Microsatellites or SSRs (simple sequence repeats) are ubiquitous short tandem duplications occurring in eukaryotic organisms. These sequences are among the best marker technologies applied in plant genetics and breeding. The abundant genomic, BAC, and EST sequences available in databases allow the survey regarding presence and location of SSR loci. Additional information concerning primer sequences is also the target of plant geneticists and breeders. In this paper, we describe a utility that integrates SSR searches, frequency of occurrence of motifs and arrangements, primer design, and PCR simulation against other databases. This simulation allows the performance of global alignments and identity and homology searches between different amplified sequences, that is, amplicons. In order to validate the tool functions, SSR discovery searches were performed in a database containing 28 469 nonredundant rice cDNA sequences.

Molecular and morphological data analyses matrices are very informative tools for the estimation of genetic distances. We used AFLP markers, morphological traits and combined analysis to estimate the genetic distances between wheat genotypes and ascertain any associations between the two techneques. Nineteen wheat (Triticum aestivum L.) genotypes were analyzed using amplified fragment length polymorphism (AFLP) markers and field evaluated for two years. The matrices obtained by morphological and molecular marker data analyses revealed a significant but moderate correlation (r = 0.47), indicating that such techniques sample distinct genome regions. The combined analysis was found to be highly correlated with AFLP (r = 0.97) and moderately correlated with morphological (r = 0.59) markers. A possible explanation for such results is a bias caused by the much higher number of AFLP (229) than morphological (17) markers. Thus, it is evident that the combined analysis is not efficient when a very dissimilar number of markers are used in each isolated technique. Therefore, to obtain a better knowledge of the degree of divergence among genotypes it is necessary to consider each analysis separately.

Rice is a model genome for cereal research, providing important information about genome structure and evolution. Retrotransposons are common components of grass genomes, showing activity at transcription, translation and integration levels. Their abundance and ability to transpose make them good potential markers. In this study, we used 2 multilocus PCR-based techniques that detect retrotransposon integration events in the genome: IRAP (inter-retrotransposon amplified polymorphism) and REMAP (retrotransposon-microsatellite amplified polymorphism). Markers derived from Tos17, a copia-like endogenous retrotransposon of rice, were used to identify genetic similarity among 51 rice cultivars (Oryza sativa L.). Genetic similarity analysis was performed by means of the Dice coefficient, and dendrograms were developed by using the average linkage distance method. A cophenetic correlation coefficient was also calculated. The clustering techniques revealed a good adjustment between matrices, with correlation coefficients of 0.74 and 0.80, or lower (0.21) but still significant, between IRAP and REMAP-based techniques. Consistent clusters were found for Japanese genotypes, while a subgroup clustered the irrigated Brazilian genotypes.

Tandem repeats (microsatellites or SSRs) are molecular markers with great potential for plant genetic studies. Modern strategies include the transfer of these markers among widely studied and orphan species. In silico analyses allow for studying distribution patterns of microsatellites and predicting which motifs would be more amenable to interspecies transfer. Transcribed sequences (Unigene) from ten species of three plant families were surveyed for the occurrence of micro and minisatellites. Transcripts from different species displayed different rates of tandem repeat occurrence, ranging from 1.47% to 11.28%. Both similar and different patterns were found within and among plant families. The results also indicate a lack of association between genome size and tandem repeat fractions in expressed regions. The conservation of motifs among species and its implication on genome evolution and dynamics are discussed.

Solos com concentrações elevadas de alumínio (Al3+), podem prejudicar o desenvolvimento e a absorção de nutrientes de plantas de arroz. O objetivo do experimento foi avaliar o desempenho de dezoito genótipos de arroz quanto a absorção de P, Mg, Ca e K e identificar genótipos com bom desempenho quando submetidos ao estresse por Al3+ em sistema hidropônico. Foram utilizados quatro níveis de Al3+ (0, 10, 20 e 30mg L-1) e o delineamento experimental foi blocos casualizados com três repetições. As plântulas permaneceram em sistema hidropônico por 20 dias sob efeito dos tratamentos, e após foram avaliadas quanto ao comprimento de raízes (CR) e teores de P, Mg, Ca e K. Todas as variáveis apresentaram reduções significativas nos seus valores, e os genótipos apresentaram diferentes desempenhos na absorção de nutrientes frente aos tratamentos, com exceção do nutriente Mg que apresentou mesma resposta para todos os genótipos avaliados. Baseado na variável CR, os genótipos Felune e Taim foram considerados como mais tolerante e sensível ao Al3+, respectivamente. Para absorção de nutrientes, os genótipos apresentaram comportamentos muito diferenciais para cada elemento avaliado, sendo que também o genótipo Felune obteve elevados índices de absorção. Todas as variáveis revelaram correlações significativas entre si.

