Archives - Allelopathy Journal

Alleopathy is the process whereby plant releases toxic compounds into environment, resulting in a detrimental effect on neighbouring plants or its own sharing the same habitat. The toxic metabolites are released into environment through volatilization, leaching, decomposition of plant residues in soil and root exudation. The phenomenon was earlier found in agricultural practice by Theophrastus (372 to 285 BC), who reported the inhibitory effect of pigweed on alfalfa. In 1832, De Candolle suggested that the soil sickness problem in agriculture might be due to exudates of crop plants. Since then, many scientists had reported the significance of toxic effects of plant residues decomposing in soil, leading to the reduction in crop productivity. The productivity of many crops (Sorghum bicolor, Medicago sativa, Oryza sativa, Asparagus officinalis, Phaseolus radiatus, Saccharum sinensis, etc.) was reduced significantly after a continuous monoculture. The crop productivity declines due to (i). crops produces phytotoxic substances in soil and (ii). the accumulation of phytotoxins causes the imbalance of microbial population, such as Fusarium oxysporum in soil. These harmful allelopathic effects could be reduced through crop rotation or improving soil drainage in field. In a unique example of pasture and forest intercropping system was demonstrated by the author that an aggressive kikuyu grass (Pennisetum clandestinum), was introduced into the deforested conifer land. The kikuyu grass suppressed the growth of weeds significantly, but was not harmful to the regeneration growth of conifer plants or seeding growth of other hardwood trees. The pasture-forest intercropping system, indeed, benefited the forest management by reducing the use of herbicide, saving expensive manpower, and enhancing forage material for livestock. Finally, the author in recent years have developed a unique system of using the plant parts, leaves, twigs, or roots, of allelopathic plants to make a cocktail of agrochemicals to replace conventional herbicides, fungicides, or insecticides, resulting in avoiding the residual effects of agrochemicals and reducing the environmental deterioration. Using advanced biotechnology, the allelopathic genes can be introduced into crops which possess the allelopathic potential to suppress its competitive weeds in the field. Thus, allelopathy has played important roles in sustainable agriculture.

The study of allelopathy as a discipline has a long and at times controversial history. Since Hans Molisch coined the term before World War II, allelopathy research has grown from a trickle of papers before 1970 to a burgeoning subdiscipline of chemical ecology represented by hundreds of papers each year. Yet, allelopathy research still suffers from a reputation for papers of poor scientific quality that equate the presence of a phytotoxic phytochemical as proof of an allelochemical function without regard for proving that the compound is bioavailable in soil at sufficient concentrations to affect vegetation either directly or indirectly through effects on soil microbes. Synergism has often been invoked without proof to explain why effects of crude extracts are sometimes greater than even the additive effects of phytotoxins known to be in the extract. Much of this work may be correct, but to be widely accepted more rigorous proof is needed. Much of this literature also makes the assumption that allelochemicals must be highly water soluble, when there are good scientific reasons to hypothesize that the most effective allelochemicals would have very limited water solubility. Very little is known about the mode of action of and mechanisms of resistance to putative allelochemicals. Nevertheless, the quality and quantity of papers on allelopathy has increased steadily over the past several decades and knowledge gaps are being filled at an ever increasing pace. There can be little doubt that allelopathy plays an important role in plant/plant interactions in nature and in agriculture. Translating this growing knowledge to technology to manage weeds in agriculture has been slow. There is only one good case of discovery of an allelochemical (leptospermone) leading to the development of a major class of herbicides (triketones). There are examples of allelopathic cover crops being used for weed management in other crops, as well as other cultural methods to employ allelopathy. However to my knowledge, there are still no cultivars of crops being sold with allelopathic properties as a selling point. Enhancement or impartation of allelopathy in crops through the use of transgenes could eventually be used to produce such a cultivar. Some of the most high profile recent examples of research in our discipline will be discussed. The study of allelopathy appears to have a bright future, especially if we can translate our research into technologies that will reduce our reliance on synthetic herbicides.

