Root system architecture and its relationship to the vegetative reproduction function in horsenettle (Solanum carolinense)

Horsenettle ( Solanum carolinense L.) is a weed species that can spread via the root system and root fragments. This study investigated the developmental pattern of the subterranean system of horsenettle in an experimental plot containing plastic plates that limited the radial growth of the individual plants in each section of the plot. The vertical architecture of the root system in the 10 month old and 16 month old plants was elucidated by excavating the plants from the experimental plot. The root system consisted of a reiterative arrangement of branching root units, which grew horizontally and then bent vertically. The relationship between the morphology of the branching roots and the vegetative reproduction in a 17 month old plant was investigated. Different sections of the rooting system had different functions: the bending part forms new shoots; the horizontal part extends into the surrounding area; and the vertical part is used for storage. Consequently, the subterranean system of horsenettle develops through a reiterative arrangement of the branching root unit, which has functionally differentiated parts.     

入侵性杂草北美刺龙葵在北京市的首次发现及防除

北美刺龙葵(Solanum carolinense L.)是一种多年生恶性杂草,本文报道了在北京药用植物园内首次发现北美刺龙葵,并对其分类、地理分布、形态特征进行了描述,同时给出了相应的防控建议。     

Time of emergence impacts the growth and reproduction of silverleaf nightshade (Solanum elaeagnifolium Cav.)

Silverleaf nightshade is one of the worst agricultural weeds on a worldwide basis. Improved understanding of its life cycle will be useful for weed management. This research showed that the growth and reproduction of silverleaf nightshade were affected significantly by the time of emergence. Plants (both root‐ and seed‐generated) that emerged early in the growing season, such as in September or November (spring), were significantly taller and produced more biomass and fruit than plants that emerged in January (summer) and March (autumn). Delayed emergence resulted in a shorter vegetative phase and less fruit production. As a result, the silverleaf nightshade plants that emerged in September produced a large amount of seeds, while the plants that emerged later in the season did not flower. Thus, control of early‐emerging plants is important. The dynamics of fruit production indicated that silverleaf nightshade fruit formed in December and peaked in March, which suggests that a control action is required before December to control the soil seed bank.     

不同贮藏条件下龙葵种子的季节性休眠特性

龙葵是农田恶性杂草?为明确龙葵种子休眠与季节温度的关系, 研究了室内和室外不同贮藏条件下其种子萌发对温度的响应规律?结果表明, 室外贮藏条件下的龙葵种子萌发呈季节性变化, 从10月到翌年5月, 龙葵种子萌发率均在95%以上, 随着夏季温度的升高, 萌发率从6月开始下降, 9月达到最低值(25.4%), 由此进行年际间休眠和非休眠周期的循环?夏季6月-9月的高温可诱导龙葵种子进入休眠状态, 而秋冬季的相对低温有利于解除种子休眠, 使种子恢复萌发状态?龙葵种子休眠和非休眠状态之间的切换受季节性温度变化的影响?室内贮藏的种子, 由于环境温度较为稳定, 其萌发率年际变化较小, 在20%~50%之间?本文明确了龙葵种子休眠的周期性变化规律, 有助于精准预测其出苗时间, 研究结果可为阐明龙葵种子休眠萌发机制和制订基于萌发调控的绿色防控策略提供依据?     

Sprouting capacity from intact root systems of Cirsium arvense and Sonchus arvensis decrease in autumn

