition in genetics
where the phenotype of the heterozygote lies outside
the phenotypical range of both homozygous parents.
Overdominance can also be described as heterozygote
advantage, wherein heterozygous individuals have a
higher fitness than homozygous individuals

45. Interlocus interaction – epistasis; interaction among alleles of
different loci
1. environmental variance – effect of environment on the
phenotype and estimated by measuring variation in a
genotypically uniform population grown in a certain location
2. GxE interaction – change in ranking and/or performance of
genotypes when grown in different environments; estimated by
computing variances of genotypes when grown in a number of
locations which are environmentally diverse.
1. heritability – the quality of a characteristic being transmissible from
parent to offspring portion of the phenotypic variation among individuals
that is due to genetic differences among them
1. Broad - is defined as the proportion of trait variance that is due to
all genetic factors including dominance and gene-gene interactions.

46. 2. Narrow - The narrow-sense heritability is the ratio
of additive genetic variance to the total phenotypic
variance.
selection intensity – the percentage of individuals
selected in a population
1. selection differential – difference between the mean
performance of genotypes selected from a
population and the overall population mean
2. gain from selection –increase in mean performance
of a population that is realized with each cycle of
selection

47. Methods of selection
1. self-pollinated crops
mass selection – plants are chosen and harvested on the basis of
phenotype and the seeds composited without progeny testing; appropriate
for qualitative characters with simple genetic inheritance

48. 2. Pureline selection – procedure
for isolating purelines from a
mixed population
1. Pureline – progeny
from self pollination of a single
homozygous plant.
3. Pedigree selection refers
to record of the ancestry of an
individual selected plant. Pedigree
breeding is a method of genetic
improvement of self-pollinated
species in which superior genotypes
are selected from segregating
generations and proper records of
the ancestry of selected plants are
maintained in each generation.

49. 4. bulk method

50. 5. Single seed Descent (SSD)
Instead of bulking whole seed
lot of selected plants, a single
seed is selected randomly from
each selected plant to make
bulk.

51. 6. Doubled haploid – haploid plants are generated from anthers or F1 plants, or by
other means, and the chromosomes of the haploid plants are doubled with
colchicine to produce homozygous diploid plants; selection may start in early
generations

52. cross-pollinated crops
1. Population improvement approach – increasing the frequency of
genes in the population for the desired breeding objective
2. recurrent selection –any breeding system designed to increase the
frequency of desired alleles for particular quantitatively inherited
character by repeated cycles of selection
3. mass selection – individual plants are chosen visually for their desirable
traits and the seeds harvested from the selected plants are bulked to
grow the following generation without any form of progeny evaluation
4. half-sib family selection
5. full-sib family selection
6. S1 progeny selection
7. S1 is the progeny following self-pollination of plants in an open-pollinated
population of in the F2 following a cross
8. reciprocal recurrent selection – improves two populations simultaneously;
plants are selected in each of two populations, with the selected plants of
one population being selfed and outcrossed as the tester to the selected
plants in the other population; remnant seed from the plants with
superior testcross progenies are grown and intercrossed to reconstitute
the two populations

53. Evaluation
Process of assessing performance of newly developed lines of a
crop through appropriate multilocational trials and tests
1. Sequence in the conduct of yield tests:
1. observational yield test – may test separate groups of
experimental lines; uses incomplete block design or triple lattice
design with 2-3 replications in one location
2. preliminary yield test – evaluation including a check variety using
incomplete block design with 2-3 replications in at least 2
locations
3. general yield test – uses randomized complete block design with
3 replications in at least 3 locations
4. advanced yield test – elite lines from general yield tests evaluated
using randomized complete block design with 4 replications in 6-
10 locations
2. Superior lines are approved to be released as varieties by the National
Seed Industry Council (NSIC; previously the Philippine Seedboard); the
variety must have passed the tests for distinctiveness (D), uniformity (U)
and stability (S) or the DUS test

54. Multiplication
seed multiplication of an entry after it has been identified for release; the
seed produced by the breeder after a strain is identified but before it is
released as a variety is termed as the stock seed. The stock seed is known as
breeder seed once the identified strain is released and notified
 seed – seed or any other propagating material used for raising a crop
 seed multiplication involves:
1. seed production – should observe proper isolation procedures to
maintain genetic purity of the variety
2. Isolation – separation of a population of plants from other genotypes
with which they are capable of mating
1. temporal isolation – isolation by differences in growth stages
2. spatial isolation – isolation by distance
3. seed processing – drying, cleaning and grading, testing (purity, viability
and moisture content determination), treating (disinfectants and
protectants), bagging and labelling

55. Types of varieties
1. hybrids – first generation offspring of a cross between two individuals differing in one
or more genes
2. synthetics – seed mixture of strains, clones, inbred, or hybrids maintained by open-
pollination for a specified number of generations; the component units are
propagated and the synthetic reconstituted at regular intervals
3. composites – mixture of genotypes from several sources, maintained by natural
pollination
4. inbreds – a pureline originating by self-pollination and selection
5. multilines – or blends; cultivars consist of mixture specially develop genotypes called
isolines
1. Isolines – lines that are genetically similar except for one gene
6. open-pollinated variety – variety maintained by natural cross pollination
7. landraces – farmer-selected cultivated forms, a local cultivar or animal breed that has
been improved by traditional agricultural methods.
Hybrid seed production
1. 3-line system – male sterile line (A), maintainer line (B) and restorer line ®
2. 2-line system – male sterile line, the expression of which is influenced by
environment and any inbred variety as pollen parent
3. 1-line system – use of apomixis to produce the F1 seeds and to maintain the
genotype of the F1

56. Distribution
classes of seeds
1. breeder seeds – controlled by the originating plant
breeder; starting point of all the subsequent classes of
seeds; seeds obtained from uniform panicles by breeders;
100% pure; carry a (white tag).
2. foundation seeds – seeds produced from breeders seeds;
source of registered and/or certified seeds; 98% pure with
at least 85% germination rate; carry a (red tag)
3. registered seeds – produced from foundation or registered
seeds and carry a (green tag)
4. certified seeds – produced from foundation, registered or
certified seeds and carry a (blue tag)
5. good seeds – produced from elite lines not yet approved
by NSIC

57. Conservation of germplasm
 germplasm – the sum total of hereditary material or genes
present in a species
 plant germplasm – genetic source material used by plant
breeders to develop new cultivars (cultivated variety)
 centers of diversity – where extensive genetic variability of
cultivated species could be found; also believed by Vavilov to be
centers of origin
 primary centers – where domestication occurred
 secondary centers – where variation continued after
domestication
 germplasm storage
1. as seeds in cold/refrigerated rooms
2. maintained as living plants in field or through slow growth in
vitro
3. cryopreservation or freeze-preservation

59. The End…