Antifungal action and induction of resistance by β-aminobutyric acid against Penicillium digitatum to control green mold in orange fruit.

Green mold, caused by Penicillium digitatum, is the most economically important postharvest disease of orange fruit worldwide. The aim of this study was to evaluate the effect of β-aminobutyric acid (BABA) treatment on the inhibition of P. digitatum both in orange fruit and in vitro as well as the possible mechanisms of action. BABA at 125 mM significantly inhibited mycelial growth, spore germination, and germ tube elongation of P. digitatum by 93.3, 90.3, and 90.5%, respectively. The relative electrical conductivity of mycelium was increased for a period of 0-36 h after treated with BABA at 125 mM. Furthermore, BABA caused a high level of malondialdehyde (MDA) in P. digitatum mycelia during four days of incubation. The ergosterol content in the plasma membrane of P. digitatum was significantly lower in BABA-treated mycelia. Also, protein and sugar leakage were increased with BABA treatment compared with that in the control. Besides, BABA caused a considerable reduction in the total lipid content of P. digitatum mycelia at 125 mM. Scanning electron microscopy (SEM) of P. digitatum treated with BABA at 125 mM showed shrunken, distorted, and collapsed mycelia. The application of BABA at 125 mM in orange fruit inoculated with P. digitatum suppressed disease incidence and disease severity by 74.6 and 77.3%, respectively, compared to untreated fruit. Moreover, the activity of defense-related enzymes, including peroxidase (POD), polyphenoloxidase (PPO), and phenylalanine ammonia-lyase (PAL) were significantly enhanced in the orange fruit treated with BABA at 125 mM.