Growth Of Barnyardgrass Research Articles

Isopropyl Cresols: Synthesis and Herbicidal Activity

AbstractIsopropyl cresols were prepared by a two‐step process: monoterpene oxidation catalyzed by CrO3 and terpenone isomerization catalyzed by 13X molecular sieves. 5‐Isopropyl‐3‐methylphenol and carvacrol were prepared from 3‐carene, whereas thymol and 4‐isopropyl‐3‐methylphenol were synthesized from α‐pinene. The two reactions followed an identical procedure, but the reaction of 3‐carene was more efficient, benefiting from the three‐membered ring in the structure. 5‐Isopropyl‐3‐methylphenol, thymol, and carvacrol were found to show higher herbicidal activity than glyphosate toward the root growth of barnyard grass. However, they exhibited slightly lower activity in preventing shoot growth. Moreover, 5‐isopropyl‐3‐methylphenol showed higher herbicidal activity than its isomers, which indicates that the relative position of substitutes is significantly associated with the herbicidal activity of isopropyl cresols.

Bioherbicidal activity of terpenes and phenylpropenes against Echinochloa crus-galli

This study was undertaken to evaluate the herbicidal activity of twelve natural compounds belonging to monoterpenes, phenylpropenes, and sesquiterpenes against Echinochloa crus-galli under laboratory and glasshouse conditions. Experiments were conducted to determine the impact of different concentrations (0.5, 1, 2, 4 and 8 mM) of these compounds on the seed germination and root and shoot growth of barnyard grass. trans-Cinnamaldehyde, eugenol, and thymol caused the highest impact on barnyard grass reducing its seed germination and shoot growth. p-Cymene (EC50 = 0.22 mM) and trans-cinnamaldehyde (EC50 = 0.34 mM) were the most potent compounds in limiting the root growth of the E. crus-galli. In a post-emergent experiment, thymol, trans-cinnamaldehyde, eugenol, farnesol, and nerolidol significantly reduced the shoot growth, fresh and dry weight of two-leaf stage barnyard grass after 2 days of the foliar treatment with the concentrations of 0.5, 1.0 and 2.0%. These compounds induced severe visible injury symptoms where trans-cinnamaldehyde, eugenol, farnesol and nerolidol showed a complete weed control at 1.0 and 2.0%. These compounds were successfully formulated as emulsifiable concentrates and showed higher herbicidal activities against barnyard grass. Altogether, our data showed that trans-cinnamaldehyde, eugenol, thymol, farnesol, and nerolidol can be developed as novel bioherbicides for managing E. crus-galli.

Carum carvi L. essential oil: A promising candidate for botanical herbicide against Echinochloa crus-galli (L.) P. Beauv. in maize cultivation

Abstract Natural, essential oil-based emulsions could be in future an alternative for synthetic herbicides. In this study, the possibility that foliar-applied caraway or peppermint essential oils (EO) can selectively inhibit the growth of Echinochloa crus-galli (L.) P. Beauv. (barnyardgrass, a typical maize weed) but not that of maize plants was tested, in attempt to develop an eco-friendly botanical herbicide. The phytotoxic potential of oil-in-water emulsions of each EO with addition of commercial adjuvant, mainly composed of fatty acids methyl esters, was examined. Their effect on visible plants injuries, biomass accumulation, chlorophyll a fluorescence and changes to biochemical patterns of both the main crop (maize) and barnyardgrass via an untargeted metabolomic approach were studied. It was found that oil-in-water emulsion containing 2.5% of adjuvant and of caraway EO did not affect significantly the growth of maize plants, did not induce foliar symptoms and did not alter the status of the photosynthetic apparatus, as revealed by chlorophyll a fluorescence. On the contrary, this emulsion exerted significantly negative effects against barnyardgrass growth, inducing foliar injuries and reducing the photosynthetic efficiency of photosystem II. It was also found that the studied emulsions caused a series of biochemical changes in the plant tissues, with caraway emulsion being more phytotoxic, as compared to the peppermint EO-emulsion. In conclusion, oil-in-water emulsion containing 2.5% of caraway EO could be used in future as a foliar-applied botanical herbicide against barnyardgrass in maize cultivation.

