Pichia caribbica combined with oligochitosan controlling black spot of tomatoes and the regulation on ROS metabolism of the fruits

Abstract

Black spot caused by Alternaria alternata is one of the main postharvest diseases of tomato fruits. This research aimed to investigate biocontrol efficacy of Pichia caribbica combined with oligochitosan (OCH) against black spot of tomato fruits and explore the mechanisms involved in improved disease resistance of the fruits by yeast combined with OCH based on analysis of reactive oxygen species (ROS) metabolism. The results indicated that in comparison with P. caribbica alone, yeast combined with OCH (2000 μg/mL) could further reduce black spot of tomato fruits. P. caribbica combined with OCH increased NADPH oxidase (NOX) activity in the fruits compared with the control and the group treated with yeast alone. The activities of enzymatic system for ROS scavenging including antioxidant enzymes, enzymes involved in ascorbate–glutathione (AsA-GSH) and GPX (glutathione peroxidase) cycles, and glutathione S-transferase (GST) in the fruits were induced by yeast combined with OCH. Additionally, the contents of ascorbic acid (AsA) and glutathione (GSH) belonging to non-enzymatic system for ROS scavenging were enhanced in the fruits. Collectively, the induction of NOX and the improvement of enzymatic and non-enzymatic systems for ROS scavenging resulted in the decrease in O2–·, H2O2 and malondialdehyde (MDA) production in the fruits, thus promoting the disease resistance of tomato fruits. This research will provide new ideas for the control of postharvest diseases of tomato fruits.