Abstract
The invasive aquatic plant Eurasian watermilfoil (Myriophyllum spicatum L.) can hybridize with the related North American native species northern watermilfoil (M. sibiricum Kom.). Hybrid watermilfoil (M. spicatum × M. sibiricum) populations have higher fitness and reduced sensitivity to some commonly used aquatic herbicides, making management more difficult. There is growing concern that management practices using herbicides in lakes with mixed populations of watermilfoil species may further select for hybrid individuals due to the difference in herbicide sensitivity. Accurate and cost-effective identification of rare hybrid individuals within populations is therefore critical for herbicide management decisions. Here we describe KASP assays for three SNPs in the ITS region to genotype individuals from both parental watermilfoil species and their hybrid, using synthesized plasmids containing the respective sequences as positive controls. Using KASP we genotyped 16 individuals from one lake and 23 individuals from a second lake, giving a highly accurate picture of Myriophyllum species distribution dynamics. We identified one hybrid individual among 16 samples from one lake, a discovery rate of <10%. Discriminant analysis showed that while a single SNP was generally sufficient for genotyping an individual, using multiple SNPs increased the reliability of genotyping. In the future, the ability to genotype many samples will provide the ability to identify the presence of rare individuals, such as a less common parental species or the inter-specific hybrid. Lakes with complex species distribution dynamics, such as a low proportion of hybrids, are where herbicide application must be carefully chosen so as not to select for the more vigorous and less herbicide-sensitive hybrid individuals.
Highlights
The invasive aquatic plant Eurasian watermilfoil (Myriophyllum spicatum L.) was introduced to the United States from Asia during the 1940s (Couch and Nelson, 1988; Moody et al, 2016)
We developed three Kompetitive Allele Specific PCR (KASP) primer sets that distinguish between the native M. sibiricum and the invasive M. spicatum species as well as inter-specific hybrids
We tested the primer sets on plasmids containing known sequences, on known lab biotypes of M. spicatum and hybrids, and on unknown Myriophyllum individuals harvested from two lakes in northern Colorado
Summary
The invasive aquatic plant Eurasian watermilfoil (Myriophyllum spicatum L.) was introduced to the United States from Asia during the 1940s (Couch and Nelson, 1988; Moody et al, 2016) After introduction, this submersed species spread rapidly throughout the USA, forming dense monotypic mats that have caused economic and ecological damage to infested lakes, streams, and reservoirs (Eiswerth et al, 2000; Olden and Tamayo, 2014). Autofragmentation usually occurs soon after flowering when stems that are relatively fragile break off from the parent plant and float away as structures that can start new colonies (Grace, 1993). One characteristic of these shoot pieces that adds to the success of autofragmentation is the development of adventitious roots. Sexual reproduction can produce new genotypes that could be better adapted to changing environments
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