Allelopathic potential in lettuce (Lactuca sativa L.) plants

Lettuce (Lactuca sativa L.) is known to contain water-soluble substances that are allelopathic. Aqueous or methanol extracts and residues from leaves of lettuce cultivar “Cheongchima”, which showed the most inhibitory effects, were assayed to determine their allelopathic effects on seed germination and early seedling growth of several plant species. The aqueous extracts applied to filter paper significantly inhibited seed germination of alfalfa with increasing of extract concentration. Methanol extracts from hexane fraction of lettuce plants showed the most inhibition on alfalfa root growth and followed by ethylacetate, butanol and water fractions. Incorporation with leaf residues of 100 g kg ⁻¹ into soil significantly inhibited shoot and root fresh weights of barnyard grass by 79 and 88%, respectively. These results suggest that extracts or residues from lettuce plants had potent allelopathic activity and that the activity differed depending on cultivar, extract or fraction.     

Potent herbicidal activity of Inula crithmoïdes L.

Aqueous (10, 20, 30 and 40 g/L) and organic (hexane, chloroform and methanol, at 3000 and 6000 ppm) extracts of Inula crithmoïdes L. (roots, stems, leaves and flowers) were evaluated for their allelopathic activities on radish, lettuce, peganum and thistle. Pot cultures were conducted by incorporation of I. crithmoïdes leaves and flowers powder (1.25 and 2.5 g/kg) in soil and by irrigation with their aqueous extracts at 40 g/L. PEG (polyethylene glycol) solutions, with similar osmotic potentials of aqueous extracts, at the highest concentration, were without effect on target species, this eliminates the extracts osmotic effect. Germination index was not affected by root and stem extracts and significantly decreased by the two other ones. For growth, leaf and flower extracts had the most significant toxicity at 40 g/L, inducing up to a total inhibition. For organic extracts, a strong toxicity was recorded for the three fractions at 6000 ppm, thistle seedling growth was more sensitive, especially to chloroform fractions. Soil incorporation of residues (at 2.5 g/kg) significantly decreased root (35–100%) and shoot (0–100%) length of target species. Irrigation soil with leaves and flower aqueous extracts was harmful for peganum and thistle, respective inhibition percentages were 100% and 66.5%. I. crithmoïdes may be favorably used for incorporating in agricultural systems for sustainable weed management.     

核桃坚果水浸液对4种植物种子萌发及生长的影响

为探究核桃果实不同部位水浸液对植物种子萌发及生长的影响,本试验以莴笋、萝卜、马蹄金、野牛草4种种子为试材,对其进行核桃种子、种仁及种皮的水浸液浸泡处理,进而研究核桃果实不同部位水浸液的化感作用,旨在探讨核桃水浸液对4种植物种子萌发及生长的影响。结果表明,在特定浓度下,核桃种子的水浸液对莴笋、萝卜、马蹄金、野牛草种子萌发均起到抑制作用,对萝卜幼苗生长的抑制作用大于莴笋幼苗的生长,对马蹄金和野牛草种子生长的抑制作用大于莴笋和萝卜。核桃种仁的水浸液对幼苗生长的抑制作用大于其余2个部位的影响,表现为:核桃种仁大于核桃种壳和核桃种子。本研究探索了核桃种子水浸液的化感作用及抑制植物种子萌发的物质,为农作物间作套种、化感抗害提供了依据和指导。     

菊芋秸秆对连作番茄幼苗生长及根结线虫的影响

以5种不同品种菊芋秸秆(‘J04’‘J06’‘J01’‘J13’‘J15’)为研究对象,以番茄为试材,采用盆栽方法,研究了不同品种菊芋秸秆对连作番茄幼苗生长及根结线虫的影响,以期筛选出利于番茄生长及防治根结线虫的优良菊芋品种。结果表明:番茄连作土中添加菊芋秸秆后,前期(30d)番茄幼苗生长受到抑制,后期表现为促进番茄幼苗生长。不同品种的菊芋秸秆对番茄幼苗生长影响不同,J13和J04处理番茄长势最好,其次是J01、J06、J15。不同品种的菊芋秸秆对于根结线虫虫卵孵化及二龄幼虫均有抑制作用,J13、J04、J06秸秆浸提液对虫卵孵化抑制效果较好,J06和J13对于根结线虫抑杀效果最好,J01对于根结线虫的抑杀效果最弱。综上,J13可作为菊芋秸秆新型开发利用及防治番茄连作障碍的参考材料。     

