Enhancing the standard of yam breeding. Conventional method of yam breeding and molecular techniques. "If we fail to keep agriculture moving in the less developed nations, poverty will continue to grow, and the social upheaval that will ensue will become a global nightmare.” Norman Borlaug

1. MARTIN A. YEBOAH

2.  Introduction Molecular markers
 Yam Stats. Linkage mapping
 Germplasm F1 mapping population
 Botany Future trends
 Biological constraints Conclusion
 Polyploidy and mapping
 Breeding history
 Yam improvement in IITA
 Breeding scheme
 Rapid propagation

3.  The world population has passed 6
billion and continues to grow.
Hunger , poverty and malnutrition
are major challenges to mankind.
 Half the world — nearly three billion
people — live on less than two
dollars a day.
 Technology advances in agriculture
and food need to continue to meet
these challenges.

4. ―If we fail to keep agriculture moving in
the less developed nations, poverty
will continue to grow, and the social
upheaval that will ensue will become
a global nightmare.”
Norman Borlaug, 1970 Nobel Peace
Price Laureate.

5.  According to UNICEF, 26,500-30,000
children die each day due to poverty.
(source www.globalissues.org).
 Iron and vitamin A deficiencies, and
infectious diseases continue to
devastate people of the developing
world.
 Non-communicable diseases
attributable to obesity are increasingly
common in developed and developing
countries.

6.  Yam diets providing micronutrients and
health-promoting phytochemicals could
alleviate both under-nutrition and obesity.
 Diversification into yam production can
contribute to poverty alleviation through
several ways.
1. Household food security at the domestic and
community level can be achieved through
increased yam production, improved
handling after harvest, processing, and
marketing.

7. 2. Yam can be consumed in the
household or sold to generate
income to purchase household
goods and pay for education of the
youth.
3. Yam can be processed using
appropriate technologies. The
processed products can be
consumed within the household or
sold as part of value-added income
generation.

8. Table 1: Production (in ‘000 tons) and Area (in’ 000 ha) of yam by
Continents
Continent Production(in’000 Area (in’000 ha) % of world
tons) production
Africa 44514.5 4598.6 94.9
Asia 234.3 15.4 0.5
Europe
2.7 0.16 0.005
Caribbean 486.8 77.8 1.03
Oceania 343.7 52.9 0.73
South America
599.9 62 1.27
World total 46920.7 4781.1 100
Source: FAO,2007

9. Continent Countries
Africa Benin, Burkina Faso, Burundi, Cameroon, Central African
Rep., Chad, Comoros, DR. Congo, Ethiopia, Garbon,
Ghana, Guinea, Kenya, Liberia, Mali, Nigeria, Sudan,Togo
Asia Japan, Philippines
Europe Portugal
Caribbean Cuba, Barbados, Dominica Republic, Guadeloupe, Haiti
Oceania Papua New Guinea, Solomon Island, Tonga, Vanuatu
South Brazil, Colombia, Guyana, Venezuela
America

11.  Yam belongs to the genus Dioscorea of family
Dioscoreaceae
 The genus contains some 600 species with more
than 10 species cultivated for food and pharma-
ceutical use (Ake Assi ,1998).
 Important staples in many areas:
◦ West Africa, southeast Asia, Pacific and Caribbean
Islands
 Yams have been cultivated for over 5000 years in
tropical Africa.

12. Sokoto Lake Chad
Katsina Jigawa Yobe N
Zamfara Borno
kebbi Kano
W E
Kaduna Bauchi Gombe
S
Niger
12 10 # #
9 Adamawa
15
# 11 # #
#
#
14 #
FCT Plateau
16 Kwara
# 17
Nasarawa #
8 7 #
Oyo #
#
13 6 Taraba Forest
# Ekiti Kogi
5 Osun Benue Derived savanna
Ogun Ondo 4 18 Guinea savanna
#
#
Lagos Edo Enugu 3 #
#
2
Imo Ebonyi
#
1
Delta Cross River
Rivers Akwam Ibom
400 0 400 800 Kilometers
Major Yam Producing Areas in Nigeria

13.  Six important staples include
1. White yam ( D. rotundata)
2. Water yam (D. alata)
3. Yellow yam (D. cayenensis)
4. Trifoliate yam (D. dumetorum)
5. Aerial yam (D. bulbifera)
6. Chinese yam (D. esculenta)

