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Inoculation of plants with bacteria that produce indole acetic acid (IAA) and 1aminocyclopropane-1-carboxylate deaminase (ACCD) often has a positive effect on alleviation of salt stress in plants. Here, we isolated, characterized and formulated halotolerant bacterial consortia from avocado trees with the aim of developing biofertilizers to improve avocado production on saline soils.Using wheat as a test plant, experiments were conducted to investigate the effects of selected bacterial consortia on growth, biomass and superoxide dismutase (SOD) activity of wheat seedlings exposed to salt stress (0.25 M and 0.45 M NaCl) under greenhouse conditions. Among 309 isolates, 17.4% were characterized as halotolerant IAA-and ACCD-producing bacteria. Based on differences in their IAA production and ACCD activities, four consortia were formulated using members of five genera: Enterobacter,Serratia,Microbacterium, Pseudomonas andAchromobacter. Inoculation with selected halotolerant bacterial consortia significantly (P≥0.05) increased the emergence, growth, biomass and SOD activity of wheat seedlings exposed to salt stress. Avocado trees and their rhizosphere soils harbor halotolerant IAA-and ACCD-producing bacteria with the potential to mitigate the salt stress effects on plants. While wheat was useful for screening, further studies are necessary to validate the effects of selected bacterial consortia on avocado growth and yields under saline conditions.

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Acidic ash derived volcanic soils (Andisols) support 50% of cereal production in Chile. Nitrogen (N) is essential for cereal crops and commonly added as urea with consequent environmental concerns due to leaching. Despite the relevance of N to plant growth, few studies have focused on understanding the application, management and ecological role of N2-fixing bacterial populations as tool for improve the N nutrition of cereal crops in Chile. It is known that N2-fixing bacteria commonly inhabits diverse plant compartments (e.g., rhizosphere and root endosphere) where they can supply N for plant growth. Here, we used culture-independent and dependent approaches to characterize and compare the putative N2-fixing bacteria associated with the rhizosphere and root endosphere of wheat plants grown in an Andisol from southern Chile. Our results showed significantly greater bacterial loads in the rhizosphere than the root endosphere. Quantitative PCR results indicated that the copy number of the 16S rRNA gene ranged from 1012~1013 and 107~108 g−1 sample in rhizosphere and root endosphere, respectively. The nifH gene copy number ranged from 105~106 and 105 g−1 sample in rhizosphere and root endosphere, respectively. The total culturable bacteria number ranged from 109~1010 and 107~108 CFU g−1 sample in rhizosphere and 104~105 and 104 CFU g−1 sample in root endosphere using LB and NM-1 media, respectively. Indirect counts of putative N2-fixing bacteria were 103 and 102~103 CFU g−1 sample in rhizosphere and root endosphere using NFb medium, respectively. Sequencing of 16S rRNA genes from randomly selected putative N2-fixing bacteria revealed the presence of members of Proteobacteria (Bosea and Roseomonas), Actinobacteria (Georgenia, Mycobacterium, Microbacterium, Leifsonia, and Arthrobacter), Bacteroidetes (Chitinophaga) and Firmicutes (Bacillus and Psychrobacillus) taxa. Differences in 16S rRNA and putative nifH-containing bacterial communities between rhizosphere and root endosphere were shown by denaturing gradient gel electrophoresis (DGGE). This study shows a compartmentalization between rhizosphere and root endosphere for both the abundance and diversity of total (16S rRNA) and putative N2-fixing bacterial communities on wheat plants grown in Chilean Andisols. This information can be relevant for the design and application of agronomic strategies to enhance sustainable N-utilization in cereal crops in Chile.

Several studies have demonstrated the relevance of endophytic bacteria on the growth and fitness of agriculturally-relevant plants. To our knowledge, however, little information is available on the composition, diversity, and interaction of endophytic bacterial communities in plants struggling for existence in the extreme environments of Chile, such as the Atacama Desert (AD) and Patagonia (PAT). The main objective of the present study was to analyze and compare the composition of endophytic bacterial communities associated with roots and leaves of representative plants growing in Chilean extreme environments. The plants sampled were: Distichlis spicate and Pluchea absinthioides from the AD, and Gaultheria mucronata and Hieracium pilosella from PAT. The abundance and composition of their endophytic bacterial communities was determined by quantitative PCR and high–throughput sequencing of 16S rRNA, respectively. Results indicated that there was a greater abundance of 16S rRNA genes in plants from PAT (1013 to 1014 copies g−1 DNA), compared with those from AD (1010 to 1012 copies g−1 DNA). In the AD, a greater bacterial diversity, as estimated by Shannon index, was found in P. absinthioides, compared with D. spicata. In both ecosystems, the greater relative abundances of endophytes were mainly attributed to members of the phyla Proteobacteria (14% to 68%), Firmicutes (26% to 41%), Actinobacteria (6 to 23%) and Bacteroidetes (1% to 21%). Our observations revealed that most of operational taxonomic units (OTUs) were not shared between tissue samples of different plant species in both locations, suggesting the effect of the plant genotype (species) on the bacterial endophyte communities in Chilean extreme environments, where Bacillaceae and Enterobacteriacea could serve as keystone taxa as revealed our linear discriminant analysis.