Invasion of exotic species is a global ecological problem and has tremendous impact on economy, environment and human health. The success of invasion for exotic plants depends on many mechanisms and in recent years the novel weapons hypothesis has been argued as an important mechanism to elucidate the invasion process. This review summarizes a large body of research including the observations of potential allelopathic phenomenon, isolation and identification of allelochemicals and the role of allelopathy in invasion of common exotic invasive plants in China such as Eupatorium adenophorum, Eucalyptus spp., Spartina anglica, Chromolaena odoratum, Eichhornia crassipes, Solidago canadensis, Alternanthera philoxeroides, Ambrosia artemisiifolia, Ambrosia trifida, Lantana camara, Wedelia trilobata, Bidens pliosa, Ageratum conyzoides and Mikania micrantha. We suggest that allelopathy plays a vital role in successful invasion of alien species in new areas. The allelochemicals of invasive alien species also serve as defence chemical weapons against native plant pathogen and herbivorous insects.

To make our modern agriculture successful, the use of new agricultural technology in a short span of 35-40 years have caused havoc by contaminating our soil, environment and food with toxic pesticides residues. Modern agriculture is exploitive of growth resources and has caused very serious problems such as environmental pollution through (i). contamination of underground drinking water resources, food and fodder with pesticides and nitrates, which are harmful to human beings and livestock, (ii). poor soil health/ soil Sickness leading to low soil productivity and (iii). poor quality of life. These problems may be overcome with the adoption of Organic Agricultural practices. The definition of Organic Agriculture used in this paper is "Organic Agriculture consists of those practices, which reduces the use of outside inputs viz., fertilizers and pesticides etc on the farm”. Therefore, various types of allelopathic strategies may be used for (a) maintenance of soil fertility (use of crop rotations, Biological Nitrogen Fixation, crop mixtures, crop residues and leaf litter etc.), (b) weed management (cover crops, crop residues as mulches, intercropping, crop rotations, phytotoxic or allelopathic varieties and natural herbicides etc.), (c) insects pest management (cropping systems, resistant varieties, insecticidal allelochemicals etc.), (d) nematodes management (plant materials, oilseed cakes, nematicidal compounds etc.), (e) diseases management (cropping systems, crop residues, organic amendments etc.) and (f) use of allelochemicals as growth regulators. Therefore, research efforts are needed to utilise inhibitory allelopathic effects of plants for natural control of crop pests (weeds, insects, nematodes, pathogens), so that use of present pesticides could be minimized or eliminated for developing Sustainable Organic Agriculture, keeping the environment clean for our future generations and reducing the cost of Organic food.

Bidens pilosa was used as test species for greenhouse and laboratory experiments. The leaves powder of R. formosanum mixed in soil at 1% concentration, moderately suppressed the growth of B. pilosa seedlings. Aqueous leachates of R. formosanum flowers, leaves, litter and organic matter inhibited the radicle growth of Ageratum houstonianum, Amaranthus inamoenus, Brassica chinensis, Bidens pilosa, Lactuca sativa and Ocimum basilicum. The leaves aqueous extract contained phytotoxins [p-hydroxybenzoic acid, trans p-coumaric acid, syringic acid, vanillic acid, cis ferulic acid, methyl ferulate, coumarin, protocatechuic acid and (-)-catechin]. These findings and identification of phytotoxins suggests that lack of understory species beneath R. formosanum canopy was due to allelopathic effects.

Isolation and identification of allelochemicals is an important step to study allelopathy. Our previous work demonstrated that Streptomyces strain 6803 showed allelopathic effects on both plants and plant fungal pathogens. In this study four macroporous resins (S-8, X-5, AB-8 and HP-20) were used to collect the allelochimcals from the fermentation broth of Streptomyces strain 6803. Among the four resins HP-20 macroporous resin had the highest adsorption capacity for bioactive compounds from the fermentation broth. Three allelochemicals [5,7-dihydroxyflavone (I), 5-hydroxy-7-methoxy- flavone (II) and di (2-ethylhexyl) phthalate] were isolated and purified from the fermentation broth of this strain by column chromatography. Their structure was identified by ESI-MS, 1HNMR, 13CNMR and IR. All isolated compounds showed herbicidal activity. Compound I and II inhibited the root growth of rape (Brassica campestris L.) by 71% and 69% at a concentration of 0.3 mmol/L, respectively. The mean diameter of inhibition zone of compounds I, II and III at 0.3 mmol/L were 22.4, 25.5 and 26.1 mm against the fungal pathogen Fusarium graminearum and 18.9, 16.2 and 15.8 mm against Glomerella cingulata (Stonem), respectively. Our results suggest that HP-20 resin can be efficiently used to collect the allelochemicals from microbial fermentation broth and the compounds I, II and III were responsible for phytotoxic and antifungal activities of Streptomyces strain 6803.

