Physiological Responses Of Blueberry To Drought Stress

Vaccinium L., Ericaceae, blueberry, is a shrub fruit trees of high economic value. Blueberry is a kind of shallow rooted plants, it can not absorb the moisture of the deep soil, and vulnerable to drought hazard. In the recent years, the introduction and extension of blueberry in Zhejiang and other southern provinces developed rapidly. The local and short-term drought frequently happened in mountain areas of southern provinces seriously impact on the cultivation and promotion of the blueberry industry. This study aimed to elucidatedthe physiological responses of different blueberry varieties to drought stress, compared their ability to adapt to drought stress in physiological, biochemicals, anatomical and other aspects; The protective effect of Paclobutrazol (pp333) on blueberry stressed by drought treatment were studied by spraying a certain concentration of paclobutrazol; finally, the cell wall polysaccharide component of the blueberry leaves under drought treatment saparated and analyzed, the possible mechanism of drought stress affecting blueberry leaf cell wall polysaccharide were also discussed.Physiological characteristics of two northern (Brigitta, Spartan) and two southern highbush blueberry cultivars (Sharpblue, O’Neal) were investigated under water controlled conditions, as to unveil the possible mechanisms of highbush blueberry in response to drought stress and to screen the drought resistant cultivars. Meanwhile, we also aimed to prove the possibility of using the Subordinate Function method based on physiological parameters to evaluate the drought-tolerance among the blueberry cultivars. The drought resistance capacity of all the four highbush blueberry cultivars were evaluated comprehensively by:the relative water content, content of the lipid peroxidation product (malondialdehyde, MDA), membrane permeation, contents of hydrogen peroxide (H2O2) and superoxide radical (O2-), the maximum photochemical efficiency of PSII (Fv/Fm), stomatal characteristics of leaves. The results showed that drought stress decreased the relative water content, Fv/Fm, stoma open rate, stomatal length and stomatal width; Meanwhile, the relative conductivity, MDA content, H2O2and O2contents and stomatal density were increased paralleled with the treatment intensity. The drought resistance abilities differed significantly among the four highbush blueberrycultivars, with the drought resistance capacity sequenced as following:O’Neal, Sharpblue, Brigitta, Spartan. The two-year field trial proved the Subordinate Function method based on physiological parameters could be used as a reliable method to screen the drought-tolerant blueberry cultivars.Two southern highbush blueberry cultivars (Sharpblue, O’Neal) were used as materials to study the protective effect of Paclobutrazol (pp333) on blueberry stressed by drought treatment. The results showed spraying aqueous solution of PP333at500mg/L significantly alleviated the damages caused by drought stress. Pre-treatment of PP333decreased the level of relative conductivity, MDA content, contents of hydrogen peroxide (H2O2) and superoxide radical (O2--); retarded the decrease of photosynthetic rate, transpiration rate, relative water content and chlorophyll content under drought stress. It indicated pre-treatment of PP333could increase the drought resistance in blueberry.Compared with the control group, the contents of water soluble pectin (WSP) and acid soluble pectin(ASP) decreased under drought stress, but the contents of1mol/L KOH soluble hemicellulose(HC1) and4mol/L KOH soluble hemicellulose (HC2) increased, the content of cellulose increased than the control group, In the molecular mass distribution of each component polysaccharide, the molecular mass distribution of WSP, ASP downshifted under drought stress, but the molecular mass of HC1and HC2did not change significantly. The WSP of blueberry leaves cell wall contained more mannose, galactose and glucose,the main monosaccharide compositions of ASP were determined to be galactose, arabinose, mannose and glucose while xylose and glucose consisted mainly of HC1and HC2. Under drought stress, the molar percentage of galactose and arabinose in WSP and ASP decreased, the molar percentage of glucose and galacturonic acid increased; the molar percentage of xylose and glucose in HC1and HC2increased. The polysaccharide content and composition in blueberry leaves cell wall changed under drought stress may be related to cell wall hardening, and affected the extension of the cell growth.