Apple Transcriptome Responses to Irradiation Treatment and Cold Storage

Harvested apples often get stored under cold refrigeration for months before they are released into the market. During this prolonged storage,apples are vulnerable to physiological disorders as well as fungal fruit decay and various pests. Irradiation is commonly used for phytosanitary purposes before storage to kill some of the most destructive apple pests such as Oriental fruit moth, codling moth, fruit flies, and light brown apple moth. According to the recent findings from Dr. Prakash\u27s lab, irradiation was shown to be very effective in mitigating the superficial scald incidence in stored “Granny Smith” apples. Superficial scald is a very common physiological disorder in stored apples characterized by skin browning, which can lead to product waste due to decrease in shelf-life and consumers’ unwillingness to purchase defective apples. The objective of this project is to investigate the overall apple transcriptome changes due to irradiation and possibly explaining the molecular mechanisms underlying the irradiation-mediated protection of apples against superficial scald. Apple peels were collected from irradiated and control apples on day zero and after 90 days of refrigeration. Total RNA was extracted from three biological replicates per treatment and RNA-Seq libraries were constructed. The libraries were pooled together and subjected to 150 bp single-end sequencing on Illumina HiSeq4000 machine. A total of 582 million high quality reads were generated and mapped to the apple genome. Compared to 90 day stored control apples, the irradiated and 90 day stored apples showed 375 genes with at least two fold differential expression. Our results will provide the first step towards understanding the molecular responses in apples to irradiation treatment