Similar and divergent responses to salinity stress of jamun (Syzygium cumini L. Skeels) genotypes

Abstract

Background: Genetic variation for salt tolerance remains elusive in jamun (Syzygium cumini).

Methods: Effects of gradually increased salinity (2.0-12.0 dS/m) were examined in 20 monoembryonic and 28 polyembryonic genotypes of jamun. Six genotypes were additionally assessed for understanding salt-induced changes in gas exchange attributes and antioxidant enzymes.

Results: Salt-induced reductions in leaf, stem, root and plant dry mass (PDM) were relatively greater in mono- than in poly-embryonic types. Reductions in PDM relative to control implied more adverse impacts of salinity on genotypes CSJ-28, CSJ-31, CSJ-43 and CSJ-47 (mono) and CSJ-1, CSJ-24, CSJ-26 and CSJ-27 (poly). Comparably, some mono- (CSJ-5, CSJ-18) and poly-embryonic (CSJ-7, CSJ-8, CSJ-14, CSJ-19) genotypes exhibited least reductions in PDM following salt treatment. Most polyembryonic genotypes showed lower reductions in root than in shoot mass, indicating that they may be more adept at absorbing water and nutrients when exposed to salt. The majority of genotypes did not exhibit leaf tip burn and marginal scorch despite significant increases in Na⁺ and Cl^-, suggesting that tissue tolerance existed for storing excess Na⁺ and Cl^- in vacuoles. Jamun genotypes were likely more efficient in Cl^- exclusion because leaf, stem and root Cl^- levels were consistently lower than those of Na⁺ under salt treatment. Leaf K⁺ was particularly little affected in genotypes with high leaf Na⁺. Lack of discernible differences in leaf, stem and root Ca²⁺ and Mg²⁺ contents between control and salt treatments was likely due to their preferential uptake. Correlation analysis suggested that Na⁺ probably had a greater inhibitory effect on biomass in both mono- and poly-embryonic types. Discriminant analysis revealed that while stem and root Cl^- probably accounted for shared responses, root Na⁺, leaf K⁺ and leaf Cl^- explained divergent responses to salt stress of mono- and poly-embryonic types. Genotypes CSJ-18 and CSJ-19 seemed efficient in fending off oxidative damage caused by salt because of their stronger antioxidant defences.

Conclusions: Polyembryonic genotypes CSJ-7, CSJ-8, CSJ-14 and CSJ-19, which showed least reductions in biomass even after prolonged exposure to salinity stress, may be used as salt-tolerant rootstocks. The biochemical and molecular underpinnings of tissue tolerance to excess Na⁺ and Cl^- as well as preferential uptake of K⁺, Ca²⁺, and Mg²⁺ need to be elucidated.

Keywords: Biomass partitioning; Ion uptake; Polyembryony; Saline conditions; Salt exclusion.