14.  IITA –the largest world collection 8 spp
>3000 accessions (391 core collections).
 CTCRI in Tryvandrum india
 VASI in Hanoi ,Vietnam
 PhilRootCrops in Babay ,Philippines.
 VARTC in Santo, Vanuatu
 INRA and CIRAD in Guadeloupe, West Indies
 China and Japan

15.  Dioscorea spp. (true yam)
 Most popular cultivated spp.
 D. rotundata - West Africa
 D. alata - Asia
 Wild/semi-domesticated spp.
D. abyssinica, D. praehensilis etc
 Vegetatively propagated
 Deiocious
 Allo - , auto-polyploid or Diploid?

16.  Long life cycle
 Dioecy and polyploidy
 Poor to non-flowering
 Vegetative propagation
 Juvenile phase
 Yam mosaic disease
 Anthracnose disease

17.  Terauchi et al.,1992, proposed that D.
rotundata was domesticated from a wild
species that shared the same chloroplast
genotype, and that D. cayenensis is a hybrid
origin and should be considered as a variety
of D. rotundata.
 However, Mignouna et al., 2005a, classified
guinea yam into seven morphotypes and
therefore separated D.cayenensis and D. alata
into two separate groups.

18. Nutrient D. alata D. esculenta D. rotundata
(s=16) (S=99) (S=3)
Moisture % 77.3 74.2 65.3
Protein % 2.06 2.04 1.52
Starch % 16.7 19.3 30.2
Sugars % 1.03 0.55 0.32
Fat % 0.08 0.06 0.09
Ca (mg/100g) 8.2 7.5 4.6
P (mg/100g) 38 39 28
Fe (mg/100g) 0.60 0.75 0.60
Zn (mg/100g) 0.39 0.46 0.30
Cu(mg/100g) 0.15 0.17 0.12
Vitamin A 0.018 0.017 0.8
(mg/100g)
Bradbury and Halloway,1988

19. Country Varieties Dry Minerals Starch Sugars Amylose Protein
(n) matter
Papua 43 23.5 5.1 67.5 3.3 17.5 12.0
New
Guinea
CV% 16.4 14.7 7.8 49.1 11.4 32
Vanuatu 48 23.4 3.3 73.1 1.85 17.2 11.9
CV% 17.15 15.2 9.1 91.3 11.6 17.8
Fiji 19 25.2 4.25 68.5 2.46 18.6 8.03
CV% 18.2 18.8 6.1 26.4 5.7 21.7
Source: SPNY,2003

20. Autopolyploidy arises from genome
duplication
X
species A
diploid
spontaneous autotetraploid
(fertile) genome (fertile)
duplication
Causes of genome duplication:
a) meiotic non-reduction of gametes (both in egg and sperm)
b) genome duplication w/o cytokinesis (after fertilization)

21. II. Allopolyploidy arises from
hybridization plus genome duplication
species A
Hybrid AB Hybrid AB Hybrid AABB
body cells during meiosis “allopolyploid”
X
species B
spontaneous
genome
duplication
aborted gamete
production
successful cell division
(fertile)
Duplicated genomes are fertile !!
Botanical term: Allopolyploids

22. III. Homologous pairing is predominant in
allopolplyoids
homologous pairing homeologous pairing

23. VI. Diploid vs. Allopolyploid hybridization
selfing generations genomes maintained
separately

24. 1. Because allopolyploids involves a merger of two fully
differentiated genome, pairing behavior during meiosis
is expected to resemble a diploid and disomic
segregation occurs.
2. In autopolyploid, during meiosis pairing can occur either
between randomly chosen pairs of homologous
chromosome call bivalent or between more than two
homologous pair of chromosomes (multivalent) and
polysomic inheritance occurs.