不同化感效应的小麦根系分泌物对黄瓜幼苗生长及根系生理生化特性的影响

以黄瓜幼苗为受体,研究了不同化感效应的小麦根系分泌物对黄瓜幼苗生长及根系生理生化特性的影响。结果表明：具有化感促进效应的小麦根系分泌物分别在处理后的不同时期提高了黄瓜幼苗根系保护酶活性、渗透调节物质含量,降低了脂膜过氧化作用,提高了黄瓜幼苗的株高、茎粗、全株干质量、叶面积及光合作用|具有化感抑制效应的小麦根系分泌物则在处理后的不同时期降低了黄瓜幼苗保护酶活性及渗透调节物质含量,增加了脂膜过氧化作用,抑制了黄瓜幼苗的生长,降低了光合作用。     

Effect of enhanced ultraviolet-B on allelopathic potential of Zanthoxylum bungeanum

The effect of enhanced ultraviolet-B on allelopathic potential of Zanthoxylum bungeanum was investigated. A significant inhibitory effect on germination rate of crop seeds under bioassay was observed at 25 g l⁻¹ and 50 g l⁻¹ by extracts from Zanthoxylum leaf both treated with enhanced ultraviolet-B radiation and untreated control. Medicago sativa and lettuce were more sensitive than radish to the extract from Zanthoxylum leaf treated with enhanced UV-B radiation, as the germination rates of M. sativa and lettuce were significantly reduced compared to control at 25 g l⁻¹ and 50 g l⁻¹, and so did alfalfa at 12.5 g l⁻¹. However, as for radish (Raphanus sativus) there was no significant reduction in germination rate at any concentration under bioassay compared to control. Content of UV-B absorbing compounds and total phenols in Zanthoxylum seedlings responded positively to enhanced UV-B radiation. The results suggest that the allelopathic potential of Z. bungeanum was generally improved under enhanced UV-B radiation.     

菊芋块茎基质漂浮育苗营养机理研究

为研发一种环保节能、成本低廉的菊芋漂浮育苗基质,找到菊芋育苗的关键影响因子和参数,采用锯末、珍珠岩、菌渣、谷壳等废弃物作为混合基质进行菊芋块茎漂浮育苗试验。结果表明:育苗基质配方2对菊芋单株株高、最大叶宽、茎粗、叶片数、鲜质量具有极显著促进效果。菊芋育苗的关键在于培育强大的根系,增加叶宽。钙和铁对总根数和最大叶宽直接效应极显著。钙增加1%,总根数增加19.450根;铁增加1%,总根数减少20.202根。回归分析表明菊芋育苗获得强大的根系时最佳总钙为0.288 0%,最佳总铁为1.311 8%。     

辣椒植株水浸提液化感作用的初步研究

以菜心和油麦菜两种蔬菜作物为受体,通过测定辣椒植株水浸液对两种蔬菜作物幼苗生长的影响,对辣椒化感物质的作用进行了研究。结果表明：①低浓度（0.02g/mL）的辣椒水浸提液对菜心的苗长和油麦菜苗长、根长和苗质量均表现为促进作用,对菜心的根长、根质量和油麦菜的根质量有抑制作用;②高浓度（0.06g/mL、0.08g/mL）的辣椒水浸提液对菜心和油麦菜幼苗根长和根质量均表现为抑制作用,随着浓度的加大,抑制作用增强,对菜心幼苗苗长和油麦菜的苗质量有一定的促进作用,随着浓度的加大,促进作用减弱;③浓度为0.04g/mL的辣椒水浸提液对菜心根质量、根长和油麦菜根质量、苗长表现为抑制作用,对菜心的苗长和油麦菜苗质量、根长表现为促进作用。     

Biological activities of essential oil,aqueous and organic extracts of Pituranthos tortuosus (Coss.) Maire

Aqueous and organic extracts, essential oil as well as the powder of Pituranthos tortuosus (Coss.) Maire were tested on the growth of flax (Linum usitatissimum) and turnip (Brassica rapa) to assess its allelopathic potentialities. Besides, biological potentialities of its essential oil were evaluated by estimating its insecticidal (on Cryptolestes ferrugineus and Culex pipiens) and antifungal (on Fusaruim graminearum and Alternaria sp.) activities. Significant growth inhibition of target species was recorded in the presence of the aqueous and acetone extracts, more than 50% in certain cases. P. tortuosus essential oil also induced growth reduction which was almost total in the presence of a concentration of 4000 ppm. In addition, essential oil caused, for C. ferrugineus, a respective mortality of 50% and of 90% at concentrations of 205.68 and 300.37 μl/l air. Otherwise, 50 ppm was sufficient to induce 100% of mortality of C. pipiens larvae, whereas LC₅₀ and LC₉₀ were 15.46 ppm and 23.62 ppm, respectively. A concentration of 4 μl/ml of P. tortuosus essential oil caused a complete inhibition of the mycelial growth of F. graminearum and Alternaria sp. Results show that essential oil as well as organic extracts could be used for the production of natural bio-pesticides which could reduce our dependence on chemical pesticides.     