Study of the allelopathic activity of Garcinia pedunculata Roxb

The allelopathic properties of plants can be used as an alternative weed control method to reduce the use of synthetic herbicides. Accordingly, the present study was carried out to determine the allelopathic activity of Garcinia pedunculata. Six different concentrations of aqueous methanol extracts of G. pedunculata fruit were prepared and used to determine their effect on the growth of eight test plants: alfalfa (Medicago sativa L.), cress (Lepidum sativum L.), lettuce (Lactuca sativa L.), rapeseed (Brassica napus L.), barnyard grass (Echinochloa crus-galli (L.) P. Beauv.), foxtail fescue (Vulpia myuros (L.) C.C. Gmel.), Italian ryegrass (Lolium multiflorum Lam.), and timothy (Phleum pratense L.). The test plants were grown in Petri dishes and after 48 h incubation, the length of the roots and shoots of the seedlings was measured and compared with control seedlings. Experiments were carried out in a completely randomized design (CRD). Analysis of variance (ANOVA) of the data was performed using the SPSS statistical package, and the I50 values were measured from a regression equation. The extracts at each concentration significantly inhibited the shoot and root growth of all the test plants, except the concentration of 0.001 g dry weight equivalent extract/mL, compared with control. At a concentration of 0.3 g of dry weight equivalent extract/mL, the shoot and root growth of all the tested plants were completely inhibited, except the shoot growth of barnyard grass. The degree of inhibition increased in line with increased extract concentration. The shoots of alfalfa and the roots of barnyard grass were determined to be the most susceptible to the G. pedunculata extract based on the concentration of extract resulting in 50% (I50) growth inhibition of the test plants. These results suggest that G. pedunculata may have allelopathic potential and may possess allelochemicals. From our study, we can conclude that G. pedunculata could be developed as an eco-friendly weed control option.

Isolation and Identification of a Growth Inhibitory Substance from Heliotropium indicum L.

Heliotropium indicum L. belongs to the family Boraginaceae. The plant has been used as a folk medicine because it contains substances of various biological activities. It is also identified as a common weed which grows wildly in crop fields in tropical and subtropical regions of the world. However, there is little information on the allelopathic effect in this plant. Therefore, this study was undertaken to investigate the growth inhibitory effect and to identify the growth inhibitory substances in H. indicum. An aqueous methanol extract of H. indicum inhibited shoot and root growth of barnyard grass, foxtail fescue, timothy, cress, lettuce and rapeseed at concentrations higher than 10 mg dry weight equivalent extract/mL. The concentrations required for 50% growth inhibition (I50) of those test plants ranged from 3–282 mg dry weight equivalent extract/mL. The extract was then separated using a sequence of chromatographic fractionations and a growth inhibitory substance was isolated and identified by spectral analysis as methyl caffeate. Methyl caffeate inhibited the growth of lettuce and foxtail fescue at concentrations higher than 1.0 mM. The results suggest that methyl caffeate may contribute to the growth inhibitory effect of H. indicum and may play an important role in the allelopathic effect of H. indicum.

Allelopathic Responses of Rice Seedlings under Some Different Stresses.

The objective of this study was to evaluate the allelopathic responses of rice seedlings under submergence stress at different temperatures (10, 25, 32, and 37 °C). The results showed that a wide range of allelopathic responses of rice seedlings depended on varieties and stress conditions, with temperature was being a key factor. It showed that the extracts of rice seedlings induced significant suppression on lettuce and radish seedling germination, but had negligible allelopathic effects on growth of barnyardgrass, whilst the emergence and growth of natural weeds was stimulated. In contrast, the root exudates of Koshihikari rice seedlings (K32) at 32 °C reduced the number of total weeds by ≈60.0% and the total dry weight of weeds by 93.0%; i.e., to a greater extent than other root exudates. Among the 13 identified phenolic acids, p-hydroxybenzoic, vanillic, syringic, sinapic and benzoic acids—at concentrations of 0.360, 0.045, 3.052, 1.309 and 5.543 μg/mL might be involved in allelopathic responses of K32, inhibiting the growth of barnyardgrass and natural weeds. Findings of the present study may provide useful information on allelopathic responses of rice under environmental stresses and thus further understand of the competitive relationships between rice and weeds under natural conditions.

