Abstract The efficiency of maize transformation mediated by Agrobacterium tumefaciens is influenced by various factors. The aim of this study was to test the effect of different concentrations of N6 salts (50% - half strength, and 100% - full strength) in the infection and cocultivation media on genetic transformation efficiency of the L3 tropical elite maize line. Immature embryos were transformed via A. tumefaciens harboring the binary vector pTF102 containing the genes uidA and BAR under control of the CaMV35S promoter. The efficiency of the transgenic events produced was 3% for full strength and 1.1% for half strength N6 salts. Although under a lower concentration of salts, GUS expression was stronger; under this concentration, regeneration was less efficient. Thus, the results showed that the presence of 100% N6 salts in the infection and cocultivation media favored genetic transformation of the L3 maize inbred line mediated by A. tumefaciens.

O objetivo deste trabalho foi avaliar a patogenicidade de 24 isolados de Beauveria contra larvas de Spodoptera frugiperda e caracterizá-los molecularmente, por meio do seqüenciamento da região ITS do rDNA e de marcadores RAPD. O seqüenciamento de fragmentos de 570 pares de bases, da região ITS do rDNA, possibilitou a identificação dos isolados como B. bassiana e B. brongniarti, pela comparação com seqüências depositadas no GenBank. Sessenta e sete fragmentos polimórficos de RAPD foram capazes de diferenciar 20 entre 24 isolados de Beauveria, e agrupá-los de acordo com o inseto hospedeiro e com a patogenicidade contra a lagarta-do-cartucho do milho. Os marcadores RAPD foram altamente associados à patogenicidade contra S. frugiperda e explicaram até 67% da variação fenotípica. Além da identificação e caracterização molecular de isolados de Beauveria, o seqüenciamento da região ITS, aliado aos marcadores RAPD, é útil na seleção de isolados potencialmente eficazes contra larvas de S. frugiperda e no monitoramento de liberações desses microrganismos em programas de biocontrole.

The objective of this work was to evaluate the pathogenicity of 24 Beauveria isolates to Spodoptera frugiperda larvae, and characterize them molecularly through rDNA-ITS sequencing and RAPD markers. Sequencing of rDNA-ITS fragments of 570 bp allowed the identification of isolates as B. bassiana or B. brongniarti by sequence comparison to GenBank. Sixty seven polymorphic RAPD fragments were capable to differentiate 20 among 24 Beauveria isolates, grouping them according to the derived host insect and to pathogenicity against maize fall armyworm larvae. Three RAPD markers were highly associated to the pathogenicity against S. frugiperda, explaining up to 67% of the phenotypic variation. Besides identification and molecular characterization of Beauveria isolates, ITS sequence and RAPD markers proved to be very useful in selecting the isolates potentially effective against S. frugiperda larvae and in monitoring field release of these microorganisms in biocontrol programs.

O objetivo deste trabalho foi desenvolver um sistema de transformação genética para genótipos tropicais de milho pelo bombardeamento de embriões imaturos com micropartículas. O bombardeamento com partículas foi realizado utilizando-se uma construção gênica contendo os genes bar e uidA sob o controle do promotor CaMV35S. As melhores condições para transformação das linhagens de milho tropical L3 e L1345 foram obtidas após o cultivo de embriões imaturos durante 4 horas, antes do bombardeamento, em alta osmolaridade, e bombardeados com a pressão de 1.100 psi de gás hélio, dois tiros por placa e uma distância de vôo da micropartícula de 6,6 cm. As freqüências de transformação obtidas variaram entre 0,9 e 2,31%. A integração dos genes heterólogos no genoma das plantas transgênicas de milho foi confirmada por análises de Southern blot e expressão dos genes bar e uidA. O protocolo de transformação genética de milho desenvolvido neste estudo irá aumentar, provavelmente, a eficiência de produção de novas linhagens tropicais de milho expressando características agronômicas desejáveis.

The objective of this work was to develop a genetic transformation system for tropical maize genotypes via particle bombardment of immature zygotic embryos. Particle bombardment was carried out using a genetic construct with bar and uidA genes under control of CaMV35S promoter. The best conditions to transform maize tropical inbred lines L3 and L1345 were obtained when immature embryos were cultivated, prior to the bombardment, in higher osmolarity during 4 hours and bombarded at an acceleration helium gas pressure of 1,100 psi, two shots per plate, and a microcarrier flying distance of 6.6 cm. Transformation frequencies obtained using these conditions ranged from 0.9 to 2.31%. Integration of foreign genes into the genome of maize plants was confirmed by Southern blot analysis as well as bar and uidA gene expressions. The maize genetic transformation protocol developed in this work will possibly improve the efficiency to produce new transgenic tropical maize lines expressing desirable agronomic characteristics.