Food security and poverty alleviation: opportunities through yam breeding


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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

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Food security and poverty alleviation: opportunities through yam breeding

  2. 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. 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. 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. 5.  According to UNICEF, 26,500-30,000 children die each day due to poverty. (source 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. 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. 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. 8. Table 1: Production (in ‘000 tons) and Area (in’ 000 ha) of yam by ContinentsContinent Production(in’000 Area (in’000 ha) % of world tons) productionAfrica 44514.5 4598.6 94.9Asia 234.3 15.4 0.5Europe 2.7 0.16 0.005Caribbean 486.8 77.8 1.03Oceania 343.7 52.9 0.73South America 599.9 62 1.27World total 46920.7 4781.1 100Source: FAO,2007
  9. 9. Continent CountriesAfrica Benin, Burkina Faso, Burundi, Cameroon, Central African Rep., Chad, Comoros, DR. Congo, Ethiopia, Garbon, Ghana, Guinea, Kenya, Liberia, Mali, Nigeria, Sudan,TogoAsia Japan, PhilippinesEurope PortugalCaribbean Cuba, Barbados, Dominica Republic, Guadeloupe, HaitiOceania Papua New Guinea, Solomon Island, Tonga, VanuatuSouth Brazil, Colombia, Guyana, VenezuelaAmerica
  10. 10.  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.
  11. 11. 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 Ibom400 0 400 800 Kilometers Major Yam Producing Areas in Nigeria
  12. 12.  Six important staples include1. 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)
  13. 13.  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
  14. 14.  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?
  15. 15.  Long life cycle Dioecy and polyploidy Poor to non-flowering Vegetative propagation Juvenile phase Yam mosaic disease Anthracnose disease
  16. 16.  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.
  17. 17. Nutrient D. alata D. esculenta D. rotundata (s=16) (S=99) (S=3)Moisture % 77.3 74.2 65.3Protein % 2.06 2.04 1.52Starch % 16.7 19.3 30.2Sugars % 1.03 0.55 0.32Fat % 0.08 0.06 0.09Ca (mg/100g) 8.2 7.5 4.6P (mg/100g) 38 39 28Fe (mg/100g) 0.60 0.75 0.60Zn (mg/100g) 0.39 0.46 0.30Cu(mg/100g) 0.15 0.17 0.12Vitamin A 0.018 0.017 0.8(mg/100g) Bradbury and Halloway,1988
  18. 18. Country Varieties Dry Minerals Starch Sugars Amylose Protein (n) matterPapua 43 23.5 5.1 67.5 3.3 17.5 12.0NewGuineaCV% 16.4 14.7 7.8 49.1 11.4 32Vanuatu 48 23.4 3.3 73.1 1.85 17.2 11.9CV% 17.15 15.2 9.1 91.3 11.6 17.8Fiji 19 25.2 4.25 68.5 2.46 18.6 8.03CV% 18.2 18.8 6.1 26.4 5.7 21.7 Source: SPNY,2003
  19. 19. Autopolyploidy arises from genome duplication Xspecies 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)
  20. 20. II. Allopolyploidy arises from hybridization plus genome duplicationspecies A Hybrid AB Hybrid AB Hybrid AABB body cells during meiosis “allopolyploid” Xspecies B spontaneous genome duplication aborted gamete production successful cell division (fertile) Duplicated genomes are fertile !! Botanical term: Allopolyploids
  21. 21. III. Homologous pairing is predominant in allopolplyoidshomologous pairing homeologous pairing
  22. 22. VI. Diploid vs. Allopolyploid hybridizationselfing generations genomes maintained separately
  23. 23. 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.
  24. 24.  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)
  25. 25. a) Disomic inheritance: Allotetraploid Strictly bivalent pairing If AAaa is selfed, there are 2 possibilities1. 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)
  26. 26. 3. AAaa test cross1. 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-:1aaaaB) 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.
  27. 27.  AAaa selfed: produces 1AA:4Aa:1aa gametesProgeny 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: triplex3. AAaa: duplex 4.Aaaa: simplex5.aaaa nulliplex
  28. 28.  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.
  29. 29.  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]
  30. 30.  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.)
  31. 31.  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.
  32. 32.  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.
  33. 33.  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.
