Evaluation of salt tolerance in jamun (Syzygium cumini L. Skeels) using morpho-physiological traits and membership function analysis

We assessed the effects of salinity stress on 48 genotypes of jamun (Syzygium cumini L. Skeels) including 20 monoembryonic and 28 polyembryonic types to identify the salt tolerant genotypes and the morpho-physiological traits that underpin salt tolerance. Salinity of irrigation water was gradually raised over a period of 21 weeks, from 2.0 to 12.0 dS/m. Control plants were irrigated using fresh water (0.70 dS/m). The experiment was conducted in a Completely Randomized Block Design with four replications. Salinity had a more repressive effect on shoot than on root biomass, regardless of the seedling type, reflecting that roots might tolerate salt concentrations high enough to inhibit the growth of shoots. Salinity had little effects on the maximum quantum yield of photosystem II (Fᵥ/Fₘ), and the relative leaf chlorophyll in most genotypes evaluated. Salt-induced decreases in photosynthetic assimilation were generally greater in genotypes with inherently high photosynthetic rates. Genotypes with strong capacities for Na⁺ exclusion (e.g., CSJ-18, and CSJ-19) were generally highly tolerant to salinity stress. Leaf Cl⁻concentrations under saline conditions were lower than Na⁺ concentrations, suggesting a more effective mechanism for Cl⁻ exclusion. Leaf K⁺, Ca²⁺ and Mg²⁺ levels were not significantly different between control and salt treatments in both mono- and poly-embryonic types. The mean membership function value (MFV) was hardly different between mono- (0.5052) and poly-embryonic (0.5254) types, given quite similar reductions in plant height (∼22.0 %), leaf area (≤ 14.0 %), leaf (35–40 %), stem (∼40 %), and root (24–29 %) biomass, and net photosynthesis (∼64 %) as well as increases in leaf Na⁺ (79–85 %) and Cl⁻ (70–76 %) under saline conditions. Based on mean MFV for all the traits, genotypes CSJ-19, CSJ-18 and CSJ-5 were found to be highly salt tolerant, whereas CSJ-1 and CSJ-31 were ranked as highly salt sensitive. We deduce that maintenance of leaf and root growth, reduced uptake of Na⁺, and preferential accumulation of K⁺, Ca²⁺ and Mg²⁺ could be the major traits underlying salinity tolerance in jamun.