Improvement in Defensive System of Indian Mustard (Brassica juncea var. RLM619) on Application of γ-Amino Butyric Acid (GABA)

Abstract

γ-amino butyric acid (GABA) has an intense capacity to induce protection in numerous plants against various pathogens. A germination study was undertaken to ascertain the effects of GABA using two different concentrations 10 and 50 ppm on defense related enzymes viz, peroxidase (POD), phenylalanine ammonia lyase (PAL) and superoxide dismutase (SOD) and total phenols in the hypocotyls and cotyledonary leaves of Brassica juncea RLM619 which has comparatively greater resistance to white rust and Alternaria blight. On the 7th day of the treatment highest increase of 3.1 fold in POD activity was observed in hypocotyls of seeds soaked with 50 ppm of GABA as compared to control (water). PAL activity also showed significant increase on treatment with both the concentrations. However, no systematic trend was observed in case of SOD activity. Higher level of total phenolic content in the hypocotyls and cotyledonary leaves was found with 10ppm concentration on 3rd and 5th DAG. Thin layer chromatography of methanolic extract of 50 ppm GABA treated hypocotyls of mustard revealed presence of new phenolic compounds with Rf values 0.58 and 0.76 on 5th DAG which were not present in the control and 10 ppm treated hypocotyls. Further these phenolic compounds get induced and can be observed on 7th DAG. These results proposed that application of GABA raises the resistance in Indian mustard by increasing the level of defense related compounds and this implies it may act as an alternative to fungicides in the search to control various fungal diseases.