Induction of pathogenesis-related proteins, phenolics and phenylalanine ammonia-lyase in groundnut by Pseudomonas fluorescens

Foliar application of a plant growth-promoting rhizobacterium, Pseudomonas fluorescens strain Pf1 significantly controlled late leaf spot and rust diseases of groundnut (Arachis hypogaea L.) under greenhouse conditions. Groundnut plants, when sprayed with P. fluorescens strain Pfl, showed increase in activity of phenylalanine ammonia-lyase 1 day after application and the maximum enzyme activity was detected at 3 days after treatment. An increase in phenolic content was observed 1 day after P. fluorescens treatment. Also chitinase and β-1,3-glucanase activities increased significantly 1 day after P. fluorescens treatment and maximum activities were reached 4 days later. Application of P. fluorescens to groundnut leaves induced accumulation of a 23-kDa thaumatin-like protein (TLP) and a 30-kDa glucanase. The induction of 23-kDa TLP was detected only in treated leaves and not in roots, stems and petioles of the groundnut plants. The 30-kDa glucanase started to accumulate 1 day after treatment and the level of the protein continued to increase throughout the experimental period of 4 days. Both TLP and glucanase were found in the intercellular fluid of P. fluorescens-sprayed groundnut leaves.