Assessing the role of field isolated Pseudomonas and Bacillus as growth-promoting rizobacteria on avocado (Persea americana) seedlings

Introduction

This research aims to assess the efficacy of two genera of rhizobacteria from avocado field isolated: Pseudomonas and Bacillus, as plant growth-promoting microorganisms in Hass avocado trees grafted onto Zutano rootstock.

Materials and Methods

The siderophore-producing and phosphate-solubilizing capacity of each isolated strain was determined and plant growth-promoting activity, nutrient accumulation, and nutrient use efficiency in Zutano variety avocado seedlings were evaluated. Molecular identification was carried out by amplification of the 16S rDNA gene of the isolated strains.

Results

Pseudomonas putida, Lysinibacillus macroides, Lysinibacillus xylanilyticus, Lysinibacillus fusiformis, Bacillus subtilis and Pseudomonas plecoglossicida, were identified as the PGPR of the Bacillus and Pseudomonas genera, predominant in the avocado rhizosphere. There was found 11 phosphate solubilizing strains and 2 siderophore-producing strains. The phosphate-solubilizing strains, B. subtilis and P. plecoglossicida, stimulated the growth of Zutano seedlings, increasing their root dry weight (g), stem dry weight (g), leaf dry weight (g) and leaf area (cm²). Significant differences were found in nutrient uptake efficiency between inoculated plants and noninoculated plants. The increase in root biomass responded to greater phosphorus and potassium absorption in plants inoculated with P. plecoglossicida, due to this strain's high phosphate solubilization efficiency (266%).

Conclusions

The highest plant growth promotion strains were Bac F (B. subtilis), Bac M (P. plecoglossicida) and P1 (P. putida), which achieved the highest increase in root and leaf dry weight, as well as the highest nutrient extractions and nutrient uptake efficiency.