Effect of heat shock treatment on stress tolerance and biocontrol efficacy of Metschnikowia fructicola.

The effect of high temperature and oxidative stress on the cell viability of the yeast antagonist, Metschnikowia fructicola was determined. A mild heat shock (HS) pretreatment (30 min at 40 °C) improved the tolerance of M. fructicola to subsequent high temperature (45 °C, 20-30 min) and oxidative stress (0.4 mol L⁻¹ hydrogen peroxide, 20-60 min). HS-treated yeast cells showed less accumulation of reactive oxygen species (ROS) than nontreated cells in response to both stresses. Additionally, HS-treated yeast exhibited significantly greater (P<0.0001) biocontrol activity against Penicillium expansum and a significantly faster (P<0.0001) growth rate in wounds of apple fruits stored at 25 °C compared with the performance of untreated yeast cells. Transcription of a trehalose-6-phosphate synthase gene (TPS1) was upregulated in response to HS and trehalose content also increased. Results indicate that the higher levels of trehalose induced by the HS may contribute to an improvement in ROS scavenging, stress tolerance, population growth in apple wounds and biocontrol activity of M. fructicola.