The mechanism involved in enhancing the biological control efficacy of Rhodotorula mucilaginosa with salicylic acid to postharvest green mold decay of oranges

The main postharvest pathogen of citrus fruit is Penicillium digitatum. The present study looked at the role of Rhodotorula mucilaginosa enhanced with 0.2 mM salicylic acid (SA) on pH, lignin content accumulation and growth dynamics as a resistance mechanism against P. digitatum in orange fruit. Our findings revealed that the increase in lignin content at 20 °C storage temperature resulted in the significant decrease (P ≤ 0.05) in the lesion diameter in fruit treated with R. mucilaginosa enhanced with or without 0.2 mM SA compared to the untreated fruit (control). In addition, the pH values of the fruit treated with R. mucilaginosa enhanced with or without 0.2 mM SA were 4.43 ± 0.07 and 4.15 ± 0.11, respectively, around the infection site compared to the untreated group. Moreover, the in vivo trial showed that the addition of 0.2 mM SA to the antagonist augmented its growth, and subdued substantially the hyphae and spore germination of P. digitatum in vitro. Also, lower levels of malondialdehyde (MDA) and hydrogen peroxide (H2O2) content were observed in fruit treated with the antagonist enhanced with or without 0.2 mM SA compared to the control. The results established that pH, lignin content accumulation and growth of the yeast played a significant role in the control of green mold decay of orange fruit.