ABSTRACT(Allelopathic activity of Hovenia dulcis Th unb. (Rhamnaceae) leaves and pseudofruits on the germination of Lactuca sativa L. (Asteraceae)). Th is paper aims to evaluate the allelopathic eff ect of dry leaves and pseudofruits of Hovenia dulcis Th unb. on lettuce seeds. Th erefore, aqueous extracts of leaves and pseudofruits were prepared in 1%, 2% and 4% (m/v) concentrations. Four replicates were done of 25 lettuce seeds distributed in Petri dishes lined with Germitest paper and humidifi ed with the extracts, maintained in germination chamber at 25 °C, constant photoperiod and light presence for fi ve days, the control being distilled water. Th e percentage, speed, germination rate index, root length and aerial-part length of the seedlings were calculated, as well as the seeds eff ect in the presence of diff erent pH solutions. It was observed that the seedlings were signifi cantly aff ected in the presence of aqueous extracts of dry leaves and pseudofruits at 2% and 4% concentrations. Th e eff ects were not linked to pH and osmotic potential, indicating, therefore, allelopathic interference of Hovenia dulcis extracts.

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Sourgrass (Digitaria insularis L.) and fleabane (Conyza spp. L.) constitute a major challenge to weed management in soybean [Glycine max (L.) Merr.] production systems in Brazil, especially when both are resistant to glyphosate and present concurrently. The aim of this study was to evaluate the interaction of haloxyfop-P-methyl [methyl(R)-2{4-{3-chloro-5(trifluoromethyl)-2-pyridyloxy] phenoxy} propanoate] and 2,4-D [2,4-Dichlorophenoxyacetic acid-N-methylmethanamine] to control sourgrass at three to four tillers and flowering stages and 12-to 15-cm fleabane at vegetative stage. The experiments were arranged in a randomized complete block design with four replicates and were conducted twice. Treatments were composed of haloxyfop-P-methyl and 2,4-D applied sequentially at 3-, 6-, and 12-d intervals.Treatments also included an untreated check, haloxyfop-P-methyl, and 2,4-D sequentially (without interval) and stand-alone applications of both herbicides. All treatments across experiments completely controlled fleabane plants, except haloxyfop-P-methyl alone. Haloxyfop-P-methyl applied ≥6 d before 2,4-D controlled flowering and three-to four-tiller sourgrass plants at rates of 50 and 100%, respectively. Based on results of this study, haloxyfop-P-methyl should be applied ≥6 d before 2,4-D in a sequential application structure to control fleabane and sourgrass (three or four tillers) when present concurrently.

In this work, we compared nitrate-supplied plants (non-nodulated) with non-nitratesupplied plants (nodulated) under oxygen privation of root system (hypoxia) and re-oxygenation (post-hypoxia; recovery) in order to verify whether N sources affect the antioxidant system during oxidative stress caused by hypoxia and post-hypoxia conditions. Antioxidant enzymatic activities, ascorbate redox state, and reactive oxygen species (ROS) levels were analyzed in roots and leaves of two soybean genotypes, Fundacep 53 RR and BRS Macota at reproductive stage R2, during hypoxia and post-hypoxia in an experiment carried out in a hydroponic system. The antioxidant system was strongly induced in roots of nitrate-supplied plants of both genotypes, with high activity of superoxide dismutase, ascorbate peroxidase, catalase, glutathione reductase and guayacol peroxidase. It also increased reduced ascorbate and ascorbate redox state and decreased ROS production under hypoxia and recovery, while in leaves of nodulated and non-nodulated plants, a slight increase on antioxidant system was observed. Nitrate may benefit soybean plants under hypoxic conditions and subsequent re-oxygenation by inducing the antioxidant system mainly in roots to cope with ROS production and reduce oxidative damage.