Enhancing bioefficacy of Bacillus amyloliquefaciens SF14 with salicylic acid for the control of the postharvest citrus green mould

• Published in: Plant stress (Amsterdam) 2023-03, Vol.7, p.100144, Article 100144
• Main Authors: Hamss, Hajar El, Kajad, Nada, Belabess, Zineb, Lahlali, Rachid
• Format: Article
• Language: English
• Subjects: Bacillus amyloliquefaciens; Bio-control agents; Biocontrol; Orange; Penicillium digitatum; Post-harvest
• ISSN: 2667-064X; 2667-064X
• DOI: 10.1016/j.stress.2023.100144

•SA at 0.5% was found to improve the biocontrol efficacy of Bacillus amyloliquefaciens SF14.•The combination of SF14 with SA did not affect the fruit quality parameters.•SF14 in combination with SA resulted in higher amounts of total polyphenols, flavonoids, and PAL.•FTIR and mineral analysis evidenced biochemical defence response in the peel of citrus fruit.•The improvement of biocontrol by SA could be by either induced resistance or direct effects on Penicillium digitatum. Penicillium digitatum is a major post-harvest pathogen of citrus fruit causing tremendous economic losses. In this study, salicylic acid (SA) and antagonistic bacteria Bacillus amyloliquefaciens (SF14) were tested in controlling P. digitatum (green mould) infections as an alternative to chemical controls. Three concentrations of SA (0.5, 1, and 2%) were tested for their antifungal activity in both in vitro and in vivo conditions alone and in combination with SF14. Fruit quality parameters including fruit firmness, weight loss, titratable acidity, and soluble solids content were evaluated. The impact of these biological treatments was also investigated by measuring the changes in organic and mineral properties of orange fruits using Fourier transform infrared spectroscopy (FT-IR). Enzymatic activity including phenylalanine ammonia-lyase (PAL), total polyphenols and flavonoids was also tested. In vitro assays showed that SF14 combined with 0.5% SA provided the highest inhibition of green mould growth reaching 72.98%. Inhibition of spore germination was also highest in the same treatment od reaching 63.40%. FTIR of fungal biomass confirmed an alteration of fungal well wall following biological treatments. Moreover, during in vivo assays, the combination of SF14 and 0.5% SA produced the lowest disease severity (5.43%) without considerably affecting the fruit quality. Further investigation of the effect of these treatments on the mineral composition of treated oranges showed that Ca, Fe, K, Mg, and Na concentrations were significantly affected. Changes in these elements may show a defence reaction induced by the biological treatments against the pathogen, which was also confirmed with the measurement of PAL activity, total polyphenols, and flavonoids. Interestingly, FTIR of citrus peel indicated significant changes in the content of bands denoting for phenolic and aromatic rings, suggesting an induced resistance against the pathogenic fungus. Overall, our findings suggested that the combina