Antonio Pedro da Silva Souza Filho

Dormancy overcoming methods of weed seeds from amazonian cultivated pasture

O objetivo do presente trabalho foi o de avaliar diferentes metodos de superacao da dormencia de sementes de plantas daninhas de areas de pastagens cultivadas da regiao amazonica brasileira. Foram estudados os metodos escarificacao termica em agua a temperatura de 80oC por 4, 8 e 12 minutos, escarificacao quimica em acido sulfurico por 5, 10, 15 e 20 minutos e nitrato de potassio nas concentracoes de 0,1; 0,2 e 0,3%. As sementes, cuja dormencia nao foi superada por esses metodos, foram colocadas para germinar na presenca de cinetina (20, 40, 60 e 80 ppm) e de giberelina (150, 300, 450 e 600 ppm). A germinacao foi monitorada em periodos de 15 dias, com contagem diaria e eliminacao das sementes germinadas. A escarificacao termica em agua nao se mostrou satisfatoria, tendo havido, para a maioria das especies, reducao da germinacao em relacao ao tratamento testemunha. O acido sulfurico foi eficiente para superar a dormencia das sementes de todas as especies, havendo, no entanto, variacoes com relacao ao tempo de imersao. O nitrato de potassio afetou positivamente a germinacao das sementes de fedegoso, de rinchao e, mais expressivamente, de Hyptis mutabilis. As sementes de jurubebao responderam, positivamente, apenas aos diferentes niveis de giberelina, atingindo valor superior de germinacao na concentracao de 600 ppm.

Potencial alelopático de forrageiras tropicais: efeitos sobre invasoras de pastagens

Aqueous extracts from seeds, aerial part and roots of grasses Brachiaria humidicola, Brachiaria decumbens and Brachiaria brizantha cv. Marandu and legumes forage Calopogonium mucunoides and Stylosant hes guianensi s cv. Mineirao were prepared in a concentration of 10% (w/v), to evaluate the allelopathic potential effects on seed germination and radicle elongation of the pasture weeds: Desmodium adscendens, Sida rhombifolia and Vernonia polyanthes. Seed germination was monitored in ten-day periods, with daily countand elimination of seed germination. At the end of the ten-day periods the radicle was measure d. The osmot ic potential effects were isolated by calculation. The donor species showed allelopathic potential that varied in function of donor and receiver species. Brachiaria brizantha and among grasses and Calopogonium mucunoides among legumes were the species that promoted the reduction more intensively on seed germination and radicle elongation of the receiver species. The aerial part of the donor species was the main source of water soluble allelopathic potential compounds. Independently of the donor species, D. adscendens and S. rhombifolia were the weeds with the greatest sensibility to allelopathic potencial effects from donor species, while V. polyanthes showed more tolerance.

Chemical constituents and allelopathic and antioxidant activities of Alchorneopsis floribunda Müll. Arg. (Euphorbiaceae)

Chemical investigation of extracts from the stems and leaves of Alchorneopsis floribunda Müll. Arg., collected in the Amazon region, was performed. The main isolated compounds were triterpenes (α-amyrin, β-amyrin, lupeol, betulin, betulinic acid, uvaol, erythrodiol and oleanolic acid) and phenolic acid derivatives from 4-hydroxybenzoic acid (gallic and protocatechuic acids and isocorilagin). In the germination assays, high inhibitory allelopathic effects of the extracts and isocorilagin were observed and 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity of isocorilagin was higher than those of the standards used (Trolox and butylated hydroxyanisole). This is the first chemical study of the genus Alchorneopsis (Euphorbiaceae).

Allelopathy: driving mechanisms governing its activity in agriculture

ABSTRACT Allelopathy determines the dynamics of plant species in different environments. Understanding this biological phenomenon could help to develop applications in both natural and agricultural systems. This review summarizes the genetic and environmental characteristics that control the production and release of allelochemicals in agroecosystems. This study highlights the current understanding of the environmental changes caused by allelochemicals and summarizes the knowledge about the mechanisms of action of these compounds. Finally, it reviews novel applications of allelopathy in agricultural production systems, including the role of allelochemicals in consortia and their potential use in no-tillage cropping systems through cover crops or mulches.

Efeitos de diferentes substratos e da profundidade de semeadura na germinação de sementes de mata-pasto e malva

As flutuacoes na germinacao de sementes no campo sao governadas por um conjunto de fatores ambientais. No presente trabalho sao analisados os efeitos do pH, da salinidade e do aluminio sobre a germinacao de sementes, e da profundidade de semeadura sobre a taxa de emergencia de plântulas das invasoras de pastagens mata-pasto (Cassia tora) e malva (Urena lobata). A excecao dos estudos de profundidade de semeadura, que foram realizados em casa de vegetacao, os demais foram realizados em laboratorio. A germinacao e a taxa de emergencia de plântulas foram monitoradas em periodos de 15 e 20 dias, respectivamente. Os resultados obtidos mostraram que o pH na faixa de 3 a 11 e a concentracao de aluminio de 0 a 2,0 meq/100 ml nao afetaram a germinacao das sementes das duas invasoras. Mata-pasto e malva responderam similarmente a salinidade ate o nivel de 150 mM. Entretanto, para a concentracao de 300 mM, malva foi mais tolerante a salinidade do que o mata-pasto, cujas sementes nao germinaram nesta concentracao do sal. A relacao entre taxa de emergencia de plântulas e profundidade de semeadura foi quadratica para ambas as especies. Mata-pasto, entretanto, evidenciou maior capacidade para emergir da profundidade de 8 cm do que a malva, que apresentou taxa de emergencia zero, quando semeada nesta profundidade.

