Showing papers on "Allelopathy published in 1978"

Suppression of Coastal Heath Vegetation by Eucalyptus baxteri

Abstract: Eucalyptus baxteri produces a zone of suppression beneath its canopy when growing in coastal heath. Dominant species including Casuarina pusilla and Leptospermum myrsinoides are suppressed, but species such as L. juniperinum and Xanthorrhoea australis are not. Investigations of shoot water potential, soil nutrient levels and shading failed to suggest suppression by competition. E. nitida produces a slightly deeper shade but fails to produce a similar pattern of differential suppression. Chemical inhibition (allelopathy) of Casuarina pusilla, Eucalyptus viminalis and Triticum aestivum by E. baxteri was shown to exist under laboratory conditions. Foliar leachates of E, baxteri are inhibitory in bioassays and contain gentisic and ellagic acids. Litter leachates are also inhibitory in bioassays and contain gentisic, gallic, sinapic, caffeic and ellagic acids. Both leachates also contain several unknown phenolic aglycones, numerous glycosides, and terpenoids. Topsoil extracts are also inhibitory and contain resins and, possibly, terpenoids. The suppression zone is associated with the allelopathic ability of E. baxteri, and is maintained either through the direct transfer of foliar leachates to leaves of suppressed species, through root absorption of foliar and litter leachates, or as a consequence of mycorrhizal inhibition by such leachates.

Allelopathic effects of goldenrod and aster on young sugar maple

Abstract: A series of field, greenhouse, and laboratory studies were undertaken to elucidate the role of allelopathy in old-field sugar maple stands. Old-field weed residue inhibited germination and growth of maple even in the absence of competing vegetation. Goldenrod and aster were important producers of water soluble compounds that inhibited germination, nutrient uptake, and growth. These allelopathic chemicals were most readily extracted from putrefied plant residues, but they appeared to be natural plant products rather than microbial breakdown products. The deleterious effects of goldenrod on nutrition and growth of maple were overcome by large additions of soluble phosphorus fertilizer.

The Potential of Allelopathy as a Tool for Weed Management in Crop Fields

Abstract: The increasing emphasis now placed on weed management as opposed to weed control raises the question of the role of allelopathy in agricultural systems. Evidence of allelopathic interactions between crops and weeds is briefly reviewed and two experiments designed to demonstrate the allelopathic effects of plant residues on seed germination are described. From these experiments it can be seen that Tagetes patula, Amaranthus dubius, bean (Phaseolus vulgaris) and cassava residues have widespread inhibitory effects on the germination of seeds of other species, while maize, Cenchrus brownii, Eleusine indica and Portulaca oleracea show considerable tolerance to the presence of such residues. Suggestions are made as to how the potential of allelopathy in weed management can be investigated and how the process can be exploited. A considerable quantity of research remains to be done in this area.

Allelopathic potential ofAmbrosia cumanensis H.B.K. (Compositae) in a tropical zone of Mexico

Abstract: Several experiments were carried out to confirm the allelopathic potential ofAmbrosia cumanensis H.B.K. (Compositae) in a tropical zone of Mexico. The aqueous extracts of leaves and roots inhibited growth of several species used in bioassays. The wash-water of the leaves inhibited some species and stimulated others. The aqueous solutions of soil, in reference to those collected in July, were significant in their general inhibitory action. Decomposition of leaves and roots, in pots where several species were growing, was highly inhibitory to some of the seedlings; microorganisms have a major role in this process.

Allelopathy as a factor in the success ofHelianthus mollis Lam.

Abstract: A method to rapidly screen species suspected of producing allelochemics, using results from simple bioassay tests, is presented. By measuring the osmotic potential ofH. mollis extracts and using mannitol solutions of comparable osmotic potential, the influence of osmotic potential in the bioassay was eliminated. Nested analysis of variance was used to examine the separate influences of (1) extract concentration, (2) source of plants used in extract preparation (edge or center of clones) (3) osmotic potential of the extract, and (4) the differential development of radicles and shoots of species used in the bioassay tests. Bioassay tests for allelopathy showed that extracts made of wholeH. mollis plants significantly inhibited both radicle and shoot development of radish and wheat, but only the radicle of little bluestem. There was a significant increase in the inhibition of radish shoots and wheat radicles at high concentration of the extract, but the radicle of little bluestem was inhibited more at the lower concentration. Extracts prepared from plants collected from the clone center inhibited radish radicle development significantly more than extracts made of plants growing at the clone edge.