Perennial weeds are often controlled by mechanical means, which aim at stimulating axillary and adventitious buds to sprout. This happens when the apical dominance of the main shoot is removed by defoliation or when the underground system is fragmented. By repeating the measures, the result is a depletion of storage compounds, which weakens the plants and reduces their capacity to grow and reproduce. However, timing is critical. Earlier research has indicated that emergence from fragments of Sonchus arvensis cease during a period in autumn, while the seasonal pattern of sprouting in Cirsium arvense appears to be inconsistent. We studied the emergence pattern of defoliated plants with undisturbed root systems, from late summer to early spring. Potted plants grown outdoors were exhumed at regular intervals, put under forcing conditions for 4 weeks, after which shoots above and below soil level were counted and weighed together with the remaining root systems. In both species, the number and weight of emerged shoots decreased during a period in the autumn. In C. arvense, underground shoots were constantly produced during the same period, while fewer underground shoots were present in S. arvensis. For the latter species, apical dominance does not fully explain the effect; thus, endodormancy might be involved. Root weight increased until withering and did not explain the lack of emergence. Our results suggest an impaired sprouting capacity of undisturbed root systems of C. arvense and S. arvensis during September–October, which has implications for the timing and method of control of these species.     

半干旱风沙区几种化学节水制剂马铃薯产量效应试验

在半干旱风沙区的山西省天镇县台地比较研究田间试验条件下保水剂、保水肥剂、济农、复绿灵等化学抗旱节水制剂对马铃薯作物的增产效应。结果表明在马铃薯开花期施用各种抗旱节水制剂,能不同程度地增加马铃薯产量,其中喷施济农和复绿灵效果最明显,值得推广。保水剂和保水肥效果不甚明显,原因是施用时间偏晚。     

Growth and reproduction of Hypochoeris radicata L.

Hypochoeris radicata L. (Asteraceae) is a perennial, native to Europe, and is widespread in several countries. The objective of the present study was to reveal the life history characteristics of H. radicata by focusing on its reproductive strategy. Flowering, seed-setting, and vegetative propagation of the species were observed in pots. Reproductive propagation of the species also was investigated in natural populations. The light and temperature requirements for seed germination were examined. The species germinated in temperatures ranging from 10–30°C, both in light and dark. With plants grown in pots, reproductive growth started when the rosette diameter reached ≈ 14–16 cm. Flowering was not day length-related, but it possibly was related to temperature. In natural populations, the flowering and seed-setting periods continued for > 6 months. Vegetative propagation occasionally occurred in plants with three or more shoots by the crown splitting below ground level.     

外来入侵物种三裂叶豚草(Ambrosia trifida L.)及其风险分析

外来入侵物种严重威胁着农业生产、生态安全及人类健康,已成为世界各国广泛关注和研究的热点。本文对外来杂草三裂叶豚草(Ambrosia trifida L.)的起源和分布、生物生态学特性、经济和生态影响及其控制管理措施等进行了系统综述。根据生物生态学特性、潜在风险及管理控制的难度等指标,初步建立了外来杂草的风险评估体系。应用该体系对三裂叶豚草进行了风险评估,得出其风险值为83,属高度危险的检疫性有害生物。     

Application timing of asulam for torpedograss (Panicum repens L.) control in sugarcane in Okinawa island

Field and glasshouse experiments were conducted from 1995 through 1996 to evaluate application timing of asulam (methyl sulfanilylcarbamate) for torpedograss (Panicum repens L.) control in relation to plant age in sugarcane. Above‐ground shoots of torpedograss were completely controlled with asulam at 2–4 kg active ingredient (a.i.) ha^?1 applied 60 or 80 days after planting (DAP) in artificially infested pots. But some newly developed rhizome buds survived after asulam application resulting in 1–25 and 76–100% or more regrowth in 60 and 80 DAP‐applied pots, respectively. Whereas the herbicide at 2–4 kg a.i. ha^?1 applied within 60 DAP completely controlled above‐ground shoots, applied 80 DAP at 2 kg a.i. ha^?1 it did not completely control the weed in the artificially infested field. Regrowth levels were 1–25 and 76–100% or more in 60 and 80 DAP‐applied plots, respectively. Asulam at 2–3 kg a.i. ha^?1 applied 20, 40, 60 or 80 DAP in a naturally infested field completely controlled above‐ground shoots and regrowth levels were 76–100 or more, 51–75, 1–25 and 26–50% in these same DAP applied plots, respectively. The herbicide applied at 4 kg a.i. ha^?1 caused chlorosis on younger sugarcane leaves (one‐leaf stage), but when applied at 2–3 kg a.i. ha^?1, no injury symptoms were shown. The herbicide at 2–4 kg a.i. ha^?1 applied within 60 DAP resulted in remarkably higher yield and shoot biomass of sugarcane than that applied 80 DAP. This study suggested that asulam at 2–3 kg a.i. ha^?1 should be applied 60 days after planting for the maximum control of torpedograss regrowth and better yield of sugarcane. This study also indicated that torpedograss cannot be completely controlled with a single application of asulam in a naturally infested field because of rhizome fragmentation by cross plowing and distribution of rhizomes into different soil layers that require different times to emerge. The shoots emerging after asulam application could not be controlled. Another study is required to determine the interval between sequential applications of asulam for better control of torpedograss in a naturally infested field.     

