3.2.3. Changes in the SI of Root Length (SIRL)

In general, in vitro potato shoot cultures responded to PEG 600 treatment with decreased SIRL values for root length, and the degree of inhibition increased with increasing PEG 600 concentration (Table 8, Figure S7a–c). The use of 2.5% PEG 600 had a stimulatory effect on the root length of four lines (C5, C20, C57 and C63) compared to the referent lines, with the highest SIRL value obtained in the C63 line (131.1). Considering the SIRL values for root length, the C63 breeding line was the best at each PEG 600 level. According to its response, the C5 line tolerated well the stress induced by each PEG 600 treatment, while the C57 and C20 lines tolerated only the mild stress (2.5% PEG 600) according to their SIRL values for root length. However, the majority of breeding lines showed lower SIRL results than those of the referent lines for root length in each PEG treatment, especially when PEG 600 was applied in the highest (7.5%) concentration.

**Table 8.** Root length SI (SIRL) values of potato genotypes under osmotic stress induced by PEG 600 added to the medium at levels of 2.5%, 5.0%, and 7.5%.



**Table 8.** *Cont.*

Symbols mark significant differences from the C107 referent line (-), or from the C103 referent line () according to LSD test; the small letters indicate significantly different means between the breeding lines within a treatment, and the capital letters indicate significantly different means between treatment levels within a breeding line according to Tukey-B test.