Allelopathic effects of bur buttercup tissue on germination and growth of various grasses and forbs in-vitro and in soil

Abstract: — The allelopathic effects of bur buttercup {Ranunculus testiculatus) tissue on selected grasses and forbs varied according to the substratum for germination and growth. The in vitro effects of an aqueous extract of buttercup tissue on germination and root development of five grasses were strongly inhibitory in all cases. However, in soil the effects of buttercup tissue on germination and growth of seven grasses and two dicotyledonous herbs were small to nonsignificant. Deleterious effects were less severe in fineas opposed to coarsetextured soils. Under field conditions, the ability of seedlings of the grasses to compete with buttercup varied with the species. Bur buttercup (Ranunculus testiculatus Crantz), a native of southeastern Europe and central Asia (Benson 1948, Davis 1965) was first collected in North America by A. O. Garrett near Salt Lake City, Utah, in 1932. Since that time, the species has spread throughout the Great Basin, the Snake River Plain, and the Columbia Plateau. In much of that area, the species exists in large populations in native vegetation and waste places of the semiarid zone. Small, isolated populations are also known from northeastern Wyoming, northern Arizona, northern California, and interior British Columbia (Buchanan 1969). The species is a diminutive annual (averaging ca. 5 cm in height) that completes its life cycle during the early spring. In northern Utah germination occurs in late fall, but at more northerly latitudes, germination may be postponed until spring (Buchanan 1969). Despite its small size, the species often forms a dense carpet over literally thousands of acres of dry farm and range land during the period from March to May in the eastern Great Basin. The invasion of bur buttercup into North America prompted an early interest in its potential as a weed. Two memoranda in the files of the Intermountain Forest and Range Experiment Station (IFRES) of the U.S. Department of Agriculture (Ogden, Utah) report early observations of bur buttercup in Utah and consider its potential as a weed (Clark 1941, and Stewart 1941). The memos, dated 18 July and 3 September 1941, respectively, discuss the plant's history, spread, importance as a weed, and possible control in the West. However, when our study began in 1966, no aspect of the dispersal or ecology of the species had been reported in the scientific literature (exclusive of floras) of North America. Because of rapid spread of bur buttercup and the dearth of information concerning the species, the Intermountain Forest and Range Experiment Station initiated a program to investigate its life history, ecology, and distribution. Concern over possible deleterious effects of bur buttercup on winter wheat crops and on range grass seedings prompted this study of the competitive and allelopathic effects of bur buttercup on wheat and on grasses used in range revegatation. Germination studies using both glass 'Research supported under contract 12-11-204-30 between the Intermountain Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture, Ogden, Utah, and the University of Utah. 'Department of Biology. University of Utah, .Salt Lake City, Utah 84112. Current address of Buchanan is Department of Agronomy, New Mexico State University, Las Cruces, 88003. Current address of Harper is Department of Botany and Range Science, Brigham Young University, Provo, Utah 84602, 'Intermotmtain Forest and Range Experiment Station, Provo, Utah 84601.

Biochemical Inhibition (Allelopathy) Exhibited By Cenchrus Ciliaris Linn and Chrysopogon Aucheri (Bioss) Stapf

Abstract: Cenchrus ciliaris and Chrysopogon aucheri are important range-grasses found in Pakistan every where upto 1800 metres. Field and laboratory experiments showed .that beside toxic root exudates,) voter extracts contained substances which proved to\ be inhibitory not only to its own growth but also to other species used in the bioassays The toxicity in both the cases increased with increasing concentration and soaking time. Cenchrus had more allelopahic potentiality than Chrysopogon. The toxicity in both the cases was species related. The possible effect of allelopathy of these grasses is discussed in relation to the vegetation dynamics .