Abstract This study aimed to evaluate the phytotoxic activity of aqueous extracts of species from the Cerrado of Mato Grosso on the germination and initial development of lettuce seedlings, as well as to determine the chemical composition of the extracts. The species studied were: Davilla elliptica, Combretum laxum, Himatanthus obovatus, Diteryx alata, Curatella americana, Qualea grandiflora, Aspidosperma macrocarpon, Caryocar brasiliense, Pleroma candolleanum and Miconia albicans. Fourier Transform Infrared Spectroscopy (FTIR) and Thin Layer Chromatography (TLC) techniques were used to identify functional groups and chemical compounds. The extracts of the species D. elliptica, C. laxum, C. brasiliense and Q. grandiflora showed greater phytotoxic activity on the germination of lettuce seeds which varied between 96 and 17%. The presence of compounds such as: phenols, alkaloids, flavonoids and terpenes with phytotoxic properties was confirmed.

The evaluations of Chorophyll a fluorescence emitted by superior plants carry structural information and photosynthetic apparatus function. Quantitative analysis apparatus of fluorescence kinetic were measured by energy flows (ABS), (TR), (ET) and (DI), known as phenomenological phenomena of OJIP test. Four furocoumarins were isolated from Ruta graveolens (Rutaceae), and chorophyll a (Chl a) fluorescence assays were performed with these compounds to evaluate the photosynthesis inhibition potential. This test was realized in spinach`s leaf discs and in Lolium perenne leaves. The results indicated the herbicide potential mainly for bergapten and chalepin.