失活处理对香石竹切花枝条扦插效果的影响

通过3个试验,研究不同失活处理对香石竹品种红芭芭拉、桃红芭芭拉、浅粉芭芭拉切花枝条扦插效果的影响。结果表明:未进行失活处理的枝条扦插效果相对较好,枝条扦插后有生根但根系不发达,枝条枯死率低,侧芽萌发较多,不同失活处理均能抑制插条生根和侧芽萌发,最终导致插条枯死。草甘膦浓度越高、浸泡部位越高、浸泡时间越长,扦插效果越差;属于枝条下部的插条易萌发侧芽,属于枝条上部的插条易生根,且萌发的侧芽易形成花蕾。     

Impact of agronomic practices on populations of Fusarium and other fungi in cereal and noncereal crop residues on the Canadian Prairies

Fusarium head blight (FHB) is an important disease which has been causing damage to wheat and barley crops in western Canada. Because crop residues are an important source of inoculum, it is important to know the ability of Fusarium spp. to colonize and survive in different residue types, and how their populations might be affected by agronomic practices. Sampling of residue types on producers’ fields for quantification of Fusarium and other fungi was conducted in 2000–2001 in eastern Saskatchewan. Fusarium spp. were isolated from most fields, whereas their mean percentage isolation (MPI) was over 50% for cereal and pulse residues, and under 30% for oilseed residues. The most common Fusarium, F. avenaceum, had a higher MPI in pulse and flax (45–48%) than in cereal or canola (10–22%) residues. This was followed by F. equiseti, F. acuminatum, F. graminearum, F. culmorum and F. poae which were isolated from all, or most, residue types. Factors affecting Fusarium abundance in residues included the current crop, cropping history, and tillage system. In cereal residues, the MPI of F. avenaceum was higher when the current crop was another cereal (24%) versus a noncereal (4–8%). When the current crop was another cereal, the lowest MPI of F. avenaceum and F. culmorum occurred when the field had been in summerfallow (SF) two years previous (F. avenaceum: 17% for SF, 28% for a crop; F. culmorum: 1% for SF, 4% for a crop); in contrast, F. equiseti and Cochliobolus sativus were most common in residues of cereal crops preceded by SF (F. equiseti: 16% for SF, 10% for a crop; C. sativus: 22% for SF, 13% for a crop). The MPI of F. graminearum was higher when the crop two years previous was an oilseed (7%) versus a cereal (4%). In regards to tillage effects, when the current crop was a cereal, the MPI of F. avenaceum was higher under minimum (MT) and zero tillage (ZT) (22–37%) than conventional tillage (CT) (15%), that of F. graminearum was lowest under ZT (3% for ZT, 7–11% for CT-MT), whereas that of C. sativus was highest under CT (27% for CT, 6–11% for MT-ZT). Under ZT, previous glyphosate applications were correlated positively with F. avenaceum and negatively with F. equiseti and C. sativus. These observations generally agreed with results from previous FHB and root rot studies of wheat and barley in the same region. Percentage isolation of F. avenaceum from noncereal and of F. graminearum from cereal residues were positively correlated with FHB severity and percentage Fusarium-damaged kernels of barley and wheat caused by the same fungi.     

除草剂草甘膦对土壤过氧化氢酶活性的影响

研究了草甘膦对土壤过氧化氢酶活性的影响。结果表明:草甘瞵对土壤中过氧化氢酶的活性有明显的影响,随着浓度的升高,对过氧化氢酶活性抑制作用有所增强,草甘瞵对离体过氧化氢酶有一定的抑制作用。高浓度时对大棚土壤过氧化氢酶活性的抑制作用明显高于对农田土壤的抑制作用。实验结果表明:草甘瞵在农业生产实际用量下属于低毒或无实际危害的农药。     

Glyphosate resistance of molecularly identified Conyza albida and Conyza bonariensis populations

