Phytotoxic effect of Sesbania virgata (Cav.) Pers. on seeds of agronomic and forestry species

Sesbania virgata (Cav.) Pers. is a pioneer species native to South America able to release allelochemicals that affect germination and development of other plant species. The aim of this work was to evaluate the allelopathic effect of S. virgata on the germination and development of co-occurring species from gallery forest and on agronomic species. Two forest native species, Enterolobium contortisiliquum (Vell.) Morong and Sapindus saponaria L., and two agronomic species (these as control), Oryza sativa L. and Solanum lycopersicum L. were used in the lab and greenhouse assays with seeds and leaf extracts of S. virgata . Agronomic species were more affected than native species when co-germinated with seeds of S. virgata . The germination percentage and speed germination index of the agronomic species were reduced in both in vitro and greenhouse assays. In the same assays, the seeds of native species showed no significant differences in the parameters mentioned. However, the initial growth of the four species assayed was affected, with reduction in plant length and shoot diameter followed by significant reduction in plantlet shoot and root weights. In the assays with irrigation of S. virgata leaf extracts, no significant inhibitory effects on germination were observed for all species. Height and shoot diameter of the native species were not affected by the leaf extracts, nor were fresh and dry weights. However, these parameters increased in the agronomic species as they were irrigated with leaf extracts. Based on our data we conclude that seed leachates of S. virgata affect germination and seedling development of other species, suggesting that its invasive behavior is due mainly to seed allelochemicals. Although with less pronounced effects on native species, allelopathy of S. virgata might also influence Interspecific competition in its natural environment.