Objectives We studied the responses of different potato cultivars to NaHCO₃ stress from the growth, photosynthetic efficiency, and physiological indices, to screen out the high NaHCO₃ tolerant cultivars, and the indicators to assess cultivars alkaline tolerance.

Methods The potato cultivars used in the hypotonic experiment included cultivars “V₇”, “Houqihong”, “Kexin 1”, “Xingjia 2”, “Holland 15” and “Kangnibeike”. The 7-day-old potato seedlings were grown in normal 1/2 Hoagland nutrient solution for 3 days, and then subjected to six alkali stress solutions containing NaHCO₃ 0, 10, 20, 30, 40 and 50 mmol/L for 7 days. The seedlings were harvested for determination of 11 physiological indexes. Principle analysis was used to screen the alkali resistant indicators.

Results With the increase of alkali stress intensity, the growth of potato seedlings was inhibited to different degrees. Compared with NaHCO₃ 0 mmol/L, the root length of V₇ increased by 54.37%, 46.04% and 25.58% under 30, 40, and 50 mmol/L stress, respectively, while the root lengths of the other five cultivars significantly decreased. Under NaHCO₃ 50 mmol/L stress, the plant height and stem diameter of all cultivars were significantly lower than under NaHCO₃ 0 mmol/L control. The leaf N and relatvie chlorophyll content of all cultivars varied differently with the increase of stress intensities, the leaf N contents of V₇, Houqihong and Kexin 1 reached the peaks under NaHCO₃ 40 mmol/L treatment, and the relative chlorophyll content of Xingjia 2 reached the peak under 50 mmol/L treatment, while the N and relative chlorophyll contents of Helan 15 and Kangnibeike reached the minimum under 50 mmol/l treatment. The root activities of all cultivar seedlings increased at first and then decreased. Under NaHCO₃ 40 mmol/L stress, the root activities of V₇ and Houqihong were significantly higher, while that of Helan 15 decreased by more than 80% under 0 mmol/L control. The content of malondialdehyde in root of all seedlings increased with the increase of stress degree, nevertheles V₇ was always recorded the lowest content among the 6 cultivars. The catalase (CAT) and superoxide dismutase (SOD) activities of all seedling roots increased first and then decreased. Cultivar V₇, Houqihong, Kexin 1 and Xingjia 2 had similar but higher CAT and SOD activities than Kangnibeike and Holland 15. After calculation of the principal component analysis, based on the 11 indicators, 5 prinsiple components were obtained with individual eigenvalue >1, and the cumulative contribution rate to alkali stress reaching 80.07%. Thereby the 11 individual indicators were screened out as seven commom physiological indexes for all the potato cultivars, including plant height, stem diameter, leaf N content, relative chlorophyll content, proline content, peroxidase (POD) activity and CAT activity.

Conclusions The indicators for the alkaline resistance assessment are plant height, stem diameter, leaf nitrogen content, relavent chlorophyll content, proline content, POD activity and CAT activity. Among the tested 6 cultivars, V₇ shows the strongest alkali resistance, Houqihong, Kexin 1 and Xingjia 2 show second strong alkali resistance, while Kangnibeike and Helan 15 are weak in alkali resistance.