A study of the phytotoxic effects of the aerial parts of Senecio westermanii Dusén (Asteraceae) on Lactuca sativa L. and Allium cepa L. seeds

The objective of this study was to evaluate the effects of the ethanolic crude extracts and fractions of the species Senecio westermanii Dusén on Lactuca sativa L. (lettuce) and Allium cepa L. (onion) seeds. We assessed the germination, growth, root respiration and photosynthesis of the target species in Petri dishes (9.0 cm diameter) containing filter paper n°6. The study was conducted using 50 seeds per plate and held in 4 replicates per concentration of each sample. In the germination there was an inhibitory effect of fractions hexane (FH) and chloroform (FCl) at concentrations of 500 and 1000 µg/mL. There was a reduction in the radicle growth of lettuce by 14 to 24% and a reduction of hypocotilum by 14 to 28%. As for the radicle of the onion was up 74% reduction to the FCl and the coleoptile was 24 and 45% reduction for FH and FCl, respectively. Inhibitory effects in the root respiration of lettuce were detected in all the samples analyzed, with results ranging from 16 to 83%. For the seeds of A. cepa, there was an encouragement for the FCl and ethyl acetate fractions (FAE), with results ranging from 94 to 142% and 76 to 150%, respectively. With regard to the photosynthesis of L. sativa, there was no significant difference between the control, and as for the A. cepa, there was a strain in inhibition concentrations of 250 and 500 µg/mL, which ranged from 27 to 68%. The samples of S. westermanii caused changes in the target species and thus can be used as a natural herbicide.

Estudio taxonómico del grupo de especies Solanum confine de la sección Geminata (solanaceae) / Taxonomic study of the group of species Solanum confine of the section Geminata (Solanaceae)

La Sección Geminata es una de las más grandes del género Solanum, incluyendo un total de 126 especies que han sido separadas en 16 grupos, de los cuales 12 están representados en Venezuela con 35 especies. El objetivo de este trabajo fue hacer la revisión taxonómica de las especies S. capillipes, S. dissimile, S. erosomarginatum, S. ombrophilum y S. tenuiflagellatum pertenecientes al Grupo de Especies Solanum confine y presentes en Venezuela. Se utilizó material fresco y de los herbarios HERZU, MER, MERF, MO, MY, PORT, US y VEN, procesado para su estudio según las técnicas taxonómicas convencionales. Se incluye descripción, distribución geográfica, hábitat e ilustración de cada una de las especies, asimismo se ofrece una clave para las especies registradas.

The Section Geminata is one of the biggest of the genus Solanum, including a total of 126 species that have beenseparated in 16 groups of which 12 are represented in Venezuela with 35 species. The objective of this work was to make the taxonomic revision of the species S. capillipes, S. dissimile, S. erosomarginatum, S. ombrophilum and S. tenuiflagellatum belonging to the Group of Species Solanum confine and present in Venezuela. Fresh material was used and dried belonging to the herbaria HERZU, MER, MERF, MO, MY, PORT, US and VEN, processed for its study according to the taxonomic conventional technical. Description, geographical distribution, habitat and illustration of each one of the species is included, also a key for the registered species.