Lethal temperature coefficient – a new parameter for interpretation of cold hardiness

SummaryLethal temperature coefficient (Qlt) 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. Qlt 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 Qlt. It is demonstrated that Qlt 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 Qlt be reported for cold hardiness research.