Production of allelopathic glycosidic resins in seeds and early development stages of Ipomoea tricolor L. (Convolvulaceae)

We analysed the production of phytotoxic glycosidic resins and tricolorin A in seeds and seven early development stages of Ipomoea tricolor (Convolvulaceae). We performed in vitro bioassays to test (i). the bioactivity of I. tricolor aqueous leachates (15%) (1% for whole and ground seeds) and organic extracts (100 μg ml⁻¹) from fresh cotyledons, true leaves, stems and roots from the seven stages of development, and (ii). the bioactivity of organic extracts of ground seeds and pure tricolorin A (isolated from the seeds) at 4 concentrations on 3 plants (amaranth, barnyard grass and tomato) and 4 phytopathogenic microorganisms (Fusarium oxysporum, Alternaria solani, Phytophtora parasitica and P. capsici). Fresh stems and roots aqueous leachates (15%) of I. tricolor and cotyledons and true leaves organic extracts (100 μg ml⁻¹) were the most phytotoxic treatments. Aqueous leachate of ground seeds (1%) of I. tricolor significantly inhibited the root growth of amaranth and tomato with no effect on barnyard grass. Organic extracts of ground seeds of I. tricolor (250 and 500 μg ml⁻¹) significantly inhibited the radial growth of Fusarium and Alternaria. Tricolorin A significantly inhibited the growth of almost all phytopathogenic microorganisms at the 4 concentrations used. Tricolorin A was more fungitoxic than Captan (commercial fungicide) on the radial growth of A. solani. This is the first report of the isolation of Tricolorin A from I. tricolor seeds, showing that it is one of the main allelopathic compounds in seedlings and young plants.