Plant growth inhibitory activity and active substances with allelopathic potential of cogongrass (Imperata cylindrica) rhizome

Cogongrass (Imperata cylindrica [L.] Raeusch.) is a perennial rhizomatous grass that belongs to the Poaceae and is widely distributed in tropical, subtropical and temperate regions over the world. The grass is strongly invasive and is suggested to have allelopathic potential. However, limited information is available on allelopathic substances in cogongrass rhizomes. Therefore, the allelopathic potential and substances in cogongrass rhizomes were investigated. The extracts of cogongrass rhizomes inhibited the root and shoot growth of barnyard grass, ryegrass, timothy, cress, lettuce and alfalfa. After bioassay‐guided separations of the extracts, four growth inhibitory substances, 5‐methoxyflavone, 5,2′‐dimethoxyflavone, methyl caffeate and abscisic acid, were isolated. 5‐Methoxyflavone, 5,2′‐dimethoxyflavone and methyl caffeate significantly inhibited the root and shoot growth of cress at concentrations of ≥0.03–0.3 m mol L−1 and their concentrations required for 50% growth inhibition were 0.079–0.24, 0.23–1.1 and 0.59–0.88 m mol L−1, respectively. The other isolated substance, abscisic acid, has been reported to have strong growth inhibitory activity. Its concentrations required for 50% growth inhibition on cress were 0.31–0.61 μ mol L−1. The present study suggests that cogongrass rhizomes might have allelopathic potential and that those four substances might contribute to that potential.

Interference of allelopathic rice with penoxsulam-resistant barnyardgrass.

Despite increasing knowledge of allelopathic rice interference with barnyardgrass, relatively little is known about its action on herbicide-resistant barnyardgrass. The incidence of herbicide-resistant barnyardgrass is escalating in paddy fields. Knowledge of the interference of allelopathic rice with herbicide-resistant barnyardgrass and the potential mechanisms involved is warranted. Penoxsulam-resistant and -susceptible barnyardgrass biotypes were identified and segregated from a putative penoxsulam-resistant population occurring in paddy fields in China. Allelopathic rice inhibited the growth of barnyardgrass roots more than shoots, regardless of biotype. In particular, there was a stronger inhibition for resistant barnyardgrass than for susceptible barnyardgrass. Allelopathic rice significantly reduced total root length, total root area, maximum root amplitude and maximum root depth in barnyardgrass. Furthermore, the rice allelochemicals tricin and momilactone B inhibited the growth of both resistant and susceptible barnyardgrass. Compared with root contact, root segregation significantly increased inhibition of barnyardgrass with an increase in rice allelochemicals. Root exudates from barnyardgrass induced the production of rice allelochemicals, but the effect of susceptible barnyardgrass was much stronger than that of resistant barnyardgrass. Allelopathic rice can interfere with the growth of penoxsulam-resistant barnyardgrass through allelochemical-mediated root interactions. This type of allelopathic interference may provide a non-herbicidal alternative for herbicide-resistant weed management in paddy systems. © 2017 Society of Chemical Industry.

