Allelopathic potential of itchgrass (Rottboellia exaltata L. f.) powder incorporated into soil

Itchgrass ( Rottboellia exaltata L. f.) is a widespread weed in northern Thailand. The farmers in this area have been using itchgrass as a mulching material in order to control other weeds in vegetable fields. Laboratory experiments were undertaken to investigate the phytotoxic activity of itchgrass powder incorporated into soil in order to evaluate the allelopathic activity in the field. The phytotoxic activity on the growth of radish seedlings ( Raphanus sativa L. var. radicula ), used as a test plant, was more pronounced in the root than in the shoot growth. The phytotoxic activity was found to be similar for the soils incorporated with the shoot or the root powder of itchgrass. The growth of the radish seedlings grown in sea sand and watered with soil water obtained from the soil previously incorporated with itchgrass powder showed a similar inhibition to those planted in the treated soil. The phytotoxic activity on the growth of the radish seedlings in the soil incorporated with the powder decreased over time. It is suggested that itchgrass releases phytotoxic compound(s) into soil water and the concentration of the active compound(s) in the soil water decreases over time.     

Growth behavior of itchgrass (Rottboellia cochinchinensis) in Peninsular Malaysia

A glasshouse experiment was conducted at University Putra Malaysia, Serdang, to study the growth pattern of itchgrass collected from 13 locations. The itchgrass was either associated with crops or found along roadsides in six infested estates located in Johor, Kedah, Pahang, Perak, Perlis and Selangor. Significant differences between populations were observed in all variables except in time to seedling emergence. Cluster analysis of the data classified the populations into three major groups. The first group comprised populations from Johor, Pahang and Perak found in association with banana, cocoa and oil palm plantations, or along the roadsides. The second group comprised populations from Kedah, Perlis and Selangor found in association with maize, upland rice, rubber, sugar cane and tobacco plantations. The third group was a distinct population found only along roadsides at Padang Kartong, Perlis. Principal component analysis was performed to determine the growth characteristics that separated the groups. The results showed that plant height, number of leaves, number of seeds/plant, secondary culm diameter and the weight of 100 intact or dehulled seeds were the most significant characteristics that differentiated the groups. The study provided strong evidence of the existence of three itchgrass groups in Peninsular Malaysia.     

Allelochemicals of barnyardgrass‐infested soil and their activities on crops and weeds

Barnyardgrass is one of the most noxious paddy weeds in the world and causes great trouble to many crops. In a bioassay, the aqueous extract of paddy soil infested with barnyardgrass showed phytotoxic action against the growth of the tested crops and paddy weeds, of which rice was the most suppressed among the crops. In contrast, barnyardgrass was the least affected paddy weed. By the use of a separation resin, 18 compounds belonging to terpenes, derivatives of cinnamic acid and ferulic acid, long‐chain fatty acids, and steroids that were potentially involved in the phytotoxic activities in barnyardgrass‐infested soil were isolated and identified by gas chromatography–mass spectrometry analysis. Of these, the quantities of linalool, 4‐terpinenol, coumaran, methyl phenethyl ketone, and methyl ester cinnamic acid were 1.42, 0.37, 0.02, 3.12, and 4.59 μg g^?1 of the wet soil, respectively. The herbicidal activity was varied among these qualified test compounds, in which methyl phenethyl ketone and methyl ester cinnamic acid were more herbicidal than coumaran, linalool, and 4‐terpinenol. A mixture of these compounds was also the least inhibitive against the growth of barnyardgrass, but exerted strong suppression against that of rice and monochoria. The present study demonstrates that barnyardgrass possesses strong phytotoxic properties and releases plant growth inhibitors into the soil to compete with rice and other paddy weeds in its vicinity by a chemical pathway.     