Inhibition of seed germination and seedling growth by hound's-tongue (Cynoglossum officinale L.) seed leachate

The leaching of phenolics from decoated seeds, seed coats and pericarps of hound's-tongue ( Cynoglossum officinale L.), factors affecting leaching, and seed germination and seedling growth inhibitory activities of the leachate were investigated. Embryonic axes and cotyledons contained a large amount of methanol-soluble phenolic substances. Decoated seeds released phenolics into an aqueous incubation medium and this solution was capable of inhibiting root elongation of several grassy and broadleaf species, but not of hound's-tongue. The leachate and the phenolic fraction of the leachate inhibited germination of bluebunch wheatgrass ( Pseudoroegnaria spicata (Pursh) A. Löve [syn. Agropyron spicatum (Pursh) Scribn. and J. G. Sm.]). The non-phenolic fraction of the leachate did not inhibit seed germination or root and shoot elongation of bluebunch wheatgrass. Low oxygen and an increasing temperature significantly increased the amount of phenolic substances leached from decoated seeds. Increased leaching of phenolic substances related to an increasing temperature was associated with the loss of seed viability. Further investigation of the role of water-extractable hound's-tongue seed phenolics in the interaction of this species with its biotic environment under field conditions is needed to determine the ecological significance of these findings.     

Effect of standing water and shoot removal plus standing water regimes on growth, regrowth and biomass production of torpedograss (Panicum repens L.)

The present study was undertaken from May 1996 to October 1997 in the glasshouse of the University of the Ryukyus, Okinawa, Japan to investigate standing water (12 cm deep) and shoot removal plus standing water regimes on morphological changes, growth, regrowth and biomass production of torpedograss ( Panicum repens L.). The stem internode was longer in standing-water-treated plants than that in untreated plants. The root-crown was developed from the submerged stem-node. Spike-like tillers and sheath-like leaf blades were observed in water-treated plants. Higher shoot biomass and lower rhizome biomass were obtained in standing-water-treated plants than that in untreated plants. Standing-water-treated plants attained higher total biomass than untreated plants. Standing-water stress was the factor that inhibited regrowth of torpedograss when the above-ground shoot was removed. Rhizomes without shoots of 6-month-old torpedograss did not survive in standing water for more than 6 months. The results indicate that torpedograss can survive in standing water if the shoots remain above the water surface. Shoot removal is one effective way to control torpedograss regrowth in standing water. The results of this study may be dependent on season, day length, water temperature, water pH, water depth and salt concentration in water.     

Interval between sequential applications of asulam for regrowth control of torpedograss (Panicum repens L.)

Two field experiments each conducted during a 1 year period at the Agricultural Experiment Farm, University of the Ryukyus, Japan evaluated the interval needed between sequential applications of asulam (3 kg ai ha⁻¹) for successful control of torpedograss ( Panicum repens L.). Regrowth of torpedograss from rhizomes was lowest when asulam was applied at 40-day intervals. Application at intervals of 70 days or longer completely controlled above-ground shoots but not regrowth from rhizomes. Above-ground biomass of torpedograss regrowth was 7- and 49-fold higher when asulam was applied at 70 and 100 day intervals, respectively, compared with 40-day intervals. Asulam applied three times at 40-day intervals starting 40 days after land preparation provided almost total torpedograss control 1 year after the initial application.     

