A cultura do feijão, no Brasil, ocupa, aproximadamente, 4 milhões de hectares, onde se obtém produtividade média de 882 kg ha -1 (Conab 2009). Isto ocorre devido, principalmente, a fatores que limitam a produtividade da cultura, como o uso de sementes de baixa qualidade, uso reduzido de insumos e controle inadequado de pragas, doenças e plantas daninhas, além do fato de os cultivos estarem concentrados, na maioria das vezes, nas mãos de ABSTRACT RESUMOprodutores que utilizam baixo nível de tecnologia (Araújo et al. 1996). Dentro deste contexto, surge a necessidade de adoção de práticas culturais que possibilitem melhorias no sistema de produção e que resultem em maiores produtividades, como, por exemplo, o manejo correto de fertilizantes, corretivos do solo e demais insumos. O feijoeiro é uma planta exigente e, por ser de ciclo curto, necessita que os nutrientes estejam prontamente disponíveis, nos estádios de maior demanda, para que não haja limitação da produtividade 1. Trabalho recebido em abr./2010 e aceito para publicação em jul./2011 (n° registro: PAT 9706/

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In this study we aimed to evaluate changes in germination, early seedling growth, and some biochemical parameters in Urochloa brizantha cultivars (Basilisk, Marandu, MG4, MG5, BRS Piatã, and Xaraés) subjected to five levels of free aluminium toxicity (0, 1, 2, 4, and 8 mmol c dm³ Al³ + ), and to verify the selection efficiency of aluminium tolerant cultivars. In the germination assay, lots were submitted to germination under simulated stress conditions in the laboratory, to quantify root protrusion, number of normal seedlings, shoot and root length, and dry mass. In the early seedling growth assay, evaluations were done on the seventh day after subjecting seedlings to aluminium stress conditions. Relative growth rate of length, and dry mass of shoots and roots, superoxide dismutase activity (SOD), and concentrations of proline, total antioxidants (TEAC), and malondialdehyde (MDA) were evaluated. During the seedling study period, up to 14 days after sowing, the most tolerant cultivar maintained root growth in aluminium stress conditions, while the most susceptible cultivar reduced root growth, and developed proportionally more shoots, as shoot growth depends on seed reserves. The germination assay indicated interference of the initial seed quality with increasing Al 3+ concentrations. The results indicate that the early seedling growth assay, which excluded germination effects, and used the measurement of root attributes, is appropriate for the discrimination of Al 3+ tolerant genotypes. The Marandu cultivar was the most similar to the Al 3+ tolerance standard Basilisk cultivar.

Approximately 80-90% of cultivated grassland areas in Brazil are covered by Urochloa brizantha [syn. Brachiaria brizantha (Hochst. ex A. Rich.) Stapf.]. Some genotypes of Urochloa have being widely used with a wrong nomenclature, like species and cultivars. In this way, the Urochloa cultivar identification is primordial for breeding programs and seed production. Considering the importance of genetic purity in commercialized seed lots, the present work aimed to evaluate the use of inter-simple sequence repeat (ISSR) markers in six cultivars of U. brizantha (Xaraés; Piatã; Basilisk; MG4; MG5 and Marandu) to discriminate and determine the contamination in seed batches. Results showed that it is possible to discriminate all cultivar with only two primers in pure samples. Basilisk was confirmed as a U. brizantha cultivar. ISSR markers showed a low polymorphism level. It was not possible to separate samples intentionally contaminated even at 5%.