Allelopathic effect of Pluchea lanceolata on growth and yield components of mustard (Brassica juncea) and its influence on selected soil properties†

Pluchea lanceolata (DC.) C.B. Clarke (Asteraceae) is a rapidly spreading perennial weed in semiarid areas of north‐west India. While preparing fields for cultivation, farmers incorporate Pluchea plant debris into the soil. In the present study, mustard grown in plots with soil‐incorporated Pluchea had significantly reduced shoot height (61 ± 8.8 cm), number of pods per plant (7 ± 3.2), number of seeds per pod (4.1 ± 3.9) and weight per seed (0.08 ± 0.03 g) of mustard compared to mustard growing in Pluchea‐free soils. Pluchea‐infested and Pluchea‐free soils were analyzed for pH, electrical conductivity, organic matter, soluble chloride, exchangeable phosphate, copper, zinc, sodium, potassium, magnesium, calcium and water‐soluble phenolics. Pluchea‐infested soils had different values for electrical conductivity, Cl, K and total phenolics when compared to Pluchea‐free soils. Data on yield reduction of mustard due to soil‐incorporated Pluchea leaves have been reported for the first time. The reduced mustard growth and yield is proposed to be partly due to water‐soluble phenolic compounds contributed by Pluchea leaves into soil.     

Allelopathic potential of wild onion (Asphodelus tenuifolius) on the germination and seedling growth of chickpea (Cicer arietinum)

Water extracts obtained from the roots, shoots, and fruits of mature wild onion ( Asphodelus tenuifolius ) plants and soil taken from an A. tenuifolius field were used to determine their allelopathic effects on the germination and seedling growth of chickpea ( Cicer arietinum ) in the laboratory. The roots, shoots, and fruits of A. tenuifolius were soaked individually in water in a ratio of 1:20 (w/v) for 24 h to prepare the extracts. Distilled water was used as the control. The germinated seeds were taken out from the Petri dishes and counted every day for 12 days. The seeds of chickpea were also sown in sand and in each of the controlled, normal soil and the soil taken from the A. tenuifolius -infested field in Petri dishes to record the length and weight of the roots and shoots 18 days after sowing. The mean germination time reached the maximum amount for the stem and fruit extracts. The fruit extract caused the most reduction in the germination index and the germination percentage of chickpea. The different wild onion organ extracts significantly reduced the root and shoot length and biomass of the chickpea seedlings compared with the distilled water. The fruit extract of wild onion proved to be the most detrimental to the root length, shoot length, and dry weight of the chickpea seedlings. The soil beneath the A. tenuifolius plants significantly reduced the emergence, root length, shoot length, shoot dry weight, and seedling dry weight but increased the root dry weight of the chickpea seedlings. It is suggested that A. tenuifolius releases phytotoxic compound(s).     

Properties of Banana Spray Oils in Relation to Sigatoka Disease Control and Phytotoxicity on Banana Leaves

Abstract

The properties of banana spray oils have been investigated by a number of researchers. The results of these investigations are reviewed in this paper, and include information on volatility (distillation range, flash point); flow characteristics (viscosity, pour point); other physical properties (specific gravity, colour, aniline point); and chemical properties (unsulphonated mineral residues, aromatics, paraffins and naphthenes).

A comparison of distillation curves is of greater significance than comparison of individual boiling points. Such a comparison will show whether any one oil product is a homogeneous oil or a mixture of heavy and light oils. Disease control is closely related to volatility of the spray oil; the lower the volatility of the oil the better the disease control. Phytotoxicity (leaf-flecking) increases as the percentage volatility of the spray oil decreases. Oil volatility governs the amount of oil remaining on the leaf after application. The initial amount of oil applied to the leaf is of less significance in the fungistatic effect than is the amount of oil remaining on or in the leaf. From a viewpoint of Sigatoka disease control, flash points are of little significance, but must be considered from the viewpoint of safety in storage, transportation and use.

As the viscosity of spray oils increases [in the range 35-100 Saybolt Universal Seconds (SUS) at 100[ddot]F] disease incidence decreases and phytotoxicity increases on sprayed banana leaves. The naphthenic oils are superior to the paraffinic oils, particularly in the viscosity range of 75-85 SUS at 100[ddot]F, for spraying bananas.

The performance of banana spray oils is related to the proportions of the major hydrocarbon groups (aromatics, naphthenes and paraffins) present in the oil. Properties such as specific gravity and aniline point are indicative of the proportions of the major hydrocarbon groups in a spray oil.

