Photosynthetic pigments, photochemical efficiency and growth of custard-apple under salt stress and potassium fertilization1

Abstract

The salt stress caused by irrigation water with high concentration of salts stands out as one of the main limiting factors in agricultural production in the semiarid region of Northeastern Brazil. In this context, the objective of this study was to evaluate the photosynthetic pigments, the photochemical efficiency, and the growth of custard-apple irrigated with saline water and potassium doses. The research was carried out under field conditions in a randomized block design in a 2 × 5 factorial scheme, corresponding to two values of electrical conductivity of irrigation water-ECw (1.3 and 4.0 dS m-1) and five potassium doses (50, 75, 100, 125 and 150% of the recommendation). The dose referring to 100% corresponded to the application of 20 g of K2 O per plant per year. ECw of 4.0 dS m-1 reduced the synthesis of chlorophyll a, total chlorophyll, and carotenoids in custard-apple, at 245 days after transplanting. Fertilization doses of 50 to 150% of the recommendation inhibited the synthesis of chlorophyll b and the absolute and relative growth rates in stem diameter of custard-apple plants irrigated with water of highest electrical conductivity. Reduction in the quantum efficiency of photosystem II in custard-apple cultivated under ECw of 4.0 dS m-1 is related to photoinhibitory damage to photosystem II. Potassium fertilization did not alleviate the stress caused by water salinity on the growth of custard-apple, during 151-245 days after transplantation.