Effect of water salinity and potassium doses on physiological traits and growth of ‘Embrapa 51’ precocious dwarf cashew (Anacardium occidentale L.) rootstock

In the semiarid regions, plants are constantly exposed to different conditions of abiotic stresses due to the occurrence of excess salts in both soil and water. Thus, it is extremely important to identify an alternative capable of minimizing the effects of salt stress on plants as a way to ensure the expansion of irrigated areas. In this context, this study aimed to evaluate the chloroplast pigments, photochemical efficiency and growth of ‘Embrapa 51’ precocious dwarf cashew as a function of irrigation with saline water and potassium fertilization in the rootstock formation stage. The study was conducted under greenhouse conditions in the municipality of Pombal, PB, Brazil, using a randomized block design in a 5 x 2 factorial scheme, corresponding to five levels of irrigation water electrical conductivity - ECw (0.4; 1.2; 2.0; 2.8 and 3.6 dS m-1) and two doses of potassium fertilization - KD (100 and 150% of the recommendation corresponding to 150 and 225 g K2O kg-1 soil), with two plants per plot and three replicates. Water salinity from 0.4 induced reductions in chlorophyll a and b synthesis, maximum and variable fluorescence and growth in sexually propagated precocious dwarf cashew seedlings and increases in carotenoid content and initial chlorophyll fluorescence. The quantum efficiency of photosystem II in cashew plants was decreased sharply with the increment in water salinity levels, standing out as indicative of damage to the photosystem II reaction centres. 'Embrapa 51' precocious dwarf cashew plants can be classified as sensitive to water salinity above 0.4 dS m-1. Potassium doses of 100 and 150% of the recommendation did not alleviate the effects of salt stress during the precocious dwarf cashew rootstock production phase.