Gas exchange of citrus rootstocks in response to intensity and duration of saline stress

Soil and water salinity cause physiological disorders in sensitive plants, such as altered gas exchange in citrus genotypes. However, it is possible to analyse these effects and to identify genotypes tolerant to salt stress. An experiment was carried out in order to evaluate the tolerance of citrus genotypes considering the irrigation with saline water during rootstock formation. The study took place under greenhouse conditions in Pombal county, Paraiba, Brazil. A randomised block design was used, with treatments arranged in a factorial scheme (5 x 8). The two factors were: [i] five salinity levels of irrigation water (0.8, 1.6, 2.4, 3.2 and 4.0 dS m(-1)) and [ii] eight genotypes of citrus rootstocks: 1. 'Santa Cruz Rangupur' lime (LCRSTC); 2. common 'Sunki' mandarin (TSKC) x 'Swingle' citrumelo (CTSW) - 028; 3. TSKC x CTSW - 033; 4. TSKC x CTSW - 041; 5. 'Volkamer' lemon (LVK) x 'Rangpur' lime (LCR) - 038; 6. 'Florida Sunki' mandarin (TSKFL); 7. TSKC and 8. 'Florida' rough lemon (LRF). Gas exchange was evaluated at 15, 30 and 60 days after the beginning of the saline water application. High water salinity reduces gas exchange in citrus genotypes, which was more evident at 15 days from the beginning of stress. The genotypes 'Santa Cruz Rangpur' lime, TSKC x CTSW - 041, LVK x LCR 038 and 'Florida' rough lemon exhibit a satisfactory physiological behaviour during the first 30 days of exposure to the stress, showing moderate tolerance to salt stress. The genotypes TSKC x CTSW - 033 and common 'Sunki' mandarin are the most sensitive to salinity.