Genomic relationships among diploid and polyploid species of the genusLudwigiaL. sectionJussiaeausing a combination of molecular cytogenetic, morphological, and crossing investigations

Abstract

The genus Ludwigia L. section Jussiaea is composed of a polyploid species complex with 2x, 4x, 6x and 10x ploidy levels, suggesting possible hybrid origins. The aim of the present study is to understand the genomic relationships among diploid and polyploid species in the section Jussiaea. Morphological and cytogenetic observations, controlled crosses, genomic in situ hybridization (GISH), and flow cytometry were used to characterize species, ploidy levels, ploidy patterns, and genomic composition across taxa. Genome sizes obtained were in agreement with the diploid, tetraploid, hexaploid, and decaploid ploidy levels. Results of GISH showed that progenitors of Ludwigia stolonifera (4x) were Ludwigia peploides subsp. montevidensis (2x) and Ludwigia helminthorrhiza (2x), which also participated for one part (2x) to the Ludwigia ascendens genome (4x). Ludwigia grandiflora subsp. hexapetala (10x) resulted from the hybridization between L. stolonifera (4x) and Ludwigia grandiflora subsp. grandiflora (6x). One progenitor of L. grandiflora subsp. grandiflora was identified as L. peploides (2x). Our results suggest the existence of several processes of hybridization, leading to polyploidy, and possibly allopolyploidy, in the section Jussiaea due to the diversity of ploidy levels. The success of GISH opens up the potential for future studies to identify other missing progenitors in Ludwigia L. as well as other taxa.

Reproductive modes in populations of late-acting self-incompatible and self-compatible polyploidLudwigia grandiflorasubsp.hexapetalain western Europe

“…However, theoretical predictions argue that this kind of higher genetic diversity favored and maintained in SI populations as compared to panmictic and SC populations must only be found on polymorphic markers highly physically linked to the genomic regions involved in the SI mechanisms that evolve under balancing selection, and also, at a lesser magnitude, on physically unlinked markers but only in small population, with less than 100 individuals including clones (Glémin et al 2001, Navascues et al 2010). The 36 SNPs we developed must randomly distribute over the 16 chromosomes inherited twice from a common ancestor with Lpm , i.e., 32 chromosomes out of 80 total chromosomes of Lgh (Barloy et al 2024), with no reason that all aggregate around the genes involved in the LSI self-recognition. In addition, individuals and populations of Lpm are reported to massively use self-fertilization, thus with no SI system (Estes& Thorp 1974, Grewel et al 2016).…”

“…Nesom and Kartesz (2000), hereafter Lgh , is one of the most invasive aquatic plants in the world (Thouvenot et al 2013). Lgh is an alloautodecaploid species (2n=10x=80 chromosomes), resulting from hybridization of different ancestral diploid species, some of which are represented more than once in the total genome of Lgh , which belongs to the genus Ludwigia L. section Jussiaea (Hoch et al 2015, Barloy et al, 2024). Interestingly, Lgh includes an autotetraploid set of chromosomes, shared with L. peploides subsp.…”

“…Interestingly, Lgh includes an autotetraploid set of chromosomes, shared with L. peploides subsp. montevidensis (2n=2x=16), hereafter Lpm , that is clearly distinct from the other ancestral part of the Lgh genome (Barloy et al 2024). Lpm is a self-compatible-only diploid species with only one common floral morphology (Estes & Thorp 1974, Grewel et al 2016).…”

“…To be sure of the ploidy level of the studied markers and that the genotyped markers did not interact with genomes of the other ancestral species of Lgh genome, we genotyped SNPs only within the autotetraploid part of the Lgh genome shared with the diploid species Lpm . The Lpm genome is sufficiently genetically distinct from the other ancestral genomes of Lgh to avoid misgenotyping (Barloy et al 2024).…”

“…Selfing also prohibits genetic mixing between different ancestral lineages, which decreases heterozygosity within individuals (David et al 2007, Hardy 2016) and strongly increases linkage disequilibrium between genes along genomes (Golding & Strobeck 1980, Norborg 2000, Lucek & Willi 2021. Around half of hermaphrodite plants restrict self-fertilization using a variety of molecular mechanisms grouped under the term "self-and F2 descendants (Portillo-Lemus 2021) while inter-species crosses only result in a low number of chlorotic and unfertile descendants (Barloy et al 2024).…”