Inhibitory and promotive allelopathy in rice (Oryza sativa L.)

Studies on allelopathic rice, which inhibits the germination and development of weeds such as barnyardgrass ( Echinochloa spp.) and ducksalad [ Heteranthera limosa (Sw.) Wild.], have been strongly conducted in the USA, the Philippines, Japan, Korea, and other countries since the 1980s. Weed-suppressing rice plants can compete with weeds for light and mineral nutrients by their rapid and thick growth characteristics, and probably also by their allelopathic effects. It was suggested that allelopathic properties were inherited from parents. Different screening methods for finding allelopathic rice simply and rapidly have been proposed. In contrast, stimulative allelopathy in rice, which promotes germination of the dormant and dormancy-awakened seeds of Monochoria vaginalis (Burm. f.) Kunth var. vaginalis , has been investigated by the authors since the 1990s. Rice seeds promoted the germination in the dark and in light under submerged conditions. Our experiments suggested that rice seeds, hulls, plants and straw contain stimulative substance(s) that promote seed germination of M. vaginalis .     

Disease protection and growth promotion of potatoes (Solanum tuberosum L.) by Paenibacillus dendritiformis

One of the challenges in developing plant‐beneficial bacterial agents for agricultural application is ensuring that an effective selection and screening procedure is in place. The sporadic success of using bacterial agents in the field is usually due to the inability of added bacteria to compete with the local microorganisms. In the present study, the effectiveness of Paenibacillus dendritiformis, a unique pattern‐forming, Gram‐positive, soil bacterium, to reduce disease indices and increase yield in potato crops was examined. This bacterium was chosen as a potential agent based on genome analysis carried out in previous studies. In vitro laboratory experiments, as well as three greenhouse and one field experiment, were conducted. The results show that, in agreement with the hypothesis, P. dendritiformis significantly reduced the maceration area of tuber slices infected by Pectobacterium carotovorum subsp. carotovorum, significantly reduced disease indices in greenhouse experiments and significantly increased tuber yield of infected plants in the field. This work demonstrates the potential of preliminary screening based on genome analysis to identify effective biocontrol agents.     

Effect herbicides on weed control, yield and quality of eggplant (Solanum melongena L.) in Trinidad

