Momoko Hirata1, Yoshiko Shimono1, Takako Kiyoshi2 and Tohru Tominaga1
1Graduate School of Agriculture, Kyoto University, Kitashirakawa-oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
2Institute of Livestock and Grassland Science, NARO, 768 Senbonmatsu, Nasu-shiobara, Tochigi 329-2793, Japan
Divergent linages of an alien species along different introduction routes would influence its post-invasion process.Lolium species are notorious weeds in croplands around the world and their seeds were introduced into Japan as contaminants of trading wheat. They spill out of wheat and establish at seaports. In addition, these species were introduced as a cultivar for forage. In Japan, Lolium species are distributed in croplands and sandy coasts. Previous studies showed that individuals in croplands are derived from forage, while individuals in coasts are derived from contaminants.
In this study, we investigated which traits cause the distribution patterns of Lolium species. We conducted reciprocal sowing experiments at two sites, a cropland and a coastal site. Populations derived from croplands yielded higher floret numbers than populations derived from sea coasts at the cropland site, but such advantages were not detected at the coastal site. Populations derived from sandy coasts showed higher survival rate than populations derived from croplands at the coastal site. Therefore, each population showed local adaptation. Timing of flowering was different between populations. In general, populations derived from croplands flowered late and they flowered two weeks later at the coastal site than at the cropland site.
Abiotic stress would be an important selective force in sandy coasts. Therefore, we compared the seed germination ability and seedling survival under a range of drought and salt conditions between populations. As a result, drought and salt tolerance of seeds and seedlings were not different between populations. Seed dormancy would also be an important trait in harsh environments, such as sandy coasts, because germination timing affects seedling survival. So, we conducted germination experiments. There were different dormancy levels between populations by dispersal forms, seeds separated from spikes or seeds remaining on spikes. Cropland populations showed high germination percentages irrespective of the dispersal forms, while coastal populations showed low germination percentages of seeds remaining on spikes. It is necessary to verify whether this difference in the dormancy causes different germination timing and survival rate in the field.