Native bacteria isolated from roots and rhizosphere of Solanum lycopersicum L. increase tomato seedling growth under a reduced fertilization regime.

In semiarid regions is important to use native strains best adapted to these environments to optimize plant-PGPR interaction. We aimed to isolate and characterize PGPR from roots and rhizosphere of a tomato crop, as well as studying the effect of its inoculation on tomato seedlings growth. We selected four strains considering their effectiveness of fixing nitrogen, solubilizing phosphate, producing siderophores and indole acetic acid. They belong to the genera Enterobacter, Pseudomonas, Cellulosimicrobium, and Ochrobactrum. In addition, we also analyzed the ability to solubilize Ca3(PO4)2, FePO4 and AlPO4 and the presence of one of the genes encoding the cofactor PQQ in their genome. Enterobacter 64S1 and Pseudomonas 42P4 showed the highest phosphorus solubilizing activity and presence of pqqE gene. Furthermore, in a tomato-based bioassay in speed-bed demonstrated that a sole inoculation at seedling stage with the strains increased dry weight of roots (49-88%) and shoots (39-55%), stem height (8-13%) and diameter (5-8%) and leaf area (22-31%) and were equal or even higher than fertilization treatment. Leaf nitrogen and chlorophyll levels were also increased (50-80% and 26-33%) compared to control. These results suggest that Enterobacter 64S1 and Pseudomonas 42P4 can be used as bio-inoculant in order to realize a nutrient integrated management.

Dissimilar evolutionary histories of two resistance gene families in the genus Solanum.

Genomic analyses have shown that most genes in eukaryotic lineages belong to families. Gene families vary in terms of number of members, nucleotide similarity, gene integrity, expression, and function. Often, the members of gene families are arranged in clusters, which contribute to maintaining similarity among gene copies and also to generate duplicates through replication errors. Gene families offer us an opportunity to examine the forces involved in the evolution of the genomes and to study recombination events and genomic rearrangements. In this work, we focused on the evolution of two plant resistance gene families, Sw5 and Mi-1, and analyzed the completely sequenced nuclear genomes of potato and tomato. We first noticed that the potato genome carries larger resistance gene families than tomato, but all gene copies are pseudogenes. Second, phylogenetic analyses indicated that Sw5 and Mi-1 gene families had dissimilar evolutionary histories. In contrast to Sw5, Mi-1 homologues suffered repeated gene conversion events among the gene copies, particularly in the tomato genome.