Plant growth-promoting rhizobacteria-elicited alterations in phenolic profile of chickpea (Cicer arietinum) infected by Sclerotium rolfsii

Efficacy of seven strains of Pseudomonas fluorescens (Pfs1-7), plant growth-promoting rhizobacteria (PGPR), were tested under field conditions for their ability to protect Cicer arietinum against Sclerotium rolfsii infection. Best protection was observed in strain Pfs3 where 23% seedling mortality was recorded in comparison to 44% in non-treated control. To correlate the induction of phenolic compounds by the PGPRs with disease resistance, qualitative and quantitative alterations of phenolic compounds in different parts of C. arietinum were estimated following PGPR application as seed treatment. High performance liquid chromatographic (HPLC) analysis of the leaves, collars and roots of the PGPR-treated and non-treated (control) plants showed the presence of gallic, ferulic, chlorogenic and cinnamic acids with varied amounts in the PGPR-treated as well as non-treated (control) plants. Maximum accumulation of cinnamic acid was observed in plants treated with PfO strain (1660 ng g(-1) fresh wt.) which was almost 19.5 times higher than untreated control plants and also significantly high when compared to other PGPR treatments. Pfs3 also caused maximum accumulation of total phenolics and gallic acid in all chickpea plant parts as compared to other treatments and untreated control. A direct relationship between the level of total phenolics and seedling survivability was observed. PGPR-mediated induction of phenolic compounds as a biochemical barrier in C. arietinum against S. rolfsii infection is envisaged.