Asian spiderflower (Cleome viscosa) germination ecology in southern Iran

Cleome viscosa is one of the most important weeds of warm‐season crops in southern Iran. Laboratory experiments were conducted to assess the impact of environmental factors on seed germination of C. viscosa . Freshly harvested seeds exhibited dormancy that was relieved (>90%) after immersion for 20 min in concentrated sulfuric acid. Regardless of the temperature regime, the final percentage of germination in light/dark (69.3%) was significantly higher than in complete darkness (58.3%). The optimum temperature for germination was 35/25°C in both light and dark. No germination was observed at constant temperatures of either 15 or 45°C. The thermal thresholds for seed germination, the base (T _b) and the mean ceiling germination temperatures (T _c(50)) were estimated to be 18.8 and 39.9°C, respectively. A base water potential ( Ψ _b(50) ) of ?0.96 MPa was identified for C. viscosa seeds. The response threshold of C. viscosa to reduce 50% of maximum germination for salinity was estimated to be 255 mM. Seeds that were placed on the soil surface had the highest percentage of seedling emergence (77.3%), and no seedlings emerged from seeds placed at a depth of 6 cm. The findings of this study could help to improve the integrated weed management strategies for this species.     

Factors affecting seed germination and emergence of Aegilops tauschii

Information on seed germination and emergence ecology of Aegilops tauschii is scant, despite it being a widespread invasive weed in China. We conducted this study to determine the effects of various factors on seed germination and seedling emergence in three A. tauschii populations. Seeds germinated across a wide range of temperatures (5–35°C), with germination of over 90% at 15–20°C. Germination was completely inhibited when dry seeds were exposed to a temperature of 160°C for 5 min; a similar response was observed for pre-soaked seeds at 100°C. Light was neither required for nor inhibited germination. Germination was not significantly affected by pH. Aegilops tauschii was relatively tolerant to low osmotic potential and high salt stress: over 80% of seeds germinated at −0.3 MPa, and all three populations germinated in the presence of 400 mM salt (NaCl) although salt tolerance varied among the populations. Seeds buried at depths of 1–3 cm emerged well, but emergence was completely inhibited at depths greater than 8 cm. The addition of maize straw caused a linear reduction in seedling emergence, although the rate of reduction varied among the populations. The results of this study have contributed to understanding the requirements of A. tauschii germination and emergence and optimising an integrated management system for this weed in Huang–Huai–Hai Plain of China. In addition, our study provides data for development of models to predict the geographical distribution of this weed.     

Regenerative capacity and response to pre‐emergent herbicides by stolon fragments of triquetrous murdannia (Murdannia triquetra) in rice

Triquetrous murdannia is an annual stoloniferous weed commonly found in wheat‐rice rotation fields in China. Disturbance after wheat harvesting can fragment stolons of triquetrous murdannia, and the regeneration of these fragments may contribute to the spread of this weed. In this study, the regenerate capacity and response to pre‐emergence (PRE) herbicides of stolon fragment of triquetrous murdannia were evaluated in a screenhouse. The experiment consisted of two types of single node fragments (2‐cm stolon node and five‐leaf stolon tips) placed under different floating, flooding and burial depth conditions. Results indicated that floating depth did not influence the survival of the two types of fragments but significantly decreased their growth (stolon length, number of branches, and biomass). The stolon nodes were more sensitive to flooding than stolon tips; no stolon node survived at a flooding depth of 6 cm. The highest survival was observed for fragments placed on the soil surface, and no fragments buried to a depth of 2 cm survived. PRE application of benzobicyclon, butachlor, metazosulfuron, and triafamone significantly decreased the branching and biomass of the stolon nodes; however, only triafamone and metazosulfuron significantly inhibited the regeneration of the stolon tips. These results suggest that stolon fragments with one node are likely to promote vegetative reproduction in triquetrous murdannia, and thus, disturbance may contribute to the spread of this weed. Tillage to bury fragments below their maximum regeneration depth and application of an effective PRE herbicide could serve as important tools for managing triquetrous murdannia.     

