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Sagittaria trifolia is a noxious paddy weed in East Asia. This weed propagates both sexually and asexually. Information on the role of sexual reproduction in the spread of herbicide‐resistant gene(s) and control of S. trifolia is important. Therefore, effects of oxygen, light, and temperature on the germination; germination percentages of fresh and stored seeds; and seed dormancy cycles were clarified. Seeds of S. trifolia require hypoxia and light with temperatures above 30/20°C for germination. Germination percentages increased after 1 month of storage on the soil surface. Germination percentages at 35/25°C for seeds submerged in the summer (simulating a well‐drained paddy during winter) and year round (simulating a poorly drained paddy) for 5 months and exhumed on April 7 were 84.7 and 94.4%, respectively, and decreased gradually to 41.3 and 40.0%, respectively, on June 2 (7 months burial). Germination percentages increased again and reached 63.7 and 94.0%, respectively, on July 25 (9 months burial). Seeds that form in summer germinate quickly at high temperatures, and the seedlings form tubers before winter. Thus, once herbicide‐resistant individuals emerge, the resistant gene or genes is/are easily distributed and fixed in the next generation. Autumn plowing and/or the spraying of herbicides is/are effective for controlling this weed. [ABSTRACT FROM AUTHOR]

In Shizuoka Prefecture, Japan, glyphosate‐resistant Lolium multiflorum is a serious problem on the levees of rice paddies and in wheat fields. The mechanism of resistance of this biotype was analyzed. Based on LD50, the resistant population was 2.8–5.0 times more resistant to glyphosate than the susceptible population. The 5‐enolpyruvyl‐shikimate‐3‐phosphate synthase (EPSPS) gene sequence of the resistant biotype did not show a non‐synonymous substitution at Pro106, and amplification of the gene was not observed in the resistant biotype. The metabolism and translocation of glyphosate were examined 4 days after application through the direct detection of glyphosate and its metabolite aminomethylphosphonic acid (AMPA) using liquid chromatograph‐tandem mass spectrometer (LC‐MS/MS). AMPA was not detected in either biotype in glyphosate‐treated leaves or the other plant parts. The respective absorption rates of the susceptible and resistant biotypes were 37.90 ± 3.63% and 41.09 ± 3.36%, respectively, which were not significantly different. The resistant biotype retained more glyphosate in a glyphosate‐treated leaf (91.36 ± 1.56% of absorbed glyphosate) and less in the untreated parts of shoots (5.90 ± 1.17%) and roots (2.76 ± 0.44%) compared with the susceptible biotype, 79.58 ± 3.73%, 15.77 ± 3.06% and 4.65 ± 0.89%, respectively. The results indicate that the resistance mechanism is neither the acquisition of a metabolic system nor limiting the absorption of glyphosate but limited translocation of the herbicide in the resistant biotype of L. multiflorum in Shizuoka Prefecture. [ABSTRACT FROM AUTHOR]

Invasive alien plants have caused negative ecological and economic impacts and numerous studies have focused on determining which traits make these plants successful invaders. Although it is commonly believed that only a small proportion of introduced species can become invasive, it is unknown why many alien species fail to establish. In order to identify the alien species that are exhibiting a limited distribution in their new habitat, the vegetation in an international trading port, which is a primary site for the introduction of alien plants, and residential areas of Kobe, western Japan, were surveyed every month from April–October, 2014. A total of 167 species, of which 59.3% were annual and 61.2% were alien, was found. Species that originated in Mediterranean regions were the dominant alien species, followed by those from North America. A principal component analysis showed that the species compositions were different between the port and the residential areas, particularly in spring. The species from the port areas were major weeds from the cereal crop fields of North America and Australia, but were limited in distribution in Japan. The residence time might be too short to allow them to expand or climatic differences between the areas where these aliens are naturally dominant and Japan could serve as ecological barriers to the range expansion of such species. [ABSTRACT FROM AUTHOR]

Nucleotide sequence variations were investigated with respect to the geographical distribution patterns of Miscanthus sinensis populations that were sampled from 26 Japanese national parks and three populations of the Ryukyu Islands. Twelve homozygous sequences in the nuclear ribosomal DNA internal transcribed spacer region were detected. The populations of M. sinensis in mainland Japan mainly were composed of a monophyletic group with a symapomorphic character, whereas those in the Ryukyu Islands included a polyphyletic group. Only an internal transcribed spacer haplotype with a plesiomorphic character was found in both mainland Japan and the Ryukyu Islands. Thus, no clear geographical isolation was observed in this species. These facts might be caused by the ability of M. sinensis as a pioneer plant to have a high migration potential and high gene flow by outcrossing. On the basis of the results of this study (nuclear ribosomal DNA) and the previous study (chloroplast DNA), a phylogeographical history of M. sinensis was presumed where the ancestral and derived lineages were distributed in the southern and northern regions of Japan, respectively, without strict geographical isolation. [ABSTRACT FROM AUTHOR]

The rapid range expansion of naturalized Italian ryegrass ( Lolium multiflorum Lam.) in farmland is a serious problem in Fukuroi city in Shizuoka Prefecture, Japan. Glyphosate has been used to control Italian ryegrass in the levees of rice paddy fields and wheat fields for ∼20 years, but this weed in Fukuroi city is poorly controlled by glyphosate. In order to elucidate the level of resistance to glyphosate in Italian ryegrass populations, seed bioassays and a foliar application experiment, using seeds collected from 16 wild populations in and around Fukuroi city and from three susceptible cultivars, were conducted. For the susceptible cultivars and one population from a site where glyphosate had not been applied for >10 years, the shoot length in the seed bioassays was greatly suppressed at a glyphosate concentration of 10 mg ai L−1 and no seedling survived after the foliar application of glyphosate at a rate of 2.3 kg ai ha−1. Nine wild populations from levees in the southern part of Fukuroi city showed vigorous shoot growth at a glyphosate concentration of 10 mg ai L−1 and had at least a 78% survival rate after the application of glyphosate at 2.3 kg ai ha−1. Four wild populations from levees in the northern part of Fukuroi city showed a slight suppression of the shoot growth as a result of the glyphosate treatment and their survival rates ranged from 20 to 64%. The results suggested that resistance to glyphosate has evolved in the wild populations of Italian ryegrass that are growing on the levees. This is the first report of a glyphosate-resistant weed in Japan. [ABSTRACT FROM AUTHOR]

As herbicide-resistant weeds have spread in the agricultural fields of grain-exporting countries, their seeds could be introduced into other countries as contaminants in imported grain. The spread of resistance genes through seed and pollen can cause significant economic loss. In order to assess the extent of the problem, we investigated the contamination by herbicide-resistant annual ryegrass ( Lolium rigidum) of wheat imported from Western Australia into Japan. Annual ryegrass seeds were recovered from wheat shipments and seed bioassays were conducted to identify resistance to the herbicides that are commonly used in Australia: diclofop-methyl, sethoxydim, chlorsulfuron, and glyphosate. Nearly 4500 ryegrass seeds were detected in 20 kg of wheat that was imported in both 2006 and 2007. About 35% and 15% of the seeds were resistant to diclofop-methyl, 5% and 6% were resistant to sethoxydim, and 56% and 60% were resistant to chlorsulfuron in 2006 and 2007, respectively. None was resistant to glyphosate in either year. As the contamination of crops by herbicide-resistant weeds is probably a common phenomenon, the monitoring of incoming grain shipments is necessary to stem the further spread of herbicide-resistant weeds into importing countries. [ABSTRACT FROM AUTHOR]