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    Historical introgressions from a wild relative of modern cassava improved important traits and may be under balancing selection

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    S19ArtWolfeHistoricalInthomDev.pdf (4.188Mb)
    Date
    2019-10
    Author
    Wolfe, M.D.
    Bauchet, G.J.
    Chan, A.W.
    Lozano, R.
    Ramu, P.
    Egesi, C.
    Kawuki, R.
    Kulakow, P.
    Rabbi, I.
    Jannink, J.L.
    Type
    Journal Article
    Target Audience
    Scientists
    Metadata
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    Abstract
    Introgression of alleles from wild relatives has often been adaptive in plant breeding. However, the significance of historical hybridization events in modern breeding is often not clear. Cassava (Manihot esculenta) is among the most important staple foods in the world, sustaining hundreds of millions of people in the tropics, especially in sub-Saharan Africa. Widespread genotyping makes cassava a model for clonally-propagated root and tuber crops in the developing world and provides an opportunity to study the modern benefits and consequences of historical introgression. We detected large introgressed M. glaziovii genome-segments in a collection of 2742 modern cassava landraces and elite germplasm, the legacy of 1930's era breeding to combat disease epidemics . African landraces and improved varieties were on average 3.8% (max 13.6% ) introgressed. Introgressions accounted for significant (mean 20% , max 56% ) portion of the heritability of tested traits. M. glaziovii alleles on the distal 10Mb of chr. 1 increased dry matter and root number. On chr. 4, introgressions in a 20Mb region improved harvest index and brown streak disease tolerance. We observed the introgression frequency on chr. 1 double over three cycles of selection and that later stage trials selectively excluded homozygotes from consideration as varieties. This indicates a heterozygous advantage of introgressions. However, we also found that maintaining large recombination-suppressed introgressions in the heterozygous state allowed the accumulation of deleterious mutations. We conclude that targeted recombination of introgressions would increase the efficiency of cassava breeding by allowing simultaneous fixation of beneficial alleles and purging of genetic load.
    https://dx.doi.org/10.1534/genetics.119.302757
    Multi standard citation
    Permanent link to this item
    https://hdl.handle.net/20.500.12478/6544
    Non-IITA Authors ORCID
    Chiedozie Egesihttps://orcid.org/0000-0002-9063-2727
    Peter Kulakowhttps://orcid.org/0000-0002-7574-2645
    Ismail Rabbihttps://orcid.org/0000-0001-9966-2941
    Jean-Luc Janninkhttps://orcid.org/0000-0003-4849-628X
    Digital Object Identifier (DOI)
    https://dx.doi.org/10.1534/genetics.119.302757
    Research Themes
    BIOTECH & PLANT BREEDING
    IITA Subjects
    Agronomy; Cassava; Plant Breeding
    Agrovoc Terms
    Cassava; Introgression; Genetics; Heterozygotes; Breeding; Africa South Of Sahara
    Regions
    Africa; East Africa; West Africa
    Countries
    Nigeria; Uganda
    Journals
    Genetics
    Collections
    • Journal and Journal Articles4137
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