In the initial screening, 18 out of 32 Conyza albida and 7 out of 28 Conyza bonariensis populations, sampled from main perennial crop regions of central and southern Greece, were found to be resistant to glyphosate. The level of resistance determined in dose–response experiments with representative populations of the two species was found to range from 7.7 to 37.3 for C. albida and from 3.4 to 7.8 for C. bonariensis. The comparison of the resistant and susceptible C. albida and C. bonariensis EPSPS gene sequences indicated that possess single nucleotide changes compared to Conyza canadensis EPSPS gene, but none of these changes is located at the position 106 that has been reported to confer resistance to glyphosate. Finally, the cpDNA sequence comparison analysis used for the most resistant population of each species and the respective susceptible counterparts was found to be a reliable tool for discrimination of conventionally classified C. albida and C. bonariensis plants that are morphologically similar. This is the first report for molecular identification of Conyza species.     

除草剂对不同种植年限柑橘园土壤氮转化过程及温室气体排放的影响

为探讨除草剂施用对柑橘园土壤氮转化及温室气体排放的影响,在实验室培养条件下,研究了0年(林地)、种植10年和30年的柑橘园土壤中分别添加除草剂草甘膦和丁草胺后,尿素态氮含量、硝化和反硝化作用以及温室气体排放的变化。研究结果表明,橘园土壤中尿素第1 d的水解率、氮肥硝化率、反硝化作用损失总量以及N_2O和CO_2排放量显著高于林地土壤(P0.05)。与10年橘园土壤相比,30年橘园土壤显著增加了尿素的水解速率、氮肥硝化率和CO_2排放量(P0.05),但二者的反硝化损失量没有显著差异。施用草甘膦和丁草胺都显著促进了林地土壤的尿素水解(P0.05),第1 d尿素态氮含量分别降低11.20%和12.43%;但对3种土壤氮肥的硝化率均没有明显影响。施用丁草胺显著降低了林地土壤的CO_2排放量(P0.05),对两种橘园土壤的CO_2排放没有明显影响,但明显增加了两种橘园土壤的N_2O排放总量(P0.05),分别比不施除草剂增加56.27%和85.41%;施用草甘膦对3种土壤的N_2O和CO_2排放均没有明显影响。可见,草甘膦和丁草胺的施用不会对柑橘园土壤的氮转化过程产生影响,但丁草胺显著增加了柑橘园土壤的N_2O排放。     

二甲四氯钠与草甘膦混用防除棉田节节草的效果

节节草是棉田入侵性难除杂草,一般除草剂难以防治,作者采用草甘膦与二甲四氯钠混合施用,其防治效果可达95％以上,药效期可保持在30天以上,比人工除草或草甘膦、二甲四氯钠盐的单一防除效果要好,且防效期更长。     

薤白EPSP合成酶基因转化烟草提高其草甘膦抗性

葱属植物薤白具有较强的草甘膦抗性.将薤白中与草甘膦抗性相关的EPSP合成酶基因(EPSPsA)cDNA重组到植物表达载体pWM101中,构建薤白植物表达EPSPsA重组载体,采用根癌农杆菌介导法将其转入烟草品种WS38,获得转薤白EPSPsA基因烟草.PCR分析表明,目的基因已经整合进烟草基因组中.对转基因烟草愈伤组织及幼苗进行的草甘膦抗性检测表明,转基因烟草对草甘膦的耐受性明显提高.     

Reduction in common milkweed (Asclepias syriaca) occurrence in Iowa cropland from 1999 to 2009

The role of common milkweed in the lifecycle of the monarch butterfly has increased interest in the presence of this weed in the north central United States. An initial survey conducted in 1999 found that low densities of common milkweed occurred in approximately 50% of Iowa corn and soybean fields. In 2009, common milkweed was present in only 8% of surveyed fields, and the area within infested fields occupied by common milkweed was reduced by approximately 90% compared to 1999. The widespread adoption of glyphosate resistant corn and soybean cultivars and the reliance on post-emergence applications of glyphosate for weed control in crop fields likely has contributed to the decline in common milkweed in agricultural fields.     

