Evaluation of drought resistance in seedlings of 11 table grape varieties and screening of drought resistance indicators

Abstract: 【Objective】Grapes are an important cash crop in the arid areas. Drought seriously affects the growth and yield of grapes and limits the development of the grape industry. Selecting table grape varieties with high drought resistance is the most effective way to cope with drought. This experiment aimed to select table grape varieties with high drought resistance suitable for cultivation in the arid areas as well as drought resistance indicators with high correlation. This study provides a reference for planting grapes in the arid areas.【Methods】The experiment was conducted in a greenhouse at the Horticulture Station of Shanxi Agricultural University. Eleven table grape varieties tested included five Shanxi varieties (Lihongbao, Jinghongbao, Qiuhongbao, Wanheibao and Wuhecuibao), three Liaoning varieties (Zaoxiameigui, Jumoli and Molixiang), two Xinjiang varieties (Thompson Seedless and Flame Seedless) and one California variety (Crimson Seedless). 1-year-old cuttings of each variety were collected in November 2021 and buried with earth. The sand-harvested cuttings were transplanted in April 2022, and the experiment was conducted after the seedlings were established in August, 2022. The aver-age air temperature during the experiment was 29.3 ℃ and the average humidity was 51.9%. Water withholding treatment was used to simulate natural drought, and 20 seedlings of each variety were selected. On the 0, 3, 6, 9 and 12 days after drought stress treatment, biological responses were recorded and chlorophyll fluorescence parameters (maximum fluorescence value (Fm), maximum photochemical efficiency (Fv/Fm), effective quantum yield of PSⅡ (Qy), non- photochemical burst coefficient (NPQ), photochemical burst coefficient (qP) and fluorescence decline rate (Rfd) were measured with a Fluor Pen FP110. The samples were taken back to the laboratory for determination of membrane leakage of the leaves and roots and photosynthetic pigment contents (chlorophyll a, chlorophyll b, carotenoids and total chlorophylls). Significance of differences between varieties at different times of drought were analyzed with the new multiple range method. Correlations between the indicators were tested by correlation analysis. Principal component analysis was used to evaluate the drought resistance of the 11 table varieties, which were classified using cluster analysis based on the principal component scores. The parameters with high correlation with drought resistance were selected using gray correlation analysis.【Results】 Drought stress had significant effects on the phenotype, membrane leakage in the leaf and root, chlorophyll content, and chlorophyll fluorescence parameters. Drought caused loss of greenness and wrinkling and wilting of grape seedlings. Membrane leakage in the leaves and roots increased significantly under drought. Chlorophyll a content and total chlorophyll content decreased significantly. Fm, Fv/Fm, effective quantum yield, non- photochemical burst coefficient, photochemical burst coefficient and fluorescence decline rate of PSⅡ all decreased. Correlation analysis of various indexes showed that Rfd and NPQ, Fm and Fp, Fv and Fv/Fm, Fp and Fv and Fv/Fm, Fv and Fv/Fm, and chlorophyll a content and total chlorophyll content were highly significantly positively correlated (p＜0.001). NPQ and Qy, chlorophyll b content and total chlorophyll content, and chlorophyll a content and carotenoid content were significantly positively correlated (p＜0.05). However, root membrane leakage and Rfd, Fm and Fp were significantly negatively correlated (p＜0.05). The order of the drought- resistance according to the principal component analysis was in a descending order of Lihongbao＞Qiuhongbao＞Molixiang＞Jumoli＞Thompson Seedless＞Jinghongbao＞Flame Seedless＞Wanheibao＞Wuhecuibao＞Crimson Seedless＞Zaoxiameigui. According to the method of cluster analysis, Qiuhongbao and Lihongbao were of higher drought resistance; Jinghongbao, Thompson Seedless, Jumoli and Molixiang of moderate drought resistance; and Flame Seedless, Wanheibao, Zaoxiameigui, Wuhecuibao and Crimson Seedless of low drought resistance. Gray correlation analysis showed that drought stress had a significant effect on all the parameters. The grey correlation analysis showed that the correlation between each index and drought was chlorophyll b content, total chlorophyll content, chlorophyll a content, carotenoid content, root relative membrane permeability, NPQ, Fp, Fv/Fm, leaf relative membrane permeability, qP, Rfd, Qy, Fv and Fm. Except for Fv, Qy, Fm and Rfd, the correlation coefficients of all the parameters with drought resistance were higher than 0.8, and the correlations of chlorophyll a, chlorophyll b, carotenoids, total chlorophyll content and root membrane leakage with drought resistance were higher than 0.85.【Conclusion】Lihongbao and Qiuhongbao were identified as of high drought resistance at seedling stage, which could be used as materials for drought resistance breeding and for study of the mechanism and regulation of drought resistance in table grapes. The photosynthetic pigment contents, membrane leakage of the roots and NPQ were highly correlated with drought resistance, which could be used as the simple and intuitive indices of drought resistance in table grapes for identifying drought resistant resources at seedling stage.