Acid adaptation and biocontrol efficacy of antagonistic marine yeast Rhodosporidium paludigenum

The objectives of this work were to assess the optimum conditions for induction of acid tolerance in the marine yeast Rhodosporidium paludigenum and evaluate the biocontrol activity of non-adapted and acid-adapted yeasts in controlling apple blue mold caused by Penicillium expansum. R. paludigenum grown in malic and lactic acid treatments were stimulated after 12 h incubation. Moreover, medium modified with malic and lactic acid significantly enhanced the acid tolerance of R. paludigenum (p < 0.05). In acid tolerance response test, the highest viability of R. paludigenum was obtained at initial pH of 5.5 in the NYDB medium modified with malic acid (91.6 %). In addition, all R. paludigenum treatments significantly reduced the disease incidences and lesion diameters of blue mold in apples. Furthermore, there was no significant difference between acid-adapted and unadapted yeasts in the apple wounds after 48 h dynamics. Acid stress improved R. paludigenum viability under acidic conditions. However, there was no significant difference between acid-adapted and unadapted yeasts in controlling P. expansum on apple fruit (p < 0.05). These results indicate the potential for maintaining the survival level of biocontrol agents by physiological inducement strategy.