Seed germination and seedling emergence of Iberian starthistle (Centaurea iberica)

Centaurea iberica has become a problematic weed in some regions of western Iran. Little published data are available in the literature regarding its seed germination and seedling emergence. Therefore, this study was conducted in order to evaluate the effects of different factors on C. iberica seed germination. The highest level of germination of C. iberica was achieved at fluctuating temperatures of 15/25°C (night/day). The seed germination of C. iberica was stimulated by light and little germination occurred under continuous darkness. The pH solution did not have any effect on its seed germination. Centaurea iberica was tolerant to both salt and water stress. The level of seedling emergence was greatest for the seeds that were located on the soil surface, declining with depth, and no seedling emerged from a soil depth of 4 cm. These results indicated that C. iberica has the potential to infest more fields in the western parts of Iran, particularly rainfed areas. Based on the results of this study, crops with a dense canopy and/or planted in narrow‐row intervals could be used to diminish the seed germination of C iberica. In addition, the adoption of tillage systems that bury the seeds of C. iberica under the 4 cm depth would effective in its management.     

Factors affecting the seed germination and seedling emergence of muskweed (Myagrum perfoliatum)

Myagrum perfoliatum is a noxious broad‐leaved weed in western Iranian farming systems. A better understanding of the timing of seedling emergence would facilitate the development of better control strategies for this weed. Therefore, the objective of this study was to examine the effects of different factors on muskweed seed germination. Only 2.8% of the seeds of this species, which are encapsulated in siliques, germinated by, while the seeds that had been removed from the siliques had a 50% germination rate. The immersion of muskweed fruits in concentrated sulfuric acid for 110 min was the best treatment for promoting germination. Gibberellic acid stimulated the germination of the naked seeds by 29.1%, potassium nitrate (40 mmol L^‐1) increased the germination rate to 71%, while higher concentrations of potassium nitrate inhibited germination. The optimum germination temperature for the naked seeds was 20/10°C (day/night) and light was not required for germination. No seedling emerged when the seeds were buried 6 cm deep. The seeds were sensitive to both osmotic and salinity stress, but they germinated to 46–49% over a pH range of 4–10. The results of this study revealed that the seeds of M . perfoliatum have physiological dormancy and that it is slowly broken via after‐ripening. However, the fruit wall can prevent germination after physiological dormancy is broken. Thus, this species has the potential to form a persistent seed bank because of the presence of the fruit wall.     

差巴嘎蒿(Artemisia Halodendron)种子萌发对土壤温度、水分和埋深的响应

差巴嘎蒿(Artemisia halodendron)是科尔沁沙地植被的关键种之一,它在沙地植被的恢复演替过程中扮演着重要角色,也被广泛应用于人工固沙活动中。为了了解差巴嘎蒿对风沙环境的适应特点,试验研究了其种子萌发对土壤温度、水分和埋藏深度的响应模式。结果表明:差巴嘎蒿种子在4月和5月的土壤温度条件下萌发良好,总萌发率可达到96%,在7月的土壤温度条件下萌发较差,总萌发率低于50%;若以试验前3天的总萌发率为准,则5月的萌发率远大于其它两个月。在0MPa、-0.1MPa、-0.2MPa、-0.4MPa、-0.8MPa和-1.6MPa水势下,差蒿种子的总萌发率分别为89%、83%、80%、46%、17%和0%。在0.5cm、1.0cm和2.0cm埋深下,最终出苗率分别为90%、32%和9%,当埋深大于4cm后,种子无法出苗。种子萌发对温度、水势和埋深的这种响应模式总体上不利于差巴嘎蒿实生苗在科尔沁沙丘生境中的存活。     

Seed germination of the invasive species Piper aduncum as influenced by high temperature and water stress

