*Article* **Responses of Potato (***Solanum tuberosum* **L.) Breeding Lines to Osmotic Stress Induced in In Vitro Shoot Culture**

**Alexandra Hanász 1,\*, Judit Dobránszki 2, Nóra Mendler-Drienyovszki 3, László Zsombik <sup>3</sup> and Katalin Magyar-Tábori <sup>3</sup>**


**Abstract:** In vitro experiments were conducted to study the responses of potato (*Solanum tuberosum* L.) genotypes to osmotic stress. In vitro shoot cultures of 27 breeding lines and their droughttolerant parents (referent lines: C103 and C107) were tested under osmotic stress induced by addition of PEG 6000 (Mw = 6000; 5.0, 7.5, 10.0%, *w*/*v*), D-mannitol (0.1, 0.2, 0.3 M) and PEG 600 (Mw = 600; 2.5, 5.0, 7.5%, *w*/*v*) to the Murashige-Skoog medium. Stress index (SI) was calculated from shoot length (SL) and root length (RL), root numbers (RN) and the rate of surviving shoots (SR) (SISL;RL;RN;SR = ParameterSL;RL;RN;SR of treated shoots/ParameterSL;RL;RN;SR of control shoots × 100) to compare genotypes. In the average of each breeding line and concentration, the osmotic agents resulted in SI values of 40.1, 60.8, 82.6 and 76.0 for SISL, SIRL, SIRN and SISR, respectively. In general, all SI values of C103 and SIRL,RN of C107 were significantly higher than those of the breeding lines. Nine breeding lines were found to be promising based on their final ranking. According to the results, 7.5% and 10% PEG 6000 or 0.2 M and 0.3 M D-mannitol treatments proved to be suitable for the selection of osmotic stress-tolerant genotypes.

**Keywords:** polyethylene glycol; D-mannitol; tissue culture; stress index; morphological traits
