Exogenous GABA prevents Marssonina apple blotch damage in 'Royal Gala' apple seedlings

Marssonina apple blotch, caused by the pathogen Marssonina coronaria, is one of the most important pre-mature defoliation diseases that affected apple production. gamma-aminobutyric acid (GABA) is a non-protein amino acid and as an endogenous metabolite and signal molecule plays a key role in the stress response in plants. Herein, we investigated the effects of GABA in improving apple resistance to Marssonina apple blotch. Soil drenching of 0.5 mM exogenous GABA was identified as the optimal concentration to reduce M. coronaria disease severity on twomonths-old apple seedlings (Malus x domestica cv. 'Royal Gala') in a growth chamber. Further study demonstrated that the application of exogenous GABA significantly reduced the chlorophyll content degradation and photosynthetic rate than inoculated and non-GABA treated plants. After inoculation with M. coronaria, the GABA content in apple leaves increased significantly in infected plants. The soil drenching of GABA further elevated the salicylic acid (SA) content and activities of chitinase and beta-1,3-glucanase compared with the inoculated nonGABA treated plants. Furthermore, phenylalanine ammonia lyase (PAL) activity and the total phenol content of GABA-treated plants were further increased compared with the inoculated non-GABA treated plants. As a component of natural plant metabolism, exogenous soil drenching of GABA maybe a promising strategy through enhancing plants own immunity to control Marssonina apple blotch prevalence.

Automated summary

The application of exogenous gamma-aminobutyric acid (GABA) can improve apple resistance to Marssonina apple blotch by reducing disease severity and maintaining normal photosynthesis. Additionally, GABA can induce the production of some disease-resistant substances in apple plants, such as salicylic acid and chitinase. Therefore, soil drenching of GABA may be a promising strategy to control the prevalence of Marssonina apple blotch.