Physiological and Biochemical Evaluation of Freezing Tolerance in Three Asparagus Cultivars in Early Spring

Asparagus cultivars grown in Southern Ontario must be winter-hardy, establishing dormancy in the fall before freezing, and maintaining dormancy during the freeze-thaw cycles of the spring. A field experiment was conducted at the Simcoe research station, Simcoe, ON, to assess freezing tolerance and associated physiological parameters in three cultivars, with varying adaptation to Southern Ontario, during dormancy release in the spring. In 2012, crowns of three cultivars [Guelph Millennium (GM), Jersey Giant (JG), and UC157] were harvested at four harvest dates and assessed for LT₅₀ (the temperature at which 50% of crowns die), carbohydrates, proline, protein, and percentage of water content. As soil temperatures increased in the spring, GM maintained higher levels of freezing tolerance than JG and UC157. With a period of decreasing temperatures during the sampling period, JG appeared to reacclimate and UC157 did not respond. Freezing tolerance was associated with carbohydares (reducing sugars and fructans), total protein and percentage of water content. Of the three cultivars tested, GM is best for maintaing freezing tolerance in the spring, and likely resists damage during freeze-thaw cycle, explaining, in part, its superior longevity compared to the other cultivars. A replicate experiment is in progress (Spring 2013).