Soil-applied herbicide use in wide- and narrow-row glyphosate-resistant soybean (Glycine max)

A field study was conducted in 2001 and 2002 at Blackville, SC, to compare the effectiveness of soil-applied herbicide programmes followed by glyphosate with sequential glyphosate applications in 19- and 97-cm row soybean. Treatments included pre-emergence applications of flumetsulam, chlorimuron plus sulfentrazone, metribuzin, or flumioxazin all applied with S-metolachlor with a subsequent application of glyphosate applied 5 wk after soybean planting (WAP). Additional treatments included sequential applications of glyphosate at 3 and 5 WAP and a non-treated control. Weed control was comparable in wide and narrow rows, and soil-applied herbicides were similar to sequential glyphosate applications in either row width. Amaranthus palmeri S. Wats., Digitaria sanguinalis (L.) Scop., and Cyperus rotundus L. control with all herbicides was 98–100%. All herbicide programmes provided at least 92% Ipomoea hederacea var. integriuscula Gray and I. lacunosa L. control. S-metolachlor plus flumetsulam followed by glyphosate provided 99% Senna obtusifolia (L.) Irwin and Barneby control, which was superior to the 88% and 90% obtained with chlorimuron plus sulfentrazone and metribuzin programmes, respectively. Flumioxazin and sulfentrazone caused up to 12% soybean injury. In 2001, soybean yields and gross profit margins were similar for soil-applied programmes followed by glyphosate and sequential glyphosate applications in wide and narrow rows. Conversely, soybean yields and profit margins in 2002 averaged across soil-applied programs were 380 kg/ha and $50/ha superior to sequential glyphosate applications in wide rows, but were similar in narrow rows. This research indicates a highly efficacious soil-applied herbicide program followed by glyphosate provides similar weed control to sequential glyphosate applications in wide- and narrow-row soybean; however, a soil-applied herbicide programme followed by glyphosate may improve yields and returns of wide-row soybean over sequential glyphosate applications alone.     

Flaxleaf fleabane (Conyza bonariensis) populations have developed glyphosate resistance in north-east Australian cropping fields

In recent years flaxleaf fleabane has become a widespread and difficult-to-control weed in no-tilled fallowed fields, where weeds are controlled by applications of glyphosate, in annual cropping systems of north-east Australia. Fifty-two populations, collected in a national survey from agricultural and non-agricultural areas, were tested in two glyphosate dose-response pot experiments. In two subsequent pot experiments, a sub-set of these populations was tested with a field rate of glyphosate when weeds of two ages were grown at different soil moistures. In the first and second experiments, most populations collected from chemical fallowed or cropped fields in north-east Australia had GR₅₀ (estimated dose for 50% biomass reduction) values three to six times greater than the susceptible populations, indicating low levels of glyphosate resistance. Several populations from roadsides adjacent to chemical fallowed or cropped fields also had higher GR₅₀ values, indicating movement of seeds from resistant plants. In the third experiment, weed biomass of all populations from chemical fallowed or cropped fields was 70-98% of unsprayed compared to 2-3% for the susceptible populations, irrespective of weed age or soil moisture. In the fourth experiment which treated older weeds, the response of several resistant populations to glyphosate was unaffected by differences in weed age and soil moisture, whereas the biomass of the other resistant populations was greater following spraying of older and/or moisture stressed plants compared with smaller non-stressed plants. Thus, exclusive reliance on glyphosate for fallow weed control in this region has resulted in the evolution of resistance in flaxleaf fleabane populations in a cropping system with annual non-transgenic crops. Prolific production of windborne seeds, combined with poor control associated with spraying large moisture-stressed weeds, is likely to have contributed also to flaxleaf fleabane becoming such a problem weed.