Achachairu (Garcinia humilis (Vahl) C.D. Adams) is a slow-growing tropical fruit tree indigenous to the Amazonian forests in Bolivia. Each tree can produce over 15,000 fruit (400 kg/tree) harvested from cultivated and wild trees. It has significant horticultural potential because the fruit is considered delicious by many people who have tasted it. Thus, its commercial cultivation has extended to Brazil, Mexico, and Australia. The responses and tolerance of this species to abiotic stresses and the use of chemical priming to mitigate stress have never been reported. The study investigated the physiological, biochemical, and morphological responses to flooding and salinity, and the priming with 24-epibrassinolide (EB) to increase flooding and salinity tolerance of G. humilis. Three-year-old achachairu seedlings were used in several sequential experiments, including applying flooding, salinity, and EB priming in different combinations and durations. Physiological variables including leaf gas exchange [net CO2 assimilation (A), stomatal conductance of H2O (gs), and intercellular CO2 concentration (Ci)], leaf chlorophyll index (LCI), and the ratio of variable to maximum chlorophyll fluorescence (Fv/Fm) were measured. Leaf and root nutrient concentrations, antioxidant responses, reactive oxygen species (ROS), and lipid peroxidation (MDA) were also measured. Results showed that G. humilis is very tolerant of prolonged flooding of up to 30 d, medium levels of salinity of up to 6 dSm-1, and the combined effect of flooding and salinity. Tolerance to these stresses was exhibited by physiological, biochemical, and morphological responses, consistent with tolerance traits, such as maintaining basal levels of photosynthesis, ion homeostasis, and nutrient balances, robust antioxidant responses to counter ROS increases, and limited lipid peroxidation, all of which may help limit physiological damage. Application of 1.0 mg L-1 EB as a foliar and root-drench before flooding or salinity treatments increased the levels of tolerance of G. humilis to salinity and flooding, most likely by reinforcing antioxidant responses which helped decrease ROS and lipid peroxidation.
