Protective Role of Plant Growth Promoting Rhizobacteria Inoculation in the Development of Drought Tolerance in Shallot: Effects on Hydroxygen Peroxide Production, Lipid Peroxidation, and Secondary Metabolite Production

Abstract

Shallot contains secondary metabolites and antioxidants that can be used as raw materials for traditional medicine. However, shallot has  the disadvantage of being intolerant to drought. Drought can affect the quality of the compounds in shallot at a certain level. Therefore,  this study investigates the protective role of Plant Growth Promoting Rhizobacteria (PGPR) inoculation in conferring drought tolerance to  shallot during different growth stages. Two factors and three replications were considered in this study. The first factor was the timing of  drought stress, comprising four treatments (vegetative phase, bulb initiation, bulb development, and maturation), with one treatment as  a control without drought stress. The second factor was the type of bacteria, consisting of two treatments (Bacillus subtilis Pb03 and  Pseudomonas fluorescens Pb04), with one treatment as a control without PGPR inoculation. The research results indicate that oxidative stress triggered by drought stress is evidenced by an increase in hydrogen peroxide production, lipid peroxidation, and secondary  metabolites at almost all stages of growth. Treatment Bacillus subtilis Pb03 inoculation was more effective than Pseudomonas  fluorescens Pb04 in mitigating drought stress in shallots. Bacillus subtilis Pb03 inoculation inhibited oxidative stress by enhancing the  activity of antioxidant enzymes. Additionally, this application suppressed the production of secondary metabolites, thereby maintaining  osmotic balance in the plants.