In Vitro Selection For Traits Related Todrought Tolerance Under PEG-6000-induced Water Stress In Potatoes

Drought is one of the main adverse conditions which plants are frequently confronted with, especially in agricultural production, influencing crop growth and yield. Water deficiency hinders the growth and development of potato susceptible to drought through affecting various growth and development stages and physiological metabolism, and thereby decreasing yield.In this research, virus-free plantlets of three potato cultivars, Favorita(susceptible to drought), Kexin 18(medium tolerance to drought) and Kexin 1(tolerance to drought), were tested under in vitro conditions, using liquid medium culture with PEG-6000-induced water stress to study the effect of water stress on morphology, physiology and yield of potato. Also, solid medium cultures of PEG-6000 induced water stress were used to study the effect of water stress on morphology indexes of potato plantlets in vitro. Differences of three potato cultivars under water stress were compared and indicators which could be used to identify the drought-tolerant potatoes were selected. These works could provide specific index and method for in vitro screening of drought tolerant potato germplasm. The main results are as follows:(1) Under liquid and solid culture conditions, with the increase of PEG-6000- induced water stress, the morphological indexes of different potato cultivars were inhibited and decreased. The magnitude of change for drought-tolerant potato cultivar was smaller than drought-susceptible one. Under liquid culture condition, 20% PEG-6000 could be used as optimal concentration to evaluate and identify potato drought tolerance due to large differences in different potato cultivars, while 8% PEG-6000 could be the optimum under solid culture condition.(2) Under liquid and solid culture conditions, on the basis of analysis of coefficient of variation and analysis of variance for morphological indexes of different potato cultivars, root fresh weight was a good indicator for identifying the drought tolerance of potatoes owing to its maximal coefficient of variation. The root length, though small coefficient of variation, could reflect differences in potato drought tolerance. Therefore, root fresh weight, followed by root length, could be used as good indicators to identify potato drought tolerance.(3) Under liquid culture, with the increase of PEG-6000- induced water stress, the MDA content and soluble sugar content were rising straightly in drought-tolerant potato cultivar, and were rising first and then falling in drought-susceptible potato cultivar. The soluble protein content was rising first and then falling. The contents of proline and the activity of SOD were rising first and then falling, and the activity of POD was rising straightly in drought-susceptible potato cultivar, however, the content of proline, and the activity of SOD and POD were rising straightly in drought-tolerant potato cultivar. Therefore, the content of proline, and the activity of SOD and POD could be used as effective index to identify potato drought tolerance.(4) Under liquid culture and PEG-6000 stress, the subordinate function analysis of seven physiological indexes was made and the results showed that the drought tolerance of Kexin 1 was the strongest, Kexin 18 was the second and Favorita was the weakest. It is feasible to use the subordinate function analysis to identify the drought tolerance of potato.(5) Under liquid culture and 20% PEG-6000-induced water stress, the microtuber yield, large sized microtuber weight, large sized microtuber percentage, the largest sized microtuber diameter and large sized microtuber number were significantly lower than control, indicating that the formation and growth of potato microtubers were inhibited under PEG-6000- induced water stress. By analysis of drought tolerance coefficient and drought tolerance index for microtuber yield of potatoes under 10% PEG-6000 – induced water stress, significant difference in both drought tolerance coefficient and drought tolerance index was found in different potato cultivars, allowing judgment of drought tolerance of potatoes. These two indices could be used to identify the drought tolerance of potatoes under 10% PEG-6000- induced water stress.