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

Application of 5% PEG 6000 to medium resulted in decreased root length in each breeding line and in referent lines (Table 4, Figure S3a). SIRL values of 10 breeding lines were significantly higher than those of the referent lines. At the level of 7.5% PEG 6000, increased SIRL values were found in some breeding lines, and the SIRL values of four breeding lines (C10, C14, C22 and C30) were significantly higher than those of both referent lines (Table 4, Figure S3b). When 10% PEG 6000 was added to medium, the SIRL value only of C22 was higher than that of referent line C103, but the SIRL value of C107 was lower than that of the majority of breeding lines (Table 4, Figure S3c).

**Breeding Line SIRL (%) 5% PEG 6000 7.5% PEG 6000 10% PEG 6000** C2 50.7 f–j B 69.5 c–h A 46.8 e–i B C3 56.6 d–j B 52.4 h–n B - 63.6 b–e A - C4 51.1 f–j A 53.7 g–m A - 51.3 d–h A C5 69.4 c–f B - 84.2 cd A - 85.1 ab A - C6 48.1 h–j B 71.4 c–h A 51.8 d–h B C8 83.8 a–c A - 58.4 f–l B 72.3 b–d C - C9 87.7 ab A - 62.8 e–j B 63.2 b–e B C10 88.2 ab A - 87.9 bc A - 57.7 c–h B C11 47.4 ij A 33.7 no B - 48.0 e–i A C12 47.2 ij A 76.7 c–f B 58.8 c–f C - C14 88.1 ab A - 111.8 a B - 57.0 c–g C C17 44.0 f A 25.2 o B - 17.3 k B - C19 67.5 c–h A - 54.8 g–l B - 39.2 f–k C C20 66.6 c–h A - 45.0 j–o B - 44.8 e–j B C21 57.3 d–j A 65.4 d–i A 51.4 d–h B C22 74.7 a–d B - 90.0 bc A - 95.9 a A - C26 49.8 g–j A 51.1 i–n A - 24.1 jk B - C28 54.2 e–j A 41.0 B l–o - 34.5 g–k B C30 91.0 a B - 106.3 ab A - 81.5 ab B - C32 45.9 ij A 53.8 g–m A - 36.9 f–k B C35 89.0 ab A - 61.5 e–k C 75.6 a–c B - C37 55.6 e–j A 39.8 m–o B - 50.3 d–h A C41 52.1 f–j A 37.5 m–o B - 25.7 i–k B - C42 63.6 d–i A 72.2 c–h A 32.6 h–k B - C57 45.8 d–f A 55.8 f–l A 20.9 k B - C58 63.2 d–j B 79.5 c–e B - 82.4 ab A - C63 71.2 b–e A - 43.0 ko B - 53.7 c–h B C103 56.5 d–j B 73.6 c–g B 84.7 ab A C107 55.4 d–j B 67.1 d–i A 46.3 e–i B

**Table 4.** Root length SI (SIRL) values of potato genotypes under osmotic stress induced by PEG 6000 added to the medium at levels of 5.0%, 7.5% and 10%.

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.

3.1.4. Changes in the SI of Root Number (SIRN)

PEG 6000 treatments strongly increased the number of roots in parental lines and in some of the breeding lines, and the best SIRN values were obtained for referent genotypes in each treatment (Table 5, Figure S4a–c). However, 5% PEG 6000 in the medium resulted in decreased root number in a dozen breeding lines. Some lines responded with increased SIRN values to raised (7.5%) PEG concentration. Increasing the PEG 6000 concentration to 10% resulted in significantly decreased SIRN values in four breeding lines (C8, C26, C41 and C57) and yielded significantly increased SIRN values in about a quarter of the lines (C2, C3, C11, C30, C35, C37 and C58) (Table 5, Figure S4c).

**Table 5.** Root number SI (SIRN) values of potato genotypes under osmotic stress induced by PEG 6000 added to the medium at levels of 5.0%, 7.5% and 10%.


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.
