Changes in the gene expression level of salicylic acid, morphological, biochemical parameters and antioxidant enzyme activity in three pretreated Egyptian citrus rootstocks by copper sulphate or mannitol to enhance their salt tolerance

Climate change is the main concern in the current global situation. Salinity is one of the most crucial side effects of climate change. Citrus genus is the most popular fruit crop in the world. In Egypt, citrus is considered the first fruit crop and is planted in several areas and in new reclaimed areas. Salinity affects several genes and parameters of citrus yield. The objective of this study was to study changes in the gene expression level of salicylic acid and antioxidant enzymes activity in three salted Egyptian citrus rootstocks (Troyer citrange, Sour orange and Volkamin lemon) and to study the effect of salt stress on some morphological and biochemical parameters and to evaluate the alleviation effect of presoaking with 20mM mannitol and 5mM CuSO4. Under salinity conditions, the results proved the significant increase in SA gene expression level. Similarly, trehalose, MDA and H2O2 contents and the activity of five antioxidant enzymes were significantly increased. Conversely, shoot length, number of leaves and photosynthetic pigments were significantly decreased under salt stress. However, root length increased as a type of adaptation. Presoaking the rootstocks with 5mM CuSO4 and 20mM mannitol significantly changed the expression level of the SA gene, recovered the harmful effect of salt stress, and weakened the oxidative stress caused by salinity and mannitol was more effective than CuSO4. Thus, the present findings displayed the changes in SA gene expression and recommend presoaking with mannitol and CuSO4 to improve the salt sensitivity of citrus rootstock for using in salted areas.