3.3. Outcome of cold stress followed by a large temperature fluctuation in-field site
In late May 2018, unusually high number of fruit drops occurred after a short period of cold in primary apple production regions of South Korea. In the experimental plots in the Apple Research Institute, Gunwi, we observed similar damage with a distinctive yellow coloured peel compared to normal fruit as well (Supporting Information Figure S1). After the daily minimum temperature reached a peak of over 20 ºC on 17th May, it decreased rapidly to 5 ºC until 20th May (Figure 1a). When the daily mean temperature data was compared to the 10-year annual mean, there was a big fluctuation and showed a maximum gap of +7 degrees on 17th and -4 degrees on the 20th (Figure 1b). This indicated an unusual cold shock starting from 17th to 20th of May, which might have induced an abnormal fruit drop among early developing apple afterward. Therefore, based on these meteorological data combined with the results of both RNA-seq and metabolomics analyses, we hypothesized that cold stress affects the abscission of early developing apple.