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Population dynamics of Parthenium hysterophorus (Asteraceae) and its biological suppression through Cassia occidentalis (Caesalpiniaceae)

Phytosociological analysis performed over 2005 to 2009 revealed that Cassia occidentalis L. is a dominant species at 3 of 4 sites in Agra district, India, that were previously observed to be dominated by heavy populations of Parthenium hysterophorus L. | J. KNOX, D. JAGGI, M. S. PAUL Research Article Turk J Bot 35 (2011) 111-119 © TÜBİTAK doi:10.3906/bot-1001-275 Population dynamics of Parthenium hysterophorus (Asteraceae) and its biological suppression through Cassia occidentalis (Caesalpiniaceae) Jai KNOX*, Disha JAGGI, Manoj Stephen PAUL Department of Botany, St. John’s College, 282002 Agra - INDIA Received: 06.01.2010 Accepted: 01.11.2010 Abstract: Phytosociological analysis performed over 2005 to 2009 revealed that Cassia occidentalis L. is a dominant species at 3 of 4 sites in Agra district, India, that were previously observed to be dominated by heavy populations of Parthenium hysterophorus L. In order to determine the role of biomolecular interaction, i.e. the allelopathic effect, if any, on this shift of floral pattern effects, aqueous shoot and root cold leachates were determined on seed germination, shoot cut bioassay, seedling bioassay, chlorophyll, nitrogen, and protein content of P. hysterophorus. A significant reduction in germination percentage, shoot cut bioassay, seedling bioassay, and chlorophyll of P. hysterophorus was noticed at higher concentration of shoot leachates. Root leachates of 100% concentration of C. occidentalis obtained after 9 days were responsible for the maximum inhibition of nitrogen percentage and protein content of Parthenium, indicating that biomolecular interaction plays a significant role in curbing the population dynamics of this obnoxious weed with enormous seed production potential. Key words: Allelopathy, bioassay, botanic agent, chlorophyll, invasive species, nitrogen, phytosociology, protein Introduction In weed biological control programmes, evaluations of the effectiveness of biological control agents are often focused on the subjective assessment (Crawley, 1989) of the performance of biocontrol agents or on effects at a plant level (McClay, 1995). Parthenium hysterophorus L. (Asteraceae) is an annual herb of neotropical origin that now has a pantropical .