Tissue Moisture Loss during Sample Preparation Lowers Exotherm Temperatures in Dormant Grape Buds

Abstract

Grapevine cold hardiness is often assessed with differential thermal analysis (DTA) of excised dormant buds. Such small tissues are prone to rapid dehydration when exposed to air during sample preparation. We show that excised buds of grape cultivars `Vignoles' and `Norton' lose as much as 6.3% and 2.9% of their total water content, respectively, during a two-minute exposure to air at 24 °C. In order to assess the impact of moisture loss on cold hardiness measurements, we prepared dormant bud samples with reduced water content and subjected them to DTA. The results demonstrate a positive correlation between average gross bud water content and median low temperature exotherm (LTEmean). In `Vignoles' and `Norton' buds, a 6.5% and a 4.3% reduction in gross water content, respectively, were sufficient to result in lower LTE temperatures (P < 0.001). The data suggest that even moderate dehydration of excised grape buds may influence the results of cold hardiness assessment by DTA. It is important that investigators be vigilant to the potential artifacts that can arise during sample preparation in order to ensure that the LTE temperatures of samples reliably characterize the cold hardiness of field populations.