Ornithine enhances common bean growth and defense against white mold disease via interfering with and diminishing the biosynthesis of oxalic acid in .

The necrotrophic fungal phytopathogen, (Lib.) de Bary, employs a multilayered strategy to infect a wide range of host plants. The current study proposed the diamine -ornithine, a non-proteinogenic amino acid that promotes the synthesis of other essential amino acids, as an alternative management strategy to boost the molecular, physiological, and biochemical responses of common bean ( L.) against white mold disease caused by . experiments showed that -ornithine significantly inhibited the mycelial growth of in a dose-dependent manner. Moreover, it markedly diminished the white mold severity under greenhouse conditions. Moreover, -ornithine stimulated the growth of treated plants suggesting that the tested concentration of -ornithine has no phytotoxicity on treated plants. Additionally, -ornithine enhanced the non-enzymatic antioxidants (total soluble phenolics and flavonoids), the enzymatic antioxidants (CAT, POX, and PPO), and upregulated the gene expression of three antioxidant-associated genes (, , and ). Moreover, analysis showed that the genome of possesses a putative oxaloacetate acetylhydrolase () protein that is highly similar in its functional analysis, conserved domains, and topology with OAH from () and (). Interestingly, the addition of -ornithine to the potato dextrose broth (PDB) medium significantly down-regulated the gene expression of in the mycelium of . Likewise, exogenous application of -ornithine significantly down-regulated the gene expression of in the fungal mycelia collected from treated plants. Finally, -ornithine application significantly diminished the secretion of oxalic acid in the PDB medium as well as infected leaves. Collectively, -ornithine plays a pivotal role in maintaining the redox status, in addition to boosting the defense responses of infected plants. The current study provides insights that may lead to innovative eco-friendly approaches for controlling white mold disease and mitigating its impact on common bean cultivation particularly, and other crops in general.