Allelopathic effect of ginger on seed germination and seedling growth of soybean and chive

The rhizome, stem and leaf aqueous extracts of ginger were assayed at 10, 20, 40, and 80 g l⁻¹ for their effects on seed germination and early seedling growth of soybean and chive. All aqueous extracts at all concentrations inhibited seed germination, seedling growth, water uptake and lipase activity of soybean and chive compared with the control, and the degree of inhibition increased with the incremental extracts concentration. The degree of toxicity of different ginger plant parts can be classified in order of decreasing inhibition as stem > leaf > rhizome. The results of this study suggest that rhizome, stem and leaf of ginger contain water-soluble allelochemicals which could inhibit seed germination and seedling growth of soybean and chive. The rhizome is the main harvested part of ginger. The residue (mainly stems and leaves) of the ginger plant should be removed from the field so as to diminish its inhibitory effect. Further work is needed to specify and verify the allelochemicals produced by this plant. The results of this study suggest that ginger allelochemicals are heterotoxic, and thus intercropping should not be practiced using ginger.     

Accumulation of phytotoxic organic acids in reused nutrient solution during hydroponic cultivation of lettuce (Lactuca sativa L.)

Proper nutrient solution management in the root zone is the first consideration for the adoption of a closed hydroponic system. Plant roots often exude numerous organic acids, which are known to inhibit growth. To investigate the accumulation of these phytotoxic organic acids as root exudates, lettuce (Lactuca sativa L.) was hydroponically grown in reused nutrient solution. Organic acids were extracted with diethyl ether from the reused nutrient solutions (RNS), root residues, and activated charcoal (AC) then quantified by GC/MS. Five individual organic acids were identified from the root residues and seven from the reused nutrient solutions. After 90 days of lettuce cultivation, in the treated AC in 3RNS, benzoic, phenylacetic, cinnamic, p-hydroxybenzoic, lauric, phthalic, vanillic, palmitic, and stearic acids were identified. In contrast, little or no organic acids were detected in the 3RNS treated with AC (3RNS/AC). Artificially applied pure organic acids ranging from 25 to 200 μM inhibited lettuce growth in a concentration-dependent manner. Lettuce growth was also greatly reduced in the nutrient solutions containing a externally applied, simulated mixture of the organic acids as in the 3RNS. Lettuce growth was not inhibited following the addition of AC (2.5 g/L) to the nutrient solution containing the mixture of organic acids. Our results demonstrated that organic acids were accumulated in reused nutrient solutions and were phytotoxic to lettuce growth. Also, this study showed that the addition of AC reduces the phytotoxic effects by eliminating the organic acids.     

Phytotoxic properties of Drosophyllum lusitanicum leaf extracts and its main compound plumbagin

The aim of this work was to evaluate the phytotoxic properties of aqueous and hexane extracts from the insectivorous plant Drosophyllum lusitanicum (L.) Link using lettuce and bread wheat as model species. The results obtained confirmed that both germination and seedling growth bioassays were sensitive and able to detect the heterotoxicity potential of D. lusitanicum extracts. Aqueous and hexane extracts at several concentrations significantly inhibited the seed germination of lettuce and wheat, although wheat was less sensitive. The inhibitory effects of plumbagin, the major compound found in D. lusitanicum hexane extracts, were also evaluated. Comparing the results of the assays obtained with extracts and plumbagin it was postulated that plumbagin is the principal compound responsible for the phytotoxic effects of the extracts on lettuce but not on wheat. Therefore, although the phytotoxic potential of D. lusitanicum was demonstrated, further studies are needed to clearly specify the compounds responsible for the inhibitory effects and to ensure if the results obtained with the model species are reproducible to weed species in field conditions.     

