Evaluation of new hybrid citrus rootstocks for Salinity under controlled conditions

The salinity of irrigation water and soil significantly affects the performance of citrus crops in semi-arid and arid areas. This study aimed to evaluate new hybrid citrus rootstocks under different salt stress levels. A total of 0 g, 2 g, and 5 g of NaCl were added to 1l of half-strength Hoagland solution to achieve salinity levels of 1.31, 4, and 9 dS/m, respectively, for irrigation. Six one-year-old cuttings were transplanted into plastic pots and evaluated. After three months of treatment, various responses from the rootstocks to salinity stress were observed. The addition of NaCl to the irrigation solution caused a decrease in fresh weight, dry weight, and chlorophyll content. In addition, proline and chloride contents in the leaves increased with higher salt levels in the irrigation solution. Our results showed that the hybrid H57 (Citrus sunki Hort. ex Tan.) x (Citrus paradisi Macf. × Poncirus trifoliata L. Raf.) is salt-sensitive, accumulating five times more chloride compared to 0 g/l NaCl. This was associated with a reduced number of leaves, low chlorophyll content of 0.75 mg/g of fresh weight, and symptoms of leaf toxicity along with low fresh and dry weights. Although the hybrid H56 (Citrus sunki Hort. ex Tan.) x (Citrus paradisi Macf. × Poncirus trifoliata L. Raf.) appeared to be salt-tolerant, accumulating less chloride in leaves compared to 0 g/l NaCl, it had a chlorophyll content of 1.23 mg/g of fresh weight, proline levels of 31.1 µg/g of dry weight, and maintained higher fresh and dry weights. These findings highlight the superior salt tolerance of H56 and support its potential as a promising rootstock candidate to be further evaluated in combination with selected scion varieties under saline conditions.