Guoqi Chen’s research while affiliated with Yangzhou University and other places

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, which 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 28/15C (day/night), 30/20C, and 35/25C 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 percent of germinated seed) and germination index (sum of the ratio of germinated seeds to the corresponding days) increased with increasing temperatures. At 28/15C, the average percentage germination of EC populations (67.5%) was significantly ( P < 0.05) higher than ECM (46.4%) and EG (43.7%); GD 50 (duration for 50% total germination) for EC populations (5.2 d) was significantly shorter than ECM (5.9 d) and EG (5.8 d). At 35/25C, the percentage germination of EC (90.7%), ECM (80.5%), and EG (80.3%) were all significantly the highest among the three temperature treatments, respectively, and the GD 50 values for EC (2.5 d), ECM (2.6 d), and EG (2.7 d) were all significantly the lowest. At 30/20C and 35/25C, average germination percentage of populations collected from transplanted rice fields were significantly higher than that 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.

Leptochloa chinensis is a troublesome rice weed in many countries, and knowledge of its seed germination ecology varied in different reports. To reveal the range and general characteristics of L. chinensis seed germination under different drought stresses, and seedling emergence under different burial depths, we conducted a serial of germination experiments with 242 L. chinensis populations collected along ranges spanning 4° latitudes and 4° longitudes from rice fields in eastern China. We found that 1000‐seed weight ranged from 0.056 to 0.129 g, with an average of 0.088 g; the OR 50 (the osmotic potentials at which the germination percentage reaches 50%) was −0.47 to −0.07 MPa, with an average of −0.28 MPa; and BR 50 (the burial depth at which the emergence percentage reaches 50%) ranged from 0.07 to 0.26 cm, with an average of 0.18 cm. At −0.5 MPa, the mean germination percentage of 242 populations was 4.1%. Seed germination percentages under 0.5 and 1.5 cm quartz sand layer were both >75%, while no seedling emerged up to the surface of quartz sand. Populations collected from rice fields in northern regions leaned to be higher in 1000‐seed weights, and OR 50 values. Moreover, populations collected from transplanting rice fields slightly and significantly leaned to be more adapted to drought stresses and soil burial depths. The ability to quickly germinate, together with seed germination sensitive to drought stress and seedling emergence sensitive to soil burial, facilitate L. chinensis to avoid suicide seed germination, occupy niches under suitable environments and escape chemical control practices on rice fields.

Leptochloa chinensis (L.) Nees is a troublesome rice weed. We collected 242 L. chinensis populations from rice fields in eastern China and studied the duration of seed dormancy and the seed germination ability at different temperatures. All L. chinensis populations studied exhibited seed dormancy. The periods required to reach 50% germination under optimal conditions were 31–235 days, with an average of 96 days. None of the populations germinated at 15 °C. Under constant temperatures of 20, 25, 30, and 35 °C, the average germination percentages of 242 populations were 0%, 71%, 79%, and 60% at 2 days after treatment (DAT), and were 56%, 84%, 88%, and 88% at 14 DAT, respectively. The duration of seed dormancy, as well as the germination ability of seeds, were significantly (p < 0.05) influenced by the agricultural region and the longitude and latitude of the collection locations. Under constant temperatures of 20 to 35 °C, the average germination percentages of seeds collected from transplanted rice fields were significantly higher than those collected from direct-seeded fields. This is the first study on seed germination biology of L. chinensis with multiple populations systematically collected from rice fields on a regional scale.

Native weeds have a long history of adaptation to local environments. Understanding the relationship between the occurrence of native weeds and their life history traits is crucial for effective weed management and risk assessment of plant invasions. In this study, we surveyed native weed species and their dominance across 666 field sites in agricultural areas of Yangzhou City, China, and each site was 13.3 hectares in area. A total of 287 native weed species were recorded, referring to 63 families, among which 45% were 50–100 cm in plant height and 47% were of an erect life type. In terms of the proportions out of the total native weed occurrence dominance, Poaceae, Compositae, and Fabaceae weeds accounted for 30%, 13%, and 11%; liana and perennials both occupied 32%; and aquatic, hygrophyte, sun plant, and shade plant all occupied < 10%. Additionally, the proportions increased with increasing seed production per plant and with increasing weediness reported worldwide. Native weed groups holding moderate vegetative reproduction abilities, moderate seed sizes, or herbicide resistance showed higher proportions. Moreover, most of the native weeds surveyed were not succulent or thorny plants and did not hold thorns, awns, obvious hairs, or mucilage on their fruits.

