Comparing the cold resistance of roots of different wine grape varieties

Winter freezing injury of wine grape refers to the phenomenon in which grape tissue cells are injured or even killed when they are exposed to temperatures lower than 0 ℃. Northern China in winter is colder and drier than areas of similar latitude elsewhere in the world. Winter freezing injury is one of the most significant limiting factors restricting the development of wine grape cultivation in northern China. Different parts of the grapevine vary in their resistance to cold. The root has the least resistance as it does not have the process of dormancy in winter. However, the cold tolerance level of the root depends on the genetic character of the wine grape varieties. An investigation into the cold resistance of roots of different wine grape varieties should provide scientific guidance on the monitoring, early warning, and prevention of winter-freezing injury of wine grape in northern China. In this paper, roots from eight common varieties of wine grape, such as 'Cabernet Sauvignon', 'Merlot', 'Marselan', 'Vidal', 'Syrah', 'Beimei', 'Beihong' and 'Longyan', in the eastern foothills of Helan Mountain were selected and tested. The freezing experiment on these roots was carried out by an artificial freezing system simulating the natural cooling and freezing processes. The temperatures of the supercooling point and the frozen point, the concentrations of the soluble sugar and the soluble protein, the relative electronic conductivity, and the semi-lethal temperature of the roots were measured in the laboratory. The critical temperatures for roots of different varieties were further identified using correlation analysis and cluster analysis. After that, the cold resistance abilities of roots of eight tested wine grapes were comprehensively analyzed for the indicators mentioned above. The following conclusions were drawn: 1) The content of soluble protein in the root significantly affected the cold resistance ability of wine grapes. 2) The cold resistance ability of roots from the eight varieties could be grouped into three categories: the light cold resistance type ('Cabernet Sauvignon', 'Merlot', 'Syrah'), for which the supercooling point was -3.8 ℃ to -3.2 ℃, the frozen point was -2.8 ℃, to -2.3 ℃, and the semi-lethal temperature was -4.34 ℃ to -3.19 ℃; the moderate cold resistance type ('Beimei', 'Marselan', 'Vidal'), for which the supercooling point was -5.4 ℃ to -4.4 ℃, the frozen point was -4.1 ℃ to -3.7 ℃, and the semi-lethal temperature was -5.90 ℃ to -4.43 ℃; the strong cold resistance type ('Beihong', 'Longyan'), for which the supercooling point was -6.4 ℃ to -6.3 ℃, the frozen point was -5.2 ℃ to -4.8 ℃, and the semi-lethal temperature was -6.55 ℃ to -6.11 ℃. 3) The cold resistance abilities of roots of the eight varieties varied from strong to light in this order: 'Beihong' > 'Longyan' > 'Beimei' > 'Vidal' > 'Marselan' > 'Cabernet Sauvignon' > 'Merlot' > 'Syrah'. The results showed that both temperatures of the supercooling point and the frozen point for the grape roots could be used as indicators to evaluate the cold resistance ability of grapes.