Physiological traits underlying sodicity tolerance in Jamun (Syzygium cumini L. Skeels) cultivars

There is a lack of research on how sodicity stress affects tree growth and physiological relations in jamun (Syzygium cumini L. Skeels). An understanding of cultivar-specific morpho-physiological changes under sodic conditions might aid in the development of more sodicity-tolerant cultivars through genetic improvement, and help identify cultivars suitable for degraded sodic soils.

We assessed the effects of sodicity stress on tree growth, physiological relations, and ion uptake in four cultivars of jamun including CISH J-37 (J-37), CISH J-42 (J-42), Konkan Bahadoli (KB), and Goma Priyanka (GP).

Jamun cultivars exhibited varying degrees of reduction in tree growth, leaf area, and gas exchange properties under sodic conditions. Elevated soil pH caused relatively larger declines in trunk cross sectional area (TCSA; >30%) and canopy volume (CV; >25%) in J-42 and KB. Reductions brought on by sodicity stress in leaf area were rather modest (<10%) across cultivars, suggesting that maintaining leaf area may be a key adaptive trait in jamun to cope with sodic conditions. In addition to displaying a notable increase in water use efficiency (WUE), cultivar J-37 also exhibited largely intact levels of relative chlorophyll and photosynthetic rate (P _n) under sodic conditions. Despite a high intrinsic P _n under control treatment, cultivar GP displayed a large drop in P _n (37.16%) when exposed to sodicity stress. Comparatively greater increases in leaf phenolics in KB and GP seemed to be at the expense of growth and photosynthesis under sodic conditions. While superoxide dismutase (SOD) and catalase (CAT) activities showed notable spikes in both J-37 and GP, proline accumulation increased substantially only in cultivar J-37 in response to sodicity stress. Despite significant increases in leaf Na⁺ and Cl^- concentrations, J-37 was found to be comparatively efficient in Na⁺ and Cl^- exclusion from leaves when compared to other cultivars. Surprisingly, sodicity stress did not alter leaf K⁺, Ca²⁺ and Mg²⁺ levels noticeably across cultivars. Correlation analysis suggested that elevated leaf Cl^- likely inhibited tree growth more than leaf Na⁺. Principal component analysis was reasonably efficient in discerning the shared and divergent responses to sodicity stress of the studied cultivars.

Membership function analysis revealed a reasonable resilience to sodicity stress only in cultivar J-37. Maintenance of photosynthesis, reduced uptake of Na⁺ and Cl^- ions, increased and synergistic activities of SOD and CAT, and a higher leaf K⁺/Na⁺ ratio likely accounted for better performance of J-37 trees in sodic soils. Further investigations are needed to elucidate the molecular underpinnings of sodicity tolerance.