Allelopathic potential of plant residues of thirty Sri Lankan traditional rice (Oryza sativa L.) varieties on Barnyardgrass (Echinochloa crusgalli)

The use of rice (Oryza sativa L.) allelopathy for weed management could reduce the need for applying herbicides to the crop. In this study a pot experiment and a laboratory bioassay were conducted to assess the allelopathic potential of residues of 30 traditional rice varieties in Sri Lanka on seed germination and seedling growth of barnyardgrass (Echinochloa crus-galli). All seeds were collected from “Farmer Federation for Conservation of Traditional Seeds and Agri Resources”. Rice residues were incorporated with silica sand (1% w/w) in small pots to prepare residue mixture and ground rice residues mixed with water (2.5g/100ml) were used to prepare residue extract for laboratory bioassay. Rice varieties exhibited marked differences in the inhibition of barnyardgrass growth and development. In the bioassay, residue extract of rice variety Herathbanda exhibited the greatest activity on the weed seedling growth, reducing dry weight by 30.7%, while Gonabaru residue extract exhibited the greatest inhibition on seed germination, reducing germination by 29.6%. In the pot experiment of residue mixture, Batapola el and Sula varieties showed the greatest inhibition percentage on germination (48.4%). However, Godaheenati showed the greatest inhibition % on plant height (27.4%) and dry weight (45.6%). These results suggest that incorporation of rice residues of tested varieties has influence on controlling barnyardgrass seedling growth.

Allelopathic Activity of Dehulled Rice and its Allelochemicals on Weed Germination

In this study, the allelopathic potential of dehulled rice, rice, and hulls of rice on germination of weeds was evaluated in laboratory. Phenolic acids in growth media of these plants were also identified and quantified using HPLC. Identified allelochemicals were reversely tested for phytotoxic effects on germination and seedling growth of barnyardgrass, lettuce, radish and rice. The results showed that the inhibitory effects of dehulled rice were stronger than those of hulls and rice. Dehulled rice caused 66.7% and 50.6% reduction in radish root length and lettuce shoot height, respectively. Dehulled rice showed strong inhibitory effects on root length of lettuce and shoot height of radish while hulls and rice exhibited stimulation. Regarding phenolic identification, vanillin and vanillic acid were detected as allelochemicals in root exudates of rice and tested plants. The results revealed that most of the vanillin and vanillic acid treatments showed high inhibitory effects on germination rates and seedling growth of lettuce and radish, high stimulatory activity on root elongation of rice. Vanillic acid (100 ppm and 200 ppm), vanillin (100 ppm) and their mixture (200 ppm) completely inhibited survival of lettuce. The findings indicate the allelopathic potential of dehulled rice which can be used for identification of more phytotoxins to produce bioherbicides in agricultural practices.

Allelopathic Activity of Dehulled Rice and its Allelochemicals on Weed Germination

In this study, the allelopathic potential of dehulled rice, rice, and hulls of rice on germination of weeds was evaluated in laboratory. Phenolic acids in growth media of these plants were also identified and quantified using HPLC. Identified allelochemicals were reversely tested for phytotoxic effects on germination and seedling growth of barnyardgrass, lettuce, radish and rice. The results showed that the inhibitory effects of dehulled rice were stronger than those of hulls and rice. Dehulled rice caused 66.7% and 50.6% reduction in radish root length and lettuce shoot height, respectively. Dehulled rice showed strong inhibitory effects on root length of lettuce and shoot height of radish while hulls and rice exhibited stimulation. Regarding phenolic identification, vanillin and vanillic acid were detected as allelochemicals in root exudates of rice and tested plants. The results revealed that most of the vanillin and vanillic acid treatments showed high inhibitory effects on germination rates and seedling growth of lettuce and radish, high stimulatory activity on root elongation of rice. Vanillic acid (100 ppm and 200 ppm), vanillin (100 ppm) and their mixture (200 ppm) completely inhibited survival of lettuce. The findings indicate the allelopathic potential of dehulled rice which can be used for identification of more phytotoxins to produce bioherbicides in agricultural practices.

