Salt tolerant screening in eucalypt genotypes (Eucalyptus spp.) using photosynthetic abilities, proline accumulation, and growth characteristics as effective indices

Eucalypts are highly regarded plantation trees due to their fast growing nature, high water consumption, tolerance to abiotic stresses, and ease of conversion to pulp and paper. We screened five genotypes of Eucalyptus camaldulensis (T5, BD4, 1-7-1, H1, and SH4) and three genotypes of the E. camaldulensis x Eucalyptus urophylla hybrid (H4, 58H2, and 27A2) for salt tolerance. Fresh weight and leaf area in hybrid genotypes (H4, 58H2, and 27A2) were greater than those in the E. camaldulensis population after plantlets were subjected to 200 mM NaCl for 14 d. The chlorophyll a content in hybrid genotypes decreased by 19.71-37.11% compared to 51.45-66.00% decline in E. camaldulensis. Similarly, total chlorophyll content was retained at a high level in the hybrid population, leading to stabilization of the net photosynthetic rate. The amount of proline, an osmolyte, was significantly increased in all Eucalyptus genotypes when exposed to 200 mM NaCl. Multivariate analyses of proline accumulation, photosynthetic pigment degradation, diminishing chlorophyll fluorescence, P (n) reduction, and growth inhibition in salt-stressed plantlets of Eucalyptus genotypes were performed to classify salt-tolerant- and salt-sensitive groupings. The hybrid eucalypt genotypes H4, 58H2, and 27A2 were identified as salt tolerant while the selection genotypes of E. camaldulensis, T5, BD4, 1-7-1, H1, and SH4, were classified as salt susceptible.