β‐Aminobutyric acid induced phytotoxicity and effectiveness against nematode is stereomer‐specific and dose‐dependent in tomato

β‐Aminobutyric acid (BABA) induces resistance to a/biotic stress but is associated with phytotoxicity in some plant species. There are two enantiomers of BABA, the R and S enantiomers. We evaluated the phytotoxicity caused by the RS BABA (racemic mixture of R and S BABA), evaluating the dose–response effect and different modes of application on tomato. Results show that RS BABA‐induced phytotoxicity in tomato is dose‐dependent and stronger with foliar applications than with soil drench. We further evaluated the phytotoxicity of the two enantiomers separately and observed that BABA‐induced phytotoxicity is stereomer‐specific. In comparison with less phytotoxic effects induced by S BABA, R BABA induces dose‐dependent and systemic phytotoxic symptoms. To investigate the possible physiological causes of this phytotoxicity, we measured levels of oxidative stress and anthocyanins and validated the findings with gene expression analyses. Our results show that high doses of RS and R BABA induce hydrogen peroxide, lipid peroxidation, and anthocyanin accumulation in tomato leaves, while this response is milder and more transient upon S BABA application. Next, we evaluated BABA induced resistance against root‐knot nematode Meloidogyne incognita in tomato. BABA‐induced resistance was found to be stereomer‐specific and dependent on dose and mode of application. R or RS BABA multiple soil drench application at low doses induces resistance to nematodes with less phytotoxic effects. Taken together, our data provide useful knowledge on how BABA can be applied in crop production by enhancing stress tolerance and limiting phytotoxicity.