The role of drought stress on the acquisition of freezing tolerance in asparagus under controlled conditions

Abstract

Cold acclimation induces freezing tolerance in asparagus ( Asparagus officinalis L.), which is important for survival and longevity in temperate climates. Previous studies indicated that cultivar “Guelph Millennium” (GM), adapted to Southern Ontario, acquired freezing tolerance earlier in the fall and maintained it later in the spring than “UC157” (UC), a cultivar commonly grown in desert climates. As the drought and cold acclimation metabolic pathways overlap, the objective of this research was to determine whether drought alone induced freezing tolerance or interacted synergistically with cold temperatures. Seedlings of GM and UC were subjected to control, drought, or cold acclimating conditions for 6 weeks. Additional treatments included 6 weeks of drought or control conditions followed by 6 weeks of cold acclimation, and plants grown for 12 weeks under control conditions. LT50, the temperature at which 50% of plants die, and metabolites or parameters associated with freezing tolerance were measured. GM had decreased LT50 levels (increased freezing tolerance) compared with UC under both drought and cold acclimating conditions, and no cultivar differences were observed under control conditions. Drought stress before cold acclimation resulted in an increased LT50 (reduced freezing tolerance) for UC compared with GM. A high root:shoot ratio and low crown water percentage were associated with increased freezing tolerance in GM, while a high crown sucrose concentration in UC was related to decreased freezing tolerance for the drought treatment. Overall, drought stress induced cultivar-specific adaptations causing differences in freezing tolerance, thus confirming the interrelationship between these two physiological pathways.