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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]

Genetic relatedness and diversity of 62 cultivars and breeding lines of tetraploid Italian ryegrass (Lolium multiflorum Lam.; 39 accessions) and its interspecific hybrids, Festulolium (18 accessions), and hybrid ryegrass (Lolium × hybridum Hausskn.; 5 accessions), mainly from Japan, were revealed based on 2,824 genome‐wide allele frequencies obtained by the genotyping by random amplicon sequencing‐direct (GRAS‐Di) method using bulk genomic DNA testing. Genomic composition of each accession was estimated according to the occurrence of 77,373 unique GRAS‐Di sequences in the reference population consisting of diploid Italian ryegrass, meadow fescue (Festuca pratensis Huds.), and perennial ryegrass (Lolium perenne L.). The high correlation coefficient (0.98) between the fescue‐specific reads ratio and the previously obtained f‐ratio of genomic in situ hybridization in Festulolium cultivars suggests the usefulness of this simple method. Both cluster analysis based on Nei's standard genetic distance (DST) and principal component analysis (PCA) showed that groups were formed largely by species. However, the complex heritage of Lolium‐Festuca (Festulolium) materials could not be determined by species registration or breeding history alone. Some Festulolium accessions were closely related to Italian ryegrass, whereas some defined as Italian ryegrass may actually be interspecific hybrids. The high genetic diversity of Festulolium compared to Italian ryegrass and hybrid ryegrass revealed by PCA seems due to the wide range of fescue‐specific read ratios (0.04–33.0%). Tetraploid Italian ryegrass did not show clear structural differentiation, but some genetic relationships attributable to breeding history were demonstrated. Mean pairwise DST of tetraploid Italian ryegrass cultivars was significantly lower than that of diploids. Tetraploids and diploids could be separated by PCA plot. Although mean expected heterozygosities of tetraploid and diploid cultivars were not significantly different, the results suggest that the utilization of diploid genetic resources is effective in maintaining and increasing the genetic diversity of breeding populations of tetraploid Italian ryegrass. [ABSTRACT FROM AUTHOR]

To reveal the genetic diversity and structure of cultivars and breeding materials of diploid Italian ryegrass (Lolium multiflorum Lam.) in Japan, using genome‐wide allele frequency data obtained by genotyping by random amplicon sequencing, direct of pooled DNA, we investigated genetic diversity among and within 89 accessions. We selected 2629 reliable alleles at 456 polymorphic loci to evaluate allele frequency in each accession. Results of hierarchical cluster analysis based on Nei's standard genetic distance and of principal component analysis and nonhierarchical cluster analysis based on the complete set of allele frequencies classified the accessions into a large group including major Japanese cultivars and their ancestral landraces with a wide range of maturity, and a small group with mainly medium maturity, including 'Gulf', introduced from overseas. The genetic relationships fully reflected the kinship inferred from the breeding history in Japan. Mean expected heterozygosity (HE) and number of alleles per locus (A) were evaluated as indices of genetic diversity within each accession. We found a significant negative correlation between the year of application for varietal registration and HE or A in 14 early‐maturing Japanese cultivars. The genetic diversity profile can be used for breeding to maintain or increase the diversity within cultivars or breeding materials. [ABSTRACT FROM AUTHOR]

Festulolium is an outbred, intergeneric hybrid between Lolium and Festuca species that might possess the agronomic advantages of both genera. As a result of DNA recombination, the chromosomes in festulolium are striped with DNA from the two genera. Using genomic in situ hybridization and image analysis techniques, we determined the genomic constitution of festulolium based on the ratio of Festuca-specific genome regions to the whole genome (the 'f ratio'). Some researchers have observed a drift in the genome balance in favor of Lolium over successive generations in amphiploid festulolium plants resulting from the cross between Lolium species and Festuca pratensis. In order to uncover the cause of the drift in favor of Lolium, we checked the f ratio drift between maternal plants and their progenies in three populations. One of the populations was a single cross progeny between parents of the backcrossed cultivar 'Icarus,' while the other two populations were isolated progenies of the amphiploid cultivar 'Nakei 1.' Because Lolium species produce more seeds than Festuca species, bulking of the seeds could cause the drift in favor of Lolium. In order to avoid this, progenies were maternally derived. In the present study, very few progeny plants had f ratios greater than 58%. The genomic drift in favor of Lolium in other studies might be due to the lack of very high f ratio plants. However, at least for one generation and with maternally derived progenies, Festuca chromosomal fragments did not disappear in either amphiploid or backcrossed festulolium cultivars, and the f ratio drift in favor of Lolium did not occur. [ABSTRACT FROM AUTHOR]

The pollen fertility and seed set of three F1 hybrid plants derived from a cross between a darnel ryegrass ( Lolium temulentum L.) line (Ba3081) and a genotype of Italian ryegrass ( L. multiflorum Lam.) were evaluated in field and greenhouse experiments under different temperatures. In the field where the daily mean temperature for 3 weeks prior to pollen dispersal was 16.5°C, the mean pollen fertility of the F1 plants was 42.8%, which was lower than the value observed in the parental species (96.0-98.1%). In two greenhouses with a daily mean temperature of 20.4 and 15.8°C, the mean pollen fertility of the F1 plants was 53.1% and 44.0%, respectively, which were higher than the values reported previously for the hybrids between L. temulentum × L. multiflorum (maximum of about 20%). The seed set of the F1 plants was 24% under open-pollinated conditions in the field compared with 4.2-8.8% under self-pollinated conditions in the two greenhouses. These results indicated that the F1 plants were self-fertile and able to set F2 seed, with a significant reduction in pollen fertility occurring with a decrease in the daily mean temperature (2.15% decrease in fertility per unit decrease in temperature). The germination rate of the F2 seeds was approximately 57%, indicating the possibility of producing an F2 population for future genetic analysis. This is the first report of F1 plants from L. temulentum × L. multiflorum with fertile pollen and with the ability to produce progeny by self-pollination. These findings suggest a possibility of developing recombinant inbred lines between L. temulentum and L. multiflorum. [ABSTRACT FROM AUTHOR]

The genus Lolium consists of nine species and includes two important forage grasses Lolium multiflorum (Italian ryegrass) and Lolium perenne (perennial ryegrass). The closely related Lolium temulentum (darnel ryegrass) is used as a model species for genomic studies of cool-season forage and turf grasses as it is diploid, self-fertile and has a short life cycle. However, only a few simple sequence repeat (SSR) markers are available for L. temulentum. Here, we report the development of 52 SSR markers suitable for inbreeding Lolium species developed from the expressed sequence tag sequences (EST) of L. temulentum and L. perenne. A total of 28 SSR markers were used for testing the usefulness of these markers across six Lolium species, three inbreeding and three outbreeding. The SSR markers developed in this study will be useful for genome mapping, quantitative trait loci analysis and genetic diversity studies in inbreeding Lolium species. [ABSTRACT FROM AUTHOR]