Genome diversity and phylogeny of the section Alatae of genus Lemna (Lemnaceae), comprising the presumed species Lemna aequinoctialis, Le. perpusilla and Le. aoukikusa

Abstract

O_LIThe Section Alatae of genus Lemna of the monocotyledonous aquatic duckweed family (Lemnaceae) consists of rather diverse accessions with unknown phylogeny and unclear taxonomic assignment. In contrast to other duckweeds, some Alatae accessions, in addition to mainly vegetative propagation, produce readily flowers and viable seeds. We analyzed the genomic diversity and phylogenetic relationship of 52 Alatae accessions. C_LIO_LIFor this purpose, we applied multiple molecular and cytogenetic approaches, including plastid and nuclear sequence polymorphisms, chromosome counting, genome size determination and genomic in situ hybridization in combination with geographic distribution. C_LIO_LIWe uncovered ploidy variation, recurrent hybridization, and backcrosses between diploid species and their hybrids. The latter successfully spread over three continents. C_LIO_LIThe results elucidate the evolution of Alatae accessions (summarized in Fig. 7) and explain the difficult taxonomic assignment of distinct accessions. Our study might be an example for analogous studies to resolve the hitherto unclear relationships among accessions of the duckweed genera Wolffiella and Wolffia. C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=166 SRC="FIGDIR/small/632899v1_fig7.gif" ALT="Figure 7"> View larger version (23K): org.highwire.dtl.DTLVardef@d05f08org.highwire.dtl.DTLVardef@f33c5org.highwire.dtl.DTLVardef@ff7adorg.highwire.dtl.DTLVardef@4da6e4_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFigure 7C_FLOATNO Hypothetical scenario of evolution within Lemna Section Alatae. In bold are accessions from America. The classically defined diploid species Le. aequinoctialis and Le. perpusilla sensu stricto were confirmed by the applied molecular methods. The previously named Le. aoukikusa accessions were uncovered as tetraploid interspecific hybrids between Le. aequinoctialis and Le. perpusilla. In addition, further tri- and tetraploid hybrids as well as tri- and tetraploid "Backcross hybrids" were detected from the USA and China, respectively. C_FIG