Effects of Tinospora tuberculata leaf methanol extract on seedling growth of rice and associated weed species in hydroponic culture

The study was conducted to evaluate the responses of rice and rice weed seedlings (barnyardgrass and weedy rice) at the three-leaf stage to Tinospora tuberculata leaf methanol extract (3.12, 6.25 and 12.5 g L−1) under hydroponic culture. It shows that the leaf methanol extract had various degrees effects depending on target plant species and each tested index (biomass, root length, shoot length, transpiration volume, chlorophyll a, chlorophyll b and carotenoid contents). The effective concentration of the leaf extract capable of reducing 50% of rice growth was higher than those of target weed species. Moreover, the root length was more tolerant to leaf methanol extract in comparison to the other plant parameters measured. A greater reduction was observed in chlorophyll a content compared to chlorophyll b and carotenoid. The results revealed that the reduction of transpiration volume closely coincided with the magnitude of growth inhibition of tested plants. Ultra-fast liquid chromatography analysis revealed 11 of 32 peaks in chemical profile, including benzoic acid, caffeic acid, chlorogenic acid, isoorientin, isovitexin, orientin, p-anisic acid, syringic acid, trans-cinnamic acid, trans-ferulic acid, and vitexin have the same retention time with those peaks of the extract. The amount of compounds was present in the range of between 4 817 and 115.5 mg kg−1 dry weight (DW). The concentration-response bioassay of all 11 individual compounds and their equimolar mixture against the seeds of barnyardgrass revealed their contribution in the allelopahic activity of T. tuberculata leaf extract. The examined compounds and their combination exhibited various degrees of growth inhibitory effects on the early growth of barnyardgrass. Therefore, the specific number, concentration, combination and inhibitory activity of bioactive compounds leads to allelopathy activity of T. tuberculata leaves which could be employable directly as a natural herbicide and its growth inhibitor compounds can be used as a template for producing new herbicides.

Emergence dynamics of barnyardgrass and jimsonweed from two depths when switching from conventional to reduced and no-till conditions

A cylinder experiment was conducted in northern Greece during 2005 and 2006 to assess emergence dynamics of barnyardgrass (Echinochloa crus-galli (L.) Beauv.) and jimsonweed (Datura stramonium L.) in the case of a switch from conventional to conservation tillage systems (CT). Emergence was surveyed from two burial depths (5 and 10 cm) and with simulation of reduced tillage (i.e. by soil disturbance) and no-till conditions. Barnyardgrass emergence was significantly affected by burial depth, having greater emergence from 5 cm depth (96%) although even 78% of seedlings emerged from 10 cm depth after the two years of study. Emergence of barnyardgrass was stable across years from the different depths and tillage regimes. Jimsonweed seeds showed lower germination than barnyardgrass during the study period, whereas its emergence was significantly affected by soil disturbance having 41% compared to 28% without disturbance. A burial depth x soil disturbance interaction was also determined, which showed higher emergence from 10 cm depth with soil disturbance. Jimsonweed was found to have significantly higher emergence from 10 cm depth with soil disturbance in Year 2. Seasonal emergence timing of barnyardgrass did not vary between the different burial depth and soil disturbance regimes, as it started in April and lasted until end of May in both years. Jimsonweed showed a bimodal pattern, with first emergence starting end of April until mid-May and the second ranging from mid-June to mid-August from 10 cm burial depth and from mid-July to mid-August from 5 cm depth, irrespective of soil disturbance in both cases.

Competitive and Allelopathic Effects of Wild Rice Accessions (Oryza longistaminata) at Different Growth Stages.

The competitive and allelopathic effects of wild rice (Oryza longistaminata) accessions on barnyard grass at different growth stages determined by days after sowing (0, 30, 60 and 90 days) were studied in greenhouse pot experiments. Wild rice accession RL159 exhibited the greatest height and tillering. The weed suppression rates of wild rice accessions OL and F1 on barnyard grass were significantly higher than for other rice accessions, with the lowest being O. sativa cultivar RD23. The highest suppression rates of OL and F1 were 80.23 and 73.96% at barnyard grass growth stages of 90 days and 60 days. At a 90 growth stage, wild rice accessions RL159 and RL169 caused 61.33 and 54.51% inhibition in barnyard grass growth, respectively. Under the same conditions, the competitive inhibition rates of OL, F1, RL159, RL169 and RL219 against barnyard grass were markedly lower than their weed suppressive effects, but were relatively similar for RD23. The allelopathic inhibition of OL and F1 on barnyard grass was significantly higher than other rice accessions. The highest allelopathic rates of OL and F1 were 60.61 and 56.87% at the 0 day growth stage. It is concluded that wild rice accessions OL and F1 exhibited the highest allelopathic activity along with moderate competitive ability against barnyard grass; wild rice accession RL159 had the highest competitive ability and moderate allelopathic activity on barnyard grass. Thus, the three wild rice accessions OL, F1 and RL159 could be used as ideal breeding materials for cultivated rice improvement.

