The interference of allelopathic weeds with crop plants might be mediated by volatile allelochemicals. In this study, the essential oil constituents of two weeds, wild oat (Avena fatua) and crabgrass (Digitaria sanguinalis), were investigated in relation to their effects on the growth and allelochemical production of wheat (Triticum aestivum). Subsequently, by means of gas chromatography and gas chromatography-mass spectrometry, 52 compounds were identified from the crabgrass essential oil, particularly a signaling compound called methyl jasmonate, while 28 constituents were detected in the wild oat essential oil. Both essential oils were rich in terpenoids and inhibited the growth of wheat in air, filter paper and soil media but their inhibition varied with the growth medium and the weed species. In both the air and the filter paper media, there were not significant differences in the dry weight of wheat between the wild oat and the crabgrass essential oils. However, there was a greater reduction in the dry weight of the wheat root and plant with the wild oat essential oil than with the crabgrass essential oil in the soil medium. Furthermore, the production of the allelochemical, 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one, in wheat was induced by the essential oils. The results suggest that allelopathic interference with wheat by wild oat and crabgrass affects not only the biomass allocation, but also the allelochemical production, of wheat.

An investigation, using herbicidal pot tests in a greenhouse condition, was conducted to determine the whole-plant dose–response relationships to several acetolactate synthase (ALS)-inhibiting herbicides of sulfonylurea (SU)-resistant Schoenoplectus juncoides with various Pro₁₉₇ mutations in ALS that was collected from Japanese rice paddy fields. All the tested SU-resistant accessions with a Pro₁₉₇ mutation were highly resistant to two commonly used SU herbicides (imazosulfuron and bensulfuron-methyl), but were much less resistant to another SU herbicide, metsulfuron-methyl, and were substantially not resistant to imazaquin-ammonium. These cross-resistance patterns have been known previously in fragments of S. juncoides and other weed species and were comprehensively confirmed in this study with a whole set of Pro₁₉₇ mutations. The analyses of resistance levels, based on ED₉₀ values, newly showed that different accessions with a common amino acid substitution in ALS1 showed similar responses to these herbicides (confirmed with four amino acid substitutions), that the rankings of resistance levels that were conferred by various Pro₁₉₇ mutations in ALS1 differed among the SU herbicides and that the resistance levels of the ALS2-mutated accessions were higher than, lower than or similar to those of the corresponding ALS1-mutated accessions, depending on the compared pair, but the deviation patterns were generally similar among the SU herbicides in each compared pair. The final finding might suggest that the abundance of ALS2 is not as stable as that of ALS1. In addition, as a result of these new findings, together with expected further research, a suggested possibility is that substituting amino acids at Pro₁₉₇ generally could be estimated by plotting each accession's ED₉₀ values of imazosulfuron and bensulfuron-methyl in a two-dimensional graph.

Rapid diagnostic methods to detect known mutations in acetolactate synthase (ALS) genes that confer sulfonylurea (SU) resistance to Schoenoplectus juncoides were developed in this study. By using 11 SU-resistant accessions (nine accessions with a Pro₁₉₇ substitution in ALS1 or ALS2, one accession with an Asp₃₇₆Glu substitution in ALS2 and one accession with a Trp₅₇₄Leu substitution in ALS2), polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) analysis for DNA fragments that were amplified simultaneously from genomic ALS1 and ALS2 and PCR–RFLP analysis for DNA fragments that were amplified from either of the genomic ALS1 or ALS2 were carried out. In each of the two PCR–RFLP analyses, a common PCR product was digested separately with the restriction enzymes, BspLI, MboI and MunI, in order to detect Pro₁₉₇ substitutions, an Asp₃₇₆Glu substitution and a Trp₅₇₄Leu substitution, respectively. In each of the lanes where the detection of SU-resistant substitutions was aimed, a specific band to suggest the existence of the said substitutions was observed in theoretically assumable ways. Separately, a direct sequencing method also was established, which was able to selectively sequence ALS1 or ALS2 from common templates containing both ALS1 and ALS2 by the isogene-selective primers that were designed to anneal either of the ALS genes. It is expected that these methods could be used for the genetic analysis of SU-resistant S. juncoides by providing rapid and accurate diagnosis.

