Comparison Of Drought Resistance On Introduced Olive Cultivars Seedlings In Liangshan

Olive (Olea europaea L.), is one of the four famous woody oil species across the world with important nutritional and pharmaceutical values. Liangshan prefecture is located in the southwest of Sichuan province, which is beneficial for olive growth and development. However, the area exhibits semi-arid climate characteristics, which limited the olive growth due to serious shortage of water. Based on this,7 olive cultivars include Picholine, Picual, Manzanillo, Koroneiki, Frantoio, Arbequina and Coratina were selected to study the physiological and photosynthesis of olive plants in response to continuous drought stresses through pot experiments. Besides, in order to screen the drought resistance assessment indexes, the multivariate analysis was used to evaluate the drought resistance of the olive cultivars. The main results are as follows:(1) The LRWC significantly decreased with the increased duration of drought across all cultivars. At the later period of stress, the cultivars showed different levels of wilting symptom than control. At 21 days after treatment (DAT), Coratina showed the highest water loss rate while Manznillo was slightly affected. This suggested that the Manznillo leaves exhibited higher water retaining capacity compared to other cultivars. Meanwhile, the LRWC of olive leaves were significantly correlated with variation of soil moisture, suggesting that the reasonable irrigation was needed to meet the water demands of olive growth.(2) The concentration of Chla, Chlb and Car were significantly decreased with the increasing duration of drought stress which was mainly resulted from the rapid degradation of chlorophyll than biosynthesis. At 21 DAT, the Chla and Chlb of Arbequina, as well as Car of Picholine were significantly declined. The photosynthetic parameters of the cultivars varied in response to drought. Generally, the Pn, Tr, Gs,and Ci decreased while the WUE increased with the drought. The change of Pn exhibited a "slow-fast-slow" pattern. Tr and Gs declined with a similar pattern, which started with a fast rate and then declined slowly. Ci exhibited a "fast-slow-fast" decline pattern, indicating that the photosynthetic pigment structure were destroyed, and thus increased the decompose of chlorophyll. Between the cultivars, the relatively evident decrease observed in Frantoio while slightly decreased in Manzanillo.(3) The concentrations of O2-· and H2O2 tended to increase as the increased duration of drought, and thus lead to the imbalance of the production and removal of ROS. From the leaf staining method, the O2-· stimulus was evident observed in Picholine, Manzanillo and Frantoio, and the over-production of H2O2 was observed in Picholine, Arbequina and Frantoio.(4) The activities of SOD, POD and CAT increased first and then decreased with the declined soil water content and duration of drought. By doing so, it could remove the over-produced ROS and improve the adaptability of plants. The activities of SOD and CAT reached the peak at 16 DAT while POD reached the peak at 11 DAT. Arbequina and Manzanillo SOD activity increased with prolonged drought. When POD and CAT activity was the highest, respectively. Picholine POD and CAT activity was higher than other cultivars.(5) The concentrations of proline, soluble protein and soluble sugar significantly increased with the drought. It suggested that the accumulation of drought-mediated organic components could increase the cell concentrations and reduced the osmotic potential, so as to maintain the plant growth. Among the components, the proline showed the similar pattern with antioxidative enzymes which increased first and then decreased after 16 DAT. The changes of soluble protein and soluble sugars differed, overall, both of them increased with the DAT. At the end of Stress Frantoio Pro and soluble protein content increasing rate is higher than other cultivars.(6) The patterns of MDA and relative electrolytic leakage increased with the duration of drought. The relative electrolytic leakage rose slowly at the beginning and then showed a rapid rise from 16th day. This indicated that the permeability of membrane changed or loosed, as well as the leakage of electrolyte due to the lipid peroxidation when exposed to the drought stresses. At 21 DAT, the Koroneiki and Coratina contained the largest concentrations of MDA and relative electrolytic leakage, respectively(7) The photosynthetic and physiological characteristics between the different cultivars significantly differed by using multiple comparison analysis. Based on the integrating correlation, principal components analysis and the subordinate function method, the drought resistance of the 7 cultivars were Manzanillo> Picual> Picholine> Frantoio> Arbequina> Koroneiki> Coratina. In addition, the Car content, Tr and SOD activity were screened as 3 drought resistance assessment indexes to evaluate the capacity of drought resistance of olive.