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Abstract
Peanut (Arachis hypogaea L.) is a segmental allotetraploid species that originated less than 10,000 years ago from the spontaneous hybridization of two diploid wild Arachis species, A.
duranensis and A. ipaënsis, followed by a whole-genome duplication event. This polyploidization
event was associated with a drastic reduction in gene pool variation. However, the merging of
different genomes during peanut’s origin triggered a genetic shock, which in turn produced various
types of genetic instability. These instability phenomena increased overall phenotypic variability
and conferred on peanut the adaptability traits typical of polyploid plants. As a result, despite the
narrow genetic basis, peanut evolved into a morphologically diverse species, colonized different
environments, and became the primary candidate for domestication within the Arachis genus. This
dissertation investigates the extent and impact of genetic instability in peanut, focusing on
homoeologous exchange, genetic recombination event between partially homologous
chromosomes from different subgenomes in a polyploid organism, and double reduction, a meiotic
process that increases homozygosity and is linked to multivalent pairing and homoeologous
recombination. We analyzed induced neoallopolyploids, derived from wild species, and cultivated
genotypes. We observed high levels of instability and novel unbalanced genomic compositions in
neoallotetraploid lines such as IpaDur1 (created from a recent cross between A. ipaënsis K 30076
and A. duranensis V 14167). Notably, IpaDur1 exhibited greater phenotypic diversity and a
stronger response to selection, including increased seed size, compared to its diploid progenitors,
suggesting that polyploidy-induced variability may have facilitated the emergence of early
domestication traits. In cultivated genotypes, including Georgia-06G, Tifguard, and Tifrunner, we
evaluated the persistence of genetic instability for several generations. In addition, we estimated
the frequency of double reduction in a BC1 population derived from a cultivated peanut × [A.
magna K 30097 × A. stenosperma V 15076]4x (MagSten). We also investigated the role of genetic
instability in contributing to seed heterogeneity, particularly in Georgia-06G and Tifguard. In
Tifrunner and Georgia-06G, over 1% of samples displayed spontaneous novel unbalanced
genomic compositions. Overall, our results demonstrate that genetic instability is a continuing
feature of the peanut genome. It contributes to genetic and phenotypic diversity but also presents
challenges for breeding programs and seed purity management.