Piper aduncum is a common woody weed throughout the tropics and a successful invader in many areas. As this species most often dominates roadsides and forest margins, and these habitats frequently experience extreme changes in temperature and water availability, it is important to understand how the seeds adapt to these stresses. This study investigated the effect of high temperatures and water stress, continuous, periodic or transient, on P. aduncum seed germination before or after imbibition. It was found that P. aduncum seeds exhibited only intermediate tolerance and did not germinate at temperatures above 35°C or water potentials below ?0.6 MPa. However, this species is well adapted to local conditions, with fruit ripening in the rainy season, seed desiccation tolerance to eRH 8%, rapid germination under wet conditions, higher temperature tolerance than the maximum ground temperature, germination of most seeds after 60 h continuous heat treatment or daily periodic heat treatments up to 5 h at 40°C and insensitivity to 12 h heat treatment at 40°C during the whole germination process. The intermediate tolerance to high temperature and water stress of P. aduncum, in combination with local environmental conditions in Xishuangbanna, makes P. aduncum an intermediate invader in this area.     

Light, temperature and burial depth effects on Rumex obtusifolius seed germination and emergence

Trials were carried out to investigate the effects of light and temperature on germination of Rumex obtusifolius L. After several months of storage, seeds gradually lost dormancy and became photosensitive. Thermal optima for germination were between 20 °C and 25 °C in light or in darkness. At lower temperatures there was a greater demand for light, so that the greatest differences in germination percentage (between low and high temperatures) were found within the 10–15 °C temperature range. The calculated thermal minima ( x -intercept method) in light and darkness were 8.3 °C and 6.1 °C respectively. Daily temperature fluctuation increased germination even after seed irradiation with far-red light, suggesting a lower demand for the far-red-absorbing form of phytochrome. Seed burial inhibited germination in proportion to depth; however, germination inhibition was independent of seed phytochrome photo-equilibrium, which had been diversified by seed pretreatment with light. Seedlings did not emerge when seeds were buried >8 cm deep. Recovery of ungerminated seeds showed that excessive burial did not impede seedling emergence but rather prevented seed germination. However, this induction of dormancy was lost once germination processes were activated (24–48 h at 20 °C) that made germination irreversible. Temperature was also involved in inhibition, and low temperature (<15 °C) induced the least inhibition. This is discussed in terms of processes of respiration and fermentation in buried seeds.     

Seed dormancy,germination, emergence and seed longevity in Galinsoga parviflora and G. quadriradiata

Galinsoga quadriradiata (hairy galinsoga) and Galinsoga parviflora (smallflower galinsoga, gallant soldier) are very troublesome weeds in many vegetable row crops in Europe. To optimise management strategies for Galinsoga spp. control, an in‐depth study of germination biology was performed. Germination experiments were conducted to evaluate the impact of light and alternating temperatures on germination of a large set of Galinsoga populations. Seedling emergence was investigated by burying seeds at different depths in a sandy and sandy loam soil. Dormancy of fresh seeds harvested in autumn was evaluated by studying germination response in light at 25/20°C with and without nitrate addition. Seed longevity was investigated in an accelerated ageing experiment by exposing seeds to 45°C and 100% relative humidity. Galinsoga spp. seeds required light for germination; light dependency varied among populations. Seedling emergence decreased drastically with increasing burial depth. Maximum depth of emergence varied between 4 and 10 mm depending on soil type and population. In a sandy soil, emergence percentages were higher and seedlings were able to emerge from greater depths than in a sandy loam soil. Freshly produced G. parviflora seeds, harvested in autumn, showed a varying but high degree of primary dormancy and were less persistent than G. quadriradiata seeds that lack primary dormancy. Lack of primary dormancy of freshly harvested G. quadriradiata seeds and light dependency for germination may be used to optimise and develop Galinsoga management strategies.     

Factors affecting the seed germination and seedling emergence of redflower ragleaf (Crassocephalum crepidioides)

