Summary

Lethal temperature coefficient (Q_lt) is introduced as a new parameter to improve the interpretation of cold hardiness. It is calculated as the slope of the linear portion of the lethal temperature-injury (LT-I) regression line within 20% to 80% injury, the range of importance to plant survival and production. Q_lt represents the rate of injury increase for one-degree decrease of lethal temperature (LT). Cold hardiness of primary buds in grapevines was used as an example to illustrate the calculation and the importance of Q_lt. It is demonstrated that Q_lt and LT to 50% plant tissues (LT₅₀) together reflect overall LT-I responses and better interpret the cultivar differences and effects of various treatments on cold hardiness of primary buds in grapevines. It is suggested both LT₅₀ and Q_lt be reported for cold hardiness research.