Colour of mineral oils is of no significance in the control of Sigatoka disease. Light mineral oils with unsulphonated mineral residue (U.M.R.) in the range of 70-99.9 are equally effective in Sigatoka disease control regardless of U.M.R. However, the degree of leaf damage (phytotoxicity) is directly related to U.M.R. value. The oils of high U.M.R. cause the least damage. The aromatic fraction of four spray oils tested (heavy paraffinic, light paraffinic, heavy naphthenic and light naphthenic) caused abundant phytotoxicity at a deposit level of 3 US gal/ac. There was little or no phytotoxicity and no appreciable disease control at a deposit level of 1.5 US gal/ac. Paraffinic and naphthenic oils of comparable U.M.R. value (94-95%) and viscosity (74-75 SUS at 100[ddot]F) provide good disease control within the deposit range 1.4-2.1 US gal/ac. At these deposit levels the naphthenic oil causes only 20 and 50% respectively as much phytotoxic flecking as the paraffinic oil. Photosynthesis is inhibited by the application of petroleum oil to banana leaves.

It is the opinion of the writer that a long-term trial (a minimum of two years) should be conducted to evaluate the effect of a comparable naphthenic and paraffinic oil on Sigatoka disease control and banana yield.     

Allelopathic potential of Trifolium resupinatum L. (Persian clover) and Trifolium alexandrium L. (Berseem clover)

This experiment was conducted in order to determine if Persian clover ( Trifolium resupinatum ) and Berseem clover ( Trifolium alexandrium ) contained water-soluble and methanol-soluble constituents that could affect the seedling growth of four test species; namely, Amaranthus retroflexus , Convolvulus arvensis (field bindweed), Secale cereale , and Sinapis arvensis (wild mustard) . The above-ground tissues of the Persian and Berseem clover plants were collected during the vegetative growth stage and oven-dried. Three concentrations of aqueous and methanolic extracts were used at full-strength (33.3 g L⁻¹), half-strength (16.7 g L⁻¹), and quarter-strength (8.3 g L⁻¹). Distilled water was used as the control. The weed seeds were placed in Petri dishes containing the legume extract or distilled water (control). The seedling growth of the weed species declined with the increasing concentration of the clover extracts. Wild mustard exhibited the highest sensitivity to both the legume extracts. Compared to the aqueous extract, the methanolic extract caused a greater decline in the seedling growth of the weeds. Berseem clover was the stronger inhibitor of the weed seedling growth, as compared to Persian clover. Therefore, the amounts of allelochemicals present might differ in these two clover species. Field bindweed showed the least sensitivity to both the legume extracts. Field bindweed showed more tolerance to the allelochemicals produced by the clover species.     

Allelopathic potential of Acacia melanoxylon on the germination and root growth of native species

Water extracts that were obtained from the flowers and phyllodes of Acacia melanoxylon were used to determine their allelopathic potential in relation to the germination and seedling growth of the native species, cocksfoot (Dactylis glomerata), perennial ryegrass (Lolium perenne), and common sorrel (Rumex acetosa), as well as a general biotest specie, lettuce (Lactuca sativa), in laboratory bioassays. The flowers and phyllodes of A. melanoxylon were soaked separately in distilled water in a ratio of 1:1 (w/v) for 24 h in order to prepare the aqueous extracts. Distilled water was used as the control. The seeds of the target species were germinated in Petri dishes and counted daily for up to 7 days. The A. melanoxylon flower extract (100%, 75%, and 50%) decreased the seed germination of D. glomerata, R. acetosa, L. perenne, and L. sativa. The flower extract caused the most reduction in the germination index and germination speed in D. glomerata, L. perenne, and L. sativa. The mean LC₅₀ value of the A. melanoxylon flower and phyllode extracts in relation to the germination inhibition of L. perenne was 43% and 41%, respectively, 40% and 38%, respectively, in R. acetosa, and 53% and 41%, respectively, in L. sativa. All four concentrations of the flower extract proved to be more phytotoxic than the phyllode extract, reducing the root length of all four species, while the phyllode extract decreased the root length of L. perenne and R. acetosa at the 100% concentration. The L. perenne and D. glomerata grass seeds were more sensitive regarding germination, as compared to L. sativa and R. acetosa. The flower aqueous extract of A. melanoxylon was more phytotoxic, as compared to the phyllode aqueous extract, even at the lowest concentration (25%).     