Florpyrauxifen-benzyl (FPB) is an important postemergence rice herbicide. This study tested the potential for seed production in an FPB-resistant barnyardgrass population. A barnyardgrass population (NL) collected from a rice field in eastern China was highly resistant to FPB with a GR 50 dose (the FPB dose causing a 50% reduction in fresh weight of aboveground parts) of 50.2 g ai ha ⁻¹ . No significant differences in the percentages of surviving seedlings after treatment with different doses of the herbicide were found between F 1 lines collected from F 0 plants surviving a 36 g ai ha ⁻¹ FPB treatment and those collected from non-treated control F 0 plants. Additionally, no significant differences were found in the rate of surviving seedlings after treatment with varying doses of FPB among the F 2 lines collected from F 1 plants that survived varying doses of FPB. At a constant temperature of 30 C, seeds from different F 1 and F 2 lines showed germination percentages of 85%‒92.0% and 68.3%‒89.0%, respectively. In the absence of competition, plants from the NL population surviving 0–144 g ai ha ⁻¹ FPB showed no significant differences in plant height, dry weight of aboveground parts, effective accumulated temperature (EAT) from sowing to seed maturation, seed production per plant, or 1000-seed weight. In the susceptible population (HJ), plants surviving 18 g ai ha ⁻¹ FPB showed no significant differences compared to the non-treated control plants of the same population for the above variables. This is the first report of FPB-resistant barnyardgrass in China. Barnyardgrass seedlings that survived FPB application showed a higher potential for accumulating in the soil seedbank and negatively affecting rice.

Knowing the proliferative capacity of herbicide-resistant weeds is the basis for the integrated management. We collected seeds of two Echinochloa glabrescens Munro ex Hook. f. populations (TS and WH) from rice (Oryza sativa L.) fields in eastern China (F0 populations), and those from individuals surviving the initial metamifop treatment (F1 lines) were tested for their responses to metamifop, and common garden experiments were conducted to compare their productivities. We found that TS was highly resistant to metamifop, and WH was susceptible. After treated with metamifop at the label dose (120 g ai ha-1), averagely 56% and 16% of TS and WH F1 lines contained surviving seedlings, and averagely 24% and 1% F1 seedlings survived among total seedlings of the same population, respectively. After treated with metamifop at a dose of 0, 60, 120 or 240 g ai ha-1, surviving F0 plants escaped from higher doses reproduced higher proportions of metamifop-resistant F1 progenies in both populations. At 120 d after sowing (DAS), TS individuals surviving 2 × label dose of metamifop showed nonsignificant difference in plant heights, biomass and seed production, compared with relative control treatment; while WH plants surviving the label dose of metamifop decreased seed production by 25%-39%. One WH and TS plant individual surviving metamifop treatment at the label dose may generate 10-21 and 490-701 progenies resistant to the label dose of metamifop, respectively.

Effective accumulated temperature (EAT) is a basic index to predict plant growing and development, while EATs for key stages during Echinochloa crus‐galli seed‐setting are still unclear. We collected three E. crus‐galli populations (Nanling [NL], Feidong [FD], and Sihong [SH]) from different rice fields in eastern China and conducted four sets of pot experiments in a greenhouse. Plants of the three populations sown on May 9–12, averagely reproduced 484–671 mature seeds per plant; showed a duration of 67–76 days from sowing to heading, with an average EAT of 1,156–1,274°C; showed a duration of 90–94 days from sowing to seeds starting maturation in plant individuals with average EATs about 1,571–1,647°C; and showed a maturation stage lasting for 14–36 days. Significant negative correlations (p < .01) were found between the period of collecting day after seed maturation and the number or 1,000‐seed weight of mature seeds collected on the day, in each set of experiment. Compared with NL individuals sown on May 9, NL individuals sown on April 10 needed significantly higher EATs for periods from sowing to seed maturation, and from heading to seed maturation. According to logistic regressions, duration days needed for 50% of seeds to mature were 93–122 days after sowing, with EATs of 1,625–1893°C for these E. crus‐galli populations. This study revealed EATs for E. crus‐galli seed‐setting, which suggested time windows for panicle‐removing control of E. crus‐galli in rice fields.