Allelopathic effects of stubble leachates (0,12.5,25,50,100%) of soybean

(Glycine max), wheat (Triticum aestivum L.) and oat (Avena sativa L.) were investigated on seed germination and seedling growth of cucumber (Cucumis sativus L.) and mycelial growth of F. oxysporum. These effects were expressed as allelopathic index (RI). The wheat stubble leachates of 50% concentration (RI = 0.382) promoted the seed germination of cucumber and other concentrations were less stimulatory. All concentrations of soybean stubble leachates promoted the seed germination and leachates (100%) were least stimulatory. Low concentration (12.5%) of oat stubble, promoted the seed germination of cucumber, but higher concentrations (100% and 50%) were inhibitory. Wheat stubble leachates promoted the plant height and root length at 100% concentration (RI = 0.630). Thus higher concentrations of wheat stubble leachates stimulated the seed germination and seedling growth of cucumber. The similar trend was observed in leachates of soybean stubble. Oats stubble leachates were most stimulatory at 12.5% concentration. Stubble leachates of wheat and soybean inhibited the mycelial growth of F. oxysporum at 100% and 50% concentrations, but stimulated the mycelial growth at 25% and 12.5% concentrations, respectively.

The inhibitory activity of 9 phenolic compounds [p-hydroxybenzoic acid, vanillin, syringic acid, vanillic acid, coumaric acid, ferulic acid, cinnamic acid, salicylic acid, benzoic acid] was investigated in vitro on the radicle and shoot growth of American ginseng (Panax quinquefolium L.) seedlings. These compounds were detected in the soils of commercially cultivated American ginseng. Their test concentrations (0.1 mmol/L to 10.0 mmol/L) were selected based on their content in soils. All phenolic compounds inhibited the radicle and shoot growth of American ginseng in a dose-dependent response and their IC50 values were also calculated. Only 5-compounds caused < 50% inhibition in radicle growth of American ginseng and their autotoxicity followed the order: salicylic acid > cinnamic acid > coumaric acid > vanillic acid > syringic acid. However, p-hydroxybenzoic acid, vanillin, ferulic acid, benzoic acids even at the highest concentration (10.0 mmol/L) did not cause 50% inhibition in radicle elongation. Thus different phenolic compounds displayed variable phytoxicity to American ginseng (Panax quinquefolium L.) and there is a close relationship between the substitutions on the benzene ring of phenolic compounds and their phytotoxicity.

Previous studies showed that Sonneratia apetala Buch.Ham could control the spread of exotic invasive plant Spartina alterniflora Loisel. However, little is known about the mechanism for control of S. alterniflora. S. apetala proved to be allelopathic, which played important role in plant interspecific competition. Thus we hypothesize that allelopathy is one of the mechanisms that allowed the S. apetala to displace the S. alterniflora. To test this hypothesis, we studied the allelopathic effects of leaf volatiles and soil of the two plants on three target spp.: Medicago sativa L., Lolium perenne L. and Sorghum Sudanense (Piper) Stapf. The volatiles of both S. apetala and S. alterniflora reduced the germination rate and seedling growth all test spp. The volatiles of S. apetala were more allelopathic than S. alterniflora. Furthermore, the soils from different communities (S. apetala community, S. apetala + S. alterniflora community, S. alterniflora community) were also allelopathic to test plants and S. apetala soil was more inhibitory than S. alterniflora. These results indicated that the S. apetala allelopathy plays an important role in the control of S. alterniflora

We studied (i). the contents of direct defence compounds (DIMBOA and phenolic acids), (ii). expression patterns of direct defence protein mediated genes (PR-2a and MPI) and (iii). expression of indirect defence volatile mediated genes (FPS and TPS) using HPLC and RT-PCR after the application of exogenous JA or SA for one week on the leaves or roots of maize variety ‘Gaoyou 115’. JA application on leaves systematically induced gene expression of MPI in the roots, but reduced the contents of DIMBOA, caffeic acid and syringic acid by 10.5%, 40.3% and 43.6% in the roots, respectively. However, JA application to roots induced gene expression of MPI and FPS in the leaves and also significantly increased the DIMBOA content (81.8%) in leaves. While SA application to the leaves systematically induced gene expression of MPI and FPS in the roots and decreased the contents of DIMBOA, coumaric acid, caffeic acid and syringic acid in roots by 45.8%, 64.2%, 60.2% and 72.4%, respectively. Yet SA application to roots only increased the DIMBOA content (95.8%) in leaves. These results suggested a close relationship between the induced defence in the leaves and roots of maize. JA or SA application on leaves can systematically trigger the defence response in the roots of maize, meanwhile JA or SA application to the roots can also systematically lead to the defence response in the leaves of maize.

