Tolerance of Watermelon Seedlings to Low-temperature Chilling Injury

Abstract

<jats:p>Watermelon [<jats:italic>Citrullus lanatus</jats:italic> (Thunb.) Matsum. &amp; 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<jats:sup>−2</jats:sup>·s<jats:sup>−1</jats:sup> photosynthetic photon flux density (<jats:italic>PPFD</jats:italic>). 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.</jats:p>

Identification and expression analyses of WRKY genes reveal their involvement in growth and abiotic stress response in watermelon (Citrullus lanatus)

“…Similarly, plants irrigated with distilled water were used as control. For cold treatment, plants were kept in a growth chamber at 4°C under a light intensity of 300 mmol•m –2 •s –1 PPFD [ 40 ], then leaves were sampled at 1, 3, 6, 12, 24, and 48 hours after the commencement of cold treatment, whereas seedlings kept at 27±1°C under the same light condition were used as control. The drought stress treatment was accomplished creating a natural drought condition [ 41 ], and the control plants were well-watered to 70 ± 5% field capacity based on weighing.…”

Effects of Cold Durations on Chilling Injury in Lagenaria Germplasm

“…Chilling treatments. Chilling tests were performed according to the method of Kozik and Wehner (2014) with some modifications. The seedling flats were moved from the greenhouse to the chilling chambers when the seedlings reached the first true leaf stage.…”

“…Plants were rated 7 and 14 d after chilling for damage on the cotyledons, first true leaf, and growing point for each plant in each plot. The scale used was 0 to 9: 0 = no damage (based on the unchilled control plants), 1 to 2 = trace of damage, 3 to 4 = slight damage (20% to 50% of tissue necrotic), 5 to 6 = moderate damage (50% to 70% of tissue necrotic), 7 to 8 = advanced damage (70% to 90% of tissue necrotic), 9 = plant dead (90% to 100% tissue necrotic) (Kozik and Wehner, 2014). Figure 1 shows the scale of 0 to 9 on the cotyledons and first true leaves in Lagenaria.…”

“…Chilling tolerance has been studied in cucumber (Chung et al, 2003;Kozik et al, 2007;Kozik and Wehner, 2008;Smeets and Wehner, 1997), watermelon (Ghanbari et al, 2018;Kozik and Wehner, 2014;Spalholz and Kubota, 2017), and melon (Diao et al, 2019;Li, 2012;Zhang et al, 2017); however, few studies have been done on bottle gourds (Ko et al, 2006;Liu et al, 2003;Xing et al, 2017), and Lagenaria genetic resources have not been screened for low temperature conditions.…”

“…Researchers concluded that genetic variation for chilling damage was greater at the first true leaf than at the cotyledon stage. Kozik and Wehner (2014) used a similar method for screening of watermelons. They tested 16 watermelon cultigens using four chilling durations (6, 12, 24, or 36 h) and 2 chilling temperatures (2 or 4°C).…”