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Valle de La Pascua, Venezuela

Rottboellia cochinchinensis is a major weed and its chemical control is mainly based on the use of the herbicide nicosulfuron; however, there has been a decrease in the effect of the herbicide on the weed which has showed some levels of resistance. In order to perform a metabolic and enzymatic characterization of the resistance of R. cochinchinensis to nicosulfuron, some experiments were conducted to confirm the selected biotype resistance through an analysis of log-logistic regression and determine the resistance index (IR). The study of the resistance nature was done through inhibition tests of the P450 monooxygenases complex by the use of malathion, and in vivo enzymatic assay where acetoin accumulation was measured by colorimetry as an indirect measure of the inhibition of ALS. The dose-response bioassay confirmed the resistance (IR = 3.87). There was no reduction in fresh biomass of resistant plants treated with malathion compared to the untreated ones, indicating that cytochrome P450 monooxygenase isozymes that could be inhibited by malathion were not involved in the degradation of nicosulfuron in this bioassay. With the in vivo enzymatic assay, we demonstrated the insensitivity of the ALS enzyme of the resistant biotype to nicosulfuron, therefore it is concluded that the resistance mechanism of this biotype is in the action site of the herbicide. Source

Gamez A.,INIA Estacion Experimental Valle de la Pascua | De Gouveia M.,INIA Estacion Experimental Valle de la Pascua | Alvarez W.,INIA Estacion Experimental Valle de la Pascua | Perez H.,INIA Estacion Experimental Valle de la Pascua

In order to contribute to the overall knowledge of the vegetation associated with production systems, a study of the diversity of weeds within a conuco type agroecosystem in the community of Santa Rosa de Ceiba Mocha, Infante municipality, Guárico State, Venezuela, was conducted. Sampling was performed using the known framework method in the minimum sampling area. In 15 sampling points, a 0.25 m2 metallic frame was launched at random, and the enclosed weeds were counted, stored and pooled. Population parameters of the weeds such as density, frequency and dominance, were calculated; the importance value index (IVI) was also determined. Twenty-four weed species in 14 botanical families were found. Poaceae was the most represented family with five species, followed with Asteraceae with three species. Species with the highest density were Cyanthillium cinereum, Bidens pilosa and Lindernia crustacea, with values of 216, 209 and 90.67 plants·m-2. The most frequent species were L. crustacea and Digitaria sanguinalis with values 90 and 80%, respectively. The highest values of dominance were reported for the species B. pilosa, L. crustacea and D. sanguinalis, with 24.08, 23.50 and 13.59%, respectively. Likewise, the species with the highest importance value index (IVI) were B. pilosa (0.50), L. crustacea (0.45), D. sanguinalis (0.31), and C. cinereum (0.28). Biodiversity of weeds present in this type of production systems was evident. © 2014 Universidad Centroccidental Lisandro Alvarado (UCLA). All rights reserved. Source

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