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A study was conducted to determine the potential and nature of root-mediated allelopathic interference of Chenopodium murale on wheat. Early growth of wheat reduced significantly in agar medium where C. murale seedlings were previously growing as well as in rhizosphere soil of C. murale. The reduction in wheat growth was due to the presence of inhibitory metabolites released by roots of C. murale in the growth media. Even the soil incorporation of root residues also reduced the wheat growth in terms of seedling length and seedling dry weight. Only a partial amelioration in growth inhibition occurred upon charcoal supplementation or nitrogen fertilization in these amended soils. Root residues did not reduce the available nutrients in the soil, which was rather nutrient rich. These results indicated the definite role of allelopathy of C. murale roots in retarding wheat growth. Root amended soils contained significantly higher amount of phytotoxic phenolics as the putative allelochemicals, which were ferulic acid, vanillic acid, p-coumaric acid and benzoic acid. The study concluded that C. murale roots and their exudates exerted allelopathic effects on wheat by releasing water-soluble phenolic acids as putative allelochemicals in soil. [ABSTRACT FROM AUTHOR]

2-Benzoxazolinone (BOA), a type of hydroxamic acid present in cereals and implicated in allelopathy, is now being viewed as a potential candidate for the development of natural herbicides. A study was conducted to determine the effect of BOA on mung bean ( Phaseolus aureus) through a multitude of bioassays to understand its physiological and biochemical action. It was observed that BOA significantly decreased the germination of mung bean and its early growth (measured in terms of seedling length and dry weight). A typical dose–response relationship was observed with BOA treatment, and I50 values (concentrations at which 50% inhibition occurs) for germination, seedling length and seedling dry weight were calculated to be 4.3, 0.71 and 0.77 mM, respectively. There was therefore a greater inhibitory effect on seedling growth than on germination. Treated seedlings were characterised by a loss of chlorophyll and decreased respiratory activity, indicating a possible adverse effect of BOA on photosynthetic and respiratory metabolism. Mitotic activity in root-tip cells of onion ( Allium cepa) was completely arrested in response to BOA treatment, and the cells exhibited abnormality in shape and size. BOA also adversely affected rhizogenesis in hypocotyl cuttings of mung bean, indicating an impact on morphogenetic potential. It was associated with significant changes in the protein content and activities of proteases and polyphenol oxidases during the root development phase. This study concludes that BOA interfered with essential biochemical processes in mung bean. Such studies provide useful information on the biochemical and physiological modes of actions of BOA, with a view to its use as a herbicidal compound. [ABSTRACT FROM AUTHOR]

A study was conducted around Chandigarh (Punjab), India to assess the effect of Populus deltoides shelterbelt on wheat. Crop density, root and shoot length, biomass and grain yield of wheat at crop maturitywere significantly lower, up to 12 +/- 1 m in the fields sheltered by P. deltoides than in unsheltered plots. The reduction of biomass and grain yield of wheat were comparatively more than that of other parameters. The observed reduction in the growth and yield of wheat could be attributed to phytotoxic interference of the phenolics from the tree with the crop. [ABSTRACT FROM AUTHOR]

A study was undertaken to explore the phytotoxicity of volatile essential oil from Eucalyptus citriodora Hook. against some weeds viz. Bidens pilosa, Amaranthus viridis, Rumex nepalensis, and Leucaena leucocephala in order to assess its herbicidal activity. Dose-response studies conducted under laboratory conditions revealed that eucalypt oils (in concentration ranging from 0.0012 to 0.06%) greatly suppress the germination and seedling height of test weeds. At 0.06% eucalypt oil concentration, none of the seed of test weeds germinated. Among the weed species tested, A. viridis was found to be the most sensitive and its germination was completed inhibited even at 0.03%. Not only the germination and seedling growth, even the chlorophyll content and respiratory activity in leaves of emerged seedlings were severely affected. In A. viridis chlorophyll content and respiratory activity were reduced by over 51% and 71%, respectively, even at a very low concentration of 0.06%. These results indicated an adverse effect of eucalypt oils on the photosynthetic and energy metabolism of the test weeds. A strong negative correlation was observed between the observed effect and the concentration of eucalypt oil. Based on the study, it can be concluded that oil from E. citriodora possess strong inhibitory potential against weeds that could be exploited for weed management.

2-Benzoxazolinone (BOA), a well-known allelochemical with strong phytotoxicity, is a potential herbicidal candidate. The aim of the present study was to determine whether phytotoxicity of BOA is due to induction of oxidative stress caused by generation of reactive oxygen species (ROS) and the changes in levels of antioxidant enzymes induced in response to BOA. Effect of BOA was studied on electrolyte leakage, lipid peroxidation (LP), hydrogen peroxide (H(2)O(2)) generation, proline (PRO) accumulation, and activities of antioxidant enzymes-superoxide dismutase (SOD, 1.15.1.1), ascorbate peroxidase (APX, 1.11.1.11), guaiacol peroxidase (GPX, 1.11.1.7), catalase (CAT, 1.11.1.6) and glutathione reductase (GR, 1.6.4.2) in Phaseolus aureus (mung bean). BOA significantly enhanced malondialdehyde (MDA) content, a product of LP, in both leaves and roots of mung bean. The amount of H(2)O(2), a product of oxidative stress, and endogenous PRO increased many-fold in response to BOA. Accumulation of PRO, MDA and H(2)O(2) indicates the cellular damage in the target tissue caused by ROS generated by BOA. In response to BOA, there was a significant increase in the activities of scavenging enzymes SOD, APX, GPX, CAT, and GR in root and leaf tissue of mung bean. At 5 mM BOA, GR activity in roots showed a nearly 22-fold increase over that in control. The present study concludes that BOA induces oxidative stress in mung bean through generation of ROS and upregulation of activities of various scavenging enzymes.

The volatile oil extracted from the leaves of Eucalyptus citriodora showed a wide spectrum of antifungal activity.