| Blueberry (Vaccinium corymbosum L.), belonging to Ericaceae, Vaccinium spp., is a kind of perennial evergreen or deciduous shrub native to North America. Three species are of major economic importance:the highbush blueberry(Vaccinium corymbosum L.), the lowbush blueberry(Vaccinium angustifolium Ait) and the rabbiteye blueberry(Vaccinium ashei Reade; syn. Vaccinium virgatum Ait.). Highbush blueberry are further separated into northern highbush blueberry, southern highbush blueberry and halfhigh blueberry depending on their chilling requirements and winter hardiness. In recent years, the introduction trials showed the northern highbush cultivars can blossom and bear fruit in Zhejiang area, a province in southeast China. However, temperatures in this area often approach40℃or even higher in the season of summer. High temperature has become the most significant abiotic stresses limiting the growth and productivity of highbush blueberry in this area. However, the heat endurance ability related to the different highbush blueberry cultivars is still unclear. In this study, efield trials were conducted to screen the cultivars suitable for Zhejiang area, the effects of heat stress on physiological responses of different blueberry culitvars were also studied to to elucidate the mechanism of blueberry adapted to heat stress.In order to screen the genotypes of blueberry which might be suitable for cultivation in subtropical area, eight shape indexs of fifteen blueberries were determined, and then analysised by membership function. The results indicated that the adapability of fifteen blueberries is in following order:’Bluebelle1>’Reka’>’Diana’>’Premier’>’Sharpblue’>’Bluecrop’>’O’Neal’>’Brigitta’>’Duck’> ’Jersey’>’Misty’>’Earliblue’>’Berkeley’>’Darrow’>’Spartan’.In order to investigate the semi-lethal temperature (LT50) and heat tolerance of two blueberry cultivars, the changes of cells injured rate at different high temperature were studied with leaves collected from two cultivars of blueberry. The temperature of breakpoint was obtained on the basis of cells injured rate and Logistic equation. Then the relative electrolyte leakage (REL), the malondialdehyde (MDA) and free proline (Pro) contents, hydrogen peroxide (H2O2) and superoxide radical (O2·-) contents were analyzed under LT50after a serial treatment period. The results showed that the cells injured rate of the both cultivars increased following an S-curve with the temperature increase and the LT50of ’Jersey’ and ’Diana’ were48.3℃and47.32℃, respectively. Under the LT50, the REL values, contents of MDA and Pro, H2O2and O2·-contents gradually increased with the extension of time.;12-24hours was considered to be a critical period for high injury of blueberry under the LT50.In order to investigate the physiological variation of different blueberry genotypes under high temperature stress, and to screen high temperature tolerant genotypes of blueberry which might be suitable for cultivation in subtropical area. Four cultivars of blueberry (’Duck’,’Brigitta’,’Sharpblue’ and ’Misty’) were exposed to different temperature stress (30℃,35℃,40℃,45℃) for6h, and subsequently the physiological parameters, chlorophyll fluorescence and ultrastructure of chloroplast in the plants were measured as compared with the controls (25℃). Exposure to high temperature resulted in significant increased levels of the relative electrolyte leakage (REL), lipid peroxidation (malondialdehyde, MDA), proline, hydrogen peroxide (H2O2) and superoxide radical (O2·-), and the initial chlorophyll fluorescence yield (Fo) in the plants, whereas the maximum photochemical efficiency of PSⅡ (Fv/Fm) and the quantum efficiency of PS2photochemistry (ΦPSⅡ) decreased, especially at40℃and45℃. The above impact of high temperature stress on bluberry plants was most pronounced in’Brigitta’ genotype, and least in’Sharpblue’. The ultrastructure of chloroplast were also damaged under high temperature stress. Chloroplast ultrastructure of ’Brigitta’ were severely damaged under heat stress, whereas those of’Sharpblue’was almost completely intact. The results indicated that ’Sharpblue’ was the most heat-tolerant blueberry genotype to heat stress, while ’Brigitta’ was the most sensitive one to heat stress, followed by ’Duck’ and ’Misty’.In order to investigate the effects of salicylic acid pretreatment on enhance heat resistance of blueberry,’Brigitta’ and’Sharpblue’were sprayed0.05,0.1,0.3,0.5mmol/L salicylic acid, then the variation of physiological indexes and chlorophyll fluorescence parameters under high temperature stress were analysed. The study showed that SA pretreatment could alleviate electrolyte osmosis, decline the increase of Fo, Fv/Fm and OPS Ⅱ in blueberry. Meanwhile, SA pretreatment increased the contents of hydrogen peroxide (H2O2) and proline under high temperature stress. The findings suggested that SA pretreatment could enhance heat resistance of blueberry, and the optimal treatment concentration of S A was0.1mmol/L. |
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