Archives - Allelopathy Journal

Sixty seven cultivars of 42 vegetable crop species from 14 families were tested in seedling growth bioassay using the used nutrient solution of Asparagus officinalis L. and replanting of Asparagus officinalis L., Colocasia esculenta Schott., Vicia faba L., Pisum sativum L. and Phaseolus vulgaris L. to select possible succeeding crops. Replanting problems due to continuous cropping is typically a chemical interference from previous crops or their residues in the soil and autotoxicity has been often suggested as one of the possible reasons. Growth performances of succeeding crops were assayed using once used nutrient solution and/or replanting soil of these crops. Bioassay using asparagus used nutrient solution with or without activated charcoal (AC) suggest the tested cultivar of cucumber, garden pea, komatsuna, melon, pak-choi cv. ‘Tyoukou’, parsley, soybean (except cv. ‘Tankurou’), cabbage cv. ‘Early Ball’ and lettuce cv. ‘Shato’ as succeeding crops. Bioassay using replanting soil with or without Activated Charcoal suggested that most of the cultivars tested can be planted after asparagus, taro, and three beans (Vicia faba L., Pisum sativum L. and Phaseolus vulgaris L.) with little adverse effects. Among the three methods of bioassay used (i). Nutrient solution, (ii). Direct seed sowing and (iii). Seedling transplanting in replant soil; the nutrient solution bioassay proved more sensitive than replanting soil bioassay. However, results of nutrient solution bioassay may not be reproducible in the field condition. Therefore, seedling transplanting method can be used as an easy and practical bioassay method to select succeeding crops for fields with replanting problems.

Under the conditions of aquatic environment pollution, algicidal effects of Alternanthera philoxeroides were analyzed by field and laboratory observations. In the alkaline habitat of A. philoxeroides, the mean BOD5 and COD were 4.38 and 42.76 mg· L-1, respectively, and the phytoplankton growth was suppressed by 31%. In laboratory trial A. philoxeroides, inhibited the Microcystis aeruginosa (52 %) and Chlorella pyrenoidosa (70%) but had a declining inhibitory effect in order of C. pyrenoidosa, M. aeruginosa and natural phytoplankton. A. philoxeroides inhibited the growth of C. pyrenoidosa and M. aeruginosa, which was closely related to the inhibition of phytoplankton observed in the study. In addition, environmental factors also had algicidal effects of A. philoxeroides in the form of a conic curve. The three principal components, COD, BOD5, and Chla showed stimulation of 37%, 33%, and 13%, respectively. In short, aquatic pollution enhanced the algicidal effects of A. philoxeroides.

The root exudates of Welsh onion (Allium fistulosum L.) were collected with the continuous root exudates trapping system and extracted with organic solvents of different polarities. The allelopathy of different extracted components on cucumber (Cucumis sativus L.) and Fusarium oxysporum f.sp. cucumerinum was studied and the composition was analyzed by using gas chromatography-mass spectrum (GCMS). All components extracted by different organic solvents promoted the growth of cucumber sprouts but inhibited the growth of F. oxysporum f.sp. cucumerinum mycelia. The components extracted by ethyl acetate had strongest allelopathic potential and were similar to those extracted by ether. Following further separation of major components, the allelopathy of components extracted by 80% ethyl acetate and 20% ethyl ether was strongest. The potential allelochemicals of Welsh onion root exudates were: diethyl phthalate, dibutyl phthalate, diisooctyl phthalate, 2-(methylthio)benzothiazole, benzothiazole, benzoic acid p-tolyl ester and cycluron. Dibutyl phthalate, benzoic acid, 4-methylphenyl ester and benzothiazole had significant allelopathic effects on the growth of cucumber sprouts and F. oxysporum f.sp. cucumerinum.

Allium is medicinal genus, rich in carbohydrates and organic-sulphur compounds such as Allicin (a precursor for the production of alkaloids, saponins and glycosides). Many phytochemicals have been isolated from various species of this genus, but only few (Allinase and Ajoene) are active as pesticides. Leaf extracts of garlic (A. sativum) controls 98% growth of citrus nematode (Tylenchulus semipenetrans). Allium cepa, A. sativum, A. fistulosum and A. ampeloparasum are fungicidal against the Alternaria alternata, A. brassicola and Myrothecium roridum. The phenol and sulphur based allelopathic compounds of genus Allium can be used for weeds and insects management in agricultural systems.

Allelopathy has been proposed as one mechanism that allows an introduced species to become invasive. The conventional techniques to evaluate the allelopathic potential of plants are the measurement of seedling growth (root and/or shoot growth, and dry weight). As the second of a 3-part investigation into the allelopathic potential of fennel (Foeniculum vulgare Mill.) on Santa Cruz Island, California (an island within Channel Islands National Park), this study compared the findings from both measurement techniques. Twelve introduced species of Mediterranean origin (6 forbs and 6 grasses species) that grow with fennel on Santa Cruz Island were selected. Two research questions guided this study: 1) How do results from root/shoot growth measurements compare with dry seedling biomass measurement? 2) Does either technique provide more accurate results regarding the allelopathic potential of fennel? Bioassays showed significant inhibition in root and shoot elongation as fennel leachate concentrations increased to the maximum (5.0%). The dry biomass technique was not sensitive to determine the significant allelopathic interactions with the same precision as the root and shoot growth techniques. Since the measurement technique used may influence the understanding of the allelopathic potential of fennel, this study has practical implications for researchers that recommend how to effectively manage this invasive species.