小麦幼苗及其次生代谢产物丁布对杂草的异株克生活性

研究了小麦活体、小麦水提液及小麦次生代谢产物丁布对几种杂草的异株克生活性。小麦与马唐、反枝苋、野燕麦、早熟禾、稗草等杂草混播的盆栽试验呈现出小麦播种密度越大,杂草种子萌发率越低的趋势。小麦水提液对马唐、反枝苋、早熟禾、稗草、野燕麦根和茎的生长均有明显的异株克生作用,IC₅₀(根)<1.5 mg/mL,IC₅₀(茎)<3.0 mg/mL,而对黑麦草、圆叶牵牛无明显的抑制活性。除马唐外,小麦水提液对供试杂草种子萌发抑制效果不明显。小麦次生代谢产物丁布对3种不同杂草的根、茎总体抑制效果为反枝苋>马唐>野燕麦,IC₅₀(根、茎)<1.5mg/mL,IC₅₀(种子萌发)<3.5 mg/mL。比较IC₅₀可知,生物活性:丁布>小麦水提液。丁布是小麦中具有异株克生活性的次生代谢物。     

Phytotoxic activity of Chinese violet (Asystasia gangetica (L.) T. Anderson) and two phytotoxic substances

Chinese violet (Asystasia gangetica (L.) T. Anderson) is a perennial invasive weed belonging to Acanthaceae. Leaves of this weed have been suggested to possess phytotoxic activity. However, phytotoxic substances in this weed have not yet been reported. Therefore, the present study investigated phytotoxic activity of Chinese violet extracts and phytotoxic substances. The extracts of Chinese violet leaves inhibited the root and shoot growth of cress, lettuce, alfalfa, barnyard grass, ryegrass, and timothy, where the level of inhibition increased with increasing extract concentrations. Bioassay‐guided separations of the extracts led to isolation of two phytotoxic substances, indole‐3‐carboxaldehyde and (6R,9S)‐3‐oxo‐α‐ionol. Indole‐3‐carboxaldehyde significantly inhibited the root and shoot growth of cress at concentrations ≥100 and 30 μmol L^?1, respectively, and concentrations of the substance required for 50% growth inhibition were 210 and 127 μmol L^?1 for cress roots and shoots, respectively. The other substance, (6R,9S)‐3‐oxo‐α‐ionol, was reported to have strongly inhibited cress roots and shoots. The present results suggest that Chinese violet contains two phytotoxic substances indole‐3‐carboxaldehyde and (6R,9S)‐3‐oxo‐α‐ionol, and those substances may play an important role in the phytotoxic activity of Chinese violet.     

黄花刺茄浸提液对番茄种子萌发及幼苗生长的影响

为明确入侵植物黄花刺茄对当地主栽经济作物番茄种子萌发和幼苗生长的影响,本文采用培养皿滤纸法,在智能光照培养箱的变温控制条件下,分别研究了黄花刺茄根、茎、叶浸提液对番茄种子发芽率、发芽指数及幼苗根长和苗高的影响。结果表明:(1)黄花刺茄不同器官的浸提液对番茄种子发芽率、发芽指数、幼苗根长和苗高的影响不同,其茎、叶浸提液的化感作用较为显著(P<0.01)。(2)黄花刺茄同部位浸提液对番茄种子发芽率、发芽指数、幼苗根长和苗高不同指标的影响也不同。根浸提液对种子发芽率、幼苗根长影响不显著(P>0.05),但对种子发芽指数的影响极显著(P<0.01)。茎和叶浸提液各浓度对种子发芽指数的影响比种子发芽率、幼苗根长和苗高的影响显著(P<0.01)。     

Velvetbean (Mucuna pruriens) extracts: impact on Meloidogyne incognita survival and on Lycopersicon esculentum and Lactuca sativa germination and growth

