Genetic diversity and in vitro assessment of salt tolerance responses and associated changes in gene expression of male poplar (Populus) trees

In vitro evaluation of salinity effects on male aspen clone W52 (Populus tremula L.) and the hybrid aspen clone T89 (Populus tremula L. x Populus tremuloides 'Michx') were investigated after seawater treatments (control, and 'concentrations' of 8.0, 12.0 and 14.0 dS/m). A salinity level of 14.0 dS/m was found to be lethal. All the vegetative parameters of both Populus clones were significantly decreased at 12.0 dS/m. The amounts of pigments and percentages of K+ and Na+, as well as peroxidase activity in the plantlets, were determined as indicators for salt stress tolerance. Also, a genetic diversity study between the two Populus clones using inter-simple sequence repeat (ISSR)-PCR analysis showed specific marker bands for the W52 clone with high molecular sizes: 1900, 1500, 1150, and 1000 bp. Furthermore, the level of transcription factor homeodomain-leucine zipper III_1 (PagHD-ZIPIII_1) gene transcripts was positively affected in response to salt stress and influenced by genotypes. Hence, the response of the two clones to salt stress was associated with the up-regulation of PagHD-ZIPIII_1 gene which could be a good candidate for in vitro selection for salt tolerance genotypes. Generally, the clone T89 is more salinity tolerant compared to the clone W52.