Phytotoxicity of glycosylated flavonols extracted from Annona coriacea (Annonaceae) on germination and initial growth of standard target species and an invasive grass

Abstract

Annona coriacea Mart. is a Brazilian native species whose phytotoxicity was described, although there is no data about the compounds responsible for it. The aim of this study was bioprospecting A. coriacea in relation to phytotoxicity on the elongation of wheat coleoptiles and on germination of diaspores and initial growth of seedlings of standard target species (lettuce and tomato) and a weed (Urochloa decumbens (Stapf) R.D. Webster). For that, ethanolic extract of of A. coriacea was fractionated affording 9 fractions, which were assayed on elongation wheat coleoptiles. Group G showed the highest inhibitory results and thus, was subjected to chromatographic separation furnishing the isolation of 11 flavonols: 1—Quercetin-3-O-gentiobioside, 2—Quercetin-3-O-robinobioside, 3—Rutin, 4—Hyperin, 5—Isoquercitrin, 6—Biorobin, 7—Nicotiflorin, 8—Keioside, 9—Narcissin, 10—Cacticin and 11—Isorhamnetin-3-O-glucoside. This is the first report of wheat coleoptile bioassay to all these compounds and it is also the first phytotoxicity results for 1, 2, 6, 8 and 10. Compounds 5, 7 and 11 showed elevated phytotoxicity in wheat coleoptiles bioassay (IC50 0.22 mM, r² 0.97; IC50 0.48 mM, r² 0.93; IC50 0.28 mM, r² 0.92, respectively). No correlation was found between the structure of the compounds and their activity. Compounds 5 and 11 were therefore tested on lettuce, tomato and U. decumbens germination and initial growth of seedlings. They did not show phytotoxic effects on lettuce and tomato. By the other hand, compound 11 significantly reduced the germination of U. decumbens in almost all concentrations, with values between 50 and 65%, demonstrating its importance to studies focused on weed control. The higher structural complexity of diaspores, when compared to wheat coleoptile, is suggested as a possible explanation for stronger inhibitory effects of isolated flavonoids on coleoptile elongation, than on germination/initial growth assays.