Variation in the Phytotoxic Activity of Tinospora tuberculata Extracts as Influenced by Solvent Type and Chemical Profile

A study was conducted to evaluate the role of secondary metabolites on the allelopathic activity of methanol and water extracts obtained from aerial parts of Tinospora tuberculata on seed germination and the radicle and hypocotyl lengths of barnyardgrass. The higher suppressive effects were observed on germination and seedling growth of barnyardgrass, when the methanol extracts of T. tuberculata stem or leaf were applied in comparison to the water extracts. Ultra-fast liquid chromatography analysis confirmed that methanol extracts and leaf extracts contained higher number and amount of chemical compounds than did those of the water extracts and stem extracts respectively. Moreover, the concentrations of 11 identified compounds of the extracts and an equimolar mixture of the chemicals required for 50% growth inhibition on barnyardgrass germination, radicle and hypocotyle were determined. Trans-cinnamic acid and benzoic acid had the highest allelopathic activity, while chlorogenic acid and orientin had the lowest on the basis of the rank values. Benzoic acid was found in the highest concentration in the methanol leaf extract, while this compound was not identified in the water leaf extract. On the other hand, the predominant compound was orientin for stem extracts. These results suggest that these compounds may be involved in the allelopathy activity of T. tuberculata depending on their number, concentration, combination and inhibitory activity. T. tuberculata could be a potential source of natural inhibitor compounds employable for eco-friendly agriculture.

Isolation and biological activities of 3-hydroxy-4(1H)-pyridone

ABSTRACT3-Hydroxy-4(4H)-pyridone (3,4-DHP), a degraded product of mimosine [β-[N-(3-hydroxy-4-oxypyridyl)]-α-aminopropionic acid], is known to cause goiters, loss of hair, and infertility in animals, but limits of 3,4-DHP on separation and purification have prevented efforts on investigating other toxicity and biological properties of 3,4-DHP. By this study, a novel and simple isolation of 3,4-DHP was developed either from Leucaena leaves using an ion-exchanged resin or mimosine degraded in high temperature (110°C, 6 h). The inhibition of mimosine on the growth of barnyardgrass was approximately fourfold higher (IC50 = 0.04 mg g−1) than that of 3,4-DHP (IC50 = 0.15 mg g−1). In general, the antifungal activity of mimosine is much stronger than that of 3,4-DHP, but it differs depending on the kind of fungi. The 1,1-diphyenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of 3,4-DHP, in contrast with the growth inhibitory activity, is about fourfold stronger [EC50 = 2.4 mg g−1 gallic acid equivalent (GAE)] than that of mimosine [EC50 = 10.3 mg g−1 GAE]. This study is the first to report on the herbicidal, antifungal, and antioxidant activities of 3,4-DHP.

Evaluation of Allelopathic Effects of Iranian Rice Cultivars (Oryza sativa L.) on Growth Factors of Barnyard Grass (Echinochloa cruss-galli L.)

In order to investigate the ability of aqueous hull extract of Iranian rice cultivars in controlling barnyard grass germination and seedlings growth, a factorial experiment was carried out at both Laboratory and greenhouse based on RCB (Randomized Complete Blocks) with 3 replication. In this study which was performed in 2010 at Tarbiat Modares University, the effects of 20 rice cultivars hull extract were considered on germination and seedling growth of barnyard grass weed at four concentrations (0, 5, 10 and 15 percent). Lab studies showed that some of the rice cultivars have stimulating effects on barnyard grass growth, while some others have inhibiting effects. Khazar cultivar showed the highest inhibiting effect on germination percentage, germination rate, radicle length, plumule length, radicle and plumule dry weight. Breeded cultivars had higher inhibition effects than natives, while the native cultivars were more stimulating on barnyard grass seed germination. The greenhouse part of study showed that Khazar cultivar causes significant reduction in germination percentage, germination rate, radicle length, radicle and plumule dry weight and whole plant dry weight of barnyard grass. Neda cultivar showed the highest effect in controlling plumule length. The study showed that various rice cultivars have different effects on inhibiting or stimulating the growth factors of barnyard grass.

