Allelopathic interference of Populus deltoides with some winter season crops

The performance of some winter season crops, namely Triticum aestivum, Lens culinaris, Phaseolus mungo, Avena sativa, Trifolium alexandrinum, Brassica juncea and Helianthus annuus was studied in association with Populus deltoides under alley cropping practice in two sets of fields in Punjab, North India. In one, the parent soil was retained (Sp), while in the other, the parent soil was replaced with soil collected from an area devoid of P. deltoides trees (Sr). Germination, plant height and biomass of the crops at 30 and 60 days after sowing (DAS) were reduced by 10 to 30% in both the P. deltoides fields compared to the ones without trees (Sc). The observed reduction was more pronounced in Sp fields than in Sr fields. Maximum reduction was observed in the case of B. juncea and least in T. alexandrinum. Germination and seedling growth of all the test crops except A. sativa and T. aestivum was found to be significantly reduced in response to the aqueous leachates of P. deltoides leaves. Likewise, the seedling length and dry weight of L. culinaris and T. aestivum were significantly reduced in litter amended soil. Litter and soil from P. deltoides fields were found to be rich in phytotoxic phenolics, the amount of which was more in Sp fields compared to Sr and control fields (Sc). Based on the study, the observed reductions could be attributed to the allelopathic interference of the tree with the crops through the release of phytotoxic phenolics from leaves and litter, which are continuously added to the soil

Allelopathic interference of Populus deltoides with some winter season crops

Abstract -The performance of some winter season crops, namely Triticum aestivum, Lens culinaris, Phaseolus mungo, Avena sativa, Trifolium alexandrinum, Brassica juncea and Helianthus annuus was studied in association with Populus deltoides under alley cropping practice in two sets of fields in Punjab, North India. In one, the parent soil was retained (S p ), while in the other, the parent soil was replaced with soil collected from an area devoid of P. deltoides trees (S r ). Germination, plant height and biomass of the crops at 30 and 60 days after sowing (DAS) were reduced by 10 to 30% in both the P. deltoides fields compared to the ones without trees (S c ). The observed reduction was more pronounced in S p fields than in S r fields. Maximum reduction was observed in the case of B. juncea and least in T. alexandrinum. Germination and seedling growth of all the test crops except A. sativa and T. aestivum was found to be significantly reduced in response to the aqueous leachates of P. deltoides leaves. Likewise, the seedling length and dry weight of L. culinaris and T. aestivum were significantly reduced in litter amended soil. Litter and soil from P. deltoides fields were found to be rich in phytotoxic phenolics, the amount of which was more in S p fields compared to S r and control fields (S c ). Based on the study, the observed reductions could be attributed to the allelopathic interference of the tree with the crops through the release of phytotoxic phenolics from leaves and litter, which are continuously added to the soil. Dans l'un des groupes le sol d'origine a été conservé (S p ), tandis que dans l'autre il a été remplacé par un sol prélevé dans un endroit dépourvu de peupliers (S r ). La germination, la taille des plantes et la biomasse des cultures 30 et 60 jours après le semis ont été réduites de 10 à 30 % dans les deux groupes de champs comparativement aux champs sans peupliers (S c ). La réduction observée était plus forte dans les champs S p que dans les S r . La réduction maximum a eu lieu pour les cultures de B. juncea et, à un moindre degré, pour T. alexandrinum. Des filtrats aqueux de feuilles de P. deltoides ont réduit significativement la germination et la croissance des pousses de toutes les cultures testées, à l'exception de A. sativa et T. aestivum. De même, la longueur des pousses et le poids sec des cultures de L. culinaris et T. aestivum ont été significativement réduits dans le sol amendé par de la litière. Nous avons trouvé que la litière et le sol des champs de P. deltoides sont riches en substances phénoliques phytotoxiques ; les quantités sont plus importantes dans les champs S p que dans les S r et les témoins (S c ). Selon cette étude les réductions observées peuvent être attribuées à l'interfé-rence allélopathique du peuplier avec les cultures par l'intermédiaire de substances phénoliques phytotoxiques provenant des feuilles et de la litière, qui s'incorporent continuellement au sol

