Abstract: A number of glucosinolates and isothiocyanates were tested for their allelopathic potential against wheat. Most of the glucosinolates showed no activity against wheat, with the exception of glucobrassicin which was moderately active, as was sinapine thiocyanate. Isothiocyanates showed high activity against wheat germination and seedling growth. The most active compound, 2-phenethyl ITC completely inhibited wheat germination at 500 ppm. Allyl ITC showed high activity whereas other isothiocyanates tested were only moderately active. The data is discussed in relation to the possible use of some mustard species for effective weed control.

Abstract: (...) Studies were conducted in which residues of corn, soybean [Glycine max (L.) Merr.], oat [Avena sativa (L.)], and mixed grass hay were extracted under N 2 gas or air. Organic debris was removed and half of each extract was filter sterilized. Corn seeds were incubated in the extracts for 96 h at 25°C. Percent germination, and lengths of coleoptile, radicle, and secondary roots were measured (...)

Abstract: Recently, Schmidt (1988) isolated from the soil under Juglans nigra L. a bacterium capable of degrading juglone, the allelotoxin reputed to inhibit neighboring vegetation (Davis, 1928; Rietveld, 1983; Rietveld et al., 1983). Schmidt's report is noteworthy because it supports the previously hypothesized degradation ofjuglone by microorganisms (Fisher, 1978; Rietveld, 1983; Rietveld et al., 1983). However, Schmidt's (1988, p. 1561) conclusion that \"Rapid degradation ofjuglone and other suspected alMochemicals by soil bacteria make it unlikely that these compounds are important mediators of plant-plant interactions under natural conditions\" appears to us to be premature. In fact, the author might have argued equally convincingly that such specialized strains of soil bacteria confirm the frequent, if not continuous, presence of putative phytotoxins in the soil, and therein lend support to the allelopathic hypothesis. Neither contention is free of ambiguity. The phytotoxicity of allelochemicals in soil solution will depend on input and output rates as well as the effective concentration (Winter, 1961; Blum and Shafer, 1988). Schmidt's Pseudomonas J1 provides one output sink forjuglone. Juglone may be removed from the soil in numerous other ways, including, as Schmidt notes, soil physical and chemical processes. However, just as plants compete with microorganisms for nutrients (Pastor et al., 1984), the roots of plants inhibited by phytotoxins are potential competitors with microorganisms for the available phytotoxins (Winter, 1961; Hoffman and Lavy, 1978; Weidenhamer et al., 1987, 1989). The outcome of this competition may determine whether or not allelopathic effects are manifested. Therefore, bacterial affinities for juglone must be evaluated relative to target plant affinities and soil abiotic processes. Output rates themselves must be weighed against input rates of juglone into the soil solution (Winter, 1961). Influx may be a function of the amount of plant biomass (Rietveld et al., 1983), root exudation, litter decay, and precipitation throughfall, although in the case of juglone little is known in this regard. The actual available concentration of juglone will reflect the various input

Abstract: SUMMARY The allelopathic influence of Parthenium hysterphorus, a gregarious and ubiquitous weed, on four multi-purpose tree species – Acacia leucophloea, Casuarina equisetifolia, Eucalyptus tereticornis and Leucaena leucocephala and three agricultural crops – cowpea, sorghum and sunflower – were tested by germinating seeds of these species in composite leachate obtained from the leaves, stem and flowers of the weed species. Germination of seeds of all test species, arboreal and arable, was severely inhibited by the leachate. In the tree crops, the magnitude of injury was the same under extracts prepared from 2 or 4 ml of distilled water per g of plant tissue. Among the arable crops, sunflower was affected to a greater extent. While radicle and plumule elongation were unaffected in the tree crops and in sunflower, plumule was curbed to a greater extent than radicle in cowpea. In sorghum, only radicle growth was impaired. The inhibition of germination and seedling growth is attributed to parthenin, an unsat...

Abstract: Kleberg bluestem [Dichmthium annuktum (Forsk) StaprJ and buffelgrass (Cmeluus ciIiur& L) may produce pbytotoxic cbemicals that inbibit germbtation and growth of legumes planted in s&g mixtures with grasses We determined the effects of leacbate from these introduced grasses on seed germination of Illinois bundleflower [Desmanthusilifuoens&(Michx) MacM] and partridge pea (Carsia~arciculoro Michx) Percent germination of Illinois bundleflower seeds on substrata moistened with Kleberg bluestem root or buffelgrass leaf leacbate was lower than that of seeds placed on substrata moistened with distilled water Buffelgrass root Ieacbate reduced germination of partridge pea more than did root leacbate from Kleberg bluestem or leafleacbate from Kleberg bluestem or buffelgrass Results of these laboratory experiments bulicate that field studies are warranted to determine the effects of buffelgrass on establishment of partridge pea and Illinois bundleflower in order to help land managers select the optimum combination of species for rangeland seeding

Abstract: The distribution of the inhibitor between root and leaves of taro and within the stems of the aroids has also been studied The content of allelochemicals in five edible aroids is also considered in relation to the degree of apparency of the plant part and its resistance to parasites

Abstract: Field observations indicated thatEuphorbia prostrata strongly interferes withCynodon dactylon (L.) Pers. Analysis of some physical and chemical soil factors indicated that competition was not the dominant factor of that interference. Soil collected from underE. prostrata stands was very inhibitory to seed germination and seeding growth of some of the test species including C.Dactylon. This suggests the presence of inhibitory compounds in soil ofE. prostrata stands. Subsequent experiments showed that aqueous extract, decaying residues, and root exudates ofE. prostrata were inhibitory to most of the test species including C.Dactylon. Thus, it appears that allelopathy is the major component of the interference, with competition probably accentuating its effect. It also was found that allelopathy is an important component of the interference byE. prostrata againstAmaranthus retroflexus, Medicago sativa, andGossypium hirsutum.

