An investigation of the frost hardiness of grapevine (Vitis vinifera) during bud break

The aim of this investigation was to assess ice nucleation and frost resist ance of two varieties of grapevine (Siegrebbe and Madeleine Angevine) durin g bud burst under radiative freezing conditions analogous to those during S pring in the UK. During bud burst, grapevines were almost entirely resistant to freezing dur ing frosts of less than -3 degrees C by virtue of their ability to supercoo l. The risk of frost damage increased significantly as bud development prog ressed, and once buds had passed growth stage DS3 they became more sensitiv e to freezing and freezing damage was more extensive. The two varieties did not differ in frost resistance but, because of its earlier developing habi t, variety Siegrebbe could be more prone to frost damage in the field. Buds were more prone to damage after freezing once bud burst had commenced and the damage could not be reversed by acclimating plants for periods of 7 to 21 days at 4 degrees C in an 8 h photoperiod. Such acclimation appeared to predispose frozen buds to more extensive damage.