Evaluation of bacterial isolates for agriculture, with beneficial properties on plant growth and crop protection

Abstract

Background: A diverse array of bacteria, including Pseudomonas species are the main plant growth promoting (PGP) agents used to promote the growth of several crops. Many of these isolates are recognized for their PGP ability and capacity to increase disease resistance of the plants. Objectives: This study aimed to isolate and characterize different rhizospheric, epiphytic and endophytic isolates from the soybean, maize, wheat and barley, and to evaluate their PGP traits, biofilm formation and antifungal activity. Methods: According to the 16S rRNA gene sequencing and from various PGP traits, 48 out of 100 isolates from the leaves, stems, roots, and seeds from different crops were selected. All the strains were additionally identified (gyrB, rpoB, and tufGPF), and 16 selected isolates marked as belonging to Risk Class 1 group, screened for in vitro antifungal activity (Rhizoctonia solani, Sclerotinia sclerotiorum, Monilinia laxa, Alternaria alternata, Alternaria infectoria, Fusarium graminearum, Fusarium verticilioides, Epicoccum nigrum) and for biofilm formation. Results: Thorough housekeeping genes sequencing highlighted representative isolates such as Pseudomonas fluorescens/putida/fulva/stutzeri/rhodesiae and Bacillus subtilis. The phosphate solubilization, siderophore and IAA production were most related to P. fluorescens/putida species, while strong lipase and protease activity are recorded for P. rhodesiae and P. fluorescens. Strong biofilm production was obtained for P. fulva, and moderate for B. subtilis. Other isolates showed no biofilm production ability. Only B. subtilis showed strong antifungal activity against all tested fungi, and two isolates from P. fluorescens/putida group. Most of the Pseudomonas isolates expressed strong activity against two Alternaria species and Epicoccum nigrum.