The Effect of Drought Stress and Decreasing Daylengths on the Acquisition of Freezing Tolerance in Asparagus (Asparagus officinalis L.) under Controlled Conditions
The acquisition of freezing tolerance is a complex and vital process for asparagus grown in temperate regions. The impact of drought and decreasing photoperiods on this trait were explored using two cultivars with varying adaptation to Southern Ontario: Guelph Millennium (GM), bred locally, and UC157 (UC), bred in California, USA. Drought stress including that before cold acclimation increased freezing tolerance for GM compared to UC. Differing adaptative strategies to drought were found through cultivar-specific changes in root:shoot ratio, crown water percentage, and sucrose/glucose concentrations. Decreasing photoperiods did not impact freezing tolerance, although combined with cold temperatures diminished root:shoot ratio and increased crown water percentage in UC; GM was non-affected. Decreasing photoperiods under warm conditions caused elevated concentrations of crown high-molecular-weight fructan, decreased glucose and proline in GM compared to UC. Varietal differences in response to drought and decreasing photoperiod could be used for the selection of new asparagus cultivars.