Culturable endophytic bacterial communities associated with field-grown soybean.

AIMS: Assess the diversity of the culturable endophytic bacterial population associated with transgenic and nontransgenic soybean grown in field trial sites in Brazil and characterize them phenotypically and genotypically focusing on characteristics related to plant growth promotion. METHODS AND RESULTS: Endophytic bacteria were isolated from roots, stems and leaves of soybean cultivars (nontransgenic (C) and glyphosate-resistant (GR) transgenic soybean), including the isogenic BRS133 and BRS245RR. Significant differences were observed in bacterial densities in relation to genotype and tissue from which the isolates were obtained. The highest number of bacteria was observed in roots and in GR soybean. Based on characteristics related to plant growth promotion, 54 strains were identified by partial 16S rRNA sequence analysis, with most of the isolates belonging to the species Enterobacter ludwigii and Variovorax paradoxus. Among the isolates, 44·4% were able to either produce indoleacetic acid (IAA) or solubilize phosphates, and 9·2% (all from GR soybean) presented both plant growth-promoting activities. CONCLUSIONS: The results from this study indicate that the abundance of endophytic bacterial communities of soybean differs between cultivars and in general it was higher in the transgenic cultivars than in nontransgenic cultivars. BRS 245 RR exhibited no significant difference in abundance compared to nontransgenic BRS133. This suggests that the impact of the management used in the GR soybean fields was comparable with the impacts of some enviromental factors. However, the bacterial endophytes associated to GR and nontransgenic soybean were different. The soybean-associated bacteria showing characteristics related to plant growth promotion were identified as belonging to the species Pantoea agglomerans and Variovorax paradoxus. SIGNIFICANCE AND IMPACT OF THE STUDY: Our study demonstrated differences concerning compostion of culturable endophytic bacterial population in nontransgenic and transgenic soybean.

Construction and characterization of a BAC library from the Coffea arabica genotype Timor Hybrid CIFC 832/2.

Most of the world's coffee production originates from Coffea arabica, an allotetraploid species with low genetic diversity and for which few genomic resources are available. Genomic libraries with large DNA fragment inserts are useful tools for the study of plant genomes, including the production of physical maps, integration studies of physical and genetic maps, genome structure analysis and gene isolation by positional cloning. Here, we report the construction and characterization of a Bacterial Artificial Chromosome (BAC) library from C. arabica Timor Hybrid CIFC 832/2, a parental genotype for several modern coffee cultivars. The BAC library consists of 56,832 clones with an average insert size of 118 kb, which represents a dihaploid genome coverage of five to sixfold. The content of organellar DNA was estimated at 1.04 and 0.5 % for chloroplast and mitochondrial DNA, respectively. The BAC library was screened for the NADPH-dependent mannose-6-phosphate reductase gene (CaM6PR) with markers positioned on four linkage groups of a partial C. arabica genetic map. A mixed approach using PCR and membrane hybridization of BAC pools allowed for the discovery of nine BAC clones with the CaM6PR gene and 53 BAC clones that were anchored to the genetic map with simple sequence repeat markers. This library will be a useful tool for future studies on comparative genomics and the identification of genes and regulatory elements controlling major traits in this economically important crop species.

Gene expression and enzymatic activity of pectin methylesterase during fruit development and ripening in Coffea arabica L.

Coffee quality is directly related to the harvest and post harvest conditions. Non-uniform maturation of coffee fruits, combined with inadequate harvest, negatively affects the final quality of the product. Pectin methylesterase (PME) plays an important role in fruit softening due to the hydrolysis of methylester groups in cell wall pectins. In order to characterize the changes occurring during coffee fruit maturation, the enzymatic activity of PME was measured during different stages of fruit ripening. PME activity progressively increased from the beginning of the ripening process to the cherry fruit stage. In silico analysis of expressed sequence tags of the Brazilian Coffee Genome Project database identified 5 isoforms of PME. We isolated and cloned a cDNA homolog of PME for further characterization. CaPME4 transcription was analyzed in pericarp, perisperm, and endosperm tissues during fruit development and ripening as well as in other plant tissues. Northern blot analysis revealed increased transcription of CaPME4 in the pericarp 300 days after flowering. Low levels of CaPME4 mRNAs were observed in the endosperm 270 days after flowering. Expression of CaPME4 transcripts was strong in the branches and lower in root and flower tissues. We showed that CaPME4 acts specifically during the later stages of fruit ripening and possibly contributes to the softening of coffee fruit, thus playing a significant role in pectin degradation in the fruit pericarp.

Resistance of maize landraces to the maize weevil Sitophilus zeamais Motsch. (Coleoptera: Curculionidae).

The maize weevil Sitophilus zeamais Motsch. is an important pest of maize that attacks the grain both in the field and during storage. The damage caused by the maize weevil S. zeamais on maize landraces, Amarelo Antigo, Asteca, Caiano, Carioca, and Ferrinho, was evaluated by no-choice tests under laboratory conditions. The commercial varieties Sol da Manhã, BR 106, BR 451, and the synthetics PC 0203 and PC 9903 were evaluated for comparisons with the maize landraces. The parameters evaluated were susceptibility index, number of weevil progeny, development time, weevil progeny dry weight, and grain dry weight loss. The landraces were more susceptible to the maize weevil as compared to the commercial varieties. Based on the cluster analysis, two groups of susceptibility to the maize weevil were observed: one of more susceptible populations formed by local landraces and BR 451, and another less susceptible, with commercial varieties, synthetics, and the landrace Amarelo.