Guoqi Chen

Lolium multiflorum is of worldwide agricultural importance as both a pasture crop and as a weed. We collected the seeds of 67 L. multiflorum populations from wheat lands in eastern China and three populations as commercial crop seeds; tested seed germination responses to temperature, osmotic potentials, and light/dark conditions; and also tested seed dormancy. Under constant temperatures, the germination percentages at 3 d after treatement (DAT) at 10, 15, 20, 25, 30, and 35 °C were 0%, 2.6 ± 0.5%, 37.1 ± 2.4%, 66.6 ± 1.9%, 68.2 ± 2.3%, and 37.3 ± 2.2%, respectively, and increased to 72.4 ± 2.0%, 95.6 ± 0.7%, 97.0 ± 0.7%, 98.3 ± 0.6%, 94.9 ± 1.0%, and 86.3 ± 1.2% at 14 DAT. The seed germination percentages in complete darkness at 14 DAT (averagely 87.4%) did not show significant differences with those in 12 h light/12 h dark treatment. The osmotic potential required for 50% germination (GO₅₀) was −0.53 to −0.13 MPa, with an average of −0.38 MPa, and the average germination percentage under −0.6 MPa at 14 DAT was 0.9%. The germination percentages of freshly mature seeds stored for 0, 15, 30, and 60 d were 61.3%, 66.5%, 68.4%, and 88.0%. L. multiflorum populations collected from wheat fields with rice as the preceding crop (paddy fields) showed significantly higher germination percentages under 10 °C, and lower germination percentages under osmotic stresses, compared with those collected from wheat fields with corn as the preceding crop (drylands). This is the first report of L. multiflorum seed germination biology based on multiple populations with different sources in China and provides insights for improving its management strategies.

American sloughgrass [ Beckmannia syzigachne (Steud.) Fernald] is a troublesome weed in wheat ( Triticum aestivum L.). We tested the germination of B. syzigachne seeds under different temperatures in growth chambers (12-h dark/12-h light, 12,000 lx), simulating temperatures during the winter wheat sowing periods: early (25/15 °C), standard (20/10 °C), late (15/5 °C), and very late (5/0 °C). We also tested the accumulated temperatures required for seedling growth to the 2- to 5-leaf stages, using 225 populations collected from wheat fields in eastern China. The average 1,000-seed weight of the 225 populations was 1.2 ± 0.01 g. Overall, the populations tested did not show seed germination after 21 d of treatment (DAT) at 5/0 °C or constant 30 °C. At 14 DAT with 25/15, 20/10, and 15/5 °C, the mean germination rates were 85.4%, 6.4%, and 0.1%, respectively. These rates increased to 99.9%, 58.6%, and 21.7% at 21 DAT. Populations collected from lower-latitude regions germinated significantly faster (P < 0.05) under optimal conditions. Accumulated temperatures required for growing the second, third, fourth, and fifth leaves were 139.0 ± 1.0, 127.8 ± 1.0, 115.6 ± 1.0, and 98.9 ± 0.7 °C, which showed a significant decreasing trend. The narrower optimal temperature range for B. syzigachne seed germination and higher thermal requirements for early seedling growth constrain its distribution, while the heterogeneous seed germination facilitates its infestations in wheat-planting areas in eastern China.

Echinochloa crus-galli and E. crus-galli var. mitis are two of the most troublesome rice weeds. Florpyrauxifen-benzyl is one of the most important post-emergence rice herbicides that has been pervasively applied in many countries since 2018. We collected 70 E. crus-galli and 158 E. crus-galli var. mitis populations from rice fields in eastern China in 2022 and tested their sensitivities to florpyrauxifen-benzyl through whole-plant bioassays. A total of 21 days after treatment with florpyrauxifen-benzyl label dose (36 g ai ha⁻¹), 71.4% of E. crus-galli and 70.9% of E. crus-galli var. mitis populations were completely controlled. The GR₅₀ doses (doses causing 50% fresh weight reductions in aboveground parts) of florpyrauxifen-benzyl applied to E. crus-galli populations ranged from 1.4 to 36.9 g ai ha⁻¹, with a baseline sensitivity dose of 4.9 g ai ha⁻¹; those for E. crus-galli var. mitis populations ranged from 1.3 to 97.6 g ai ha⁻¹, with a baseline sensitivity dose of 5.0 g ai ha⁻¹. No significant differences between E. crus-galli and E. crus-galli var. mitis were found in GR₅₀ values. Among 70 E. crus-galli populations, 61.4%, 35.7%, and 2.9% showed no, low, and moderate resistance to florpyrauxifen-benzyl, while among 158 E. crus-galli var. mitis populations, 54.4%, 36.1%, 1.9%, and 1.9% showed no, low, moderate, and high resistance to florpyrauxifen-benzyl, respectively. Moreover, the frequency of florpyrauxifen-benzyl-resistant populations of E. crus-galli var. mitis tended to be higher in southwestern areas.

