Abstract
Intercropping Ageratum conyzoides in citrus orchards may effectively suppress weeds and control other pests. Investigations showed that the inhibition of major weeds and soil pathogenic fungi in citrus orchards was significantly correlated with the allelochemicals released into the soil by intercropped A. conyzoides. Three flavones, ageratochromene, and its two dimers were isolated and identified from the A. conyzoides intercropped citrus orchard soil. These allelochemicals had different biological actions on major weeds and soil pathogenic fungi in the citrus orchard. Three flavones and ageratochromene could significantly inhibit the growth of weeds Bidens pilosa, Digitaria sanguinalis and Cyperus difformis, and spores germination of soil pathogenic fungi Phytophthora citrophthora, Pythium aphanidermatum and Fusarium solani. However, two dimers of ageratochromene had no inhibitory actions on them. The presence of these allelochemicals in soils suggests that they may be able to make a major contribution to control some weeds and diseases in citrus orchards. Further studies revealed that dynamic transformation between ageratochromene and its two dimers in the A. conyzoides intercropped citrus orchard soil was reversible, that is, ageratochromene released from ground A. conyzoides plants was transformed into its dimers, and the dimers can be remonomerized in the soils. However, this dynamic transformation did not occur in the soil with low organic matter and fertility. The dimerization was not correlated with microorganisms in the soil, but the biodegradation of both ageratochromene and its two dimers may have occurred, particularly in the soil with low organic matter and fertility. Our results strongly suggest that the reversible transformation between ageratochromene and its dimers in the A. conyzoides intercropped citrus orchard soil can be an important mechanism maintaining bioactive allelochemicals at an effective concentration, thus, sustaining the inhibition of weeds and pathogenic fungi in soil.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Adesogan E K and Okunade A L 1979 A new flavone from Ageratum conyzoides. Phytochemistry 18, 1863–1864.
Blum U 1995 The value of model plant microbe-soil system for understanding processes associated with allelopathic interactions: One example. ACS Symp. Ser. 582, 127–131.
Blum U 1998 Effects of microbial utilization of phenolic acids and their phenolic acid breakdown products on allelopathic interactions. J. Chem. Ecol. 24, 685–708.
Blum U, Worsham A D, King L D and Gerig T M1994 Use of water and EDTA extractions to estimate available (free and reversibly bound) phenolic acids in Cecil soils. J. Chem. Ecol. 20, 341–359.
Bugg R L, Phatak S C and Dutcher J D 1990 Insects associated with cool-season cover crops in southern Georgia: implications for pest control in truck-farm and pecan agroecosystem. Biol. Agric. Hortic. 7, 17–45.
Dalton B R 1989 Physiochemical and biological processes affecting the recovery of exogenously applied ferulic acid from tropical soils. Plant Soil 115, 13–22.
Foy C L 1999 How to make bioassays for allelopathy more relevant to field conditions with particular reference to cropland weeds. In Principle and Practices in Plant Ecology: Allelochemical Interactions. Eds. K MInderjit, M Dakshini and C L Foy. pp 25–33. CRC Press, Boca Raton, FL.
Fye R E 1983 Cover crop manipulation for building pear Psylla (Homoptera: Psyllidae) predator populations in pear orchards. J. Econ. Entomol. 76, 306–310.
Gonzalez A G, Aguiar Z E, Grillo T A, Luis J G, Rivera A and Calle J 1991 Methoxyflavones from Ageratum conyzoides. Phytochemistry 30,1269–1271.
Hassan M S, El-Behadli A H and Alsaadawi I S 1989 Citrus replant problem in Iraq I. Possible role of soil fungi and nematodes. Plant Soil 116, 151–155.
Horie T, Tominaga H and Kawamura Y 1993 Revised structure of a natural flavone from Ageratum conyzoides. Phytochemistry 32, 1078–1077.
House G J and Alzugaray M D R 1989 Influence of cover cropping and no-tillage practices on community composition of soil arthropods in a North Carolina agroecosystem. Environ. Emtomol. 18, 302–307.
Inderjit, Cheng H H and Nishimura H 1999 Plant phenolics and terpenoids: Transformation, degradation and potential for allelopathic interactions. In Principle and Practices in Plant Ecology: Allelochemical Interactions. Eds. K M Inderjit, M Dakshini and C L Foy. pp. 255–266. CRC Press, Boca Raton, FL.
Kasturi T R, Abraham E M and Brown P 1973 Structure of a dimer of ageratochromene. J. Chem. Soc. Perkin I. 2468–2470.
Kong C H, Hu F, Xu T and Lu Y H 1999 Allelopathic potential and chemical constituents of volatile oil from Ageratum conyzoides. J. Chem. Ecol. 25, 2347–2356.
Kong C H, Hu F and Xu X H 2002 Allelopathic potential and chemical constituents of volatile from Ageratum conyzoides under stress. J. Chem. Ecol. 28, 1173–1182.
Lawton J K 1982 Vacant niches and unsaturated communities: A comparison of blacken herbivores at sites on two continents. J. Ecol. 51, 573–595.
Liang W and Huang M 1994 Influence of citrus orchard ground cover plants on arthropod communities in China: A review. Agric. Ecosyst. Environ. 50, 29–37.
Okunade A L 2002 Ageratum conyzoides L. Asteraceae). Fitoterapia 73, 1–16.
Pari K, Rao P J, Subrahmanyam B, Rasthogi J N and Devakumar G 1998 Benzofuran and other constituents of the essential oil of Ageratum conyzoides. Phytochemistry 49, 1385–1388.
Ribeiro O K 1978 A Source Book of the Genus Phytophthora. Strass and Gmbh Press.
Roder W, Phenchanh S and Keoboulapha B 1997 Weeds in slash and burn rice fields in northern Loas. Weed Res. 37, 111–119.
Suzuki Y, Esumi Y, Hyakutake H, Kono Y and Sakurai A 1996 Isolation of 5-(8 Z-heptadecenyl)-resorcinol from etiolated rice seedlings as an antifungal agent. Phytochemistry 41, 1485–1489.
Vyas A V and Mulchandani N B 1986 Polyoxygenated flavones from Ageratum conyzoides. Phytochemistry 25, 2625–2627.
Weidenhamer J D, Hartnett D C and Romeo J T 1989 Density-dependent phytotoxicity: Distinguishing resource competition and allelopathic interference in plants. J. Appl. Ecol. 26, 613–624.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Kong, C., Liang, W., Hu, F. et al. Allelochemicals and their transformations in the Ageratum conyzoides intercropped citrus orchard soils. Plant Soil 264, 149–157 (2004). https://doi.org/10.1023/B:PLSO.0000047759.65133.fa
Issue Date:
DOI: https://doi.org/10.1023/B:PLSO.0000047759.65133.fa