Castor Bean Cake Mitigates Saline Stress in Basil Plants

Purpose Salinity affects crop yield, photosynthesis, and metabolism. However, adequate nutritional supplementation, mainly with organic sources, may mitigate the salinity effects. Thus, the aim of this study was to evaluate doses of castor bean cake in the mitigation of different levels of salinity in basil plants. Methods Plants were irrigated with five water electrical conductivities (0.5, 1.2, 3.0, 4.7, and 5.5 dS m −1 ) and five castor bean cake doses (0.0, 1.4, 5.0, 8.5, and 10 t ha −1 ). The dry mass accumulation, gas exchanges, relative water content, oxidative stress, proteins, and antioxidant enzyme activity were evaluated. Results All salinity levels reduced dry mass accumulation of basil plants, being that gas exchanges, relative water content, and activity of ascorbate peroxidase, peroxidase, and catalase were increased under mild salinity (up to 3 dS m −1 ) but reduced under the higher salinity level (5.5 dS m −1 ). The use of castor bean cake up to 5 t ha −1 stimulated photosynthesis, dry mass accumulation, relative water content, protein synthesis, and antioxidant enzyme activity, while most of these parameters were reduced under higher castor bean cake doses (10 t ha −1 ), combined or not with high salinity. Conclusions The use of castor bean cake up to 5 t ha −1 mitigated the deleterious effect of mild salinity (3 dS m −1 ) on biomass accumulation of basil plants by increasing antioxidant defense, but the combination of saline water with high doses of castor bean cake (10 t ha −1 ) caused oxidative damages, reducing dry mass accumulation and gas exchanges.