Alternative control of littleseed canary grass using eucalypt oil

Globally, huge amounts of synthetic herbicides are used to manage weeds in arable lands. However, their widespread use has resulted in various toxicological effects on the environment and human health, besides resulting in the emergence of herbicide-resistant weed biotypes. To overcome these problems, there is an urgent need to search for novel compounds, particularly natural plant products, with potential herbicidal activity. In this area, we studied the phytotoxic effect of volatile oil from lemon-scented eucalypt on littleseed canary grass, a noxious weed of wheat fields. Our findings show that under laboratory conditions the emergence and earlier growth of the weed decreased and completely ceased using a very low concentration of eucalypt oil (0.0714%, v/v). Treatment with eucalypt oil of the 4-week-old pot-raised weeds caused visible damage such as chlorosis and necrosis, wilting and even plant death. The effect was concentration-dependent. At low concentrations, 2.5 and 5%, v/v of eucalypt oil, plants were damaged but recovered later, whereas at concentrations higher than 5%, v/v, of eucalypt oil plants showed severe injury with little or no sign of recovery, and death. There was a severe effect on the photosynthetic and respiratory ability of treated plants 7 and 21 days after treatment. Eucalypt oil treatment caused a rapid electrolyte leakage in the P. minor leaf tissues, indicating a loss of membrane integrity. The study concludes that lemon-scented eucalypt oil offers a good option for control of littleseed canary grass and could be included as a viable component of integrated weed management under sustainable agricultural practices

Status of floor vegetation under some monoculture and mixculture plantations in North India

A study conducted to assess the floor vegetation shows the presence of 17 species under Populus deltoides in comparison to 28, 29 and 35 under Albizia lebbeck, Dalbergia sissoo and mix-culture plantations, respectively. Further, the biomass and density of floor vegetation is considerably reduced under P. deltoides compared to other plantations. In addition, the indices for species richness, evenness, dominance and diversity are also reduced under P. deltoides showing some inhibitory mechanism being operative under these plantations. Based on available literature, allelopathy is speculated to be responsible for this reduction

Phenolic allelochemicals released by Chenopodium murale affect the growth, nodulation and macromolecule content in chickpea and pea

The present study was conducted to investigate the effect of the residue of Chenopodium murale L. on growth, nodulation and macromolecule content of two legume crops, viz., Cicer arietinum L. (chickpea) and Pisum sativum L. (pea). A significant reduction in root and shoot length as well as dry matter accumulation occurred when both the legumes were grown in the soil amended with 5, 10, 20 and 40 g residue kg<SUP>-1</SUP>soil. In general, a gradual decline in growth was associated with an increasing amount of residues in the soil. There was also a significant reduction in total chlorophyll content and the amounts of protein and carbohydrates (macromolecules) in plants growing in the residue-amended soil. The nodulation was completely absent in chickpea and pea when the plants were grown in the soil amended with 10 and 20 g residue kg<SUP>-1</SUP> soil, respectively. At a lower rate of residue amendment (5 g kg<SUP>-1</SUP> soil), a significant decline in nodule number and weight, and leghaemoglobin content was recorded. Root oxidizability, an indirect measure of tissue viability and cellular respiration, was adversely affected in both the legumes under various treatments of residue amendment. The observed growth reduction concomitant with increased proline accumulation indicated the presence of some inhibitory compounds in the residue-amended soil. It was rich in phenolics identified as protocatechuic, ferulic, p-coumaric and syringic acid with 12.8, 30.4, 20.2 and 33.6% relative content, respectively. The results suggest that the residue of C. murale releases phenolic allelochemicals, which deleteriously affect the growth, nodulation and macromolecule content of chickpea and pea

Eucalyptus essential oil as a natural pesticide

Eucalyptus (family Myrtaceae), an Australian native, represented by around 700 species is a genus of tall, evergreen and magnificent trees cultivated world over for its oil, gum, pulp, timber, medicine and aesthetic value. Among the various wood and non-wood products, essential oil found in its foliage is the most important one and finds extensive use in food, perfumery and pharmaceutical industry. In addition, the oil possesses a wide spectrum of biological activity including anti-microbial, fungicidal, insecticidal/insect repellent, herbicidal, acaricidal and nematicidal. The present paper discusses this environmentally benign pest control using eucalyptus oils against bacteria, fungi, insects, nematodes, weeds and mites. The use of eucalyptus oil as a natural pesticide is of immense significance in view of the environmental and toxicological implications of the indiscriminate use of synthetic pesticides and overcoming/reducing the problem of increasing pest resistance