Velvetbean (Mucuna spp.) is a summer annual that has been used as a cover crop to reduce erosion, fix nitrogen and suppress weeds and plant-parasitic nematodes. Crude aqueous extracts (1:15 dry weight plant/volume water) were made from velvetbean plant parts, and various concentrations of the extracts were evaluated in vitro for toxicities to different stages of Meloidogyne incognita (Kofoid and White) Chitwood and for suppression of hypocotyl and root growth and inhibition of germination of tomato (Lycopersicon esculentum L.) and lettuce (Lactuca sativa L.). Germination was only affected by the full-strength extract from leaf blades. Lettuce root growth was the most sensitive indicator of allelopathic activity of the plant part extracts. Lettuce and tomato root growth was more sensitive to the extract from main roots than to extracts of other plant parts, with lethal concentration (LC50) values of 1.2 and 1.1% respectively. Meloidogyne incognita egg hatch was less sensitive to extracts from velvetbean than the juvenile (J2) stage. There was no difference among LC50 values of the extracts from different plant parts against the egg stage. Based on LC50 values, the extract from fine roots was the least toxic to J2 (LC50 39.9%), and the extract from vines the most toxic (LC50 7.8%). The effects of the extracts were nematicidal because LC50 values did not change when the extracts were removed and replaced with water.     

Enhanced weed‐crop competition effects on growth and seed production of herbicide‐resistant and herbicide‐susceptible annual sowthistle (Sonchus oleraceus)

Enhanced crop competition could aid in the management of annual sowthistle (Sonchus oleraceus L.), a dominant weed of Australian cropping systems. A two‐year pot study was conducted to evaluate the effect of wheat (Triticum aestivum L.) planting densities (0, 82, and 164 wheat plants/m²) on growth and seed production of glyphosate‐resistant (GR) and glyphosate‐susceptible (GS) biotypes of annual sowthistle. Without competition, both biotypes produced a similar number of leaves and biomass, but the GS biotype produced 80% more seeds (46,050 per plant) than the GR biotype. In competition with 164 wheat plants/m², the number of leaves in the GR and GS biotypes was reduced by 62 and 61%, respectively, in comparison with the no‐competition treatment, and similarly, weed biomass was reduced by 78 and 77%, respectively. Compared to no‐competition treatment, the seed production of GR and GS biotypes was reduced by 33 and 69%, respectively, when grown with 82 wheat plants/m², but increasing wheat density from 82 to 164 plants/m² reduced the number of seeds only in the GS biotype (81%). Both biotypes produced greater than 6,000 seeds per plant when grown in competition with 164 plants/m², suggesting that increased crop density should be integrated with other weed management strategies for efficient control of annual sowthistle.     

Allelopathic activity of leaching from dry leaves and exudate from roots of ground cover plants assayed on agar

The effects of leaches from dry leaves of 71 ground cover plant species on lettuce were tested at the first screening. The inhibitory effects on radicle and hypocotyl elongations of lettuce varied with the different species of cover plants that were used. Eight species of Oxalis showed strong inhibitions (4–27% of untreated control on radicle elongation). Inhibitory activities of seven species of cover plants on three weed species, live amaranth ( Amaranthus lividus ), southern crabgrass ( Digitaria ciliaris ) and common lambsquarters ( Chenopodium album ), were tested at the second screening. Moss pink ( Phlox subulata ), trefoil ( Oxalis brasiliensis ), red spiderlily ( Lycoris radiata ), creeping thyme ( Thymus serpyllum ), European pennyroyal ( Mentha pulegium ), roman chamomile ( Chamaemelum nobile ) and star-of-Bethlehem ( Ornithogalum umbellatum ) were selected as donor plants because of their high inhibitory effects on lettuce growth and their usefulness as ornamental ground cover plants. Effects of leaches from dry leaves and exudates from the roots of these species were assayed on agar. Radicle elongations of all tested weed species were inhibited by leaches from trefoil and red spiderlily (8–31% and 14–24% of untreated control, respectively) and exudates from moss pink, trefoil and creeping thyme (11–43%, 31–74% and 22–67% of untreated control, respectively).     

