Induction of defense responses and biological control of blue mold of apple fruit (Penicillium expansum) with Rhodotorula mucilaginosa A1

In this study, Rhodotorula mucilaginosa isolate A1 was recovered from healthy apple surface and Penicillium expansum was isolated from infected apple. The yeast isolate was evaluated as a potential biological control agent for apple blue mold caused by P. expansum. Dual culture, extracellular metabolite and volatile compounds tests were used in in vitro assays. The yeast inhibited growth of P. expansum, the inhibition by yeast was 60.97%, in dual culture, 90.57% in volatile gases and 83.36% in cell free metabolite tests. Apple fruit were wound-inoculated using 40 µl of yeast cell suspension (107cell/ml) followed 24 h later by P.expansum (105 conidia/ml). The apples were then incubated at 20 and 5°C. The yeast reduced the decayed area at both (20 and 5 °C) temperatures. In the second section of this study, the ability of yeast to induce catalase, peroxidase and phenolic compounds in apple tissue was investigated. The apples were first treated with the yeast, then inoculated with the pathogen and incubated for 10 days at 20 °C. Peroxidase, catalase activities and levels of phenolic compounds were measured 2, 4, 6, 8 and 10 days after inoculation with P. expansum. R. mucilaginosa A1 caused increase in peroxidase and catalase activities that reached their maximum level 6 days after inoculation with pathogen. The highest level of phenolic compounds was observed at 6 days after pathogen inoculation in treatments of R. mucilaginosa A1and Penicillium compared with control (apple treated with distilled water). The ability of R. mucilaginosa to increase activities of peroxidase, catalase and levels of phenolic compounds may be some of the mechanisms responsible for its biocontrol activities.