25.  Chromosome pairing in tetraploids can occur
that only homologue pair or such that any
two homeologue may pair.
 This two type of pairing may affect the
segregation pattern e.g. diploid or tetraploid
genetics.
 AFLP markers segregated like a diploid in
cross pollinated population, suggesting D.
rotundata is an allotetraploid 2n=4x=40,
(Mignouna and Asiedu,1999)

26. a) Disomic inheritance: Allotetraploid
 Strictly bivalent pairing
 If AAaa is selfed, there are 2 possibilities
1. Homologues are homozygous:
e.g. AA and aa; implies all gametes are Aa;
progeny are all AAaa.
2.Homologues are heterozygous: Aa,Aa
gametes are in ratio of 1AA:2Aa:1aa
Progeny are 15A-:1aaaa
(1AAAA:4AAAa:6AAaa:4Aaaa:1aaaa)

27. 3. AAaa test cross
1. Homologues are homozygous: AA ,aa all
gametes are Aa with all progenies being Aa.
2. If homologues are heterozygous Aa, Aa then
gametes are = 1AA:2Aa:1aa
All progenies are 3A-:1aaaa
B) Tetrasomic inheritance: polysomic
polyploidy (autotetraploids)
1. Any chromosome can pair with up to 3
homologues therefore we can have higher
order pairings e.g. quadrivalent.

28.  AAaa selfed: produces 1AA:4Aa:1aa gametes
Progeny ratio of 35A-:1aaaa
(1AAAA:8AAAa:18AAaa:8Aaaa:1aaaa)
 However AAaa testcross (x aaaa) gives
progeny 5A-:1aaaa.
 With tetraploids five different genotypes and
multiple alleles are possible:
1. AAAA:quadriplex 2.AAAa: triplex
3. AAaa: duplex 4.Aaaa: simplex
5.aaaa nulliplex

29.  Complex segregation e.g.
1.Selfing a duplex AAaa gives :
1/36 AAAA: 2/9 AAAa:1/2AAaa: 2/9 Aaaa:
1/36 aaaa.
2.While selfing a diploid Aa gives: 1/4 AA:
1/2Aa:1/4 aa.
 The situation becomes more complex at
higher ploidy level.

30.  It may not always be possible to distinguish
each of the heterozygous genotypes or
distinguish them from the homozygous
dominant depending on the type of marker
used.
 With a dominant marker, the genotype AAAA,
AAAa, AAaa, Aaaa, can not be distinguished
from one another.
 Therefore selfing a duplex AAaa will give a
segregation ratio of 35/36 [A] and 1/36 [a]

31.  With co-dominant markers genotype AAAA
and aaaa can be distinguished from
heterozygous AAAa, AAaa, Aaaa genotypes.
 Also the intensity of the electrophoretic band
may discriminate among the three
heterozygotes forms (Dubreuil et al.,1999.)

32.  The segregation of a duplex will be
informative , neglecting the homozygous
genotypes.
Therefore the segregation ratio of
2/9 AAAa:1/2AAaa: 2/9 Aaaa
is observed being close to that of a diploid
1/4AA:1/2Aa:1/4aa
 According to Wu et al., 1992, analysis of the
segregation should be based on the presence
or absence of a fragment in the progeny.

33.  A fragment represented by a single dose in a
parent is equivalent to an allele in the
heterozygous simplex state (Mmmm) M for
presence and m for absence.
 Half of the gamete will contain the allele and
half will not.
 A cross between a simplex plant and a
nulliplex plant (no fragment) will give a ratio
of 1:1 segregation regardless of the ploidy
level.

34.  Double dose restrictive fragment (DDRF)
genotypes (MMmm) can also be considered in
the same way to yield
1/6MMmm:2/3Mmmm:1/10 mmmm
 However, triple dose fragment (MMMm) will
not be informative because no segregation
will result if it is crossed to a plant with
absent or no fragments.

35. Dosage Diploid Tetraploid Hexapod Octaploid
1 1/2 1/2 1/2 1/2
2 1 5/6 4/5 11/14
3 1 19/20 13/14
4 1 1 39/70
Source: Ripol et al., 1999

36. 1. Improvement in agronomic traits e.g.
vegetative organs.
2. Increase in the differences between extreme
genotypes at each locus leading to greater
genetic variance.
3. Increase in genetic variability due to
presence of more than two alleles at one
locus with interactions between more than
two alleles.
4. Greater homeostasis in varying and variable
environment due to buffering capacity.

37. 1. Several International Research have
contributed to breeding.
2. Most researched species include D. alata D.
cayenensis and D. rotundata
3. Environment for research includes Nigeria,
India , Guadeloupe and Vanuatu
4. Other cultivated spp. are D.bulbifera,D.
esculenta, D.nummularia,D.opposita, D.
pentaphylla, D. transversa and D. trifida.

