The largest numbers of the Brazilian traditional upland rice varieties are found in the Maranhão state, Northeast region of Brazil. However, no information is available on the diazotrophic bacterial population associated as well as the plant growth promoting potential when these traditional genotypes are inoculated with native strains. Here, we evaluated the response of ten traditional rice varieties to inoculation with ten diazotrophic strains, previously isolated from rice soil of this region and screened for their ability to produce indole-3-acetic acid (IAA) in vitro. The procedure for selection of the best diazotrophic strain/rice variety interaction involved three steps: gnotobiotic conditions, soil pot and field experiments. The gnotobiotic experiment showed that the Azospirillum amazonense strain AR3122 increased the biomass of the traditional varieties Cana Roxa and Cana Forte (28 and 48%, respectively) while this effect was less evident for the other combination of strains/rice varieties. The soil pot experiment showed that the combination of Burkholderia vietnamiensis strain AR 1122 and traditional variety Arroz 70 was superior to the other strains/varieties and the treatment fertilized with 100 kg N ha −1. The best performance of the Burkholderia vietnamiensis strain AR1122/variety Arroz 70 was confirmed in the field experiment. There was an increase of up 10 and 29% in the grain yield in comparison to both the N fertilization and Herbaspirillum seropedicae ZAE 94 strain treatments, respectively. In contrast, the response of the commercial variety Bonanç a to inoculation with strain AR1122 was much lower, suggesting that a biofertilizer inoculation program for traditional rice varieties should consider the genetic interaction between strain and rice variety. The diazotrophic B. vietmaniensis strain AR1122 was a good biofertilizer candidate for inoculation of traditional rice varieties and therefore should be used for further studies to confirm the strain-genotype effect envisaging a sustainable rice crop system mainly in the Northeast region of Brazil.

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Resumo -O objetivo deste trabalho foi avaliar o efeito isolado ou simultâneo dos estresses hídrico e térmico na expressão gênica em nódulos de feijão-caupi. A bactéria Bradyrhizobium japonicum (estirpe BR 3267) foi inoculada em sementes de feijão-caupi da cultivar IPA 206 e, 35 dias após a germinação, as plantas foram submetidas a diferentes regimes de disponibilidade hídrica e a estresse térmico, em casa de vegetação. Para a identificação dos genes diferencialmente expressos, foi utilizada a técnica de cDNA-AFLP, tendo-se isolado 67 fragmentos derivados de transcritos (FDTs) diferencialmente expressos. Após o sequenciamento dos FDTs e das análises de similaridade, com uso do programa Blastx, foram identificados 14 genes diferencialmente expressos envolvidos em diferentes processos metabólicos. O padrão de expressão de seis genes sob estresse abiótico foi confirmado por RT-qPCR, e observou-se indução de genes pertencentes a diferentes categorias funcionais, como biossíntese de ácido abscísico, sinalização celular, transportador de prolina e biossíntese de lipídeos de membranas. A expressão desses genes indica sua participação em processos relacionados à proteção dos nódulos ao estresse abiótico.Termos para indexação: Vigna unguiculata, cDNA-AFLP, fixação biológica de nitrogênio, genômica funcional. Gene expression induced by abiotic stress in cowpea nodulesAbstract -The objective of this work was to evaluate the isolated or concomitant effect of drought and heat stresses on the gene expression of cowpea nodules. The bacterium Bradyrhizobium japonicum (strain BR 3267) was inoculated in cowpea seeds from the cultivar IPA 206 and, 35 days after germination, the plants were subjected to different water availability regimes and to heat stress under greenhouse conditions. To identify differentially expressed genes, the cDNA-AFLP technique was used, and 67 differentially expressed transcript-derived fragments (TDFs) were isolated. After TDFs sequencing and similarity analyses, using the Blastx program, 14 differentially expressed genes were identified, which are involved in different metabolic processes. The expression pattern of six genes under abiotic stress conditions was confirmed by RT-qPCR, and the induction of different functional gene categories, such as abscisic acid biosynthesis, cell signaling, proline transporter, and lipid membrane biosynthesis, was observed. The expression of these genes indicates their participation in processes related to nodule protection under abiotic stresses.Index terms: Vigna unguiculata, cDNA-AFLP, biological nitrogen fixation, functional genomics. IntroduçãoEm condições tropicais, a produtividade agrícola pode ser negativamente afetada por uma série de estresses bióticos e abióticos que alteram o crescimento e o desenvolvimento vegetal. Nesse contexto, destacamse a deficiência de nutrientes, como nitrogênio e fósforo, bem como os estresses decorrentes da baixa disponibilidade hídrica e das altas temperaturas.A fixação biológica de nitrogênio (FBN) é um processo complexo que pode ...