Chromosomal Inheritance in Myriophyllum spicatum x M. sibiricum hybrids

Allopolyploidy and autopolyploidy are common genome complexities in plants and can be distinguished on the basis of how their duplicated sets of chromosomes align during meiosis. Differences in chromosomal inheritance pattern changes the way molecular markers are generated and studied under each model. Eurasian watermilfoil (Myriophyllum spicatum L.; EWM) and interspecific hybrids with northern watermilfoil (Myriophyllum sibiricum Komarov; NWM) are invasive aquatic weeds in the United States. However, EWM, NWM, and their hybrids are hexaploid (2n = 6x = 42), which complicates genotyping and genetic analysis. We created a mapping population by self-pollinating a single hybrid EWM x NWM watermilfoil and determined genotypes genome-wide using genotyping-by-sequencing. These sequencing data were analyzed using both a de novo genome and reference-based approach to determine the most likely inheritance type in these polyploid hybrids. We found overwhelming evidence for allopolyploid inheritance of chromosomes in Eurasian, northern, and hybrid watermilfoil. Our confirmation of disomic inheritance and diploidized markers will improve the ability to conduct basic population genetic analyses of watermilfoil, including distinguishing sexual versus asexual (clonal) reproduction, population structure, hybridization, and introgression.