Abstract Background: Other tools for weed management should be considered in addition to the use of herbicides. In this context, the identification and use of allelopathic compounds deserves attention. Question: To quantify phenolic compounds and evaluate the allelopathic potential of extracts of Conyza sumatrensis on the germination of Bidens pilosa. Studied species: Conyza sumatrensis (Retz.) E.Walker, Bidens pilosa L. (Asteraceae) Study site: Palotina, state of Paraná, Brazil. Methods: The aqueous extracts were prepared with shoot and root portions of C. sumatrensis in concentrations: 0, 1, 5 and 10 %. Germination and germination speed index were evaluated. The total flavonoids and phenols of the tested extracts were also quantified. Results: With increasing concentrations of the extracts there was an increased inhibition of germination of B. pilosa and delays in the germination process. The extracts from the shoot of C. sumatrensis had a more expressive effect on seed germination when compared to the extracts obtained from the root. At concentration of 10 %, the extract from the shoot reduced in 83 % the percentage of germination. This may be related to the higher concentration of total flavonoids and phenols found. Conclusion: The allelopathic potential of C. sumatrensis plants can be considered since both shoot and root extracts inhibited and/or reduced the germination of B. pilosa.

Resumen Antecedentes: Se deben considerar otras herramientas para el manejo de malezas además del uso de herbicidas. En este contexto, la identificación y el uso de compuestos alelopáticos merece atención. Problema: Cuantificar compuestos fenólicos y evaluar el potencial alelopático de extractos de Conyza sumatrensis en la germinación de Bidens pilosa. Especies de estudio: Conyza sumatrensis (Retz.) E.Walker, Bidens pilosa L. (Asteraceae) Sitio de estudio: Palotina, estado de Paraná, Brasil. Métodos: Los extractos acuosos se prepararon con porciones de brotes y raíces de C. sumatrensis en concentraciones: 0, 1, 5 y 10 %. Se evaluaron la germinación y el índice de velocidad de germinación. También se cuantificaron los flavonoides y fenoles totales de los extractos probados. Resultados: Con el aumento de las concentraciones de los extractos hubo una mayor inhibición de la germinación de B. pilosa y retrasos en el proceso de germinación. Los extractos del brote de C. sumatrensis tuvieron un efecto más expresivo sobre la germinación de las semillas en comparación con los extractos obtenidos de la raíz. En la concentración de 10 %, el extracto del brote redujo en 83 % el porcentaje de germinación. Esto puede estar relacionado con la mayor concentración de flavonoides y fenoles totales encontrados. Conclusión: El potencial alelopático de las plantas de C. sumatrensis puede considerarse ya que tanto los extractos de brotes como los de raíz inhibieron y/o redujeron la germinación de B. pilosa.

A resistência ao glifosato é conferida à soja (Glycine max L. Merrill) pela incorporação de um gene que codifica a enzima CP4-EPSP sintase, uma variante da EPSP sintase, insensível ao glifosato, que atua na via do chiquimato/corismato, importante rota metabólica envolvida na lignificação. O objetivo deste trabalho foi o de investigar o crescimento e os teores de lignina nas raízes de cultivares de soja, suscetíveis (CD 201 e OC 14) e resistentes (CD 214RR e CD 213RR) ao glifosato. Para isso, plântulas com três dias de desenvolvimento foram cultivadas em solução nutritiva de Hoagland, meia-força (pH 6,0), em câmara de crescimento (25°C, fotoperíodo de 12 h, irradiância de 280 μmol m-2 s-1) de 24 a 96h. Os resultados revelaram que as cultivares resistentes ao glifosato (CD 213RR e CD 214RR) apresentaram elevado crescimento das raízes quando comparadas com as cultivares convencionais (OC-14 e CD 201). A cultivar CD 213RR apresentou altos teores de lignina e reduzido crescimento das raízes em comparação com a cultivar convencional (OC 14). O mesmo não foi observado nas cultivares CD 214RR e CD 201. Com base nos resultados, é possível concluir que (1) uma forma diferente de EPSP sintase pode interferir na via de fenilpropanoides e, posteriormente, na síntese de lignina, e (2) outras características genéticas inerentes a cada cultivar pode afetar os conteúdos de lignina nas raízes, haja vista que a lignificação na cultivar CD 214RR não foi afetada de similar maneira que na cultivar CD 213RR.

Glyphosate resistance is conferred to soybean (Glycine max L. Merril) by incorporating a gene encoding a glyphosate-insensitive enzyme (CP4-EPSP synthase) that acts in the shikimate/chorismate pathway, an important metabolic route in the lignification process. The aim of this work was to investigate the root growth and lignin contents of susceptible (CD 201 and OC 14) and glyphosate-resistant (CD 214RR and CD 213RR) soybean cultivars. To this end, three-day-old seedlings were cultivated in half-strength Hoagland nutrient solution (pH 6.0) in a growth chamber (25°C, 12-h photoperiod, irradiance of 280 μmol m-2 s-1) for 24 to 96 hours. The results revealed that glyphosate-resistant (CD 213RR and CD 214RR) cultivars showed high root growth when compared to the conventional (OC-14 and CD 201) cultivars. CD 213RR showed high root lignin content and reduced root weight compared to the conventional (OC 14) cultivar, although CD 214RR and CD 201 did not follow the same trend. Based on these results, it is possible to conclude that (1) the different form of EPSP synthase encoded in RR soybean may interfere in phenylpropanoid pathway and further in lignin biosynthesis, and (2) other genetic characteristics inherent to each cultivar may affect roots lignin content in soybean seedlings since lignification in CD 214 RR was not affected of similar manner than cultivar CD 213 RR.