Form and development of nitrogen in plant waste extracts,effects of papain on nitrogen transfer and use of extracts for lettuce fertigation

Summary

Liquid organic fertilisers made from extracts of plant residues can provide a sustainable alternative for vegetable production, since they are not produced using fossil fuels and are easy to apply as side-dressing fertilisers. The aims of this study were: (i) to evaluate the influence of extraction time and the addition of papain on the composition of aqueous extracts of cauliflower, tomato leaf, or whole tomato plant residues; and (ii) to explore the fertigation potential of such extracts for lettuce cultivation. After 10 d of extraction, approx. 30% of all plant residue nitrogen (N) was transferred to the liquid fraction, of which 8 – 15% was in mineral form. Ammonium was the main mineral form of N in all extracts. Nitrate concentrations were higher in whole tomato plant residues than in tomato leaves or cauliflower residues. The addition of papain increased the amount of total N in solution when used at concentrations ≥ 400 mg l^–1.

Compared to the mineral nutrient solution (control), plant extracts were comparable in mineral N, lower in phosphate, and higher in all other nutrients examined, as well as in Na⁺ and Cl^– ions. The application of each extract to lettuce seedlings resulted in reduced plant growth in all treatments compared to the control, probably due to their higher electrical conductivity and, possibly, ammonium toxicity. Further research is needed in order to balance the nutrient composition and to increase the transfer of plant residue nutrients into the extracts.     

秸秆及绿肥浸提液对莴苣种子的化感作用

采用室内培养试验,通过测定稻草、油菜秸秆、紫云英及紫云英+油菜浸提液对莴苣种子发
芽及幼苗生长的影响,研究秸秆及绿肥浸提液对莴苣种子的化感作用。结果表明：各秸秆及绿肥浸提液处
理均会延迟莴苣种子的发芽速度,且高浓度抑制种子萌发;各浸提液处理对莴苣幼苗苗高表现为低促高
抑,而对根长表现为抑制;莴苣幼苗鲜质量及干质量均随各浸提液浓度的增加先增加后降低,其中稻草、
油菜秸秆、紫云英及紫云英+油菜浸提液对幼苗鲜质量的最大促进作用分别为27.33%、27.52%、1.28%、
19.24%;不同浓度下,稻草、紫云英浸提液对莴苣的化感综合效应为抑制,油菜秸秆及紫云英+油菜为低
促高抑;紫云英与油菜混合可作为改善紫云英、油菜单独使用效果的有效途径。     

Two potent allelopathic substances in cucumber plants

Since cucumber plants are mostly discarded as large waste after crop harvesting, allelopathy of cucumber plants was investigated for possible weed management options and utilization of the waste. Two potent growth inhibitory substances were isolated from an aqueous methanol extract of cucumber (Cucumis sativus L. cv. Phung Tuong) plants. These substances were determined as 9-hydroxy-4,7-megastigmadien-9-one (HMO) and (6S,7E,9S)-6,9,10-trihydroxy-4,7-megastigmadien-3-one (THMO) by the analysis of MS, ¹H NMR spectra and optical rotation. HMO inhibited the growth of cress (Lepidium sativum L.) and Echinochloa crus-galli (L.) Beauv seedlings at concentrations greater than 0.3 and 1 μM, respectively. THMO inhibited the growth of cress and E. crus-galli seedlings at concentrations greater than 1 and 3 μM, respectively. The concentrations required for 50% growth inhibition on roots and shoots of cress and E. crus-galli were 2.4–29.3 μM for HMO and 8.1–52.2 μM for THMO. The endogenous levels of HMO and THMO in cucumber plants were 31.8 and 43.5 μg g⁻¹ dry weight, respectively. These results suggest that HMO and THMO may be the causal factors for the growth inhibitory effect of cucumber plants. Therefore, cucumber plants may be potentially useful for weed management options in an agricultural setting, such as a cover crop and soil admixture, which should be investigated further in the field.     

Bio-efficiency of compost extracts on the wet rot incidence,morphological and physiological growth of okra (Abelmoschus esculentus [(L.) Moench])

An experiment was carried out to investigate the efficacy of rice straw and empty fruit bunch (EFB) of oil palm compost extracts either fortified or unfortified with Trichoderma harzianum on morpho-physiological growth and occurrence of Choanephora wet rot of okra. Treatments tested were water (control) (T1), rice straw (RST) compost extract (T2), Trichoderma-enriched RST compost extract (T3), empty fruit bunch of oil palm compost extract (T4), Trichoderma-enriched EFB compost extract (T5), aqueous suspension of Trichoderma (T6), and a fungicide Dithane M-45^® (2 g l⁻¹ of water) (T7). The experimental results revealed significant variations amongst the treatments in respect of morphological characters, e.g. shoot length, tap root length, number of leaves per plant, and leaf area. The shoot and tap root length, number of leaves per plant, leaf area were significantly (P ≤ 0.05) higher in Trichoderma-enriched RST compost extracts (T3) followed by Dithane M-45^® (T7), Trichoderma-enriched EFB extracts (T5), RST (T2), EFB (T4) and aqueous suspension of T. harzianum (T6) in both Choanephora inoculated and uninoculated (control) plots. Similarly, net photosynthetic rate and chlorophyll content were higher in plants receiving Trichoderma-enriched RST compost extracts (T3) with 76.2% reduction in Choanephora wet rot incidence when compared with rest of the treatments. These experimental results revealed that morpho-physiological characters of okra could be modified by the application of Trichoderma-enriched compost extracts. This suggests that use of Trichoderma-enriched compost extracts would be more beneficial in environmentally friendly okra cultivation and may be used as an alternative to inorganic fertilizers/fungicides to enhance plant growth and reduce disease incidence subsequently, resulting in higher yield.     

