Ascorbic acid on the induction of salt stress tolerance in guava in the seedling formation phase.

Guava is a fruit crop widely exploited in the Northeast region of Brazil. However, its exploitation is limited by water scarcity and, in many cases, producers are forced to use water with high levels of salts in irrigation. Thus, it is necessary to develop techniques to induce plant tolerance to salt stress, and the foliar application of a non-enzymatic compound such as ascorbic acid is a promising alternative to mitigate the deleterious effects on plants. The objective was to evaluate the effects of foliar application of ascorbic acid on guava plants, irrigated with saline waters in the seedling formation phase in a semi-arid region. The experiment was carried out in a greenhouse adopting a randomized block design, in a 5 × 4 factorial scheme, with five levels of electrical conductivity of water - ECw (0.3, 1.3, 2.3, 3.3 and 4.3 dS m) and four concentrations of ascorbic acid - AsA (0, 200, 400 and 600 mg L) with four replicates. Water salinity from 0.57 dS m compromised the gas exchange and biosynthesis of photosynthetic pigments, besides inhibiting the growth and quality of guava seedlings cv. Paluma. The concentration of 375 mg L AsA increases the production of photosynthetic pigments under low salinity conditions (0.3 dS m) and increases the number of leaves and dry matter of seedlings up to 1.55 dS m. Foliar application of up to 450 mg L attenuated the deleterious effects of salt stress on gas exchange and growth of guava seedlings. Guava cv. Paluma seedlings present higher quality when produced with an ECw of 0.55 dS m and under a concentration of 75 mg L of AsA at 150 days after sowing.