Allelopathy of gymnospermous trees

The present paper reviews the available literature on the allelopathy of gymnosperms which constitute the famous boreal forests known for their high quality timber and other products of great commercial importance. Nineteen genera belonging to six of the seven taxonomic families of conifers comprising one of the most dominating and largest group of present day gymnosperms, are reported to show the phenomena of allelopathy. The available information signifies the role these mighty trees play in determining the understorey vegetation, ecological succession and forests dynamics besides causing regeneration problems to the donor trees. The allelochemicals, identified from these plants, responsible for such interactions have also been summarised. In most of the cases the leaching of phenolics from the litter predominantly of tree needles, which remain on the ground for a longer time due to slow decomposition rate, are held responsible for these interactions

Arsenic-induced root growth inhibition in mung bean (Phaseolus aureus Roxb.) is due to oxidative stress resulting from enhanced lipid peroxidation

Arsenic (As) toxicity and its biochemical effects have been mostly evaluated in ferns and a few higher plants. In this study, we investigated the effect of As (10.0 and 50.0 &#956;M) on seedling growth, root anatomy, lipid peroxidation (malondialdehyde and conjugated dienes), electrolyte leakage, H<SUB>2</SUB>O<SUB>2</SUB> content, root oxidizability and the activities of antioxidant enzymes in mung bean (Phaseolus aureus Roxb.). Arsenic significantly enhanced lipid peroxidation (by 52% at 50.0 &#956;M As), electrolyte leakage and oxidizability in roots. However, there was no significant change in H<SUB>2</SUB>O<SUB>2</SUB> content. Arsenic toxicity was associated with an increase in the activities of superoxide dismutase (SOD), guaiacol peroxidase (GPX) and glutathione reductase (GR). In response to 50.0 &#956;M As, the activities of SOD and GR increased by over 60% and 90%, respectively. At 10.0 &#956;M As, the activity of ascorbate peroxidase (APX) increased by 83%, whereas at 50.0 &#956;M it declined significantly. The catalase (CAT) activity, on the other hand, decreased in response to As exposure, and it corresponded to the observed decrease in H<SUB>2</SUB>O<SUB>2</SUB> content. We conclude that As causes a reduction in root elongation by inducing an oxidative stress that is related to enhanced lipid peroxidation, but not to H<SUB>2</SUB>O<SUB>2</SUB> accumulation

Role of root-mediated interactions in phytotoxic interference of Ageratum conyzoides with rice (Oryza sativa)

Ageratum conyzoides L. (billy goat weed; Asteraceae) is an annual invasive weed native of tropical America and has now naturalized worldwide, particularly in Southeast Asia. The present study investigated the nature and potential of root-mediated allelopathic interference of A. conyzoides against rice (Oryza sativa). Root and shoot length and biomass accumulation of rice were significantly reduced (by 18-30%) when grown in the rhizosphere soil of the weed indicating the release of putative allelochemicals from the weed into the soil. The growth of rice was also progressively reduced in the soil amended with increasing amounts of root residues (5, 10 and 20 g kg-1 soil) of A. conyzoides. The addition of activated charcoal, an inert material with high affinity for organic biomolecules, partly ameliorated the negative effects of root residues amended in the soil. Further, there was no negative effect on the availability of soil nutrients in the root-amended soils. These were rather nutrient rich with greater electrical conductivity, and higher amount of organic matter, thus indicating no role in observed growth reduction. The reduction in allelopathic effects of root residue upon charcoal addition further indicated that putative phytotoxins released from the weed roots are water-soluble phenolic compounds. A significant amount of water-soluble phenolics were present in rhizosphere (~6-times higher) and root-amended soils (&#8707; 5-10-fold higher) and their content was reduced (to &#8707; 3.6-7.0-fold higher) when charcoal was added. The observed growth reduction in Ageratum rhizospheric or root-amended soils was concomitant with the amount of phenolic compounds. Upon HPLC analyses, these were identified as p-coumaric acid, gallic acid, ferulic acid, p-hydroxybenzoic acid and anisic acid. Under laboratory conditions, these phenolic acids reduced the root length and seedling weight of rice individually as well as in equimolar mixture, though no synergistic effect was noticed. The study concludes that root exudates and residues of A. conyzoides suppress the growth of rice by releasing phenolic allelochemicals into the soil rhizosphere and not through alteration of soil nutrients, and allelopathy plays a significant role in root-mediated negative interference of A. conyzoides