Prediction of competition between oilseed rape and Stellaria media

Ten experiments have investigated competition between winter oilseed rape and Stellaria media (common chickweed). Yield losses caused by this weed were often high, but differed greatly between experiments, 5% yield loss being calculated to be caused by 1.4–328 plants m^?2. Predictions of yield loss based on relative weed dry weights [weed dry weights/(crop + weed dry weights)] in December were somewhat less variable than those based on weed density, 5% yield loss being caused by 1.4–10.6% relative weed dry weight. The variations in yield loss were related to variations in the competitiveness of the oilseed rape and the S. media, caused by weather differences between years and sites, and the long period between weed assessment and harvest (8–10 months). However, despite the lack of precise relationships, there were indications that the greater the crop dry weights in December, the lower the final yield loss. Delayed sowing of oilseed rape until late September did not clearly increase the competitive effects of the weed compared with late August/early September sowings. Weed competition was not clearly affected by reduced crop density (44–113 plants m^?2), because of the compensatory ability of the lowest density. The results of the experiments are discussed in relation to the prediction of yield loss and, thus, possible adjustment of weed control strategies to meet expected crop losses.     

Emergence of Chenopodium album and Stellaria media of different origins under different climatic conditions

Summary The emergence behaviour of weed species in relation to cultural and meteorological events was studied. Dissimilarities between populations in dormancy and germination ecology, between-year maturation conditions and seed quality and burial site climate all contribute to potentially unpredictable variability. Therefore, a weed emergence data set was produced for weed seeds of Stellaria media and Chenopodium album matured and collected from three populations (Italy, Sweden and UK). The seeds were collected in two consecutive seasons (1999 and 2000) and subsequently buried in the autumn of the same year of maturation in eight contrasting climatic locations throughout Europe and the USA. The experiment sought to explore and explain differences between the three populations in their emergence behaviour. Evidence was demonstrated of synchrony in the timing of the emergence of different populations of a species at a given burial site. The relative magnitudes of emergence from the three populations at a given burial site in a given year were generally similar across all the burial sites in the study. The resulting data set was also used to construct a simple weed emergence model, which was tested for its application to the range of different burial environments and populations. The study demonstrated the possibility of using a simple thermal time-based model to describe part of the emergence behaviour across different burial sites, seed populations and seasons, and a simple winter chilling relationship to adjust for the magnitude of the flush of emergence at a given burial site. This study demonstrates the possibility of developing robust generic models for simple predictions of emergence timing across populations.     

棉花苗期到盛花期倒四叶激素变化研究初报

研究苗期到盛花期棉花倒四叶的内源激素变化情况,以及激素和棉花各生长部位相互关系。结果表明:IAA的含量随着棉花的生长呈现下降的趋势,进入盛花期后,IAA开始上升;CTK随着棉花的生长呈现上升的趋势;GA3在花铃期有下降的趋势,GA3和蕾中的GA3变化相反;ABA的高峰值和花芽中ABA的高峰值的出现有时间差。叶片中各激素比值在现蕾期与叶片中养分N、K的变化趋势有相似之处;与茎中N、K的变化存在时间差;在花铃期与营养器官中的N的变化趋势相似,和K的变化趋势相反。激素比值变化对各部位的P没有显著影响。     

云南德宏柠檬花期蓟马种类调查及药剂防治

蓟马在柠檬开花初期、盛花期和末花期均可对柠檬花造成严重危害.本研究进行了德宏柠檬花期蓟马为害观察、标本采集、种类鉴定,以及大田防治药剂的筛选试验.结果表明,为害柠檬花的蓟马有9种,分别为黄胸蓟马(Thrips hawaiiensis)、杜鹃蓟马(T.andrewsi)、色蓟马(T.coloratus)、棕榈蓟马(T.palmi)、黄蓟马(T.flavus)、西花蓟马(Frankliniella occidentalis)、花蓟马(F.intonsa)、端大蓟马(Megalurothri ps distalis)和蓟马属一种(Thrips sp.),其中以黄胸蓟马为柠檬花期蓟马的优势种.供试的7种药剂中,以25％噻虫嗪水分散粒剂3 500倍液、24％灭多威水剂2 000倍液和20％丁硫克百威乳油1 000倍液的防治效果较好,其施药后3d的虫口减退率分别为93.07％、90.90％和81.57％,校正防效分别为95.36％、93.91％和87.64％;施药后5d的虫口减退率分别为97.90％、95.32％和92.75％,校正防效分别为98.75％、97.21％和95.68％.药剂筛选试验为柠檬花期蓟马的大田防治提供了重要的参考.     

