Freezing Tolerance Attributes during Spring Deacclimation for Three Asparagus Cultivars with Varying Adaptation to Southern Ontario

Abstract

Winterhardiness in asparagus (Asparagus officinalis) may be related to proper cold acclimation and induction of freezing tolerance in the fall, levels and maintenance of freezing tolerance in the winter, and the timing of deacclimation in the spring. Premature deacclimation and the inability to reacclimate could result in crown damage from spring freeze-thaw cycles. A field experiment was conducted, replicated over 2 years, to determine how three cultivars with varying adaptation to southern Ontario deacclimate in the spring by assessing LT50 (the temperature at which 50% of plants die) and biochemical and physiological parameters associated with freezing tolerance. ‘UC 157’ (UC), the least-adapted cultivar, deacclimated after soil temperatures rose above freezing; LT50 values increased linearly over time and were unaffected by fluctuations in soil temperature. ‘Jersey Giant’ (JG), a cultivar with moderate adaptation, rapidly deacclimated with increased soil temperature but appeared to partially reacclimate as temperatures decreased. For ‘Guelph Millennium’ (GM), the most-adapted cultivar, LT50 values did not change, maintaining the greatest levels of freezing tolerance during the spring sampling period. Although LT50 values did not differ among cultivars on the first spring sampling date, ranking for freezing tolerance at the final sampling in each year was GM>JG>UC, which is consistent with adaptation. Rhizome traits were most associated with freezing tolerance and included high concentrations of low-molecular-weight fructans (LFs), glucose, and proline and low percentage water and sucrose concentration. Overall, data suggest that the timing of deacclimation and loss of freezing tolerance in the spring may significantly affect winterhardiness; cultivars that lose freezing tolerance early and cannot reacclimate could suffer most from late spring freeze-thaw cycles.