Introduction pathways and evolutionary mechanisms of the spread of alien species of Lolium on sandy coasts in Japan

1. Estimating the role of specific processes in the spread of alien species necessitates the determination of introduction pathways and source populations of invaded areas. Alien grasses in the genus Lolium that have become widely invasive in Japan provide provides a unique opportunity to estimate the expansion process through a direct comparison between source and naturalised populations because the introduction pathways, contaminants in grain commodities and commercial cultivars for fodder crops or revegetation materials are well-known. Therefore, by directly comparing between source and naturalised populations, we estimated the introduction pathways and whether adaptative evolution occurred in Lolium species on sandy coasts in Japan.
2. Lolium individuals sampled from naturalised populations in croplands, seaports and sandy coasts were compared with those from two introduction sources for morphological and genetic variations based on a genome-wide single nucleotide polymorphism analy..., Plant materials
For contaminant seeds from imported grains, we obtained three 20-kg samples of five wheat classes imported between 2006 and 2007: three classes of U.S. wheat (Hard Red Winter wheat: HRW, Western White wheat: WW and Dark Northern Spring wheat: DNS), one class of Canadian wheat (No.1 Canada Western Red Spring wheat:1CW), and one class of Australian wheat (Australian Standard White wheat: ASW) (Table S1). Furthermore, we obtained three types of fodder crops imported from Australia between 2016 and 2017: ground barley, wheat straw and oat hay (Table S1). The seeds of Lolium species were selected from each sample, according to the method described by Shimono et al. (2010).
For cultivated varieties, we purchased 1 kg bags each of Italian ryegrass seeds and perennial ryegrass seeds from Snow Brand Seed Co., Ltd. (Hokkaido, Japan) and Takii Seed Co., Ltd. (Kyoto, Japan) in 2012. We selected the most currently available commodity, ‘Common’ (a generic term, not a cultivar name), f...,