Selection for salt tolerance in callus culture of oil flax

Flax (Linum usitatissimum L.) represents a crop of substantial agronomic and economic significance, with its derivatives utilized across multiple industrial sectors. It is predominantly esteemed for its seeds, which are abundant in alpha- linolenic acid, a type of omega-3 polyunsaturated fatty acid. However, the cultivation range of flax is constrained by its pronounced sensitivity to saline environments. Among the innovative strategies to develop salt-tolerant genotypes, in vitro cell selection stands out as a promising approach. This study was aimed to evaluate the feasibility of obtaining oilseed flax genotypes tolerant to sodium chloride (NaCl) through callus culture methodology. Two genetically distinct flax varieties, namely Zaporizkyi bohatyr and Evryka, served as the experimental material.Segments of callus tissue were cultured on Murashige and Skoog (MS) and N6 media supplemented with NaCl at concentrations of 0.3 %, 0.6 %, 0.9 %, and 1.2 %. Following the cultivation period, the proportion of necrotic calli and the capacity for cellular proliferation were evaluated. Subsequently, the morphogenetic potential of callus tissue was evaluated under saline conditions, and the regenerants were evaluated for their ability to withstand salt- induced stress. The morphogenetic response of callus was assessed under sodium chloride concentrations of 0.3 % and 0.6 % by quantifying the proportion of callus samples exhibiting regeneration zones. To determine the efficacy of selection pressure, regenerated shoots with residual callus were transferred to MS medium containing 0.2 % and 0.4 % NaCl. Parameters such as the survival rate and continued growth of shoots, presence of necrotic lesions, and shoot etiolation were recorded. The results indicated that a sodium chloride concentration of 0.3 % was optimal for in vitro selection. Elevated salinity levels adversely affected callus viability, resulting in inhibited callus growth, disrupted development, and tissue degradation. Selection pressure applied at 0.3 % NaCl enhanced the frequency of salt-tolerant regenerants, as evidenced under subsequent exposure to 0.2 % NaCl. In Zaporizkyi bohatyr variety, the survival rate of regenerated shoots that successfully survived under salt stress conditions was 36.7 %, compared to 13.3 % in the control group where selection was not performed. For Evryka variety, the respective figures were 28.0 % and 4.0 %. At a sodium chloride concentration of 0.4 %, the few surviving shoots exhibited no further development and ultimately perished. Selection at NaCl concentrations exceeding 0.3 % resulted in pronounced suppression of the morphogenetic capacity of callus tissue, rendering it incapable of producing viable shoots.The tested flax genotypes demonstrated considerable variability in their physiological response to salt-induced stress, with Zaporizkyi bohatyr variety displaying superior adaptability.