Ceratocarpus arenarius is a problematic and noxious weed of dryland farming in North Khorasan, Iran. Experiments were conducted to investigate the mechanism of seed dormancy, as well as the effect of environmental factors on germination and emergence of this species. Results showed that the pericarp is the major obstacle to seed germination; seeds without an intact pericarp had germination rates exceeding 90%. Ceratocarpus arenarius had identical germination rates in either light ⁄ dark and continuous dark conditions, indicating that this weed species is non-photoblastic. Germination was >35% over a range of alternating light ⁄ dark temperatures (10 ⁄ 5, 20 ⁄ 10, 25 ⁄ 15, 30 ⁄ 20 and 35 ⁄ 25°C), with maximum germination (96%) at 25 ⁄ 15°C. Ceratocarpus arenarius seeds germinated at rates >20% in high levels of salinity (800 mM) and osmotic potential ()1 MPa), indicating that this species is tolerant to saline conditions and drought stress during germination and early seedling growth. Maximum germination of C. arenarius seeds occurred at a pH range of 7-9. Seedlings emerged from burial depths ranging from 0 (without covering with filter paper) to 6 cm, and the maximum emergence (94%) was observed in seeds placed on the soil surface covered with three layers of filter paper. This suggests that minimum-and no-till systems would increase seedling emergence of this species through maintaining crop residues and seeds on the soil surface. These attributes, coupled with tolerance to salinity and drought stress during germination, should be taken into account when managing C. arenarius.

Common lambsquarters, a summer annual weed, has occupied comparatively different ecogeographical regions around the globe. To investigate the extent to which germination and emergence traits have differentiated in two natural populations of common lambsquarters from different environments (Denmark as mesic and Iran as xeric population), experiments were conducted in the laboratory. Germination of both populations was stimulated by light. The greatest germination percentage of xeric and mesic populations occurred at 25/15 and 20/10 C, respectively. The xeric population showed significantly greater germinability at the lowest (15/5 C) and the highest (35/25 C) fluctuating temperature regimes. Germination of the xeric population was only slightly affected, and the mesic population was severely retarded at a salinity level of 20 desi siemens (DS) m−1. Greater than 42% of the xeric seeds germinated at 30 dS m−1salinity, while the mesic germination almost ceased at this salinity level. Germination of seeds placed in distilled water after the 14-d salinity exposure treatments (recovery rates) was also greater for the xeric vs. mesic populations. Xeric populations showed more than 65% germination up to the osmotic potential of −0.4 MPa, while decreasing osmotic potential from 0 to −0.4 MPa caused an 80% reduction in mesic population germinability (9% germination). The greatest emergence of xeric (77%) and mesic (70%) populations occurred for seeds placed on the soil surface and no seedlings emerged from burial depth 3 cm. These study results suggest that common lambsquarters populations have differentiated for heat, salinity, and drought tolerance at germination stage. These contrasting germination patterns are appeared to be due to either adaptation via natural selection or maternal effects, or some combination of both. Though this study has certain limitations, it, through its findings and their propositions, adds to the existing knowledge about interpopulation differences in germination requirements of common lambsquarters, as a globally distributed species.

Wild radish is a major weed of field crops in southern Australia. The effects of various densities of wild radish and wheat on the growth and reproductive output of each other were investigated in field studies in 2003 and 2004. The experiments were established as a factorial combination of wheat (0, 100, 200, and 400 plants m−2) and wild radish (0, 15, 30, and 60 plants m−2) densities. The effect of wild radish density on wheat yield loss and wild radish seed production were described with a rectangular hyperbola model. The presence of wild radish in wheat reduced aboveground dry matter, leaf-area index (LAI), and grain yield of wheat, and the magnitude of this reduction was dependent on weed density. Increasing the density of wheat substantially reduced the adverse effects of wild radish on wheat. As crop density increased, wild radish dry matter, LAI, and seed production per unit area decreased. The maximum seed production of wild radish was achieved at its highest density (60 plants m−2), and was 43,300 and 61,200 seeds m−2for the first and second year, respectively. The results indicated that higher densities of wheat were able to suppress seed production of this weed species. From a practical viewpoint, this study shows that increased wheat density in the range of 200 to 400 wheat plants m−2can reduce wild radish seed production and also give some reduction in crop yield loss, and could be an important component of an integrated weed management program.

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