Characterization of plant growth promoting rhizobacteria and their potential as bioprotectant against tomato bacterial wilt caused by Ralstonia solanacearum

Greenhouse experiments were conducted to study the effect of plant growth promoting rhizobacteria (PGPR; Bacillus pumilus SE 34, Pseudomonas putida 89B61, BioYield, and Equity), acibenzolar-S-methyl (Actigard), and a soil amendment with S-H mixture (contains agricultural and industrial wastes such as bagasse, rice husk, oyster shell powder, urea, potassium nitrate, calcium super phosphate, and mineral ash) on bacterial wilt incidence caused by Ralstonia solanacearum (race 1, biovar 1) in susceptible tomato (Lycopersicon esculentum cv. Solar Set). In experiments with PGPR, Pseudomonas putida 89B61 significantly reduced bacterial wilt incidence when applied to the transplants at the time of seeding and 1 week prior to inoculation with Ralstonia solanacearum. BioYield, a formulated PGPR that contained two Bacillus strains, decreased disease significantly in three experiments. Equity, a formulation containing more than 40 different microbial strains, did not reduced wilt incidence compared with the untreated control. With inoculum at low pathogen densities of 1 × 105 and 1 × 106 CFU/ml, disease incidence of Actigard-treated plants was significantly less than with nontreated plants. This is the first report of Actigard-mediated reduction of bacterial wilt incidence in a susceptible tomato cultivar. When PGPR and Actigard applications were combined, Actigard plus P. putida 89B61 or BioYield reduced bacterial wilt incidence compared with the untreated control. Incorporation of S-H mixture into infested soil 2 weeks before transplanting reduced bacterial wilt incidence in one experiment. Combination of Actigard with the S-H mixture significantly reduced bacterial wilt incidence in tomato in two experiments.

Download Full-text

Screening and Biocontrol Potential of Rhizobacteria Native to Gangetic Plains and Hilly Regions to Induce Systemic Resistance and Promote Plant Growth in Chilli against Bacterial Wilt Disease

Plants ◽

10.3390/plants10102125 ◽

2021 ◽

Vol 10 (10) ◽

pp. 2125

Author(s):

Abhijeet Kashyap ◽

Nazia Manzar ◽

Mahendra Rajawat ◽

Amit Kesharwani ◽

Ravinder Singh ◽

...

Keyword(s):

Bacillus Subtilis ◽

Plant Growth ◽

Bacterial Wilt ◽

Ralstonia Solanacearum ◽

Growth Parameters ◽

Plant Growth Promoting Rhizobacteria ◽

Wilt Disease ◽

Plant Growth Promoting ◽

Growth Promoting ◽

Biocontrol Potential

Plant growth-promoting rhizobacteria (PGPR) is a microbial population found in the rhizosphere of plants that can stimulate plant development and restrict the growth of plant diseases directly or indirectly. In this study, 90 rhizospheric soil samples from five agro climatic zones of chilli (Capsicum annuum L.) were collected and rhizobacteria were isolated, screened, and characterized at morphological, biochemical, and molecular levels. In total, 38% of rhizobacteria exhibited the antagonistic capacity to suppress Ralstonia solanacearum growth and showed PGPR activities such as indole acetic acid production by 67.64% from total screened rhizobacteria isolates, phosphorus solubilization by 79.41%, ammonia by 67.75%, HCN by 58.82%, and siderophore by 55.88%. We performed a principal component analysis depicting correlation and significance among plant growth-promoting activities, growth parameters of chilli, and rhizobacterial strains. Plant inoculation studies indicated a significant increase in growth parameters, and PDS1 strain showed maximum 71.11% biocontrol efficiency against wilt disease. The best five rhizobacterial isolates demonstrating both plant growth-promotion traits and biocontrol potential were characterized and identified as PDS1—Pseudomonas fluorescens (MN368159), BDS1—Bacillus subtilis (MN395039), UK4—Bacillus cereus (MT491099), UK2—Bacillus amyloliquefaciens (MT491100), and KA9—Bacillus subtilis (MT491101). These rhizobacteria have the potential natural elicitors to be used as biopesticides and biofertilizers to improve crop health while warding off soil-borne pathogens. The chilli cv. Pusa Jwala treated with Bacillus subtilis KA9 and Pseudomonas fluorescens PDS1 showed enhancement in the defensive enzymes PO, PPO, SOD, and PAL activities in chilli leaf and root tissues, which collectively contributed to induced resistance in chilli plants against Ralstonia solanacearum. The induction of these defense enzymes was found higher in leave tissues (PO—4.87-fold, PP0—9.30-fold, SOD—9.49-fold, and PAL—1.04-fold, respectively) in comparison to roots tissue at 48 h after pathogen inoculation. The findings support the view that plant growth-promoting rhizobacteria boost defense-related enzymes and limit pathogen growth in chilli plants, respectively, hence managing the chilli bacterial wilt.

Download Full-text