Quantum efficiency of photosystem II and production of orange under salt stress and nitrogen fertilization

This study aimed to evaluate the salt tolerance of 'Mimo do Ceu' orange grafted onto three rootstocks using physiological parameters such as maximum quantum efficiency of photosystem II (PSII) and the production of fruits. It also evaluated the effectiveness of increased nitrogen (N) fertilization in reducing the effects of salt stress. Two concomitant experiments were carried out under controlled conditions, using drainage lysimeters. The Experiment I evaluated the effects of the application of five levels of saline water on three combinations of scion-rootstocks grafted with 'Mimo de Ceu' orange, in a randomized block design with three replicates in a 5 x 3 factorial scheme. The Experiment II evaluated the application of two N levels (100 and 200% of recommendation) in three scion-rootstock combinations irrigated with water of electrical conductivity of 3.0 dS m(-1), in a 3 x 2 factorial scheme, with three replicates. The maximum quantum efficiency of PSII was inhibited in citrus plants under salt stress. 'Mimo do Ceu' orange grafted onto 'Common' Rangpur lime has higher yield potential. The increase in N dose did not reduce the deleterious effects of water salinity on fruit production.