38.  Significant breeding effort for D.trifida made
by INRA in 1960 in Guadeloupe
 Selections obtained in 1971 for yield of
30t/ha unstaked
 IITA yam breeding and selection since 1970
focusing on D. rotundata.
Principal objectives :
1. High stable yield of marketable tubers
2. Suitability to cropping systems
3. Good quality e.g. DM, texture ,taste etc.

39. 4. Resistant to biotic stresses in the field.
5. Good postharvest storage.
The long term objective are:
to release genotypes adapted to non-stake
conditions and to partial or complete
mechanical harvesting. Tubers with shallow
settings, oval or round , tough skinned,
several tubers /plant are preferred

40.  The objectives of INRA, CIRAD and CTCRI for
D. alata are:
1. Major diseases e.g. Anthracnose cause by C.
gloeosporioides.
2. Physico-chemical characteristics of D. alata

41.  Goal: Develop and disseminate improve
technologies to increase the productivity of
yam based system in partnership with NARES
through:
1. strategies for integrated control of pests
and diseases in the field, during storage and
soil management.
2. reduced labor input in yam base system
3. manipulation of tuber dormancy to increase
efficiency in propagation and flexibility in
crop cycle

42. 3. Expand utilization opportunities through
processing into value added product.
4. Improving market channels to improve
productivity
Specific objectives:
1. High stable yield of marketable tubers
2. Host plant resistance for nematodes,
viruses, and fungi e.g. anthracnose
3. High tuber quality and characteristics
preferred by consumers.

43. 4. Suitability to the cropping system and
tolerance to abiotic stress i) nutrient
responsiveness and ii) tolerance to terminal
drought etc.
Problem of sexual hybridization
1. Sparse flowering
2. Poor synchronization of male and female
phase
3. Poor pollination mechanism

44. Achievement on sexual hybridization
1. Many parental genotypes that combine
good agronomic trait with reliable flowering
identified
2. Techniques to manipulate the flowering
period to enhance synchronization and
extended pollination established.
3. Anthesis period of pollination viability and
stigma receptivity have been determined for
the relevant species.
4. Pollen storage over two years has been
demonstrated

45. 1. Rapid propagation of introduced genotypes
as parents in selection cycle.
2. Rapid propagation of improved hybrids for
advanced clonal evaluation or for
distribution.
3. Best ways are the use of the mini-sett
technique, rooted stem cuttings and in vitro
growth of nodal segments.

46.  Determine Objectives.
 Identify Source of Genetic Variation/
Genetic Recombination.
 Selection of Superior Progenies/ Generation
Advance.
 Testing of Experimental Varieties/ Release

47. 1. Conventional plant breeding
2. Biotechnology (molecular markers , wide
crosses, double haploids) to overcome
species barrier/improve breeding efficiency.
3. Interdisciplinary collaboration

48.  Characterization and germplasm evaluation
1. field performance
2. tuber quality
3. morphology
4. ploidy status
 Selection of parents for hybridization
through biparental crosses.
 Open pollination among selected clones
planted in isolation.

49.  Seedling evaluation in nurseries
 Clonal trial for selection of superior genotypes
1. Unreplicated observational trial
2. Preliminary yield trial
3. Advance yield trial etc.
 Evaluations of cooking quality ,processing
etc.
 Multiplication of propagules
 Regional collaborative trial with partners

50. Yam improvement scheme
CLONAL COLLECTION
CLONAL COLLECTION
Evaluation and selection
Evaluation and selection
Send to
NARS HYBRIDIZATION BLOCKS
HYBRIDIZATION BLOCKS
Send from
NARS
SEEDLING NURSERY
SEEDLING NURSERY
Year 1 evaluate resistance to diseases
and pests
Evaluation and selection
CLONAL EVALUATION Year 2-3 evaluate resistance to diseases
CLONAL EVALUATION
and pests
Evaluation and selection
PRILIMINARY YIELD TRIAL Year 4 evaluate resistance to diseases
PRILIMINARY YIELD TRIAL and pests ; tuber conformation and yield
Evaluation and selection
ADVANCED YIELD TRIAL Year 5-6 evaluate resistance to
ADVANCED YIELD TRIAL diseases and pests ;tuber
conformation , yield and quality
Evaluation and selection
MULTIPLICATION, VIRUS ELIMINATION, DISTRIBUTION
MULTIPLICATION, VIRUS ELIMINATION, DISTRIBUTION
V
V
REGIONAL COLLABORATIVE TRIAL WITH NARS Evaluate resistance to diseases and
pests; tuber conformation, yield
and quality

