Comparison of mid-Winter cold-hardiness and soluble sugars contents in the shoots of 21 highbush blueberry (Vaccinium corymbosum) cultivars

Cold-hardiness and the soluble sugars contents of the shoots of 21 highbush blueberry (Vaccinium corymbosum) cultivars ('Berkeley', 'Bluecrop', 'Bluegold', 'Bluehaven', 'Bluejay', 'Burlington', 'Chippewa', 'Collins', 'Dixi', 'Duke', 'Herbert', 'Jersey', 'Nelson', 'Northblue', 'Northland', 'Polaris', 'Rancocas', 'Sharpblue', 'Sierra', 'Spartan', and 'Sunrise') were compared in mid-Winter.The level of cold-hardiness was determined by measuring electrolyte leakage at various freezing temperatures and was expressed as LT₅₀, the temperature at which the incidence of injury reached 50%, and as T_max, the temperature at which the rate of injury was maximal. The LT₅₀ and T_max values for the shoots of all 21 highbush blueberry cultivars ranged from -31.8° ± 0.09°C to -41.1° ± 0.12°C, and from -29.7° ± 0.06°C to -36.9° ± 0.13°C, respectively. T_max values were significantly positively correlated with LT₅₀ values (r = 0.98**, P ≤ 0.01). Based on their levels of cold-hardiness in terms of LT₅₀ values, the 21 highbush blueberry cultivars were ranked in order as follows: 'Jersey' > 'Northland' > 'Northblue' > 'Dixi' > 'Berkeley' = 'Sierra' > 'Chippewa' > 'Bluegold' > 'Burlington' > 'Bluejay'>'Spartan' > 'Bluecrop' = 'Polaris' > 'Sunrise' > 'Duke' > 'Rancocas' > 'Herbert' > 'Sharpblue' > 'Collins' 'Bluehaven'> 'Nelson'. Cold-hardiness, as estimated by LT₅₀ and T_max, was highly negatively correlated with total soluble sugars content (r = -0.78**, P ≤ 0.01 and r = -0.69**, P ≤ 0.01 for LT₅₀ and T_max, respectively). Among the soluble sugars detected, fructose and glucose concentrations, in particular, were significantly positively correlated with the levels of cold-hardiness in the shoots of all 21 highbush blueberry cultivars, but sucrose and raffinose concentrations were not correlated with cold-hardiness. Knowledge of intra-species differences in mid-Winter cold-hardiness in relation to soluble sugars contents will be useful during the breeding and cultivation of highbush blueberries.