Comprehensive valuation and indicators of the tolerance to higher soil pH stress of 11 northern highbush blueberry varieties

Abstract:【Objective】In this study, we investigated the effects of higher soil pH stress on the growth and the physiological characteristics of northern highbush blueberry (Vaccinium Spp.) cutting seedlings of 11 varieties, to screen the varieties with strong tolerance to higher soil pH stress and the indicators of the tolerance to provide a theoretical basis and technical support for breeding new variety with resis- tance to higher pH and rational cultivation of blueberries.【Methods】Changes of the relative height growth, malonaldehyde (MDA) content, superoxide dismutase (SOD) activity, peroxidase (POD) activi- ty, catalase (CAT) activity, Chlorophyll content, gas exchange parameters, and chlorophyll fluorescence parameters of Eleven Northern highbush blueberries(including‘Bluecrop’‘Reka’‘D-IIMSU54’

‘Spartan’‘Cara’s Choice’‘Elizabeth’‘Chandler’‘Brigitta’‘Duke’‘Sweetheart’and‘Elliott’) were determined to evaluate the tolerance of different blueberry varieties to the higher soil pH stress, and to select the indicators of the tolerance, using their one-year-old cutting seedlings under the higher soil pH (6.0) treatment and the control (pH 5.0).【Results】The relative growth of height of the cutting seedlings of‘D-IIMSU54’and‘Elizabeth’treated with higher pH was not significantly lower than that of the seedlings of the control, the relative growth of height of the seedlings under higher soil pH stress of the other varieties were significantly lower than those of the seedlings of the control.‘D-IIMSU54’and‘Sweetheart’were mildly injured with an injury index of 2.00% and 6.67% respectively;

‘Spartan’and‘Duke’were seriously injured with an injury index of 73.33% and 53.33% respectively; the damage degree of the other varieties sat in the mid under the higher soil pH stress. Compared with the control, the MDA content and CAT activity of all tested varieties significantly increased, intercellu- lar carbon dioxide (Ci) mainly kept stable, the chlorophyll (Chl) content and maximal quantum efficien- cy of photosystem II (Fv/Fm) significantly decreased. In addition, net photosynthetic rate (Pn), transpira- tion rate (Tr), stomatal conductance (Gs), electron transport rate (ETR) and photochemical quenching co- efficient (qp) of the majority of the blueberry varieties were significantly decreased, the non-photochemi- cal quenching coefficient (NPQ) of the varieties with strong tolerance to the higher soil pH stress signifi- cantly increased under higher soil pH stress for 90 days. The principal component analysis showed that

the relative values of those indices were classified into two independent comprehensive indices (princi- pal component). The principal component 1 mainly reflected the information of the plant height growth characteristics, the CAT activity, the main leaf physiological characteristics and the fluorescence param- eters; the principal component 2 mainly reflected the information of the SOD activity. Comprehensive evaluation of the higher soil pH stress-tolerance (D value) showed that the ability of tolerance to the higher soil pH stress decreased in order of‘D-IIMSU54’>‘Sweetheart’>‘Elizabeth’>‘Elliott’>

‘Chandler’>‘Bluecrop’> Reka’>‘Cara’s Choice’>‘Brigitta’>‘Duke’>‘Spartan’. Eleven blueberry varieties were divided into three categories by clustering analysis: the higher soil pH tolerant type, the middle type, and the higher soil pH intolerant type. The correlation degree between the rela- tive values of fifteen indexes and the D value decreased in order of Tr > Gs > height relative growth > ETR > CAT activity > Chl content > qP > Pn >NPQ > POD activity > SOD activity > Ci > Fv/Fm > MDA content by grey correlation analysis【. Conclusion】The higher soil pH stress had significant influence on each index during growth stage of the cutting seedings of blueberry. Compared with the blueberry vari- ety with intolerance to the higher soil pH stress, the CAT activity of the tolerant varieties maintained a in a relatively high level, the photosynthetic structure was slightly damaged, the photosynthesis was less affected, as a result, the high relative growth was less affected and the damage was less. Eleven North- ern highbush varieties were divided into three categories by clustering analysis: the higher soil pH stress-tolerant type (including‘D-IIMSU54’‘Sweetheart’‘Elizabeth’‘Elliott’‘Chandler’), the in- termediate type (including‘Bluecrop’‘Reka’and‘Cara’s Choice’) and the higher soil pH stress-in- tolerant type (including‘Brigitta’‘Duke’and‘Spartan’). Among the fourteen higher soil pH toler- ance related indexes of the Northern highbush blueberry under higher soil pH stress, Tr, Gs, the relative growth of height, the ETR, the CAT activity and the Chl content could be used as key indexes to identi- fy the tolerance of the Northern highbush blueberry to the higher soil pH.