A perspective on the measurement of time in plant disease epidemiology

The growth and development of plant pathogens and their hosts generally respond strongly to the temperature of their environment. However, most studies of plant pathology record pathogen/host measurements against physical time (e.g. hours or days) rather than thermal time (e.g. degree-days or degree-hours). This confounds the comparison of epidemiological measurements across experiments and limits the value of the scientific literature.     

西北地区春季沙尘暴的区域性时间变化特征

本文应用方差极大准则下的正交旋转因子分析(REOF),对我国西北地区近46a(1960-2005年)春季沙尘暴日数资料序列进行客观分区,并采用11年滑动平均方法和morlet小波对其各区区域性时间变化特征进行分析研究。结果表明:1)西北地区春季沙尘暴可划分为5区,它们是河套区、南疆区、高原区、河西区和北疆区。2)西北各区的春季沙尘暴日数自1960年以来有下降趋势,南疆区下降趋势最快,北疆区下降趋势较缓,其它三区数值接近,且夹与上述两区之间。3)在年代际变化方面,南疆区下降趋势明显,各年代也呈现下降趋势。河套区和河西区沙尘暴从60年代开始有增加,分别在70年代初和70年代末达到峰值,然后转而下降。除南疆区以外的其它4个区春季沙尘暴日数较少,总体呈波动下降趋势,在90年代中期开始有所回升,到21世纪初又呈现下降趋势。4)在年际变化方面,利用小波分析方法清晰分析出西北各区域春季沙尘暴日数的年际变化,对小波功率谱进行90%的信度检验,提高小波分析结果的可靠性。同时得出了各区周期主要集中在2~3a和4~8a周期尺度上。     

中国介质蝴蝶兰输美检疫监管工作初探

介质种苗的检疫问题一直以来是该产品的出口瓶颈,美国一直都限制携带介质的种苗直接输入境。但随着《中国介质兰花输往美国工作计划》及相关法案的发布,中国大陆介质兰花输往美国有望在近期成为现实。本文分析了介质蝴蝶兰出口存在的检疫风险、中美双方存在的监管差异,并提出措施以帮助我国出口企业顺利打开美国市场。     

Motivating rice farmers in the Mekong Delta to modify pest management and related practices through mass media

A participatory planning process was applied to develop a media campaign to motivate rice farmers in the Mekong Delta to modify pest management practices together with seed and fertilizer inputs. Locally named ‘Ba Giam Ba Tang’ or ‘Three Reductions, Three Gains’, campaigns were launched in two provinces, Can Tho and Tien Giang. In both provinces, farmers' practices changed significantly. Their insecticide sprays reduced by 13–33% while their seed rates dropped ～10% and nitrogen rates, ～7% and proportion of farmers using insecticides declined by ～11%. These practices were supported by modifications in belief attitudes that favored high inputs. Farmers who reported significant reductions in the three inputs also changed their perception of yield loss. The campaigns in Can Tho and Tien Giang had significant multiplier effects. They stimulated several provincial governments as well as the Ministry of Agriculture and Rural Development to provide additional resources to reproduce the materials and campaign process for local use which eventually reached more than 3 million farmers in south and central Vietnam.     

Genetic relationships and isozyme variability in the Heterodera avenae complex determined by isoelectrofocusing