Abstract: Putative allelochemicals found in the soil of no-tillage and conventional-tillage wheat plots near Stillwater, Oklahoma, were obtained by a mild alkaline aqueous extraction procedure, bioassayed to determine their biological activity, purified, and analyzed with a capillary gas chromatography-mass spectrometry-data analysis system. The most significant inhibition was found in bioassays of extracts from soil collected immediately after harvest in June, July, and August. No-tillage soils produced significant inhibition during the rest of the year also. Mass spectrometry showed fatty acids as the most abundant compounds. However, when bioassayed authentic samples of the five free fatty acids showed no significant biological activity toward wheat.

Abstract: Abstract Volatile compounds which are released from fresh leaves of Thuja occidentalis inhibited germination of seeds of Amaranthus caudatus and Lepidium sativum. The volatile compounds were obtained by a vacuum method applied to the leaves, by direct analysis of the content of secretory organs and by solvent extraction of leaves. The bioactive compounds proved to be monoterpenes. The highest bioactivity were found for alcoholic compounds followed by ketones, esters and finally hydrocarbons. Non-volatile germination inhibitors which were ex- tracted with hot water were abscisic acid (3-4 µg/g fresh weight of leaves), and two oxidation products of thujone, 2-[2′-acetyl-l′-isopropyl]cyclopropylacetic acid (“Thujaketosaure”) and 3-isopropyl-5-oxohex-2-enoic acid. These compounds could also be prepared from thujone. The relationship of these compounds with possible allelopathic effects of Thuja occidentalis is discussed.

Abstract: After testing organic solid, organic liquid and inoraganic liquid culture media one by one and improving culture conditions, sterilized seedlings of water hyacinth (Eichhornia crassipes Solms.) with normal growth were established from axillary buds. A bioassay test was conducted to examine the allelopathic effect of the sterilized seedlings on Chlamydomonas reinhardtii. The results indicated that the extract from the water in which water hyacinth had been cultured under sterilized conditions still showed allelopathic effect. It means that the allelopathic compounds were exuded by water hyacinth itself, not by microbes living in its root zone.

Abstract: As part of an investigation into the allelopathic interactions of members of the Florida scrub community of plants, the release of allelochemicals by the Florida wild rosemary, Ceratiola ericoides (Empetraceae) was monitored. Aqueous extracts of whole leaves, water-rinses of leaves, aqueous litter extracts, and aqueous soil extracts were monitored monthly, or twice monthly in the summer months, for the dihydrochalcone ceratiolin, its decomposition product hydrocinnamic acid, the microbial degradation product of hydrocinnamic acid, acetophenone, and trans-cinnamic acid. High performance liquid chromatography was used to quantify the four compounds. The amounts of ceratiolin, hydrocinnamic acid, acetophenone, and trans-cinnamic acid in the leaf extracts varied seasonally; the largest amounts were observed in the months of September and October. These months are in the midst of the rainy season in the Florida scrub. Observed amounts of the four analytes in the leaf mists were much lower, and there was no seasonal variation. The soil and litter extracts also contained hydrocinnamic acid in varying amounts; the maximum concentrations again occurred in the late summer. The efficiency of extraction of exogenously applied hydrocinnamic acid to scrub soil was determined to be dependent on the level at which the compound was applied, and ranged from 18% at a level of 1 vig/g soil to 79% at a level of 64 yg/g soil in non-sterile soil. In sterile soil, the recovery was 91%, 78%, and 80% for levels of 2 yg/g, 4 yg/g, and 8 yg/g soil respectively. Allelochemicals that were released into the environment as volatile compounds were collected by dynamic headspace sampling and trapping on Tenax TA adsorbent. Thermal desorption and cryogenic focusing were utilized to introduce the compounds into a capillary column for analysis by gas chromatography-mass spectrometry. The volatile compound composition of whole leaves varied seasonally. Among the more abundant compounds were ethyl acetate, 3-methyl-l-butanol, and 1-hexanol. Of the volatile compounds collected from the litter and soil, 1-octene, 3-methyl-l-butanol, and 3-octanol were the most abundant.

Abstract: The role of terpenoid natural products in plant defense against herbivory by insects has been well established.1–2 This phenomenon extends to arid and semi-arid plants, even though taxa from these latter habitats have been less frequently examined.3 In this chapter, we compare the terpenoid chemistry of desert sunflowers of the genus Encelia, with the performance of a generalist insect feeding on extracts of these plants, in an attempt to define the role of the terpenoid allelochemicals as protective agents against herbivory.