GC-MS and SPME-GC/MS Analysis and Bioactive Potential Evaluation of Essential Oils from Two Viola Species Belonging to the V. calcarata Complex

Viola calcarata L. and Viola dubyana Burnat ex Gremli belong to the V. calcarata complex in Viola section Melanium (Violaceae family). For the first time, the essential oils (EOS) obtained by hydrodistillation from dried flowers, were analyzed by GC/MS and SPME-GC/MS to describe their volatile chemical profile. Differences in the qualitative and quantitative composition between the two violets have been found. A total of 43 compounds were identified among which methyl salicylate was the most abundant (from 45.5 to 68.0%) both in the vapor and liquid phase. The performed bioactivity tests pointed out the greater effect of V. dubyana EO compared to that obtained from V. calcarata. Nevertheless, both EOs proved to be good scavengers, especially toward the ABTS⋅+ radical. They also showed a dose-dependent phytotoxic action against Sinapis alba and Lolium multiflorum. Their seed germination was inhibited up to 100% and 25%, respectively, in response to the highest used dose (100 μL) of each EO. Furthermore, a significant decrease in root and shoot length was observed. The resulting seedling vigor index was reduced by 15–100% and 8–82% for S. alba and by 11–91% and 4–91% for L. multiflorum by V. dubyana and V. calcarata EOS, respectively.