The effects of six herbicides on weed control, yield and quality of transplanted.‘Early Long Purple’eggplant (Solantam melongena L.,) were evaluated in two replicated field experiments during the wet seasons (June to December) of 1976 and 1977 on River Estate loam soil in trifluralin 0 kg and had gave the best yield and excellent weed control for 8 weeks. Benfluralin (kg and ha) isopropalin (1.5 kg m.a ha) and diphenamid (5.0 kg and ha) gave acceptable weed control for 8 weeks and satisfactory yields, but chlorthal-dimethyl (1 kg a ha) and hotra (40 kg a ha) were less satisfactory. All the herbicides tested controlled weed for 4 weeks. There was no crop injury. Effet des herbicides sur le desherbage de sendement et la qualite de l'aubergine (Solanum melongena L.,) d Trinidad Les effets de herbicides sur le desherbage, le rendement et la qualite de preds transplantes d'aubergine (Solantum melongena L.,) var ‘Farly Long Purple’, ont ete evalues dans deux experiences au champ, durant les sarsons humides (june to December repetees en 1976 et 1977, sur un sol argileux de River Estate a Trinidad La triflurraline 1.0 kg m a has donne le meilleut rendement et un excellent desherbage pendant S sernames I a benfluraline (1.1 kg m.a. ha) l'isopropaline (1.5kg ma. Ha) et le diphenamide (5.0 kg m.a ba) ont donne un desherbage acceptable et des rendements satisfaisant mais le chlorthal dimethyl (10.0 kg m.a ha) et la butraline (4.0 kg m.a ha) ont ete moins satisfaisants Tous les herbicides essayes ont maitrise les measures herbes pendant 4 semaines II n'y a pas eu de degats sur la recolte. Emsatz von Herbizalen in Eterfruchen Solanum melongena in Trinidad Wirkane aut Unkraut. Ertrag und Qualdat. Es wurde die Ergnung von wchs Herniziden fur die Unkraut-bekämpfung in gepfltanzten Eterfrüchten (Solaman melongena L.) der Sorte ‘Early Long Purple’ sowie the Wirkung aut Ertrag und Qualität in zwer Feldversuchen wahrend der Regen zen (Juni bis December) in den Jahren 1976 und 1977 auf einem River-Estate-Lehmnoden in Trinidad gepruit. Mit Trifluralin (1.0 kg ha AS) wurden die hochsten Ertage und cine ausgezetchnete Unkrauthekämpfung über acht Wechen erzielt Benfluralin (1.1 kh ha AS) Isopropalin (1.5 kg ha AS) und Dephenamid (5.0 kg ha AS) wirkten uber acht Wochen zufriedenstellend und führlen zu mittleren Ertagen; Chlorthaldimethyl (10.0 kg ha AS) und Butralin (4.0 kg ha AS) befriedigten weniger. Alle gepruften Herbicide bekämpften die Unkrauter uber cine Zeit von 4 Wochen. Schaden an der Kulturpflanze konnten nicht festgestellt werden.     

Cultural Characteristics, Pathogenicity and Vegetative Compatibility of Fusarium udum Isolates from Pigeonpea (Cajanus cajan (L.) Millsp.) in Kenya

Seventy-nine single-spore isolates of Fusarium udum, the causal agent of wilt disease of pigeonpea, from Kenya, India and Malawi were characterized according to their cultural characteristics, pathogenicity and vegetative compatibility group (VCG). The isolates exhibited high variation in pathogenicity on a wilt-susceptible pigeonpea variety, and in mycelial growth and sporulation on potato dextrose agar medium. The 79 isolates were categorized into two virulence groups, two groups of radial mycelial growth and four groups of sporulation. Radial mycelial growth showed a moderate negative correlation (r = –0.40; P = 0.01) with sporulation. However, mycelial growth and sporulation had no correlation with virulence. Pairings between complementary nitrate non-utilizing (nit) mutants of F. udum generated on chlorate containing minimal medium revealed that all the isolates belonged to a single VCG (VCG 1) with two subgroups, VCG 1 I and VCG 1 II. Vegetative compatibility was independent of cultural characteristics and pathogenicity. This is the first report of vegetative compatibility in F. udum.     

The effects of sowing depth and flooding on the emergence, survival, and growth of Fimbristylis miliacea (L.) Vahl

Glasshouse experiments were conducted from March to July 2003 to determine the effects of sowing depth, and the time, duration, and depth of flooding on the emergence, survival, and growth of Fimbristylis miliacea (L.) Vahl. The treatments that were evaluated in the first experiment were three seeding depths (0, 0.5, and 1.0 cm), while in the second experiment, three flooding depths (saturated soil with no standing water and soil with water depths of 5 and 10 cm) and three flooding durations (7, 14, and 21 days from sowing) were evaluated. In the third experiment, three flooding depths (saturated soil with no standing water, and soil with water depths of 5 and 10 cm) and four flooding regimes (7, 14, 21 or 28 days after sowing [DAS]) were evaluated. Surface seeding gave the highest emergence rate compared to the 0.5 cm and 1.0 cm soil depths. A significantly higher emergence rate was recorded with the saturated conditions than with the flooded conditions. A flooding duration of ≥ 14 days showed a clear trend of reduced emergence with increasing flooding depth. A significantly higher survival rate, plant height, root length, number of leaves, and dry matter were recorded at soil saturation followed by the 5 cm and 10 cm flooding depths when flooding was simulated at 7 and 14 DAS. When the flooding was delayed to 21 and 28 DAS, the 10 cm flooding depth was required to suppress this weed. The results provide sufficient evidence to confirm that from deeper seed burial (1 cm sowing depth), flooding depths of ≥ 5 cm of durations of 14 and 21 days and at the onset of flooding within 14 DAS were effective in suppressing the emergence and growth of F. miliacea .     