Weeds represent increasingly troublesome threats to modern wheat production. Jiangsu Province, China, is one of the largest wheat-planting areas, characterized by a high level of agricultural mechanization, in the country. In 2024, we surveyed weed communities of 924 wheat lands from 308 sites in Jiangsu and compared them with historical data surveyed in 1999–2000 in this province. A total of 156 weed species belonging to 103 genera and 39 families were recorded. Compositae and Poaceae showed the highest species richness, with 26 and 23 species, respectively. Poaceae weeds accounted for 54.3% of the overall weeds in dominance values. Beckmannia syzigachne showed the highest proportion of the overall weeds in dominance values (19.2%). Compared with the historical data, weed diversity increased by 33.3% in species, and by 62.5% in families; grassy weeds such as Beckmannia syzigachne, Alopecurus japonicus, and Alopecurus myosuroides became more dominant, while several low-growing grassy weeds became less dominant. The dominance of broadleaf weeds, such as Galium spp., Vicia spp., and Veronica spp., decreased greatly, and a clear trend of weed homogenization among different areas and types of wheat lands was observed. This is the first investigation of weed community succession against the background of agricultural modernization in China.

BACKGROUND: Various mechanisms or factors may cause the wide infestation of herbicide‐resistant weeds with different contributions, such as target‐site resistance (TSR), non‐target‐site resistance (NTSR), hormesis, and dissemination of herbicide‐resistant weeds. Here we tested this hypothesis in eastern China in Leptochloa chinensis , for which cyhalofop resistance is a major challenge to rice planting. RESULTS: Our results revealed that 30% of the total 242 populations held high (10 < RI < 100) or very high resistance (RI > 100) to cyhalofop. Resistance increased from north to south, and from transplanted rice fields to direct‐seeded rice fields. Six mutant types conferring TSR to cyhalofop were found in 89% sampled populations, with 18% carrying two types, 2% carrying three types, and another 2% carrying four types of mutations. W2027C was the most frequent TSR mutation, present in 47.3% of sampled populations, followed by I2041N (21.8%), W1999C (20%), L1818F (20%), W1999G (5.5%) and C2088R (1.8%). Non‐target‐site resistance linked with P450 monooxygenases (P450) and glutathione S‐transferases (GST) were observed in 7% and 10% cyhalofop‐resistant populations sampled. No significant correlation between genetic and geographic distances were observed among cyhalofop‐resistant populations. Hormetic effects of cyhalofop to L. chinensis were evident in 13% of overall populations. CONCLUSIONS: This study compared the contribution of different mechanisms towards herbicide resistance, revealed herbicide hormesis and revealed the distribution of resistance. Insights from this study could be important for weed management practices in other areas of the world. © 2025 Society of Chemical Industry.

BACKGROUND: Leptochloa fusca is a new dominant grass weed in paddy ecosystem of local region in China. The extensive herbicide application has selected the cyhalofop‐butyl‐resistant L. fusca populations. Here, we aimed to (i) characterize the target‐site resistance mechanisms to ACCase inhibitors, and (ii) establish an efficient and rapid method for detecting mutations.RESULTS: The L. fusca population (SFC‐R) was resistant to cyhalofop‐butyl (RF = 5.4), metamifop (RF = 5.5), and fenoxaprop‐P‐ethyl (RF = 6.8). Gene sequencing revealed that the Ile‐1781‐Val mutation was the molecular basis of resistance. A recombinase‐aided amplification (RAA) combined with CRISPR/Cas12a method was successfully developed, which could rapidly and visually detect the single nucleotide variation underling the Ile‐1781‐Val substitution in L. fusca.CONCLUSION: This study confirmed that target‐site mutation (Ile‐1781‐Val) endowed resistance to ACCase inhibitors in L. fusca, and represented the first report of applying the RAA‐CRISPR/Cas12a assay for mutation detection in resistant weeds. Considering its simplicity and specificity, this technique may be used in monitoring and early warning of resistant weeds. © 2025 Society of Chemical Industry.