Phytotoxic interference of volatile organic compounds and water extracts of Tinospora tuberculata Beumee on growth of weeds in rice fields

Abstract Tinospora tuberculata Beumee is an aromatic shrub with pharmacological properties and belongs to the Menispermaceae family. We assessed T. tuberculata for its ability to suppress growth of weeds in rice fields. In seedling bioassays, the rate of seed germination and the radicle and hypocotyl lengths of barnyardgrass, rice and weedy rice seedlings were reduced as the concentration of aqueous water extracts and volatile organic compounds increased compared to the control. In a glasshouse experiment, T. tuberculata leaf powder also exhibited effective reduction in the emergence and growth of weeds in rice fields. Applications at rates of 4 t ha− 1 completely suppressed emergence of barnyardgrass, sprangletop and smallflower umbrella. The chemical compositions of extracts and volatiles were analyzed by GC–MS and HS-SPME-GC–MS. The results showed that 7 of 43 components in the leaf aqueous extract, as compared to 5 of 15 compounds in the stem aqueous extract, are known to be toxic compounds. Moreover, eight main volatile organic compounds were identified, which accounted for 97 and 95% of the whole fresh and dry leaf volatiles, respectively. We observed qualitative and quantitative differences in the compounds present in the dry and fresh leaf. Confocal laser scanning microscope images showed that the volatile emissions and aqueous extracts also inhibited the main root diameter, and the number and elongation of root hairs of tested weeds in rice fields. These results suggest that T. tuberculata contains a significant source of plant growth inhibitors. Hence, it can be used as a mulch to suppress weeds in rice fields and for developing new herbicide based on phytotoxic compounds release by this plant.

Deep phosphorus fertiliser placement and reduced irrigation methods for rice (Oryza sativa L.) combine to knock-out competition from its nemesis, barnyard grass (Echinochloa crus-galli (L.) P.Beauv)

Productivity of rice is increasingly being constrained by limitations in the quantity, quality, and cost of water and nutrients, and competition from weeds. This is a ‘commentary’ on the recent work of Weerarathne et al. (2015). They reported new discoveries from greenhouse experiments that showed that precise deep placement of phosphorus (P) fertilizer 15 to 20 cm below ground level in low-phosphorus-containing soils irrigated using methods such as “alternating wetting and drying” that reduce water use, dramatically increased the competiveness of rice against its most widespread and costly weed pest, barnyardgrass (Echinochloa crus-galli). The growth of barnyardgrass was severely stunted because its roots did not reach the depth necessary to readily access the P fertilizer. In contrast, rice plants maintained robust growth under these conditions because they adapted by lengthening their roots and adding more fine roots, which allowed them to reach, take up, and utilize the deeply placed P.

Effect of incorporating the residues of Sri Lankan improved rice (Oryza sativa L.) varieties on germination and growth of barnyard grass (Echinochloa crus-galli)

The Journal of the National Science Foundation of Sri Lanka publishes the results of research in all aspects of Science and Technology. The journal also has a website at http://www.nsf.gov.lk/. 2021 Impact Factor: 0.682The JNSF provides immediate open access to its content on the principle that making research freely available to the public supports a greater global exchange of knowledge.Cover :Leatherback (a), green (b - adult & f - hatchling), hawksbill (c) and olive ridley (d) turtles who nest in Sri Lankan beaches, green turtle crawl marks (e) and by-catch of sea turtles in fisheries (c & d)Photo credits: SJ Perera (a & c), WPN Perera (b & e), K Ekaratne (d & f)