Isozyme variability was assessed among the principal species of the cereal cyst nematode complex to complete and enhance the information provided by classical nematode systematics, in order to clarify inter- and intraspecific relationships within this complex. Twenty populations of cereal cyst nematodes ( Heterodera avenae , H. filipjevi , H. latipons and H. mani ) were compared by means of five different isoenzymatic systems (esterase, malate dehydrogenase, phosphoglucoisomerase, phosphoglucomutase and superoxide dismutase) using isoelectrofocusing (IEF) on the electrophoretic separation. The results are in agreement with previous morphological and biochemical characterizations, which established genetic diversity between the Gotland strain and H. avenae and identified the Gotland strain with H. filipjevi . Populations from Israel, all included in the H. avenae group, exhibited well-defined intraspecific dissimilarity. The highest degree of polymorphism was found in the H. avenae group for all five enzymatic systems studied. The H. mani population was also included in the H. avenae group by these isozyme analyses. Malate dehydrogenase, phosphoglucoisomerase and phosphoglucomutase isozymes, fractionated for the first time by IEF in the cereal cyst nematode complex, displayed a higher level of polymorphism than using conventional electrophoresis. Isoelectric focusing has proved to be a useful tool for detecting genetic diversity within and among species of the cereal cyst nematode complex and for taxonomic purposes.     

时间序列分析在橡胶白粉病预测中的应用研究

运用指数平滑法、自回归分析法、移动平均分析法、自回归移动平均法对1962-2003年期间海南农垦橡胶树白粉病的病情指数进行预测,并对这4种方法研究结果进行比较。结果表明,4种分析方法均能较好地预测橡胶白粉病的发生趋势,但自回归移动平均法的预测效果较好。因此可以利用时间序列分析法预测橡胶白粉病。     

农田降水渗透深度的影响因素

根据农田水分平衡原理和溢满渗透理论,利用2006～2009年河南省4个土壤水分自动观测站点的土壤湿度监测资料和水分渗透模型,分析了降水渗透深度与影响因子之间的关系.结果表明:降水渗透深度与初始土壤湿度、过程降水f和雨后日数有明显的线性关系,随着三者的增大而渗透深度加深;其中初始土壤湿度影响最大,过程降水量和雨后日数相继...     

复合微生态制剂对黄瓜根际土壤微生物数量和酶活性的影响

[目的]研究施入复合微生态制剂对黄瓜根际土壤的影响.[方法]采用盆栽试验的方法,对不同生育时期施入复合微生态制剂的黄瓜根际土壤微生物数量及土壤酶活性进行了测定.[结果]与对照相比,在花期施入复合微生态制剂,可使根际土壤细菌和放线菌的数量分别增加27.9％和20.6％,而真菌和尖孢镰刀菌的数量分别减少64.5％和66.7％;可使土壤脲酶、蔗糖酶、中性磷酸酶活性分别提高130.8％、190.5％、123.5％,差异均显著.黄瓜不同生育时期施入复合微生态制剂对过氧化氢酶作用不明显.[结论]本研究在花期施入复合微生态制剂后,在一定程度上,可提高黄瓜根际土壤细菌和放线菌的数量,减少真菌及尖孢镰刀菌的数量,提高土壤脲酶、蔗糖酶和中性磷酸酶的活性.     

The role of infection time in the differential response of sorghum cultivars to Striga hermonthica infection

Striga hermonthica is an important parasitic weed that severely reduces yields of sorghum in sub‐Saharan Africa. Pot experiments with the sensitive sorghum cultivar CK60‐B and the tolerant Tiémarifing were conducted in 1999 and 2000 to investigate the role of infection time on the interaction between sorghum and Striga hermonthica. Timing of Striga inoculation was used to establish delays of one and two weeks in first attachment of the parasite. In 1999, early Striga inoculation resulted in a relatively early first Striga attachment on CK60‐B. Although first infection of Tiémarifing occurred one week later, an identical final number of emerged Striga plants was observed. Plants of CK60‐B were more severely affected and supported a higher total Striga biomass. Only with this cultivar the interaction between host and parasite was significantly affected by delayed infection. Parasite biomass was most sensitive and already significantly reduced following a 1‐week delay in infection time. With a further 1‐week delay, an additional reduction in parasite biomass was accompanied by a strong and significant increase in total and panicle dry weight of the host plant. In 2000, first infection of CK60‐B was relatively late and occurred simultaneously with first infection of Tiémarifing and no significant effect of delayed infection on Striga biomass or host‐plant performance was observed. The results indicate that the influence of delayed infection strongly depends on actual infection time and confirm that earlier observed differences in time of first infection between the two cultivars do contribute to the more tolerant response of Tiémarifing to Striga infection.     

