Serratia strains isolated from the rhizosphere of raulí ( Nothofagus alpina ) in volcanic soils harbour PGPR mechanisms and promote raulí plantlet growth

Abstract

[EN] Raulí is one of the most emblematic tree species of the Chilean temperate forests. Due to the high quality wood, this tree has been used for furniture and handicrafts manufacturing, which has positioned raulí as one of the most important commercial timber species in Chile. Currently, the international market demands sustainable production system for forest production, more specifically in plantlets production. In this regard, plant growthpromoting rhizobacteria (PGPR) inoculants may enhance the growth and survival of plantlets in nurseries, which means an increase in the effectiveness of replanting operations. Therefore, the aim of the present study was to isolate, characterize and screen rhizosphere-associated bacteria with PGPR potential, isolated from raulí that growth in volcanic soils in southern Chile. A total of 1,261 bacterial strains were isolated from different volcanic soils. Out of 1,261 isolates, 100 were selected based on their high levels of indole acetic acid (IAA) production. These isolates were then subjected to screening for 1-aminocyclopropane-1-carboxylic acid deaminase activity, and their ability to fix nitrogen was determined. From the 100 selected isolates, 7 were chosen for producing the highest amount of IAA to continue with genetic characterization based on their 16S rRNA gene sequences. These 7 isolates were characterized as members of the Serratia genus and were used to develop multi-strain inoculant mixtures. Later, a nursery study followed to determine the effect of inoculation with the Serratia strains on the growth of RA88 raulí clone plantlets. The nursery experiment demonstrated that Serratia strains have the potential to increase the root collar diameter, height, relative chlorophyll content, biomass and nitrogen content of raulí plantlets. The study concluded, that Serratia strains have the potential to be used as biofertilizers to increase plant growth in nursery conditions.