2.10. Starch content determination
Starch content determination was performed by the underwater weight method (Bárta & Bártová, 2008) using the special Hošpes–Pecold scales ESPRA (SATEC, Ltd., Chrudim, Czech Republic) and expressed as % per fresh matter of tubers.
2.11. Statistical analysis
Statistical analyses were performed using the software Statistica 7.1 (StatSoft, GB) by two-way ANOVA method of analysis of variance with Tukey HSD test and F-test of significance at the level of significance p ⩽ 0.05. Further linear correlation analysis and linear regression was performed.