Bioactive terpenes from Tagetes minuta L. on seed germination

M. L. LÓPEZ; J. A. ZYGADLO

Curitiba, Brasil

Congreso; I Encontro Brasilero de Ecologia Química; 1999

Tagetes minuta L. is an Asteraceae native from the temperate grasslands and montagne regions of southern South America. It is often found growing in recent disturbed areas as side of roads and abandoned sites. Sometimes it is referred as a weed. There is bibliography about secondary compounds from weeds that are released to the environment by different ways. The presence of such compounds in the field can interfere with other neighbour plants within a community (allelopathy). The essential oil from Tagetes minuta L. is very rich in terpenes. What kind of role plays these terpenes in the establishment or colonization of the plant? could it be an allelopathic role? The objective of this work was to evaluate the phytotoxic potential of terpenes from Tagetes minuta L. on germination. Plant material on flowering stage was collected in the Sierras de Córdoba, Argentina and hydrodistilled in a Clevenger apparatus. The essential oil obtained was primarily tested on a TLC-agar plate bioassay. The fraction on TLC that was bioactive from the bioassay, was studied by gas liquid chromatography and spectrometry mass (GC-MS). An enough amount of the bioactive fraction was recuperated from TLC to test its activity on seed germination. Different concentrations of the fraction were mixed with 10 ml of agar 0.5% and 20 seed of Medicago sativa L. (Alfalfa) and Raphanus sativus L. (Radish) were sown on Petri dishes. Seeds were keep in a growth chamber at 27 C in darkness by 48 h. Percentage of germination was evaluated in relation to control (0 ul). Germination bioassays were repeated four times. Data were analyzed by one way ANOCVA and LSD test. The TLC-Agar plate bioassay showed only one fraction from the essential oil that was bioactive against germination. The identification and quantification of the compounds present in the fraction, revealed us that the bioactive fraction is constituted mainly by oxygenated terpenes, with important amounts of ocimenones (Z-E), and lowers quantities of tagetones (cis-trans), dihydrotagetones, and other oxygenated compounds. Bioassay on seed germination showed marked differences in relation to control. Quantities a 10 an 15 ul were very aggressive against germination since the percentage of germination was zero in both species tested.