Physiological Responses Of Apple Rootstocks To Drought Stress And Evaluation Of Drought Resistance

Ten two-year-old apple rootstock varieties (M. baccata, M. toringoides, M. xiaojinensis, M. kansuensis, M. sikkimensis, M. sieboldii, M. hupehensis var.taishanensis, M. baccata.'Zhaai Shandingzi', M. manshurica, M. hupehensis var.pinyiensis) grown in pots were adopted in this research. Physiological and biochemical indexes were measured, and physiological responses of apple rootstocks to drought stress were studied. The results were as follows:1. The leaf RWC of apple rootstock decreased at different level under drought stress. Of them, the RWC of'Taishanhaitang','Longdonghaitang'and'Maoshandingzi'decreased to a large degree. After rewater, the RWC of rootstocks all recovered to the control level.2. Under drought stress, there existed accumulation at different level about osmoregulation substance. The changes of praline contents appeared two trends, one was sligt change, the other tend was great increase after 9th day of drought stress, and reached maximum on 15th day of drought stress. After rewater, proline contents decreased rapidly and recovered to control level. Soluble sugar contents increased at first and decreased then,but starch contents decreased at first and increased then. The change trends of soluble sugar and starch contents was opposite. Change trend of soluble protein contents was basically consistent. During drought stress, soluble protein contents appeared a slight decrease on 6th day, and presented a single peak. After rewater,'Longdonghaitang'was significantly lower than its control, and others recovered to the control.3. Generally, MDA content and production rate of O2-·showed a increasing trend, and reached the peak at the 15th day after drought stress. There was no significant difference of production rate of O2-·after rewater.4. Under drought stress, there were fluctuating changes of POD, CAT activity and carotenoids content, among them, changes of POD and CAT activity showed trends of double peak curve and single peak curve . Carotenoids content increased greatly at later period of drought stress. After rewater, carotenoids content of'Maoshandingzi'and'Xiaojinbianye'was significantly higher than its control, others all recovered to control level.5. Under drought stress, there was down in chlorophyll content, Pn, and fluctuating changes of SLW for apple rootstocks. After rewater, chlorophyll content and Pn of partial apple rootstocks recovered to control level. There was difference of WUE between species, the WUE of'Xiaojinbianye','Shandingzi','Deqinhaitang','Pingyitiancha'was higher than their control, and the WUE of'Zhaaishandinzi','Fuxianhongsanye','Yajiangbianye','Taishanhaitang','Maoshandingzi'and'Longdonghaitang'was lower than their control.6. The results of correlation analysis showed that there were positive or negative correlations between some physiological indexes of apple rootstocks under drought stress. There were a positive correlation between RWC and chlorophyll content, a negative correlation between chlorophyll content and O2-·, and a significantly negative correlation between MDA and chlorophyll content. 7. Principal components analysis was applied to determine the index weight, the analysis shows that drought resistance of apple rootstocks was decided by CAT activity, MDA content, RWC, carotenoids content, and chlorophyll content. Drought resistance value of apple rootstocks was calculated to compare by the method of membership functions, The sequence of drought resistance was:'Shandingzi'>'Xiaojinbianye'>'Pingyitiancha'>'Deqinhaitang'>'Zhaaishandingzi'>'Yajiangbianye'>'Taishanhaitang'>'Fuxianhongsanye'>'Longdonghaitang'>'Maoshandingzi'. And drought resistence of apple rootstocks was comprehensive evaluated by fuzzy clustering based on drought resistence value, drought resistance of apple rootstocks can be classified into three categories: (1) Strong drought resistance:'Shandingzi','Xiaojinbianye','Pingyitiancha','Deqinhaitang','Zhaaishandingzi'; (2) Medium drought resistance :'Yajiangbianye','Taishanhaitang','Fuxianhongsanye'; (3) Weak drought resistance:'Longdonghaitang','Maoshandingzi'.