Wheat resistance against infection by Pyricularia oryzae is potentiated by β-aminobutyric acid and not affected by γ-aminobutyric acid

Epidemics of blast, caused by Pyricularia oryzae, have caused great yield losses in wheat. Disease control has relied only on using resistant cultivars combined with fungicide spray. Other control strategies need to be investigated and the use of inducers of host resistance may become an environmentally friendly and viable strategy for blast management. In this context, the potential of using the acids β-aminobutyric (BABA) and γ-aminobutyric (GABA) to induce wheat resistance against blast was investigated. This goal was achieved by examining the photosynthetic performance [fluorescence of chlorophyll (Chl) a measurements and photosynthetic pigments pools (Chl a+b and carotenoids)], host defense responses [activities of chitinase (CHI), β-1,3-glucanase (GLU), peroxidase, phenylalanine ammonia-lyase (PAL), polyphenoloxidase (PPO), and lipoxygenase (LOX)], concentrations of phenolics and lignin, antioxidative metabolism [activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase] as well as oxidative stress [concentrations of malondialdehyde, hydrogen peroxide (H2O2), and superoxide anion radical (O2•-)] of non-inoculated and inoculated plants from cultivar BRS Guamirim (susceptible to blast) sprayed with water or with solutions (100 mM) of BABA or GABA. Blast progressed much faster on water- and GABA-sprayed plants than on BABA-sprayed plants. The area under blast progress curve was significantly higher by 52 and 47 % for plants from control and GABA treatments, respectively, compared to BABA treatment. Values of Chl a fluorescence parameters (variable-to-maximum Chl a fluorescence ratio, photochemical yield, and yield for dissipation by down-regulation) linked to Chl a+b and carotenoids concentrations were higher for BABA-sprayed plants than for water- or GABA-sprayed plants. Activities of CHI, GLU, PAL, PPO, and LOX were more remarkable for BABA-sprayed plants than for those sprayed with either water or GABA. Greater activities of APX, CAT, and SOD for BABA-sprayed plants helped to alleviate the stress imposed by higher concentrations of H2O2 and O2•- in contrast to those sprayed with water or GABA. Taken together, these results allowed the conclusion that supplying BABA to wheat plants increased their resistance against blast in a scenario where the photosynthetic apparatus was preserved along with a boosted defense response and a more robust antioxidative metabolism. •Blast progressed faster on the le