Discovery and characterization of sweetpotato’s closest tetraploid relative

Abstract

Summary The origin of sweetpotato, a hexaploid species, is poorly understood, partly because the identity of its tetraploid progenitor remains unknown. In this study, we identify, describe and characterize a new species of Ipomoea that is sweetpotato’s closest tetraploid relative known to date and probably a direct descendant of its tetraploid progenitor. We integrate morphological, phylogenetic, and genomic analyses of herbarium and germplasm accessions of the hexaploid sweetpotato, its closest known diploid relative Ipomoea trifida, and various tetraploid plants closely related to them from across the American continent. We identify wild autotetraploid plants from Ecuador that are morphologically distinct from Ipomoea batatas and I. trifida, but monophyletic and sister to I. batatas in phylogenetic analysis of nuclear data. We describe this new species as Ipomoea aequatoriensis T. Wells & P. Muñoz sp. nov., distinguish it from hybrid tetraploid material collected in Mexico; and show that it likely played a direct role in the origin of sweetpotato’s hexaploid genome. This discovery transforms our understanding of sweetpotato’s origin.

Horizontal transferred T-DNA and haplotype-based phylogenetic analysis uncovers the origin of sweetpotato

“…There are two speculations about the relationship between the basal 4x and sweetpotato. The first one considers the basal 4x as the tetraploid progenitor of sweetpotato 22 , whilst the second one treats the basal 4x as hybrid offsprings between sweetpotato and I. trifida 23 . In current study, we simulated three tetraploid hybrids of I. trifida and sweetpotato by randomly sampling reads from the closest accession of I. trifida (CIP698014) related to sweetpotato, and three sweetpotato cultivars at a ratio of 1:3 and integrating the sampled reads respectively.…”

“…The origin of sweetpotato is still the subject of fierce debate. Competing hypotheses have been put forward proposing that sweetpotato is an autopolyploid, a segmental allopolyploid, or an allopolyploid 8,9,16,18,19,22,23,40,41 . The genetic origin of sweetpotato has remained unresolved because of the high complexity of the genome, due to its hexaploid nature and high degree of heterozygosity 5,26 .…”

Out of the wild: the wild (and often weedy) roots of our crops

“…Such hybridisation events between crops and CWRs can obscure historical patterns and create novel combinations that are seen as ‘ringers’ in the evolutionary story, as Muñoz‐Rodríguez et al . (2022) document with sweetpotato.…”

“…Understanding the ancestry and evolutionary history of crops is challenging, however, and requires the unification of two, often widely separated, knowledge systemsplant breeding and biodiversity science. In this issue of New Phytologist, Muñoz-Rodr ıguez et al (2022; pp. 1185-1194 provide a compelling example of how the two can meet with their investigation into the ancestry of the cultivated sweetpotato (Ipomoea batatas (L.) Lam.…”

“…Ladefoged et al, 2005;Roullier et al, 2013a, b). Muñoz-Rodr ıguez et al (2022) identify and name a new species that represents the closest tetraploid relative of the cultivated sweetpotato. Sweetpotato is a hexaploid crop and was originally thought to be of autoploid origin, where genome doubling without hybridisation in I. trifida, a diploid ancestor native to the Caribbean (Roullier et al, 2013b;Muñoz-Rodr ıguez et al, 2018), gave rise to the cultivated species.…”