Archives - Allelopathy Journal

Essential oils are responsible for many activities in plants viz., interaction with other plants through allelopathic effects. The essential oil of Matricaria chamomilla was tested for allelopathic effects using the bioautography test and characterized by GC/MS. It was then fractioned by TLC, whereby the fraction and compounds responsible for the activity were identified. The fraction with the better growth inhibitions was bisabolol, which is also the main compound, followed by the fraction containing espathulenol, bisabolol oxide and another with polyenes. The bioautography test proved very effective, economic and speedy method to identify the allelopathic compounds.

The allelopathic potential of wheat (Triticum aestivum) plants was assayed on different growth stages of potato (Solanum tuberosum) by mixing the donor plant material (wheat component powder) with agar in solid tissue culture method. The allelopathic mechanism was examined using the un-sterile shoots of wheat plants, a combination of un-sterile shoots of wheat and the Alopecurus aequalis weed. Wheat biomass inhibited the growth of potato seedlings and the inhibition intensity was closely related to the donor material type, sampling stage, cultivar and test conditions. Allelopathic effects of wheat on potato declined in order: shoots > rhizosphere soil > roots. Wheat seedlings and mature plants proved most allelopathic. Transgenic potato displayed stronger resistance to allelopathic effects of wheat than conventional potato. The application of activated carbon and biomass of A. aequalis and Medicago sativa, wheat showed no effect, synergistic and antagonistic effects, respectively. However, under sterile conditions, all donor materials promoted the growth of potato seedlings, suggesting the conversion from allelopathic inhibition to nutrients supplementation. Wheat plant material also lead to the accumulation of oxygen radical species (O2-• and H2O2, MDA) in leaves of potato seedlings and increased the membrane permeability and altered the activity of SOD and APX enzymes.

Herbicidal resistance in Horse purslane (Trianthema portulacastrum) threatens the quality and yield of Kharif crops in India, prompting research to discover novel natural plant compounds with herbicidal properties. Due to its novel nature and potentially interesting chemistry, the American native, Sunflower (Helianthus annuus), was tested for its ability to suppress Horse purslane growth and its feasibility for use in weed control strategies. Aqueous extract of sunflower significantly inhibited seed germination, seedling growth and dry matter accumulation of T. portulacastrum in laboratory bioassays at concentrations of 5, 10 and 15% (w/v). In pot trials, sunflower rhizosphere soil (SRSS), at the stage of 60 days after sunflower sowing (DAS), inhibited above 50% of growth and yield attributes of T. portulacastrum. Extract fractionation showed the highest phytotoxicity against shoot and root growth of test weeds at 100 ppm. Several phenolic acids were identified in stem and leaf extracts through paper chromatography. Their identity was confirmed through spraying with diazotized-p-nitro aniline, sufanilic acid, ferric chloride-potassium ferricyanide and also tested with Hoepfner'scoplin reaction. These results suggest that sunflower is an important potential source of compounds for control of horse purslane in kharif crops

Rice plants that exhibit allelopathic behavior represent potential options for sustainable weed management. Previous studies have shown that the Sathi rice variety (an indica-type) shows high allelopathic potential (HAP), whereas the Nongan rice variety (a japonica-type) shows low allelopathic potential (LAP). Hence, in this study, we assessed the F6 and F7 generations of 180 recombinant inbred lines (RILs) derived from crossing Nongan/Sathi planted in Seoul, Korea. A laboratory assessment (double pots allelopathy bioassay) and a field assessment (rice ratoon interplanting barnyardgrass seedling) were used to screen the allelopathic potential of the rice cross. Both methods used barnyardgrass (Echinochloa crus-galli Beauv. var. frumentaceae) as a plant (weed) indicator to evaluate how rice suppressed plant growth. The results indicated that some prospective lines have HAP, exhibiting high suppression of barnyardgrass height and shoot dry-weight. Further selection for desired agronomical characteristics was performed for F8 RILs in the field in Korea, with some selected F9 lines exhibiting HAP and LAP during repeated planting in Bogor, Indonesia. The allelopathic potential of the Nongan/Sathi rice cross was confirmed on F10 RILs by evaluating agronomic performance. Through this multi-generation work, some promising lines derived from japonica and indica rice-types exhibiting high and low allelopathic traits, may be used in closely monitored agronomic field trials.

Ten biotypes of Gaozhou (Guangdong, China) common wild rice (Oryza rufipogon W. Griffith) were bioassayed to evaluate their allelopathic potential against seedling growth of barnyardgrass (Echinochloa crus-galli L.). Aqueous stem leachates of Gaozhou 2 inhibited the root growth of barnyardgrass by 70.6%. HPLC analyses showed the presence of several phenolic acids but none of them was significantly correlated with the phytotoxicity. Aqueous leachates of Gaozhou 2 leaf residues after 7–day-decomposition had the strongest inhibition against root growth of barnyardgrass. The phytotoxicity of residue leachates was highest when prepared at low temp (14°C). Aqueous leachates of leaf residues decomposed in different water content had variable inhibitory effect on the seedling growth of barnyardgrass.