The vegetation cover during the non-cropping season could have important implications for the maintenance and recovery of soil fertility, as well as for biodiversity conservation in croplands. In this study, five fertilization regimes (control: non-fertilization; N: inorganic N fertilization; P: inorganic P fertilization; NPK: balanced fertilization with inorganic N, P and K; NPKM: balanced NPK plus farmyard manure) were conducted from 1981 in a double-rice (Oryza sativa L.)-cropping system in subtropical China. The effects of long-term fertilization were investigated on the weed growth, diversity and community structure during the fallow period. The results showed that, relative to the control, both inorganic fertilization alone (N, P and NPK) and NPKM in the rice-growing season significantly increased the weed density and biomass during the fallow period in the paddy field. There was no significant difference in the weed species richness (the number of species) among the treatments. Compared with the control, fertilization tended to reduce the weed diversity (Shannon's H′) and evenness (Shannon's E), especially in the N treatment. Long-term fertilization resulted in a significant shift in weed community's composition during the fallow period. The weed community's structure was affected by soil nutrients in the order P > N > K.

Although momilactone is known to play an important role in the allelopathy of rice (Oryza sativa L.), there is no information available about the mode of action of momilactone on the allelopathy of Arabidopsis. The present research describes the allelopathic activity of momilactone A and B on the germination of Arabidopsis thaliana and the effects of momilactone A and B on protein expression during germination. Momilactone A and B inhibited the germination of Arabidopsis at concentrations >30 and 10 μmol L⁻¹, respectively. The protein bands of 18, 19 and 21 kDa on sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) were abundant in the momilactone A- and B-treated Arabidopsis compared with the control. The protein bands of 18, 19 and 21 kDa were identified by the N-terminal amino acid sequencing as cruciferin 2, cruciferina and cruciferin 3, respectively. Cruciferins and cruciferina are important storage proteins and play an important role as the initial source of nitrogen for seed germination. These results suggest that momilactone A and B may inhibit the germination of Arabidopsis seeds by inhibiting the degradation process of cruciferin and cruciferina.

Rattail fescue has become increasingly problematic in North America as a result of the greater adoption of no-till practices. While rattail fescue is described generally as a winter annual, there exists a wide variation in the life history documentation of the species. In some instances, rattail fescue has been observed behaving as a spring annual. In order to assess the vernalization plasticity of rattail fescue, laboratory-germinated seedlings from two climatically different rattail fescue populations, eastern versus western Oregon, were exposed to 4, 7 or 10°C temperatures for 0, 2, 4, 5, 6, 6.5, 7 or 8 weeks of vernalization. Following vernalization, the seedlings were transferred to a greenhouse and the developmental stages were recorded. After 13 weeks, the emergent inflorescences were clipped and the seeds were tested for germinability. The initiation of sexual development in the eastern population was affected significantly by the vernalization temperature and length, while the western population only responded to the vernalization length. In general, a faster progression through the reproductive stages of development was associated with longer vernalization lengths. Lastly, there was an increase in the germination rate of the seeds that were produced on the parent plants that were subjected to longer vernalization lengths, regardless of the population or vernalization temperature. The level of plasticity in the vernalization response between the two tested populations indicates that land managers should monitor local population life history traits in order to ensure that effective weed control is implemented at the correct growth stage.

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.

Precise hill-direct-seeded rice, which is both cost- and labor-saving, is based on the direct seeding of rice by using a precision rice hill-drop drilling machine. Weedy rice (Oryza sativa f. spontanea), also known as “red rice”, is a major weed in precise hill-direct-seeded rice, causing an ≤80% yield loss and a reduction in grain quality. The aim of this study was to evaluate the control efficiency of weedy rice by pretilachlor (a pre-emergence herbicide) and fenclorim (a safener) and their safety for precise hill-direct-seeded rice in two consecutive years. The amount of rice seed germination was accelerated by soaking the seeds in the safener at 0.67 g ai L⁻¹ for 1 h before sowing. The pre-emergence pretilachlor treatments were applied 2 days after sowing cultured rice. The inhibition of the shoot fresh weight of the cultured rice was reduced by 3.3, 6.4 and 7.4% with 450, 900 and 1350 g ai ha⁻¹ of pretilachlor at 32 days after sowing (DAS) and that of the root fresh weight was reduced by 2.6, 4.9 and 8.1%, respectively. With fenclorim and pretilachlor in a precise hill-direct-seeded rice field in 2010 and 2011, the weedy rice control efficiency at 32 DAS was reduced by 100 and 98.0%, respectively. The pre-emergence pretilachlor treatments that were applied at 2 DAS were much more efficient in the weedy rice control and less inhibitory to the cultured rice growth. The rice yield was increased by 26.1–26.7% in the mechanical precise hill-direct-seeded rice, relative to the manual-seeding rice, with the application of fenclorim and pretilachlor.