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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 extensively invaded Japan provide a unique opportunity to estimate the expansion process through 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 source and naturalised populations, we estimated the introduction pathways and whether adaptative evolution occurred in Lolium species on sandy coasts in Japan.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 analysis and a common garden experiment. Furthermore, we conducted a reciprocal transplant experiment between cropland and sandy coast.Populations naturalised in croplands were closely related to the cultivars, whereas those naturalised in seaports and sandy coasts were associated with contaminants. These results indicate that the cropland and sandy coast populations are derived from cultivars and contaminants, respectively. In addition, asymmetric gene flow from cropland populations to sandy coast populations was observed. The reciprocal transplant experiment clearly demonstrated the home site advantage; populations derived from croplands yielded higher floret numbers than those derived from other habitats at the cropland site; sandy coast populations had higher survival rates than those from croplands at the coastal site. Port populations exhibited a similar tendency as sandy coast populations, indicating that contaminants may be originally adapted to salty and dry environments, such as that in sandy coasts. The flowering phenology in the sandy coast populations evolved in the late flowering; therefore, late flowering alleles may have been transferred from cropland populations to sandy coast populations.Synthesis. We demonstrated that two congeneric species with different ecological characteristics were introduced through multiple introduction pathways and spread across different habitats. A direct comparison between source and naturalised populations can considerably elucidate the patterns and processes of biological invasions. [ABSTRACT FROM AUTHOR]

Compared with natural seed dispersal, human-mediated seed dispersal could spread herbicide resistance genes on a much larger scale. Herbicide-resistant weed seeds have been reported as contaminants in commercial grain. We investigated the contamination of seeds of Lolium species with target-site mutations conferring resistance to acetolactate synthase ( ALS)-inhibiting herbicides in wheat imported from the USA, Canada and Australia into Japan. We also investigated the establishment of ALS-inhibiting herbicide-resistant Lolium species in 12 seaports in Japan that are major entry points for international commodities. We found herbicide-resistant Lolium spp. seeds from all classes of wheat samples. Resistant individuals became established at six of eight ports where more than 50 kt of imported wheat is unloaded every year. The establishment of resistant Lolium spp. individuals was common at major grain landing ports. Monitoring over 3 years at one port revealed that the frequency of resistant individuals did not fluctuate between years. Many resistant individuals were distributed in front of the entrance of a fodder company, but a few resistant individuals were found in areas 2 km away from the port. The results indicate that gene flow is rare through pollen or seed movement from resistant plants to peripheral populations. Further extensive and long-term monitoring is necessary to perform a comprehensive risk assessment of herbicide-resistant plants entering Japan through major commercial ports. [ABSTRACT FROM AUTHOR]

The potential impact of postdispersal seed predation by the field cricket, Teleogryllus emma (Ohmachi et Matsuura), on the seedling emergence of Italian ryegrass ( Lolium multiflorum Lam.), a non-native grass weed in Japan, was determined. The relationship between cricket density and the proportion of seedling emergence was investigated by conducting manipulative experiments in duplicate, using enclosures. One-thousand seeds of Italian ryegrass were exposed to adult crickets at different densities (zero, one, two, four and eight individuals per 2.25 m2 enclosure) for 2 weeks. The proportion of seedling emergence decreased with increasing cricket density. The proportion of seedling emergence in the enclosures without the crickets was 90.9-97.2%, whereas the seedling emergence in the enclosures with eight crickets greatly decreased, to 0.5-2.5%. These results suggest that postdispersal seed predation by T. emma can substantially decrease the abundance of Italian ryegrass at an early life stage and reduce its population in environments with a high density of crickets. [ABSTRACT FROM AUTHOR]

Kurokawa S, Kobayashi H & Ikeda K (2010). Genetic background of an invasive Lolium population in central Japan using chloroplast DNA and SSR markers. Weed Research 50, 245–252. To determine the genetic background of an invasive population of Lolium spp., we compared three non-coding regions of chloroplast DNA (cpDNA) and nine SSR loci of the population with those of 30 cultivars of Lolium multiflorum, Lolium perenne or their hybrid and two accessions of Lolium rigidum. For the cultivars and L. rigidum, bulked DNA was used for all analyses, due to variations within cultivars. Two of three regions in cpDNA were polymorphic among samples, generating four haplotypes (A–D). We found haplotypes A and B in L. multiflorum and L. rigidum, and haplotypes C and D only in L. perenne. All 48 individuals of the invasive population were discriminated as haplotype A, suggesting annual maternal origin. Nine loci of SSR generated 55 alleles in total in the invasive population. The presence or absence of these 55 alleles was counted for the bulked DNA of cultivars and L. rigidum. There were significant differences among species in the correspondences of alleles with those of the invasive populations. The correspondence of alleles with L. multiflorum was significantly higher than that with L. perenne or L. rigidum. These results suggested that the genetic background of the invasive population was very close to L. multiflorum. Although common traits among cultivars genetically close to the invasive population were not found, the wide variation in allele correspondence among L. multiflorum cultivars may indicate that non-invasive cultivar breeding may be possible in the future. [ABSTRACT FROM AUTHOR]

Italian ryegrass ( Lolium multiflorum Lam.) is an exotic winter annual weed that recently has seriously infested wheat fields in central Japan. To understand the influence of tillage systems on the germination ecology and seedbank dynamics of naturalized Italian ryegrass, we compared the fate of the seeds that were after-ripened in the soil with that of the seeds on the soil surface, and then examined the germination characteristics of the seeds retrieved from both treatments by germination tests in both a light/dark (12 h photoperiod) condition and in constant darkness. The seedling emergence was greater initially for the seeds after-ripened on the soil surface than for the seeds in the soil. The component of emergent seeds after-ripened on the soil surface increased as time passed during the summer, whereas that of emergent seeds in the soil scarcely increased. This contrasting emergence was, in part, attributable to the ability of the seeds to germinate at higher temperatures in the light/dark condition than in constant darkness. These results suggest that untilled systems, which leave many seeds on the soil surface, might promote the rapid depletion of Italian ryegrass seeds through germination before wheat sowing in early winter. In contrast, seed burial by tillage might inhibit the germination of the seeds and form a large transient seed bank available to germinate during the wheat-growing season. [ABSTRACT FROM AUTHOR]

The apparent digestibility of diets based on timothy hay harvested in Hidaka in Hokkaido (HT) and Italian ryegrass hay harvested in Miyazaki in Kyushu (MI) were compared in Thoroughbreds undergoing exercise. The nitrogen retention and plasma-free amino acid (AA) concentrations were also examined to evaluate the quality of the protein contained in the two types of hay. Four male Thoroughbreds (aged 34.4 ± 0.9 months (mean ± standard deviation) and weighing 506.3 ± 30.4 kg) undergoing exercise training at 80% of maximal heart rate were used for the study, and the apparent digestibility of the diets based on HT and MI was assessed. The net nitrogen balance was also measured by subtracting the amount of nitrogen excreted in the feces and urine from the total nitrogen intake. The apparent digestibilities of dry matter, energy, neutral detergent fiber and ether extract were all higher in the MI group than in the HT group ( P < 0.05). The larger energy digestibility in the MI group (56.8 ± 3.3%) compared with that in the HT group (51.6 ± 2.4%) was attributed to the relatively easy digestibility of hemicellulose. The net nitrogen balance and plasma AA concentrations did not differ significantly between the two forage groups. We concluded that the nutritive value of MI is adequate for exercising horses, even though the timothy and Italian ryegrass used in this study were second cuttings, and their nutrient values were not easily comparable. [ABSTRACT FROM AUTHOR]