Effect of the relative time of emergence on the growth allometry of Galium aparine in competition with Triticum aestivum

The impact of the relative time of emergence on the growth allometry of Galium aparine L. (cleavers) in competition with Triticum aestivum L. (spring wheat) was studied in a greenhouse experiment. The hypothesis that changes in growth allometry, particularly in the leaf area/height ratio, caused by a shift in the relative time of emergence, could lead to plants overcoming the competition or to competitive suppression was tested. The plant height, dry weight, total leaf area and vertical distribution were analyzed during the first 83 days of growth. The late emergence of G. aparine substantially influenced the growth dynamics for the dry weight and total leaf area. The dynamics of height growth were affected only following a significant delay in G. aparine emergence. The ratio of dry weight to total leaf area was almost unaffected by the competition. By contrast, the allometric relationship between the plant height and total leaf area was highly sensitive to the relative time of emergence. The results suggest that height is the most important growth trait for the plants to resist increasing competition. Even though the plants responded to competition with elongation, the physiological costs linked with “shade avoidance” caused reductions in the dry weight and leaf area growth that resulted in the total suppression of the late‐emerging individuals, in particular when their emergence was >10 days after that of the crop.     

1644-1911年宁夏西海固干旱灾害时空变化及驱动力分析

通过对历史文献资料的收集、统计和分析,对1644-1911年西海固地区干旱灾害的时间变化、空间变化、等级序列以及驱动力因子进行了研究。结果表明:1644-1911年西海固地区有记载的干旱灾害82次,平均3.27年发生一次;旱灾以春旱和夏旱最多,占发生次数的38.5%和25.3%;西海固地区的干旱灾害划分出四个等级序列,共发生轻度旱灾24次,占旱灾总数的29.3%;发生中度旱灾50次,占旱灾总数的60.97%;发生大旱灾和特大旱灾共8次,占旱灾总数的9.73%;西海固发生干旱灾害可分为5个阶段:旱灾的多发期包括:1710-1770年代、1800-1860年代(1820年代除外)。少旱灾期包括:1640年代-1700年代、1780-1790年代、1870-1910年代(1890年代除外);这一时期的中期西海固发生干旱灾害发生频率较高;旱灾高发区主要集中在西海固与陕西交接的南部,其中固原发生干旱的频次远远高于其他地区;影响干旱灾害时空变化的驱动力因子包括气候、生态和人口因子,其中气候因子起到了决定的作用。     

模拟降雨条件下苏南黄壤产流起始时间及影响因素研究

运用人工模拟降雨装置研究了暴雨条件下苏南典型丘陵土壤上纯草、纯灌、灌草3种经营模式下坡度、降雨强度、土壤前期含水量、植被覆盖度对开始产生径流时间的影响。研究表明:纯草模式下影响开始产流时间的最主要因子为土壤前期含水量,同时建立了3种植被组合下影响开始产流时间的多因子回归方程。通过方程,由植被覆盖度、坡度、土壤前期含水量和降雨强度四个易于获得的因子可预测不同植被组合下开始产生径流的时间。     

Development of Oculimacula yallundae and O. acuformis (eyespot) lesions on stems of winter wheat in relation to thermal time in the UK

Relationships between development of eyespot, caused by Oculimacula yallundae (OY) or O. acuformis (OA) on stems of winter wheat (cv. Avalon), and thermal time (°C days after sowing) were investigated in field experiments in 1985/86, 1986/87 and 1987/88 (two experiments). In all experiments, the incidence and severity of stem eyespot (uninoculated plots, OY- and OA-inoculated plots) were linearly related to accumulated thermal time after sowing. There were ca. 600–800°C days from the time of the first sample when eyespot lesions were recorded on stems to the time when maximum eyespot incidence or severity was recorded. Relationships between stem eyespot incidence or severity and thermal time differed between seasons, with more severe eyespot in 1986/87 and 1987/88 than 1985/86. Both the severity and volume of stem lesions were initially greater in OY-inoculated plots than OA-inoculated plots in spring but differences were less by harvest in all seasons. The percentage of plants with stems colonized by OY or OA over all plots (including uninoculated) showed a consistent pattern in 1986/87 and 1987/88 (two experiments), with the percentage colonized by OY greater initially and the percentage colonized by OA gradually increasing with time towards harvest.