Determination of drought stress responses and recovery abilities in some apricot cultivars

This study aimed to determine the responses of important apricot cultivars grown in Turkiye (Alkaya, Çataloğlu, Çöloğlu, Hacıhaliloğlu, Hasanbey, Kabaaşı, Kadıoğlu, Soğancı, Şalak, Şekerpare, and Tokaloğlu) to drought stress and their recovery status after re-irrigation under uncontrolled greenhouse conditions. Morphological, physiological, biochemical, and some antioxidant enzyme properties were determined, and these characteristics were evaluated at two different periods: during drought stress and after re-irrigation. Damage indices were calculated for the determined morphological characteristics, and scoring was performed for physiological, biochemical, and antioxidant enzyme properties to assess the tolerance of cultivars to drought stress and their recovery abilities. For this purpose, seedlings obtained by grafting and ungrafted apricot seedlings (çöğür) were potted, and after sufficient shoot development, irrigation was cut off until the first signs of drought were observed in May 2021, and then re-irrigation was applied for one week for recovery. The results showed that drought stress significantly reduced shoot length, leaf area, specific leaf weight, and the fresh and dry weights of plants. According to the damage index for morphological characteristics, the most drought-tolerant cultivars were Kabaaşı (29.70), Çöğür (28.07), and Hasanbey (20.26), while the most sensitive cultivars were determined as Alkaya (48.20), Çöloğlu (54.18), and Hacıhaliloğlu (51.26). Although improvements in morphological characteristics of plants were observed with re-irrigation, the determined period was not sufficient for complete recovery of plants. Drought stress reduced physiological characteristics such as stomatal conductance and leaf relative water content in all cultivars while increasing membrane permeability. Generally, recovery was observed in all physiological characteristics after re-irrigation. Based on the scoring conducted for physiological characteristics in the post-stress period, Çataloğlu (44), Kabaaşı (42), and Hasanbey (33) stood out, while Hacıhaliloğlu (5), Çöloğlu (17), and Kadıoğlu (20) were identified as the most sensitive cultivars. Drought stress increased the levels of total carbohydrates, MDA, H2O2, proline, and flavonoid contents in leaves, while decreasing protein, chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid contents. Based on the scoring for biochemical characteristics, tolerant cultivars were Çöğür (98), Şekerpare (85), and Çataloğlu (77), while sensitive cultivars were Hacıhaliloğlu (37), Kadıoğlu (39), and Alkaya (44). All measured antioxidant enzyme activities (SOD, POD, APX, GR, ALR) increased in response to drought stress, and in this context, the cultivars with high tolerance were identified as Hasanbey (50), Çöğür (49), and Çataloğlu (44). Taking into account all parameters, the cultivars that scored the highest were Kabaaşı (202), Hasanbey (201), and Çöğür (199), while Hacıhaliloğlu (67), Kadıoğlu (116), and Alkaya (117) had the lowest scores. In conclusion, based on the information, the order of cultivars from tolerant to sensitive to drought stress was determined as Kabaaşı, Hasanbey, Çöğür, Çataloğlu, Şekerpare, Soğancı, Tokaloğlu, Çöloğlu, Şalak, Alkaya, Kadıoğlu, and Hacıhaliloğlu.