Treatment of rice seeds with thiamethoxam: refections on physiological performance 1 Andreia da Silva Almeida 2 , Cristiane Deuner 2 , Carolina Terra Borges 2 *, Géri Eduardo Meneghello 2 , Adilson Jauer 3 , Francisco Amaral Villela 2 ABSTRACT - Thiamethoxam is a systemic insecticide that is transported within the plant through its cells and can activate various physiological reactions such as protein expression. These proteins interact with defense mechanisms against stress in adverse growing conditions. The objective of this study was to evaluate the effect of thiamethoxam in rice seeds and the potential benefts that it can provide. Two experiments were carried out and, in both, seeds were treated with commercial product containing 350 g of thiamethoxam active ingredient per liter of product, at doses 0, 100, 200, 300 and 400 mL.100 kg -1 of seeds: 1) it was conducted with three lots of IRGA BR 424 cultivar rice seeds, which were submitted to the following laboratory tests: germination, cold test, accelerated aging test, as well as feld assessment: total seedling length, root system length, number of panicles and productivity; 2) four lots of IRGA BR 424 cultivar rice seeds, two high and two low-vigor, were subjected to the following tests: germination, cold test and greenhouse seedling emergence test. Thiamethoxam rice seed treatment positively favors the seed quality. Index terms: Oryza sativa, bioactivator, vigor. Potencial fsiológico de sementes de arroz tratadas com tiametoxam RESUMO - O tiametoxam é um inseticida sistêmico que é transportado dentro da planta através de suas células e pode ativar várias reações fsiológicas como a expressão de proteínas. Estas proteínas interagem com mecanismos de defesa a estresses em condições adversas de cultivo. O objetivo deste trabalho foi avaliar o efeito do tiametoxam em sementes de arroz e os potenciais benefícios que o tratamento possa proporcionar. Foram realizados dois experimentos, sendo em ambos as sementes tratadas com produto comercial contendo 350 gramas de ingrediente ativo de tiametoxam por litro nas concentrações de 0, 100, 200, 300 e 400 mL.100 kg -1 de sementes: 1) realizado com três lotes de sementes de arroz, da cultivar IRGA BR 424, as quais foram submetidas a testes no laboratório: germinação, teste de frio, envelhecimento acelerado, e avaliações à campo: comprimento total de plântula e radicular, número de panículas e produtividade; 2) utilizados quatro lotes de sementes da cultivar IRGA BR 424, sendo dois de alto vigor e dois de baixo, submetidos aos seguintes testes: germinação, teste de frio e emergência em casa de vegetação. O tratamento de sementes de arroz com tiametoxam favorece o desempenho ou potencial fsiológico das sementes. Termos para indexação: Oryza sativa, bioativador, vigor. 1 Submitted on 03/06/2014. Accepted for publication on 05/29/2014. 2 Departamento de Fitotecnia, UFPel, Caixa Postal 354, 96010-900 - Capão do Leão, RS, Brasil. 3 Syngenta Proteção de Cultivos LTDA, 86010-020 - Londrina, PR, Brasil. *Corresponding author <carol_tborges@hotmail.com> Introduction In Brazil, rice is the third most important agricultural product after soybeans and corn (Mielezrski et al., 2008), and the State of Rio Grande do Sul is the largest producer with 1,0666 million hectares, representing 44.5% of the national territory and 67.0% of Brazilian production (CONAB, 2013). A set of techniques contribute towards achieving this productivity, among them, the use of agrochemicals such as fungicides, herbicides and insecticides. However, some insecticides may induce effects that are still unknown, modifying plant metabolism and morphology, with particular reference to physiological and morphological changes in plants caused by carbofuran (Freitas et al., 2001) and 458 Journal of Seed Science, v.36, n.4, p.458-464, 2014 RESEARCH NOTE http://dx.doi.org/10.1590/2317-1545v36n4980