  34. 34. Dosage Diploid Tetraploid Hexapod Octaploid1 1/2 1/2 1/2 1/22 1 5/6 4/5 11/143 1 19/20 13/144 1 1 39/70Source: Ripol et al., 1999
  35. 35. 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.
  36. 36. 1. Several International Research have contributed to breeding.2. Most researched species include D. alata D. cayenensis and D. rotundata3. Environment for research includes Nigeria, India , Guadeloupe and Vanuatu4. Other cultivated spp. are D.bulbifera,D. esculenta, D.nummularia,D.opposita, D. pentaphylla, D. transversa and D. trifida.
  37. 37.  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 tubers2. Suitability to cropping systems3. Good quality e.g. DM, texture ,taste etc.
  38. 38. 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
  39. 39.  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
  40. 40.  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 system3. manipulation of tuber dormancy to increase efficiency in propagation and flexibility in crop cycle
  41. 41. 3. Expand utilization opportunities through processing into value added product.4. Improving market channels to improve productivitySpecific objectives:1. High stable yield of marketable tubers2. Host plant resistance for nematodes, viruses, and fungi e.g. anthracnose3. High tuber quality and characteristics preferred by consumers.
  42. 42. 4. Suitability to the cropping system and tolerance to abiotic stress i) nutrient responsiveness and ii) tolerance to terminal drought etc.Problem of sexual hybridization1. Sparse flowering2. Poor synchronization of male and female phase3. Poor pollination mechanism
  43. 43. Achievement on sexual hybridization1. Many parental genotypes that combine good agronomic trait with reliable flowering identified2. 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
  44. 44. 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.
  45. 45.  Determine Objectives. Identify Source of Genetic Variation/ Genetic Recombination. Selection of Superior Progenies/ Generation Advance. Testing of Experimental Varieties/ Release
  46. 46. 1. Conventional plant breeding2. Biotechnology (molecular markers , wide crosses, double haploids) to overcome species barrier/improve breeding efficiency.3. Interdisciplinary collaboration
  47. 47.  Characterization and germplasm evaluation1. field performance2. tuber quality3. morphology4. ploidy status Selection of parents for hybridization through biparental crosses. Open pollination among selected clones planted in isolation.
  48. 48.  Seedling evaluation in nurseries Clonal trial for selection of superior genotypes1. Unreplicated observational trial2. Preliminary yield trial3. Advance yield trial etc. Evaluations of cooking quality ,processing etc. Multiplication of propagules Regional collaborative trial with partners
  49. 49. Yam improvement scheme CLONAL COLLECTION CLONAL COLLECTION Evaluation and selection Evaluation and selectionSend 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
  50. 50.  Isozymes:1. Low cost , allows screening of large number of accessions2. Low polymorphism DNA markers (RFLP, AFLP,SSR and RAPD)1. More accurate2. Expensive3. Labor -intensive
  51. 51.  Molecular markers: characterization and early screening. Tissue culture: haploidization and mapping population development. Genome studies: ploidy , QTL mapping Plant genetic transformation: gene transfer
  52. 52. 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.
  53. 53. 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.
  54. 54.  Could also apply to co-dominant markers forIntercross, maternal and paternal informative mating types.
  55. 55.  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 .
  56. 56.  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 vitamin A (β-carotene) Fe, Ca and Zn (nutrient fortification) . Embryo rescue to unlock genetic potential in wild yam via wide crosses
  57. 57.  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.
  58. 58.  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.
  59. 59. Table 6: The Glycemic index of Yam carb/serveFood and Manufacturer GI serve (g) (g) GLYam, peeled, boiled 35 150 36 13Yam 54 150 36 19Yam, steamed 51 150 36 18Yam (Dioscorea spp.), boiled 74 150 38 28Yam (Dioscorea spp.), boiled, consumed with 74 150 38 284.24 g saltCoco yam (Xanthosoma spp.), peeled, cubed, 61 150 46 28boiled 30 minLucea Yam (Dioscorea rotundata), peeled, 74 150 27 20cubed, boiled 30Lucea Yam (Dioscorea rotundata), peeled, 77 150 38 29roasted on preheated charcoal Source
  60. 60.  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.