Echinochloa crus-galli (L.) P. Beauv. (EC), E. crus-galli var. mitis (Pursh) Petermann (ECM), and E. glabrescens Munro ex Hook.f. (EG) are all troublesome weeds and frequently managed as one species on rice (Oryza sativa) fields. To examine inter- and intra-specific differences in seed germination responses to drought stresses, we conducted seed germination experiments with 57 EC, 112 ECM, and 92 EG populations. In all drought stress treatments, EC exhibited higher and faster germination than ECM and EG. Under 0 MPa, seed germinations of all populations initiated on 3 DAT (day after treatment). Accumulative seed germination percentages of EC, ECM, and EG under −0.1 MPa did not show significant differences with the same species treated with 0 MPa, while significantly decreased with the osmotic potential treated decreasing to −0.4 MPa or lower. OR₅₀ values (the osmotic potential at which 50% germination occurs) for EC, ECM, and EG were −0.55 MPa, −0.49 MPa, and −0.45 MPa, respectively. Intra-specific variation within all three species increased as osmotic potential decreased from −0.1 MPa to −0.8 MPa. Moreover, seed germination was significantly correlated with 1000-seed weight and latitudes of population-collected locations. In four treatments, seeds produced by Echinochloa weeds growing in transplanted rice fields exhibited significantly higher germination percentages than those from direct-seeded rice fields.

Systematically monitoring the baseline sensitivity of troublesome weeds to herbicides is a crucial step in the early detection of their market lifespan. Florpyrauxifen-benzyl is one of the most important herbicides used in rice production throughout the world, and has been used for 5 yr in China. Barnyardgrass is one of the main targeted weed species of florpyrauxifen-benzyl. In total, 114 barnyardgrass populations were collected from rice fields in Jiangsu Province, China, and using whole-plant bioassays they were screened for susceptibility to florpyrauxifen-benzyl. The GR₅₀ values (representing the dose that causes a 50% reduction in fresh weight of aboveground parts) of florpyrauxifen-benzyl for all populations ranged from 1.0 to 34.5 g ai ha⁻¹, with an average of 6.8 g ai ha⁻¹, a baseline sensitivity dose of 3.3 g ai ha⁻¹, and a baseline sensitivity index of 34.5. Twenty-one days after treatment with florpyrauxifen-benzyl at the labeled dose (36 g ai ha⁻¹), 90% of the barnyardgrass populations exhibited >95% reductions in fresh weight of aboveground parts. Compared with the baseline sensitivity dose, 63, 44, and 7 populations had, respectively, no resistance (55%), low resistance (39%), and moderate resistance (6%) to florpyrauxifen-benzyl. Furthermore, the GR₅₀ distribution of barnyardgrass populations did not show a significant correlation with collection location, planting method (direct-seeding or transplanting), or rice species (Oryza sativa L. ssp. indica or ssp. japonica) at any of rice fields where seeds had been collected (P > 0.05). In conclusion, florpyrauxifen-benzyl remains effective for barnyardgrass control in rice fields despite serious resistance challenges.

Echinochloa crus-galli var. crus-galli (L.) P. Beauv. (EC), Echinochloa crus-galli var. mitis (Pursh) Petermann (ECM), and Echinochloa glabrescens Munro ex Hook. f. (EG) are all serious rice (Oryza sativa L.) weeds that are usually treated as a single species in weed management practices. To determine interspecific and intraspecific differences in seed germination responding to different temperatures among the three Echinochloa weeds, we conducted field surveys and collected 66 EC, 141 ECM, and 120 EG populations from rice fields of East China in 2022; and tested their seed germination under 28/15 C (day/night), 30/20 C, and 35/25 C regimes, simulating temperatures of rice-planting periods for double-cropping early rice, single-cropping rice, and double-cropping late rice, respectively. In EC, ECM, and EG, seed percentage germination (cumulative percentage of germinated seed) and germination index (sum of the ratio of germinated seeds to the corresponding days) increased with increasing temperatures. At 28/15 C, the average percentage germination of EC populations (67.5%) was significantly (P < 0.05) higher compared with ECM (46.4%) and EG (43.7%); GD₅₀ (duration for 50% total germination) for EC populations (5.2 d) was significantly shorter compared with ECM (5.9 d) and EG (5.8 d). At 35/25 C, the percentage germinations of EC (90.7%), ECM (80.5%), and EG (80.3%) were all significantly the highest among the three temperature treatments, respectively, and the GD₅₀ values for EC (2.5 d), ECM (2.6 d), and EG (2.7 d) were all significantly the lowest. At 30/20 C and 35/25 C, the average germination percentages of populations collected from transplanted rice fields were significantly higher than those of populations collected from direct-seeded rice fields. Moreover, among EG populations, the longitudes and latitudes of collection locations were significantly correlated with seed percentage germination and germination indices. According to the interspecific differences and intraspecific variations of Echinochloa species, weed management strategies should also be customized according to the species and population characteristics in seed germination.