| In China, citrus orchards mainly distribute in the south, particularly in the hills, mountains and shallows. Due to uneven distribution of rainfall in time and space in these areas, drought or waterlogging stress often occurs in citrus orchards. It seriously impeded the improvement of citrus production and quality. Seven citrus rootstock cultivars, Trifoliate orange (Poncirus trifoliate (L.) Raf), Red tangerine (C. tangerine), Carriao citrange (C. sinensis Osb.×P. trifoliate Raf), Cleopatra mandarin (C. reshni Hort.), Ziyangxiangcheng (C. junos (Sieb.)), Ichang papeda (C. ichangensis Swingle) and Goutou sour orange (C. aurantium L), were treated under drought stress and waterlogging stress in this study. Morphological indexes, photosynthetic parameters, biochemical indexes and chlorophyll (Chl) of leaves were measured regularly. Based on the data of the photosynthetic parameters and biochemical indexes, principal component analysis and subordinate function were performed to evaluate the tolerance of seven citrus rootstocks to drought or waterlogging stress. The results are as follows.1. Evaluation the tolerance of seven citrus rootstock to drought stress1.1Cluster analysis of index of drought injury and death rate indicated that the drought tolerance of seven citrus rootstocks can be divided into four levels:the strong tolerant rootstock (R) including Trifoliate orange, the tolerant rootstock (MR) including Carriao citrange and Cleopatra mandarin, the moderate resistance rootstock (M) including Red tangerine, Ziyangxiangcheng and Ichang papeda, and the sensitive rootstock (S) including Goutou sour orange.1.2Correlation analysis showed that there was no significant correlation between stomatal density and drought tolerance (P＞0.05), but leaf area and thickness were significantly negative correlation with drought resistance.1.3Under drought conditions, the Chl contents were decreased in all rootstocks, but which did not show significantly relationship with drought tolerance. Measurement of photosynthetic indexes showed net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) were gradually decreased with aggravating of drought, and the change of substomatal CO2concentration (Ci) was difference in different cultivars. Of which, the Pn was significantly positive correlation with drought tolerance, while Gs, Ci and Tr were no correlation with drought tolerance. This result suggests that Pn could be used as indicating index to evaluate drought tolerant of rootstocks.1.4Measurement of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), malondialdehyde (MDA), Proline (Pro) and soluble protein showed that a single indicator was difficult to judge the drought tolerance of citrus rootstocks. Therefore, principal component analysis and subordinate function were used to evaluate the drought tolerance based on the data of photosynthetic parameters and physiological and biochemical indexes under the conditions of normal water supply and drought stress. The results indicate that the ability of drought tolerance was Trifoliate orange> Carriao citrange> Cleopatra mandarin> Red tangerine> Ziyangxiangcheng> Ichang papeda> Goutou sour orange, which is consistent with the cluster analysis of index of drought injury and death rate under drought.In conclusion, according to both cluster analysis of index of drought injury and death rate and comprehensive evaluation based on the data of photosynthetic parameters and biochemical indexes, the drought tolerance of seven rootstocks was Trifoliate orange> Carriao citrange> Cleopatra mandarin> Red tangerine> Ziyangxiangcheng> Ichang papeda> Goutou sour orange.2. Evaluation the tolerance of seven citrus rootstock cultivars to waterlogging stress2.1Cluster analysis of waterlogging index and death rate under waterlogging indicated that the waterlogging tolerance can be divided into three levels:the tolerant rootstock (R) including Ziyangxiangcheng, Carriao citrange and Cleopatra mandarin, the moderate tolerant rootstock (M) including Trifoliate orange, and the sensitive rootstock (S) including Red tangerine, Goutou sour orange and Ichang papeda.2.2Under waterlogging conditions, the Chl contents were decreased in all rootstocks, but which did not show significantly relationship with waterlogging tolerance. Measurement of photosynthetic indexes showed Pn, Gs and Tr were gradually decreased with extension of waterlogging time, and the change of Ci was difference in different rootstocks. The Pn, Gs and Tr in Ziyangxiangcheng, Carriao citrange, Cleopatra mandarin and Trifoliate orange were significantly higher than in Red tangerine, Goutou sour orange and Ichang papeda.2.3Measurement of SOD, POD, CAT, MDA, Pro and soluble protein showed that a single indicator was difficult to judge the waterlogging tolerance of citrus rootstocks. Therefore, principal component analysis and subordinate function were used to evaluate the waterlogging tolerance based on the data of the photosynthetic parameters and physiological and biochemical indexes under the conditions of normol water supply and waterlogging stress. The results indicate that the ability of waterlogging tolerance was Ziyangxiangcheng>Carriao citrange>Cleopatra mandarin>Trifoliate orange> Goutou sour orange>Ichang papeda>Red tangerine, which is consistent with the cluster analysis of index of waterlogging injury and death rate under waterlogging.In summary, combining with cluster analysis of index of waterlogging injury and death rate under waterlogging and comprehensive evaluation based on the data of the photosynthetic parameters and physiological and biochemical indexes, the ability of waterlogging tolerance was Ziyangxiangcheng>Carriao citrange>Cleopatra mandarin>Trifoliate orange>Goutou sour orange>Ichang papeda>Red tangerine. |
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