51.  Isozymes:
1. Low cost , allows screening of large number
of accessions
2. Low polymorphism
 DNA markers (RFLP, AFLP,SSR and RAPD)
1. More accurate
2. Expensive
3. Labor -intensive

52.  Molecular markers: characterization and early
screening.
 Tissue culture: haploidization and mapping
population development.
 Genome studies: ploidy , QTL mapping
 Plant genetic transformation: gene transfer

53. 1. Two heterozygous parents (P1, P2) are
mated to produce a full sib F1 family which
is subsequently replicated through cloning
(tissue culture)
2. QTL mapping is conducted using
phenotypic measurements on the F1 clones.
3. Suitable for species like yam where full sib
crosses is difficult , vegetative propagation
is easy and hybrids are heterotic .
4. Mainly use dominant markers for pseudo
test cross analysis.

54. 1. With dominant markers the design can be
reduced to the paternal and maternal
backcross mating types hence the name
pseudo test cross (PTC).
2. The PTC mating has Aa and aa genotypic
classes which can be discerned with
dominant markers.
3. Expedient for spp. not widely studied as a
genetic models or poor pedigree records.
4. Failed PCR not disquishable from null allele.

55.  Could also apply to co-dominant markers for
Intercross, maternal and paternal informative
mating types.

56.  Easy exchange or sharing of germplasm
with other countries and institutions.
 Marker assisted selection (MAS) should be
given priority for resistance breeding for
both biotic and abiotic stresses.
 Varieties suitable for low inputs eg
fertilizer, pesticide, weedicide etc. should
be bred for the resource poor farmers.
 Interspecific hybridization of wild spp. and
cultivated spp for disease resistance
breeding .

57.  Application of haploids in breeding should
be investigated to speed up breeding
process .
 Varieties with improved shelf life, rich in
nutritive values and suitable for
processing should be developed e.g.pro-
vitamin A (β-carotene) Fe, Ca and Zn
(nutrient fortification) .
 Embryo rescue to unlock genetic potential
in wild yam via wide crosses

58.  Varieties with increased opportunities for
market for the fresh and value added
products e.g. High quality flour, starch,
storage , taste , flavor , anthocyanin, starch
for tablets, baby food etc.
 Acceptable varieties as dietary source of pro-
vitamin A, Fe, Zn to address nutrition and
health issues.

59.  Need for the improvement of starch and
carbohydrate quality of yam, since high
glycemic index starches (high amylopectin
with low amylose content) are related with
conditions such as type 2 diabetes and
insulin resistance.
 Modification of starch in yam to increase
amylose and amylopectin ratio would improve
the glycemic index (effect on blood sugar
level) to improve the nutritional quality and
subsquently have effect on health.

60. Table 6: The Glycemic index of Yam
carb/serve
Food and Manufacturer
GI serve (g) (g) GL
Yam, peeled, boiled 35 150 36 13
Yam 54 150 36 19
Yam, steamed 51 150 36 18
Yam (Dioscorea spp.), boiled 74 150 38 28
Yam (Dioscorea spp.), boiled, consumed with
74 150 38 28
4.24 g salt
Coco yam (Xanthosoma spp.), peeled, cubed,
61 150 46 28
boiled 30 min
Lucea Yam (Dioscorea rotundata), peeled,
74 150 27 20
cubed, boiled 30
Lucea Yam (Dioscorea rotundata), peeled,
77 150 38 29
roasted on preheated charcoal
Source http://www.glycemicindex.com/

61.  From a technical point of view, it may be
concluded that the key step for enhancing the
standard of yam breeding is to meet its
objectives is to build a bridge between
conventional breeding and molecular
techniques .
 Where molecular markers linked to target
genes can be identified accurately so that
breeders can make selection based on the
genotype of each plant by molecular markers.