加拿大蓬水提液对甜白菜和油菜幼苗化感作用

以加拿大蓬（Conyza Canadensis L.）为供体植物,甜白菜（Sweet Cabbage）和油菜（Brassica Chinensis L.）种子为受体,采用培养皿滤纸法,测定加拿大蓬的茎叶水提液对甜白菜和油菜幼苗的根长、苗高和鲜质量的化感作用。研究结果表明,加拿大蓬地上部分的水提液对甜白菜和油菜幼苗植株生长有明显的化感作用,且不同浓度水提液对不同作物的影响存在差异;对二者根系生长均有明显的抑制作用,且随着浓度的增大抑制作用增强;当浓度为0.25 g/mL,0.50 g/mL和1.00 g/mL时,甜白菜幼苗的根长分别比对照减少69.3%,95.1%和100.0%,油菜幼苗的根长分别比对照减少69%,93.7%和100%;对株高表现为＂低促高抑＂的趋势。     

番茄、花椰菜水浸提液对玉米种子萌发的影响

采用生物测定方法,研究番茄、花椰菜植株及根际土壤水浸提液0.025、0.050、0.075、0.100 g/mL 4个浓度梯度对玉米种子萌发及幼苗生长的影响。研究结果表明,花椰菜根际土壤水浸提液对玉米化感效应最强,水浸提液浓度越大,化感效应越强;番茄、花椰菜不同部位水浸提液对玉米根长、芽长的抑制率明显不同,花椰菜植株水浸提液抑制率最强,番茄植株水浸提液抑制率次之,番茄根际土壤水浸提液抑制率最弱,花椰菜根际土壤水浸提液对玉米根长、芽长有一定促进作用。     

苦瓜对8种蔬菜的化感作用

以8种海南主要栽培的蔬菜为受体,采用室内生测法研究苦瓜(Momordica charantiaL.)茎叶水浸提液对其化感作用。结果表明:苦瓜茎叶水浸提液对8种受体植物的种子萌发和幼苗生长均有一定的化感效应,且化感作用方式和强度在受体间及指标间存在显著差异;化感作用综合效应的平均值大小顺序为:辣椒黄瓜豇豆菜豆萝卜樱桃番茄胡萝卜番茄。试验结果为建立合理的栽培制度提供了理论和试验依据。     

Weed control and yield response of soil solarization with different plastic films in lettuce

Phase out of most chemicals available for weed management renewed the interest in soil solarization as a technically effective and environmentally safe practice for lettuce weed control in hot summer areas. Properties of solarizing films and lettuce crop system may considerably affect weed control and yield response of soil solarization. Different solarizing films, including low-density polyethylene, ethylene-vinyl acetate copolymer, low-density polyethylene–ethylene-vinyl acetate coextruded and a biodegradable corn starch-based film, were evaluated in 2003 and 2004 for weed control and lettuce yield response under field and greenhouse conditions in Southern Italy. Soil solarization strongly reduced weed density and biomass in both greenhouse and in the field, with no significant differences among the tested plastic films. Most annual weeds were completely controlled by soil solarization, except amaranth, Amaranthus spp., in soil solarized with biodegradable film in the field. Emergence of mediterranean sweetclover, Melilotus sulcatus, was stimulated by soil solarization in greenhouse. In the field, Cyprus vetch, Lathyrus ochrus, was found in solarized plots though absent in untreated soil. Perennial weeds were not affected by soil solarization, except a strong control of canadian thistle, Cirsium arvense, in the field. Lettuce yield resulted significantly higher in solarized soil than in control plots, with no significant differences among the solarizing materials. All tested materials proved to be technically effective for soil solarization in lettuce, though low resistance and short durability of biodegradable film may suggest its application mainly to soil solarization in greenhouse or in organic systems.