Tolerance of Watermelon Seedlings to Low-temperature Chilling Injury

Abstract

Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] is one of the Cucurbitaceae species and subtropical crops that exhibit chilling injury (CI) when exposed to low temperatures. Watermelon seedlings were tested for chilling tolerance using methods modified from cucumber. Three experiments were conducted using different combinations of chilling durations of 6, 12, 24, or 36 hours and chilling temperatures of 2 or 4 °C. Watermelon seedlings were more resistant to low temperatures than cucumber seedlings, so it was necessary to use long chilling durations to induce significant foliar damage. A diverse set of 16 watermelon cultigens was tested: Allsweet, Black Diamond, Chubby Gray, Charlee, Charleston Gray, Dixielee, Golden, Golden Honey, New Winter, NH Midget, Sugar Baby, Sugarlee, Sunshade, PI 189225, PI 244018, and PI 595203. Experiments were conducted in a controlled environment with a light intensity of 500 mmol·m−2·s−1 photosynthetic photon flux density (PPFD). Optimal conditions for chilling treatment were 36 hours at 4 °C or 24 hours at 2 °C. The most resistant cultigen was PI 244018, and the most susceptible cultigens were NH Midget and Golden.