Redflower ragleaf (Crassocephalum crepidioides) is a weed, as well as a minor vegetable, in tropical and subtropical regions of the world. The influence of environmental factors and seed conditions on the germination and emergence of redflower ragleaf have been evaluated in order to help understand its distribution and to develop effective management strategies. The seeds germinated at a constant temperature in the range of 10–30°C and reached a maximum at 15–20°C. The highest germination rate was recorded at an alternating temperature of 20/15°C (day/night). The seeds germinated over a wide pH range (2–12), with the highest germination rate at between 4 and 10. Germination under saturated and flooded conditions was also high. The germination of seeds from opened (mature) capitula was significantly higher than from partially opened or unopened capitula. The germination of seeds without a pappus was significantly higher than for seeds with a pappus. The germination rate of 1 year old seeds decreased drastically when compared to that of freshly harvested seeds. The seedling emergence rate was ～63% for those seeds placed on the soil surface, but no seedling emerged from a depth of ≥1 cm. These results indicate that redflower ragleaf seeds can germinate in various environmental conditions, but that the percentage that germinates will be different in different environments. Regeneration could be effectively prevented by at least a 1 cm soil covering or by destroying the plant before the capitula open. In contrast, freshly harvested seeds from opened capitula should be sown on the soil surface when redflower ragleaf is to be cultivated as a vegetable.     

Effects of the seed weight and burial depth on the seed behavior of common ragweed (Ambrosia artemisiifolia)

Common ragweed (Ambrosia artemisiifolia L.) is one of the annual plants that were described recently as invasive weeds in Europe. This species is described as an invasive plant that produces seeds that are highly variable. Its production of variably sized seeds is regarded as promoting its spread in different environments. Experiments were carried out to determine the influence of the seed weight and temperature on germination and the influence of the seed weight and burial depth on seedling emergence. The seeds were divided into a number of classes of weight and the seed weight effect on germination was evaluated by Petri dish assays. In another experiment, the seeds were buried at different depths in a clay soil/sand mix to estimate the burial effect on germination and seedling emergence. The germination level of A. artemisiifolia was high overall, between 76.8% and 94.2%. The seed germination was modified by temperature but it was not influenced by the seed weight. The amounts of germination and seedling emergence were greater for the seeds on the soil surface and decreased with an increasing burial depth, from 2 to 8 cm. No germination or emergence was observed for the seeds that were buried at 10 and 12 cm. The lightest seeds were more sensitive to burial. A greater level of seedling emergence for those seeds that were placed near the soil surface could explain the success of this species in open habitats, where the probability of deeper burial is low. After high seed production, the management of A. artemisiifolia in fields could be partly achieved through soil tillage, burying seeds below 10 cm, and not carrying out deep soil tillage the following year.     

土壤和水体中20种除草剂的气相色谱-质谱法多残留分析

建立了土壤和水体中20种除草剂残留的气相色谱-质谱(GC-MS)分析方法。土壤样本通过乙腈提取,Florisil固相萃取柱净化,V(石油醚):V(乙酸乙酯)=9:1洗脱,GC-MS测定;水体样本用C18固相萃取柱进行富集和净化,以V(甲醇):V(乙酸乙酯)=1:1洗脱,GC-MS测定。20种除草剂在土壤和水体中的平均添加回收率分别为72%～109%和77%～113%,相对标准偏差(RSD)分别在0.15%～16.5%和0.45%～16.3%之间,方法定量限(LOQ)在土壤中为0.01 mg/kg,在水体中为0.1 μg/L。用所建方法可同时检测土壤和水中20种常用除草剂,方法净化效果好、灵敏度高、重现性好、简便快速。     

盐分和水分胁迫对补血草种子萌发的影响

在不同昼夜温度条件下用不同浓度NaCl(mmol/L)溶液及等渗聚乙二醇溶液处理大叶补血草(Limo-nium gmelinii(Willd.)Kuntze)和耳叶补血草(Limonium otolepis(Schrenk)Kuntze)种子,分别测定其萌发率、发芽势和发芽指数,测定处理9 d未萌发的种子移入蒸馏水后的萌发恢复率,以研究温度、盐胁迫和模拟干旱胁迫对种子萌发的影响。结果表明:两种补血草种子萌发的最适温度为25~15℃,在蒸馏水中的萌发率最高,随着盐浓度和PEG6000溶液浓度的增加,种子的萌发率、发芽势和发芽指数递减,对萌发产生抑制作用;PEG6000溶液对种子的萌发抑制程度与等渗NaCl溶液相当。较高盐浓度和PEG6000溶液处理下的种子复水后萌发可以恢复。     