Plantas daninhas de uma pastagem cultivada de baixa produtividade no Nordeste Paraense

Presently there are 23 million hectares of cultivated pasture in forest ecosystem of the Amazon Region. From that area, 5 million hectares are low yield or in some stage of degradation and invaded by weeds. Aiming to identify the weed species that occur in degraded pastures of Terra Alta, state of Para (0o 58” S e 47o 52” W. Gr. ), a botanical survey was carried out, colleting samples of all weed species presents in the area. Thirty-four families were recorded represented by 118 species, being Leguminosae, Gramineae, Malvaceae, Myrtaceae, Cyperaceae and Asteraceae the most important families with 21, 16, 8, 7, 6 and 6 species respectively. The most important weed species were: Borreira verticillata, Rolandra argentea, Desmodium canum, Davilla rugosa, Vismia guianensis e Imperata brasiliensis.

Allelopathic Potential and Systematic Evaluation of Organic Extracts from Canavalia ensiformis Leaves (Jack Beans)

Abstract This article describes the assessment of possible allelopathic potential of organic extracts obtained from leaves of Canavalia ensiformis under laboratory conditions. Furthermore, a systematic evaluation of these extracts was carried out using specific protocols developed in capillary electrophoresis (CE) to determine some groups of secondary metabolites. After the identification and quantification of compounds, the effects of compounds on germination of some common weeds was investigated, which are becoming a real problem in pastures in the state of Pará, Brazil.This article describes the assessment of possible allelopathic potential of organic extracts obtained from leaves of Canavalia ensiformis under laboratory conditions. Furthermore, a systematic evaluation of these extracts was carried out using specific protocols developed in capillary electrophoresis (CE) to determine some groups of secondary metabolites. After the identification and quantification of compounds, the effects of compounds on germination of some common weeds was investigated, which are becoming a real problem in pastures in the state of Pará, Brazil.

Chemical investigation of Cyperus distans L. and inhibitory activity of scabequinone in seed germination and seedling growth bioassays

Chemical investigation of the rhizomes of Cyperus distans (Cyperaceae) led to the identification of α-ciperone, cyperotundone and scabequinone, besides other common constituents. Complete assignment of the 13C NMR data of scabequinone is being published for the first time. The inhibitory effects of C. distans extracts and scabequinone on the seed germination and seedling growth of Mimosa pudica, Senna obtusifolia and Pueraria phaseoloides were evaluated. Seed germination inhibition bioassay revealed that S. obtusifolia (52–53%) was more sensitive to the hexane and the methanol extracts at 1% than M. pudica (0–10%). Scabequinone at 250 mg L–1 displayed seed germination inhibitions more than 50% and radicle growth reduction of more than 35% of the test species S. obtusifolia and P. phaseoloides, while the hypocotyl growth of M. pudica was significantly affected (>50%) by the quinone at the same concentration. These results demonstrate that scabequinone contributes to the overall inhibitory activities of C. distans.

Essential Oil Components of Pogostemon heyneanus Benth, Piper hispidinervum C. DC. and Ocimum americanum L. Obtained in the Amazon

Abstract The study aimed to characterize the essential oil components of leaves and twigs of Pogostemon heyneanus Benth, Piper hispidinervum C. DC. and Ocimum americanum L. collected around the city of Belém, Pará. The essential oils were obtained by hydrodistillation and analyzed by gas chromatography coupled to a mass spectrometer. The main components identified in the essential oils were patchouli alcohol 21.9 % (Pogostemon heyneanus Benth), safrole 64.3 % (Piper hispidinervum C. DC.) and limonene 24 % (Ocimum americanum L.).

Phytotoxic activity of compounds from Moutabea guianensis aubl. on Amazonian invasive species

This study aimed establish the variations in the phytotoxic activity of hexane, ethyl acetate and methanol extracts of Moutabea guianensis, and methyl caffeate and scopoletin isolated from the ethyl acetate extract, variyng the concentration and the receptor species. Phytotoxic activity bioassays of germination (at 25 °C and 12 hours of photoperiod) and development of radicle and hypocotyl (25 °C and 24 hours of photoperiod) were developed. The seed germination of Mimosa pudica was sensitive to the roots hexane, ethyl acetate and methanol extracts at 1% (w/v), with inhibition potentials in 92%, 100% and 100%, respectively. Comparative analysis on the phytotoxic activity of the tested compounds revealed that scopoletin showed a higher inhibition potential on the seed germination bioassay against Mimosa pudica. Senna obtusifolia was not sensitive to the tested compounds. Methyl caffeate showed the highest potential to inhibit the development of radicle and hypocotyls, and the intensity of the allelopathic effects varied with the concentrations.