Comparison of physiological effects of fluazifop-butyl and sethoxydim on oat (Avena sativa L.)

Laboratory experiments were conducted to compare the physiological effects of two herbicides: fluazifop-butyl {butyl ( RS )-2-[4-(5-trifluoromethyl-2-pyridyloxy)phenoxy]-propionate} and sethoxydim {(±)-2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} on oat ( Avena sativa L. cv. Zenshin). The herbicides strongly inhibited growth of oat and induced chlorosis at the basal part of shoots and ethylene production from the seedlings. The phytotoxicity of these herbicides in oat seedlings was alleviated by 2,4-D (2,4-dichlorophenoxyacetic acid), but not by IAA (indole-3-acetic acid). Coleoptile elongation induced by 2,4-D or IAA was inhibited by fluazifop-butyl and sethoxydim, suggesting both herbicides possess the activity to inhibit this auxin action. Fluazifop (free acid) and sethoxydim inhibited proton excretion from oat roots but fluazifop-butyl did not. This proton excretion was not restored by 2,4-D or IAA. Furthermore, cellular electrolyte leakage in oat shoots was increased by both herbicides, indicating that the membrane permeability was increased. We conclude that fluazifop-butyl and sethoxydim may have the same mechanism of action which leads to disruption of membrane integrity, although fluazifop-butyl acts as a free acid after hydrolysis (fluazifop).     

Effect of nitrogen fertilizer application on growth, biomass production and N-uptake of torpedograss (Panicum repens L.)

A glasshouse study was conducted to evaluate the effects of different rates (0, 50, 100, 200 and 400 kg ha^?1) of nitrogen (N) fertilizer application on the growth, biomass production and N‐uptake efficiency of torpedograss. The growth responses of torpedograss to the N application were significant throughout the observation periods. Torpedograss grown for 60 days obtained the highest total biomass of 23.0 g plant^?1 with an application of 200 kg ha^?1 N, followed by 20.4 g plant^?1 with an application of 100 kg ha^?1 N; when it was grown for 90 days a significantly higher biomass of 102.3–106.0 g plant^?1 was obtained with the 200–400 kg ha^?1 N than the biomass (68.0 g plant^?1) obtained with the fertilizer applied at a lower rate. When the torpedograss was grown for 130 days the highest biomass was 230.0 g plant^?1 with the 400 kg ha^?1 N application, followed by a biomass of 150.0 g plant^?1 with the 200 kg ha^?1 N application, but the above‐ground shoot in all treatments was over mature for animal food. The ratio of the above‐ground shoot to the underground part increased with the increase in N application up to 400 kg ha^?1 during the 90 days after planting (DAP), but the above‐ground shoot biomass was the same with the 200 and 400 kg ha^?1 N. The agronomic efficiency of the N application decreased to 5–38 with the increase in N application to 400 kg ha^?1, which was less than half the agronomic efficiency with the 200 kg ha^?1 N. The agronomic efficiency of N was very low (5–22) during the 60 DAP, which indicated that the N application would not be economically viable in this period for torpedograss as a pasture, and short‐duration plants could be cultivated in torpedograss‐infested fields to minimize weed‐crop competition. The nitrogen concentration (%) in the torpedograss increased with the increase in N application, but N‐uptake efficiency was the opposite and the value was very low with the 400 kg ha^?1 N. The above results lead us to conclude that the N application rate of 200 kg ha^?1 is the most effective for torpedograss growth.