Assessment of the total phenols content (TPC) and biochemical impact of H. sosnowskyi on perennial ryegrass (monocots) and winter rapeseed (dicots) seed germination was done ex situ. Aqueous extracts of 2-yr old H. sosnowslyi exhibited higher phytotoxicity than 1-yr. old plant extracts. The phytotoxic effects of H. sosnowskyi aqueous extracts on the germination depended extract concentration (0.02-0.2%), plant age (1-year, 2-year), plant parts (shoot: stem, leaf, blossom, seed; root) and growth stage (rosette-ripening). The phytotoxicity of H. sosnowskyi determined extract was most strong at flowering stage due to highest TPC (30.42 mg ml-1). All parts of H. sosnowskyi produced phenolics, which inhibited the acceptor-species seed germination. The results suggested that invasive plant species may acquire spreading advantage in new territories through use of their allelochemicals to inhibit germination. Nonetheless, species evidence for allelopathic effects should not be restricted to analysis of the plant extracts in the lab, but also include research in natural environment.

To confirm if Vitex negundo can replace the invasive Chromolaena odorata, we studied the allelopathic interactions between C. odorata and V. negundo in pot culture experiment in greenhouse. The aqueous extracts of C. odorata did not inhibit the seed germination, seedling and plant growth of V. negundo, indicating the tolerance of V. negundo to the allelochemicals of C. odorata weed. Contrarily, the aqueous extracts of V. negundo inhibited the seed germination, seedling and plant growth of C. odorata. Field investigation also showed that V. negundo was not affected by C. odorata. These results suggest that V. negundo is a promising native species to replace the invasive C. odorata.

In Cerrado, Zanthoxylum rhoifolium Lam. stands out because it interferes with the growth and development of other plants. The preliminary phytochemical analyses showed the presence of polyphenols and flavonoids. The Z. rhoifolium extract inhibited the germination index (5 mg mL-1=0.5%; 10mg mL-1=37.5% and 20mg mL-1=85.5%) decreased the germination and the lettuce seedlings growth (roots and the hypocotyls) and reduced the mitotic index than control. The extract of 1000 µg mL-1conc contained (165.20 mg and 45.74 mg, phenols and total flavonoids, respectively) and had higher antioxidant activity (80.52%). We concluded that Z. rhofolium possesses allelopathic potential.

Allelopathic potential of aqueous leaf extracts of Datura stramonium L. was assessed on seed germination, seedling growth, root tip morphology, anatomy, and cell division of soybean. The extracts inhibited the seed germination and the degree of inhibition was concentration dependent. The extracts inhibited the primary root elongation and lateral root development and the degree of inhibition increased with increasing extract concentration; contrarily hypocotyl length was not affected. The higher extract concentrations inhibited the root hair development as shown by decreased root hair length and density.The extracts also altered the morphology and anatomy of root tips. At higher concentrations, the extracts inhibited the normal cell division in root tips and caused chromosomal aberration index and micronucleus index.

The effects of winter wheat varieties exudates were tested on the germination of Orobanche minor seeds through hydroponical culture and field experiments. The results indicated that allelopathic potential of wheat on stimulating O. minor seeds germination varied with tested varieties, growth stages, extraction solvents and extract concentrations. The methanolic extracts of all wheat varieties displayed a stronger induction of O. minor seeds germination than the aqueous extracts. The aqueous extracts at 10% and 1% effectively stimulated the germination, but the undiluted (100%) and 0.1% extracts did not induce the seed germination. Likewise, the methanolic extracts also induced the seeds germination. The methanolic extract of variety `Xiaoyan No. 22’ induced O. minor seed germination up to 56.8%. Thus O. minor seeds could be induced to germinate by the aqueous and methanolic extracts of winter wheat varieties. Winter wheat especially at the seedling and heading stages contained allelopathic substances to induce O. minor seeds germination. It is possible that wheat allelopathy could be used to stimulate the germination of O. minor, thereby rapidly depleting the seed bank of this problematic parasitic weed.

We studied the effects of aqueous extracts of ginger plants on the growth membrane permeability and antioxidant enzymes in leaves of ginger seedlings. Ginger seedlings were sprayed with aqueous extracts of ginger rhizomes, stems and leaves at 10, 20, 40 or 80 g L–1 concentrations. Higher concentrations of extracts significantly inhibited the shoot height, underground (i.e. rhizome yield), total biomass of ginger seedlings and decreased the total chlorophyll content but increased the lipid peroxidation and membrane permeability. The increased concentrations of stem and leaf extracts deceased the activities of major antioxidant enzymes (superoxide dismutase, peroxidase, catalase and ascorbate peroxidase) in leaves of ginger seedlings. The rhizome extracts were less stimulatory at lower concentrations but became inhibitory at higher concentrations. The phytotoxicity of extract at same concentrations followed the order of decreasing inhibition: stem > leaf > rhizome. These results showed that ginger has autotoxic potential, hence, its residues (stems, leaves) should be removed from the fields to reduce the autotoxic effects on next ginger crop seedlings.