Contribution of ammonium to stimulation of smooth pigweed (Amaranthus hybridus L.) germination by extracts of hairy vetch (Vicia villosa Roth) residue

Hairy vetch is a leguminous winter annual cover crop that provides a significant contribution toward meeting the nitrogen requirement of succeeding crops. Hairy vetch residue is capable of suppressing weeds, but low levels of residue can intermittently stimulate the emergence of weeds, particularly smooth pigweed. This research was conducted to assess the inhibitory and stimulatory effects of hairy vetch extracts on two smooth pigweed lots with differing dormancy conditions under differing germination conditions (25 or 35°C in light or dark). Full-strength extracts inhibited germination of both lots under all conditions, a result explained by the inhibitory osmotic potential of the full-strength extract. At ≤ 0.1× proportions of the hairy vetch extract, there was a slight stimulation of germination above that of the control (average = 11%) of both lots of pigweed under all germination conditions, except for a large stimulation (87%) by the more dormant lot at 25°C in light. A similar response to ammonium hydroxide solutions was observed, in which germination stimulation averaged 7% for all conditions except for germination of the dormant pigweed lot that was stimulated 115% by 15 p.p.m. of ammonium (     ) at 25°C in light. As the     concentration in the hairy vetch extract was similar to that in the ammonium hydroxide solutions that promoted the largest stimulation of germination, and because there was a high correlation between the degree of germination stimulation by hairy vetch extracts and by ammonium hydroxide,     appears to be the principle ingredient in the extract responsible for stimulation of smooth pigweed germination.     

7种激素对蒺藜状苜蓿种子发芽的影响

本实验旨在研究蒺藜状苜蓿种子发芽对外源激素的响应。使用6-BA、GA3、ABA、NAA、乙烯利I、AA和IBA共7种激素,每一激素各设0.1、1.0、1.5、2.0、5、10、201、000μmol/L共8种浓度梯度,浸湿滤纸发芽床,置50粒蒺藜状苜蓿种子进行发芽试验,以蒸馏水处理为对照,设3个重复,统计发芽率、发芽势、发芽指数和发芽天数。结果显示:外源激素20μmol/L 6-BA、GA3、乙烯利和5μmol/L IAAI、BA促进蒺藜状苜蓿种子发芽,NAA和ABA抑制蒺藜状苜蓿种子发芽,ABA抑制能力较强。     

Potential allelopathic effects of Mikania micrantha on the seed germination and seedling growth of Coix lacryma‐jobi

The allelopathic potential of Mikania micrantha H.B.K. to affect the seed germination and seedling growth of Coix lacryma‐jobi L. was investigated. Water‐soluble allelopathic substances were found in the water extracts of M. micrantha. The effect of the water extracts on the seed germination and seedling growth of C. lacryma‐jobi was concentration‐dependent. The water extracts from the different plant parts (leaf, stem, and root) of M. micrantha differed in their effect on the germination and seedling growth of C. lacryma‐jobi, with the effect of the leaf extract being the least inhibitory. The malondialdehyde (MDA) content in the C. lacryma‐jobi seedlings increased by 64%, 45%, and 52% of the control with increasing concentrations of the extracts of the root, stem, and leaf (80, 400, and 400 g L^?1, respectively). The extract from the M. micrantha roots significantly increased the catalase (CAT) activity of the C. lacryma‐jobi seedlings (48% and 54% of the control at the concentrations of 20 g L^?1 and 80 g L^?1, respectively). The extracts from the leaves and stems at low concentrations increased the CAT activity, but at high concentrations, the extracts decreased the CAT activity. The extracts from the roots, stems, and leaves at concentrations of 80, 400, and 400 g L^?1 also significantly decreased the peroxidase (POD) activity of the C. lacryma‐jobi seedlings to 27%, 52%, and 34% of the control, respectively. These results indicate that the water extracts of M. micrantha could inhibit the seed germination and seedling growth of C. lacryma‐jobi through the regulation of anti‐oxidase activity, such as POD and CAT in the cells. The growth inhibition of the C. lacryma‐jobi seedlings is probably related to injury after oxidization of the cell membranes with the increase of MDA content.