Biocontrol activity of Rhodotorula mucilaginosa combined with salicylic acid against Penicillium digitatum infection in oranges

The effectiveness of Rhodotorula mucilaginosa in combination with salicylic acid (SA) was explored for the control of green mold decay of oranges and the mechanisms involved. The results of the study showed that treatments with the diverse concentrations of SA was remarkable in reducing the disease incidence of oranges and that SA at a concentration of 0.2 mM reduced the decay of oranges from 93.06% to 61.12%. At an incubation temperature of 20 degrees C and RH of 95% the disease incidence and lesion diameter in fruit treated with R. mucilaginosa enhanced with or without SA were significantly reduced compared to that of the control (P < 0.05). Moreover, the growth of the antagonist was enhanced in vivo by the combination of SA (0.2 mM) at both 20 degrees C and 4 degrees C, whiles it did not have any influence on the antagonist in vitro. Mycelia growth and spore germination of P. digitatum in orange wounds were found to be significantly inhibited by the combination of R. mucilaginosa and SA (0.2 mM) from the scanned electron micrographs. Postharvest qualifies of orange fruit were not impaired by the combination of the antagonist with SA. Additionally, the combination of the antagonist with SA (0.2 mM) led to an upsurge in polypenoloxidase (PPO), peroxidase (POD), phenylalanine ammonia lyase (PAL), catalase (CAT), ascorbate peroxidase (APX) and beta-1,3-glucase (GLU) activities. The improved control via SA could be ascribed either to direct effect or induce resistance of this organic chemical. Thus, the proper combination of R. mucilaginosa and SA can offer a vigorous approach to lessen postharvest decay of oranges.