In response to wounding, harvested fruit tissues of apple and citrus exhibit the production of
reactive oxygen species (ROS). ROS production is greater when yeast antagonists used as biocontrol agents are applied in the
wounds. These phenomena result in an oxidative stress environment for the yeast antagonists. It has been demonstrated that pre-exposure of some of these yeast antagonists to sublethal abiotic stress (heat or
hydrogen peroxide), or stress-ameliorating compounds such as
glycine betaine (GB) can induce subsequent oxidative stress tolerance in the antagonistic yeast. The increased level of oxidative stress tolerance has been demonstrated in vitro and is characterized by higher levels of
antioxidant gene expression, increased production of
trehalose, and lower levels of ROS when yeast are exposed to a subsequent oxidative stress. The current study determined whether or not the effects of GB on yeast antagonists determined in vitro persist and are present in planta when yeast are applied to wounded apples. The effect of exogenous GB on the production of ROS in the yeast antagonist, Candida oleophila, was determined after the yeast was placed in apple
wounds. Oxidative damage to yeast cells recovered from apple
wounds was also monitored. Results indicated that GB treatment improved the adaptation of C. oleophila to apple fruit
wounds. Compared to untreated control yeast cells, GB-treated cells recovered from the oxidative stress environment of apple
wounds exhibited less accumulation of ROS and lower levels of oxidative damage to cellular
proteins and
lipids. Additionally, GB-treated yeast exhibited greater biocontrol activity against Penicillium expansum and Botrytis cinerea, and faster growth in
wounds of apple fruits compared to untreated yeast. The expression of major
antioxidant genes, including peroxisomal
catalase,
peroxiredoxin TSA1, and
glutathione peroxidase was elevated in the yeast by GB treatment. This study supports the premise that activation of
antioxidant response in biocontrol yeast can improve biocontrol efficacy.