Effects Of Phosphorus On Plant Drought Tolerance And Potassium On Tuber Processing Quality In Potatoes

Potato as the fourth largest food crop has played a very important role in food security. Drought stress is one of the main factors causing agricultural production reduction in potato and the browning of tuber seriously reduces its processing quality. The period study on screening low P nutrition and K nutrition tolerance materials found that there may be some relationship between phosphorus and drought tolerance, potassium and tuber starch content, browning, respectively. In order to research those interactions, a total of 60 lines with 30-day-old seedlings chosen from two segregating populations of distant-hybridization progenies were cultured in 1/2 MS mineral nutrient solution with two treatments of normal phosphorus (+P) and without phosphorus (-P) for 16 d respectively. Then, 8% PEG8000 was used to simulate drought stress for 3 h. Before and after drought stress, we sampled and determined physiological indicators. At the same time, we selected three materials (Mira, Zhongnongâ…§-2, N6-22) which were different in potassium efficiency and set up five potassium concentrations [0mmol·L^-1 (K₁), 5mmol·L^-1 (K₂), 10 mmol·L^-1 (K₃), 15mmol·L^-1(K₄), 20mmol·L^-1 (K₅)]. Plants watering with 1/2 MS mineral nutrient solution were cultured in quartz sand and determined tuber starch content and indexes related to tuber browning.(1) Effect of phosphorus deficiency on drought tolerance of potato plantsPlants in +P treatment showed more vegetative growth and had bigger leaf-area. While plants in -P treatment were dwarfish and had reduced leaf-area, dark green leaves with a leathery texture. Both treatments plants grown out many lateral roots but -P treatment had more. After 3 h drought stress, plants in P deficient treatment did not wilted, but plants in P sufficient treatment showed severely wilting. Stomatal densities of leaves lower epidermis in—P treatment were decreasing with phosphorus deficiency water culture. While, in +P treatment, Stomatal densities were increasing.After 16d phosphorus deficiency culture, osmoregulation objects soluble sugar and Pro contents in leaves and roots were very significantly higher than that of Phosphorus sufficient treatment. The contents of soluble sugar (SS) in leaves and roots increased by 135.26% and 123.01%, respectively to Pro, 74.39%and 121.37%. The contents of SS in -P team were still higher than that in +P team, after drought stress. The Pro contents of roots in -P still reached about 2 times higher compared to P sufficient plants. The activities of SOD showed not obvious difference between two P levels before drought stress, but the activities in -P treatment increased by 26.64% after 3h drought stress, while to +P treatments, activities dropped. Contrasted with +P treatment the POD activities of -P treatment increased by 85.45% before drought stress. -P treatment activities still significantly higher than that of +P treatment after drought stress. Phosphorus deficiency caused MDA contents increase by 25.99%. After drought stress, MDA contents of -P and +P treatments increased by 27.55% and 72.63% respectively.Therefore, we can conclude that the morphological and physiological changes adapting to P deficiency enhance the drought tolerance of potatoes.(2) Effect of potassium nutrition on processing quality of potato tubersWith potassium content increasing, reducing sugar content in tubers of three materials was near to"V"-shaped change. The contents of K₁ and K₂ treatments were very significantly higher than that of K₃-K₅ treatments. Reducing sugar of N6-22 was lowest in three materials. The dark brown extent of chips fried in tubers handing potassium was significantly lower than that of non-potassium treatment.Like reducing sugar, starch content in tubers of three materials was near to "V"-shaped change too. Starch content of tubers Mira are more fixed, but potassium nutrition was great influence on starch content of N6-22 and Zhongnongâ…§-2 and the differences between adjacent potassium concentration treatments reached very significant levels. Potassium content of tubers in Mira and N6-22 are fixed, but handling potassium treatments of Zhongnongâ…§-2 were significantly higher than that of non potassium treatments. The tuber water content of handling potassium treatments were higher than that of non potassium treatment, and reached very significant levels in Zhongnongâ…§-2 and Mira. With potassium content increasing, potassium content in plants of three materials was near to single front curve change, lowest in K₁ and highest in K₃. The differences between adjacent potassium concentration treatments reached very significant levels in N6-22 and Zhongnongâ…§-2 while to Mira the impact of potassium nutrition on K⁺ content of plant was small.The correlation analysis on potassium content, water content, starch content and reducing sugar content in tuber, potassium content in plant show: correlation performance in different materials was consistent, but significance was difference. There was very significant negative correlation between reducing sugar content in tuber and potassium content in plant.we can conclude that: Non potassium treatment increased reducing sugar content and dark brown level of chips fried; the impact degree of potassium level in environment on starch, water, potassium contents in tuber were different in three materials and it maybe due to different genetic background; plant potassium content of mature tubers can be used as a assessment indicator to reducing sugar content of tuber; potassium nutrition did nothave a strong impact on enzymatic browning in tubers and regularity was not satisfactory.