RESUMO -(Níveis críticos dos ácidos acético, propiônico e butírico para estudos de toxicidade em arroz em solução nutritiva). A ocorrência de condições anaeróbias nos solos hidromórficos, associada com a presença de matéria orgânica favorece o desenvolvimento de microrganismos anaeróbios que produzem substâncias fitotóxicas, principalmente ácidos orgânicos de cadeia curta. A seleção de constituições genéticas de arroz promissoras para utilização nestas situações requer avaliações de difícil execução em campo, sendo simplificada pela utilização de sistemas hidropônicos. O objetivo deste trabalho foi determinar a faixa de concentração e as respostas mais apropriadas para serem utilizadas em seleção de genótipos de arroz para tolerância a ácidos orgânicos em sistemas hidropônicos. Foram estudados os efeitos de seis concentrações dos três principais ácidos formados no solo: ácido acético (0; 4; 8; 12; 16 e 20 mM), ácido propiônico (0; 3; 6; 9; 12; e 15 mM) e ácido butírico (0; 2; 4; 6; 8 e 10 mM) em dois genótipos de elevada divergência (BRS-7-TAIM e SAIBAN). Os resultados indicam que as faixas de concentração mais adequadas para estudos de tolerância de arroz a ácidos orgânicos estão entre 8,4 e 15,8; 4,2 e 9,1 e 3,7 e 7,7 mM para os ácidos acético, propiônico e butírico respectivamente, e a variável mais responsiva foi comprimento de raízes. Palavras-chave: Oryza sativa, ácidos orgânicos, toxidezABSTRACT -(Critical levels of acetic, propionic and butyric acids for toxicity studies of rice in nutrient solution). The occurrence of anaerobic conditions in hydromorphic soils, associated with the presence of organic matter favors the development of anaerobic microorganisms that produce phytotoxic substances, especially short chain organic acids. Selection of promising rice genotypes for use under these conditions requires difficult field evaluations, which may be simplified with the use of hydroponic culture. The aim of this work was to determine the range of concentration and the dependent variables most appropriate to selecting rice genotypes for tolerance to organic acids in hydroponic culture. Six concentrations of the three main acids formed in the soil: acetic acid (0; 4; 8; 12; 16 and 20 mM), propionic acid (0; 3; 6; 9; 12; and 15 mM) and butyric acid (0; 2; 4; 6; 8 and 10 mM) and two genotypes of high divergence (BRS-7-TAIM and SAIBAN) were used. The results indicate that the most appropriate concentration ranges for studies of rice tolerance to organic acids are: 8.4 and 15.8; 4.2 and 9.1 and 3.7 and 7.7 mM for acetic, propionic and butyric acids, respectively, and the most responsive variable was root length.

Association between traits and path analysis in half-sib progeny selection of Brachiaria ruziziensisHigh association between fresh and dry mass weight can facilitate early selection of superior genotypes of B. ruziziensis R. Germ. & C.M. Evrard. The aim of this study was to verify the associations between traits in the selection of B. ruziziensis genotypes. The experiment was arranged in a complete randomized block design with two replications. The traits evaluated were height and vigor of plants; weight of fresh mass and percentage of dry matter of the whole plant, stem and leaf; dry mass weight of total herbage, stem, and leaf and the ratio between productivity of leaf and stem. Estimation of simple correlations and path analysis were performed considering the dry mass weight as the main variable. The correlations were mostly low, but significant higher correlations were observed between fresh mass weight and dry mass weight, dry weight of the stem and dry weight of leaves. The path coefficients showed that the direct effects of different explanatory variables on the dry mass weight were mostly low. More significant direct effects were obtained with fresh mass weight, stem dry weight and leaf dry weight, indicating that the fresh mass weight allows for the indirect selection for dry mass weight. Associação alta entre peso de massa seca e peso de massa verde pode facilitar a seleção antecipada de genótipos superiores de B. ruziziensis. Objetivou-se neste estudo verificar as associações entre características morfo-agronômi-cas na seleção de genótipos de B. ruziziensis. O delineamento experimental foi o de blocos completos casualizados com duas repetições. Foram avaliadas as características altura e vigor das plantas, peso de massa verde e porcentagem de matéria seca da planta inteira, do caule e da folha, peso de massa seca da forragem total, de caule, e de folha e, relação entre produtividade de folha e caule de massa verde. As análises consistiram da estimação das correlações simples entre os caracteres e da análise de trilha considerando o peso de massa seca total como variável básica e as demais explicativas. Correlações mais elevadas foram observadas entre peso de massa seca e peso de massa verde, peso seco de caule e peso de massa verde e, peso seco de folhas e peso de massa verde. Pelos coeficientes de trilha, verificou-se que os efeitos diretos das diferentes variáveis explicativas sobre o peso de massa seca foram, em sua maioria, baixos. Os efeitos diretos mais relevantes sobre o peso de massa seca foram verificados via peso de massa verde, peso seco de caule e peso seco de folhas, indicando que o peso de massa verde viabiliza a seleção indireta para peso de massa seca. Palavras-chaves:Correlação, seleção indireta, melhoramento de forrageiras.

AbstrAct:The increase of yield potential in new rice (Oryza sativa L.) varieties has been a major challenge for genetic improvement.The generation of mutants, followed by their characterization, constitutes a great possibility to isolate and select genes and genotypes that present agronomic traits of interest. This study significance. The results show that there is genetic variability among the mutant families, suggesting that the mutagen EMS at 1.5% is effective for generating mutants for all assessed traits. Among the characters, plant height was the most affected by the mutagen, which provided an increase in the character. For the main panicle length character, seven families showed means above the control; for main panicle weight and grain weight, four and six mutant families were observed, respectively, with a superior performance in comparison to the control.