The oil mobilization is a major source of sugar, which is substrate of carbon and energy metabolism during seed germination and seedling growth of cucumber. Here, we analyzed the effect of cinnamic acid (CA), one of the most important autotoxins in root exudates of cucumber on sugar content, respiration rate and expression of genes involved in oil mobilization in cucumber. Exposure of seeds to CA at 0.25mM significantly reduced the seedling growth followed by a decrease in total sugar, sucrose and hexose contents and this decrease was significantly attenuated by co-imbibitions with 0.5% sucrose. There was a significant decrease in the total respiration rate (VT) and an increase in the KCN-resistant respiration rate (VKCN) when treated with CA and an opposite trend was observed in seedlings exposed to sucrose. Transcript levels for genes involved in the oil mobilization were down-regulated in germinated seeds exposed to CA and up-regulated by sucrose. Notably, the presence of sucrose in the growth medium could attenuate the inhibitory effects caused by CA on respiration and gene transcripts.

We studied the mechanisms of cassava (Manihot esculenta crantz) allelopathy on radish (Raphanus sativus L.) and ryegrass (Lolium perenne L). The water leachates from cassava leaves inhibited the seed germination and seedling growth of both receptor plants decreased the root vigour and chlorophyll content. However, the permeability of cell membrane and MDA content were significantly increased. The leachates spray at >0.025 g·ml-1 concentration decreased the soluble protein in seedlings of both receptor plants, but increase the activity of POD. Contrarily, the leachates application <0.0125 g·ml-1 concentration increased the content of soluble protein and reduced the activity of POD. While between 0.05 g·ml-1 and 0.0125 g·ml-1 concentrations, the leachates enhanced the PAL activity of both receptor plants. Spraying of leachates increased the activities of SOD and PPO in the seedlings of radish and ryegrass but decrease the PPO.

Harmful algal bloom (HAB), caused by intense eutrophication, are threatening the biodiversity and ecological function of marine ecosystems. We studied the potential allelopathy of Salicornia bigelovii, a euhalophyte, to inhibit the growth of Skeletonema costatum, a marine bloom forming diatom. Experiments were done in 3 culture systems (alga +euhalophyte co-culture, monoculture of marine alga, monoculture of euhalophyte) to determine the allelopathic effect of S. bigelovii against S. costatum. Lower nutrient removal rate by S. bigelovii was observed in co-culture system compared to monoculture system. The chlorophyll a and cell density of S. costatum in co-culture system were much lower than in alga monoculture system. Moreover, the aqueous extract from S. bigelovii roots showed dose-dependent inhibition against the algal growth and the half maximal inhibitory concentration (IC50) of root extract was 10.37 g FW L-1. Therefore, rather than nutrient competition, allelopathy was accounted for the growth inhibition of S. costatum by S. bigelovii. Our finding implies that S. bigelovii, as a euhalophyte, may play an active role in HAB prevention.

In Laboratory bioassay and Pot culture, the allelopathic potential of alfalfa (Medicago sativa L. cv. Alfaking), hairy vetch (Vicia rillosa Roth.) and yellow sweet clover (Melilotus officinalis Desr.) was determined on seed germination and seedling growth of barnyard grass (Echinochloa crusgalli [L.] Beauv.), annual bluegrass (Poa annua L.) and Veronica persica Poir. The 10% (FW/V) aqueous extracts of alfalfa, hairy vetch and yellow sweet clover significantly inhibited the seed germination and seedling growth of test weeds. At the same concentration, the seed germination of annual bluegrass was inhibited more by aqueous extract of yellow sweet clover than of alfalfa and hairy vetch. In pot experiments, the dry powdered mass of alfalfa, hairy vetch and yellow sweet clover at 90g/m2 inhibited the emergence and growth of barnyard grass and annual bluegrass. The application of yellow sweet clover dry powder inhibited the emergence and growth of Veronica persica Poir. Yellow sweet clover powdered biomass caused drastic inhibition in weeds growth, thus it may be used as natural herbicide for weed control in crops through intercropping, rotation or soil mulching.

