Characterization of Some Plant Growth-Promoting Rhizobacteria Isolated From Sugar Beet Rhizosphere

Abstract

Plant growth promoting rhizobacteria (PGPR) are the rhizosphere bacteria that can be used to perform important functions such as increasing plant growth and protecting from several diseases caused by plant pathogens. This study aimed to characterize the native PGPR strains isolated from sugar beet rhizosphere and to evaluate their antagonistic activity against three of the common phytopathogen. Therefore, thirty bacterial strains were isolated from sugar beet rhizosphere and some of their morphological characteristics were investigated. Enzymatic (catalase, gelatinase & amylase) activities reflected a high degree of variability amongst strains. The antibiotic resistance to seven different antibiotics were significantly varied as revealed by zone-diameter around antibiotic disk. In vitro antagonistic activity against F. solani, F. oxysporium and R. solani, revealed a considerable diversity of antagonism. Many isolates were significantly reduced mycelial growth of F. solani (57%). Some isolates showed a good degree of antagonism against F. oxysporium (60%) while such activity against R. solani were varied from 0.0 to 56.5%. Partial-length of 16S rRNA gene (~ 1200 bp) was amplified and sequenced from two isolates, AM-15 and AM-26, that displayed a substantial antagonistic activity against studied pathogens. Nucleotide BLAST of AM-26 16S rRNA sequence showed the highest similarity (>99.5%) to many Pseudomonas chlororaphis subsp. aurantiaca, Pseudomonas chlororaphis & Pseudomonas sp. strains. However, AM-26 16S rRNA partial sequence shared a high similarity (>99.63%) with its corresponding sequence of Bacillus subtilis strain RRLKE01 (ACNO KF029595.1) and 99.54% similarity were detected with many other Bacillus subtilis and Bacillus sp. strains as well.