Response of Cucumber (Cucumis sativus L.) and Squash (Cucurbita pepo L. var. melopepo) Roots to Chilling Stress during Early Stages of Seedling Development

Abstract

Roots of `Golden Girl' squash (Cucurbita pepo var. melopepo) and `Encore' cucumber (Cucumis sativus L.), 4- and 3-days-old, respectively, were exposed to 2, 6, 10, and 15C for 24, 48, 96, 144, and 192 hours to compare the sensitivity to chilling temperatures and the subsequent recovery at more favorable temperatures. Seedlings were more sensitive to chilling at 2 and 6C when measured by their ability to resume growth when returned to 26C. Root growth decreased after 48 hours of chilling. Seedlings stressed at 10 and 15C were able to continue root growth at these temperatures and when returned to 26C. However, seedlings at 10C exhibited root-tip browning in both crop species, suggesting disfunction in metabolic pathways that were repressed in seedlings growing at 2C where those symptoms were not present. Effects on root dry weight occurred in the first 24 hours at all temperatures studied. After 96 hours of treatment, seedlings grown at 2 and 6C were irreversibly damaged, as evidenced by their inability to resume growth when returned to 26C. Leakage of electrolytes from squash and cucumber roots increased after 48 hours at 2C. Potassium, Na+, and PO4-2 were lost in greater amounts than Mg+2, Cl-, and SO4-2. No difference in ionic leakage occurred at 10 and 15C, and Ca+2 leakage was not detected at any chilling stress temperature.