不同环境因素对节节麦萌发的影响

节节麦Aegilops tauschii Coss.是麦田难治杂草,研究环境条件对节节麦发芽的影响对预测其适生区域及综合治理有重要意义。以采自陕西、山东和河南的3个节节麦种群为对象,通过室内和室外萌发试验研究了水势、pH、盐分和播种深度与节节麦萌发的关系。结果表明,3个节节麦种群在不同的环境条件下表现出相似的萌发及出苗特性,其萌发对水势敏感,发芽率随水势的下降而降低,当渗透势小于-1.0 MPa时,种子不萌发;节节麦萌发对pH要求不高,在pH 3～10条件下发芽率均超过70%;其萌发具有一定的耐盐性,盐浓度为0 mmol/L时,发芽率最高,盐浓度大于420 mmol/L时,节节麦不能萌发;节节麦出苗率随播种深度的增加而降低,播种在土壤表面时,出苗率最高,播种深度大于10 cm时,未发现节节麦出苗。3个节节麦种群发芽对上述不同环境因子的反应差异不显著。     

Phytotoxic sites of action for molecular design of modern herbicides (Part 2): Amino acid, lipid and cell wall biosynthesis, and other targets for future herbicides

A bird's eye review was tried in Part 2 of this series, 'Phytotoxic sites of action for molecular design of modern herbicides', in order to select the best selection of known and some novel plant-specific targets for molecular design of modern herbicides, which affect amino acid, lipid and cell wall biosynthesis. Although amino acid biosynthesis pathways, particularly those for aromatic amino acids, ammonia assimilation and branched amino acids, have been confirmed as reasonable herbicidal target domains, the other targets affecting plant growth more markedly than inhibition of 5-enolpyruvylshikimate-3-phosphate synthase, glutamine synthetase and acetolactate synthase are discussed. In three essential enzymes involved in fatty acid biosynthesis in or in the vicinity of chloroplasts, acetyl-CoA carboxylase (ACCase), elongase(s) for very long chain fatty acids (VLCFA) and linolate monogalactosyldiacylglycerol desaturase, ACCase and elongase are more important targets for new herbicides. Although the effect of cellulose biosynthesis inhibitors is restricted to cell wall formation in growing plant cells only, there is a good chance to design the low-use rate herbicides also in this class of inhibitors. Other possible targets for new herbicides are also discussed.     

Comparison of seed germination of four Artemisia species (Asteraceae) in northeastern Inner Mongolia, China

Two psammophile-dominated Artemisia semi-shrubs (A.wudanica and A.halodendron) and two annual Artemisia forbs (A.sieversiana and A.scoparia) bear significant ecological functions in Horqin Sandy Land,but systematical information on their achenes' germination is very limited.A set of studies were conducted to evaluate seed germination responses to storage periods and methods,different temperatures,lights conditions and sand burial depths,in order to determine inter-specific germination variation in the same genus and to explain how the species adapt to its microhabitat.Fresh achenes of A.wudanica,A.halodendron and A.sieversiana showed high germination capacities,but those of A.scoparia had obvious innate dormancy,which could be broken by chilling and dry storage,especially long-term dry storage.Achene germination of the two semi-shrubs preferred lower temperature fluctuation (10 to 22oC) and was not sensitive to light.But the two annuals preferred higher temperature fluctuation (34 to 22oC) and strong light for their achene germination.These four Artemisia species showed similar responses to sand burial,i.e.soil surface was most favorable for seedling emergence,and the deeper the sand burial,the fewer the seedling emergence.For the two semi-shrubs,their microhabitats are sand dunes with high temperature and intense light,which are not favorable for germination and seedling survival.Only rainfall contributes to temporary decrease of temperature and then triggers germination.We deduced that germination is not the main but a supplementary reproductive mode for the two semi-shrubs in sand dunes.For the two annuals,achene germination is the only reproductive mode,but different responses have been developed for microhabitat adaptation.For A.sieversiana,high germination capacities in wide temperature ranges and all light conditions could improve its competition and advancement in the wettest microhabitats.For A.scoparia,obvious innate dormancy of fresh achenes and germination inhabitation under unfavorable conditions are important adaptation to environmental disturbances.