Studies on Induction of Systemic Resistance in Rose by Pseudomonas and Bacillus Strains Against Diplocarpon Rosae

The innate plant resistance is an efficient and eco-friendly tool to avoid diseases of agricultural crops. However most of the commercial cultivars are susceptible to different diseases at different susceptibility level. Fungicides are usually the only option that farmers use against these pathogens. These fungicides are hazardous for our environment and human health as these toxify food commodities and ground water reserves. Moreover, pesticides can never be the best option to manage the disease due to their extensive toxicity and minuscule degradability. The innate resistance may be elevated by applying nonpathogenic microbial inducers; thus, termed as induced systemic resistance (ISR). The native rhizospheric bacterial inducers may manage disease by inducing systemic resistance in plants. The similar measure has been adopted to manage black spot disease in rose plants by using Pseudomonas fluorescens RB4 and Bacillus subtilis RB11 as biological inducers. § In the first phase of study, surveys were performed to assess disease attributes of black spot disease of rose caused by Diplocarpon rosae. During this survey, 120 pathogenic isolates of D. rosae were collected. After infecting healthy rose plants with isolates of D. rosae, most virulent strain D. rosae DR19 was selected for further experimentations. § During greenhouse studies, different rhizospheric strains of bacillus and pseudomonas, isolated from rhizosphere of healthy rose plants, were screened for induction of systemic resistance in rose plants against black spot disease. These isolated bacterial strains were interacted with rose plants in the presence of black spot pathogen. Here two strains, viz: P. fluorescens RB4 and B. subtilis RB11 provided most significant reduction in disease index. § Both of these strains induced significant higher amounts of defense related biochemicals including total phenolics, ascorbic acid and some defense related enzymes involved in phenylpropenoid pathway. Moreover, these strains were capable to enhance quantity of defense related physical barriers in plants such as lignin, pectin and cellulose as compared to control plants. § In another independent experiment, effect of P. fluorescens RB4 and Bacillus subtilis RB11 was assessed on nutrient contents and growth attributes of rose plants. These strains significantly enhanced nutrient contents including N, P, K, Ca, Mg, Mn, Zn, Cu and Fe in treated plants. Along with that, growth of rose plants was significantly improved under influence of these bacterial strains. § In next phase of study, different carrier materials such as sugarcane press mud, bentonite, sand, rock phosphate and perlite were used to prepare formulations of best performing bacterial strains. Sugarcane press mud showed maximum viability of bacterial strains after prolonged storage at room temperature followed by ‘bentonite’. Sugarcane press mud based bacterial formulations supported disease managing potential of P. fluorescens RB4 and B. subtilis RB11, and reduced disease index up to 59 and 76% respectively in both season field experiments. This formulation also significantly improved agro economic traits of rose plants. § In last phase of study, potential ISR elicitor present in bacterial inducer was isolated and identified. For this purpose, Column Chromatography and GC/MS techniques were used to analyze metabolites of B. subtilis RB11 for identification of bioactive compound responsible for resistance induction and disease management. It was found that octadecane was the bioactive compound inducing resistance in rose plants against D. rosae. It was also observed that the isolation of octadecane present in B. subtilis RB11 metabolites was directly correlated with the concentration of ethyl acetate in extraction solvent. § To assess the significance of the results obtained during various experiments data was subjected to a number of statistical analyses. These analyses include analysis of variance (ANOVA) and Duncan’s Multiple Range Test (DMRT). From present research it is concluded that P. fluorescens RB4 and B. subtilis RB11, may be successfully used to manage black spot disease of roses caused by D. rosae. These bacterial strains are capable to enhance innate resistance of rose plants along with growth promotion. Moreover, octadecane synthesized by B. subtilis RB11 may be isolated and applied to rose plants as antifungal compound against D. rosae.