The study was conducted to find the changes in physiological responses of water stressed Phaseolus mungo seedlings to leachate of aromatic plant, Mentha piperata L. The water stress was imposed by withholding the water for 6 d. Water stress significantly decreased the relative water content, pigments (chlorophyll a, chlorophyll b, total chlorophyll and caroteniods) and protein contents of P. mungo. This decrease was more drastic when the seedlings were subjected to combined stresses of allelochemicals and water. Activities of various antioxidants were influenced variously in different treatments. Lipid peroxidation and malondialdehyde content increased under water stress and with higher concentration of leachate. When the seedlings were subjected to combined stresses, lipid peroxidation and malondialdehyde contents increased further. Thus the antioxidant activity of seedlings failed to scavenge excess of reactive oxygen species and resulted in inhibited seedling growth.

We studied the autotoxic effects of maize (Zea mays) on some biophysical and biochemical parameters. In addition, we observed the role of plant growth promoting rhizobacterium Paenibacillus polymyxa in mitigating the adverse effects of autotoxicity. The seedlings inoculated with P. polymyxa and without extract produced maximum dry weight, root and shoot length. Autotoxicity decreased the dry weight, root and shoot length of maize seedlings. A significant decrease in total chlorophyll, protein content and nitrate reductase activity was found in the maize seedlings treated with residue extract without bacterial inoculation. However, chlorophyll and protein contents increased in inoculated seedlings treated with lower concentration of extract. The inoculation also increased the nitrate reductase activity in inoculated maize seedlings than non inoculated control and also influenced the activities of various antioxidant enzymes. Extract at higher concentration decreased the activities of antioxidant enzymes, viz. superoxide dismutase, catalase and peroxidase. Inoculation of seedlings with the bacterium significantly altered the activities of antioxidants and decreased the electrolyte leakage and lipid peroxidation. These results suggested the protective nature of P. polymyxa against autotoxicity of maize.

To search the natural and eco-friendly herbicides, different mixtures of sorghum (Sorghum bicolor), sunflower (Helianthus annuus), brassica (Brassica napus) and mulberry (Morus alba) aqueous extracts were investigated against germination and growth of horse purslane (Trianthema portulacastrum). In laboratory bioassays, the mixture (100%) of sorghum + sunflower + brassica + mulberry aqueous extracts completely inhibited the germination and seedling growth of T. portulacastrum. In pot culture, two foliar sprays of sorghum + sunflower + brassica + mulberry water extracts inhibited its growth (leaf area, root and shoot length) and drastically reduced the dry matter production (96%). Thus mixture of foliar spray of sorghum + sunflower + brassica + mulberry aqueous extracts may be used as natural herbicide for T. portulacastrum control.

In pot culture, the effects of aqueous leaf extracts (0, 1 and 2% concentrations) of Ageratum conyzoides L., Anagallis arvensis L., Chenopodium album L, Parthenium hysterophorus L. and Rumex dentatus L. were studied on growth of green gram (Vigna radiata Wilczek) var. K 851. The leaf extracts of all test weed species significantly reduced all growth parameters (viz., root length, shoot length, leaf area, root biomass, shoot biomass, total biomass, pod number and seed weight) of green gram. The effects of weed leaf extracts were concentration dependant.

Agroforestry trees in fields may affect the germination and growth of agricultural crops through release of allelochemicals. Allelopathic effects of Dalbergia sissoo Roxb. (Shisham) fresh and dry leaves extract (25, 50, and 100%) were investigated on germination and growth of maize (Zea mays L.), pearlmillet (Pennisetum glaucum L.) and rice (Oryza sativa L.). In laboratory bioassay, the 100% dry leaves extract completely inhibited the germination of pearlmillet and rice and caused 80% reduction in maize. In pot culture, foliar spray of fresh and dry leaves extracts either had no effect on growth of pearlmillet and rice or slightly promoted their growth. Dry leaves extract (100%) enhanced the maize dry matter production (140%) over control. Dry leaves water extract was more effective than fresh leaves.

Bermudagrass [Cynodon dactylon (L.) Pers] is a C4 perennial grass and is one of the 10 worst world weeds. Its roots produces phenolic acids and cyanogenic compounds, which adversely impacts the growth and yield of field crops. Its rhizomes contains laevulose, triticin, vanillin, saponin, agropyrene (antimicrobial substance), iron and other minerals. Bermudagrass is used in traditional medicine as an anti-inflammatory, diuretic, antiemetic and purifying agent and to treat dysentery. Its essential oil has weak activity against some microbes.

