Differential sensitivity of four highbush blueberry (Vaccinium corymbosum L.) cultivars to heat stress

Highbush blueberry (vaccinium corymbosum l.) has recently been introduced into southeast china,a typical subtropical area with a high temperature climate in summer. understanding of the thermal tolerance among different genotypes of highbush blueberry is needed to select appropriate cultivars. four highbush blueberry cultivars ('duck','brigitta','sharpblue' and 'misty') were exposed for 6 h to different temperatures (25,30,35,40 and 45°c),and then various physiological parameters and ultrastructure of chloroplast were assessed. exposure to high temperature significantly increased the level of relative electrolyte leakage (rel),contents of malondialdehyde (mda),proline content,hydrogen peroxide (h2o2),superoxide radical (o2.-) rate,and the initial chlorophyll fluorescence yield (fo). whereas the maximum photochemical efficiency of psii (fv/fm) and the quantum efficiency of psii photochemistry (f{cyrillic}ps ii) decreased under high temperature conditions. the most pronounced effect by high temperature stress was obtained in 'brigitta',while the least effect existed in 'sharpblue'. furthermore,the chloroplast ultrastructure in 'brigitta' was severely damaged under heat temperature stress,whereas that of 'sharpblue' was almost intact. the results indicated that the 'sharpblue' was the most heat-tolerant blueberry cultivar while 'brigitta' was the most sensitive to heat temperature stress,followed by 'duck' and 'misty'. these were consistent with results observed from the field trial. this study proved that photosynthetic parameters stressed by short-term heat stress were fairly reliable to evaluate the thermal endurance in highbush blueberry.