Efficacy of rhizobacteria on plant growth promotion and disease suppression in vitro

This research examines the effect of selected rhizobacteria for pathogen antagonistic and plant growth promotion activities in potato. A total of 22 rhizobacterial isolates collected from potato fields were tested in vitro for antagonism against R. solani and also for their plant growth promotion, indole acetic acid (IAA), 1-aminocyclopropane-1-carboxylate (ACC) deaminase production, phosphate solubilization ability and pathogen suppression activities in potato. Of 22 isolates, 11 were identified as Pseudomonas spp., 10 were identified as Bacillus spp. and one as an Enterobacter sp. All 22 isolates showed antagonistic activity on plate assays against R. solani ranging from 26.9 to 53.4% while the positive controls namely, Bacillus subtilis FZB24 WG and Pseudomonas fluorescens CHAO suppressed the growth of R. solani by 21.3 and 19.8%. Four isolates (18%) positively produced the phytohormone IAA, 17 (77%) had ACC deaminase activity and 19 (86%) solubilized phosphorous. Bacteria were examined for their plant growth promotion and disease suppression effects in in vitro potato after one week bacterization followed by three weeks of pathogen challenge. Over half of the rhizobacterial strains showed a significant effect on plant growth in vitro with a total plant fresh weight ranging from 1.44 to 2.04 g while the control, Bacillus subtilis FZB24 WG and Pseudomonas fluorescens CHAO had a fresh weight of 1.34, 1.62 and 1.51 g, respectively. Disease suppression activity was measured in terms of plant weight which ranged from 1.10 to 1.76 g while the control, Bacillus subtilis FZB24 WG and Pseudomonas fluorescens CHAO had 1.15, 1.33 and 1.29 g, respectively. These preliminary results suggest that the rhizobacteria studied have potential as biocontrol agents.