To explore the inducible mechanism of weed-suppressive potential in allelopatic rice accession mediated by phosphorus nutrient deficiency, we studied the molecular physiological properties of allelopathic rice regulated by different phosphorus concentrations in hydroponics. We found that in hydroponics, the weed-suppressive potential of allelopathic rice PI312777 was enhanced under low phosphorus treatment, showing higher inhibitory effects on the dry weight of barnyard grass in presence of root exudates of allelopathic rice PI312777 than control (normal nutrient condition). However, reverse was true in non-allelopathic rice Lemont. The expression of four genes encoded the key enzymes involved in phenolic metabolism pathway were all up-regulated in allelopathic rice PI312777, but down-regulated in non-allelopathic rice Lemont, except slightly up-regulated phenylalanine ammonia-lyase. The HPLC analysis showed that some phenolic acids (Cinnamic acid, caffeic acid, 4-hydroxybenzoic acid, syringic acid and ferulic acid) were enhanced in the leaves, roots and root exudates of allelopathic rice PI312777 under low phosphorus treatment compared to control. But they were not influenced in non-allelopathic rice Lemont. Thus low phosphorus stress increased the allelopathic potential of allelopathic rice PI312777 to prevent the competitor to absorb the nutrients in hydroponics. The enhanced weed-suppressive potential in allelopathic rice mediated by low phosphorus stress was due to the up-regulation of the genes associated with phenolic metabolism, which led to the accumulation of phenolic acids in hydroponic solution from the roots of donor plant.

Toxicity effects of aqueous root extracts of 4 plant species on the maize growth and arbuscular mycorrhizal fungal (AMF; Glomus mosseae) colonization were studied in a greenhouse experiment. The root extracts (0.15%, w/v) of 2 dicotyledons [stinging nettle (Urtica dioica L.) and red clover (Trifolium pratense L.)] and 2 monocotyledons [meadow fescue (Festuca pratensis Huds.) and maize (Zea mays L.)] were applied weekly to non-inoculated and AMF-inoculated maize plants. The root extracts of monocots (F. pratensis and Z. mays) contained 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), allelopathic to neighbouring plants, whereas it was not found in dicots root extracts. Maize root dry weight was lower in non-inoculated maize plants watered with fescue and maize root extracts, showing toxicity and autotoxicity effects, respectively, that were not observed in equally treated AMF-inoculated plants. However, watering with maize root extract resulted in decreased AMF colonization in maize roots [AMF frequency (F%) and intensity (M%)]. These results indicate the potential of AMF application in continuous monoculture of maize to alleviate autotoxicity.

The allelopathic potential of rye crop to inhibit the weeds growth may reduce the herbicide use in Agriculture. In pot culture, four rye (Secale cereale L.) cultivars (Fasto, Forestier, Nikita, Primizia) were grown in open with two nitrogen rates (0 and 50 kg N ha-1) to determine their weed suppressiveness on three warm-season weeds (Chenopodium album L., Amaranthus retroflexus L., and Portulaca oleracea L.) in greenhouse. The contents of benzoxazinoids, DIBOA and DIBOA-Glucose were determined in rye cultivars tissues. Total benzoxazinoid content ranged from 80 to 450 µg g-1 d.m. and differed between the cultivars. Nitrogen application increased the benzoxazinoid content, 50 kg N ha-1 produced more benzoxazinoid content than 0 kg N ha-1 (258 vs. 154 µg g-1, i.e. +41% higher). The rye mulch obtained from different cultivars and from two N fertilisation levels (0 and 50 kg N ha-1) inhibited the growth of test weed spp. There was no correlation between the total benzoxazinoid content and the number of weed seedlings suppressed. The field study determined the allelopathic effects of rye cover crop on weeds (grass and broadleaf) in maize grown with two tillage systems (no-tillage, conventional tillage) at three nitrogen rates (0, 250, 300 kg N ha-1). The mulching significantly reduced the density of grass and broadleaf weeds by 61% and 96%, respectively. In no-tillage, residual nitrogen drastically reduced the broadleaf weeds density (83-90%), but the conventional tillage, increased their population (61-65%). Linear regressions between DIBOA and DIBOA-Glucose in the mulch and weed inhibition (%) were statistically significant, with R2 of 0.59 and R2 of 0.65 for grass and broadleaf weeds, respectively.