Pre breeding procedures and methods introgression
- 2. Aim of the module At the end of the module, we should be able to: • provide a definition of pre-breeding; • explain the usefulness and scope of pre- breeding; • describe the context in which pre-breeding is carried out; and • identify the situations to which pre-breeding is best applied
- 3. Second GPA for PGRFA as template •Collections •In-Situ •Ex-Situ Conservation • Crop Improvement • Breeding • Pre-breeding Utilization •Seed Sectors •Formal •Informal Delivery The PGRFA Management Continuum Building Sustainable Institutional and Human Capacities
- 4. Introduction Premise • Present day agriculture = Evolution + Selections by farmers • Plant breeding is the science (and art) of combining important traits in varieties of commercial, social or aesthetic interest • Plant genetic resources for food and agriculture (PGRFA) as building blocks for ‘designing’ new varieties • Crop improvement is akin to a pipeline: – Ingredients (genes) are fed in at beginning -- blended, tested, selected, tested some more -- and finished product (improved varieties) emerges for farmers to use • Pre-breeding is the beginning segment of this pipeline
- 5. What is pre-breeding? • Broadly, the management of PGRFA involves two basic components: conservation and use • Pre-breeding refers to all activities designed to: – identify desirable characteristics and/or genes from non- adapted (exotic or semi-exotic) materials, and – transfer these traits into an intermediate set of materials • Plant breeders, should ultimately, be able to manipulate the intermediate materials further to develop new varieties • Pre-breeding is at the interface of conservation of PGRFA and plant breeding – Is therefore a multi-disciplinary endeavor
- 6. Stock taking • Since the beginning of the 20th century, plant breeders have methodically leveraged an ever-increasing set of knowledge, skills and tools to: – add value to PGRFA , and – hence make crops better for humankind • But, current crop varieties may be unsuited to the burgeoning set of challenges and opportunities. So, – What are the alternatives? – How to achieve genetic in the absence of easily exploitable traits (and genes)? – How can genes be accessed to address this multiplicity of needs?
- 7. Stock taking • Fortunately, existing variants of most crops have quite a broad genetic base – Significant efforts and investments have resulted in the collection, characterization, evaluation, documentation, conservation and distribution of PGRFA • Most of the world’s important crops are in genebanks • These genebanks are the reservoirs for: – different variations of the traits still used by farmers; – traits that are no longer needed by farmers; – traits that evolved but may never previously have been used by farmers; or – traits that have not yet been discovered
- 8. Stock taking • About 7.2 million accessions in over 1300 genebanks1 • But these accessions are not used optimally in crop improvement because: – Lack of documentation and adequate description of collections – Insufficient evaluation of the collection – Limited input by breeders during documentation to understand what information would be most valuable – Accessions with limited environmental adaptability – Accessible materials not always suited to agronomic needs – Adequate quantities of seed are not available in a timely manner 1The Second Report on the State of the World’s PGRFA. FAO. 2010. http://www.fao.org/docrep/013/i1500e/i1500e00.htm
- 9. Pre-breeding Aims at: • Introgression; or • base broadening Pre-breeding vs breeding? • Generally, in a pre-breeding scheme: – By necessity close collaboration between genebank managers and breeders; – Greater likelihood of more complex hybridization issues; – Linkage drags – End product of pre-breeding is raw material for breeding • Breeding results in a new variety
- 10. Pre-breeding • Rule of thumb – multidisciplinarity and communication between – Genebank managers, and – Plant breeders – They jointly set out a strategy for combining resources and expertise to achieve a common goal • Generating intermediate materials utilizable in plant breeding • The interface includes – evaluation for traits of interest & data management, – study of reproductive biology, – additional multiplication to make materials available for crossing, and – collaboration in hybridization
- 11. Judicious pre-breeding: ‘Decision tree’ • No pre-breeding needed if one of the following is available: – Commercially-available adapted and acceptable varieties – Advanced selections, well-adapted to the target environment – Genebank accessions that are well-adapted to the target environment • Pre-breeding probably needed if only one of the following is available: – Genebank accessions not well-adapted to the target environment – Closely related wild species easily crossed with the crop species – Wild species less closely related and more difficult to cross
- 12. Some Examples of Pre-breeding • Maize • Musa • Sesame • Cassava • Sugarcane • Common bean
- 13. Use of CWR in plant breeding Natural introgression of traits from CWRs to cultivars, e.g. sorghum in Mali?
- 14. Tips ….. Pre-breeding efforts will be enhanced by • Information on gene pool origins, domestication syndrome traits, molecular diversity, and mapping data of the wild forms; • Indirect screening for biotic and abiotic stresses; and • Marker-assisted selection
- 15. Conclusions • Domestication and selections (plant breeding and farmers) have narrowed the genetic base of most of our crop genepools • But, plant breeding continues to yield gains • Concerns over long-term sustainability of crop improvement resulting in enhanced conservation and sustainable use of PGRFA • Use of genebank accessions directly in breeding programmes is fraught with constraints • Pre-breeding is, in effect, a bridge between genebanks and breeding programmes
- 16. Summary • Pre-breeding should aim to: – identify potentially useful genes in a well- organized and documented genebank, and – design strategies that lead to development of an improved germplasm ready to use in varietal development • Pre-breeding is a collaborative endeavour, that is buttressed by communication, between genebank curators and breeders