Improving Potato Tuber Quality and Production by Targeted Calcium Nutrition: the Discovery of Tuber Roots Leading to a New Concept in Potato Nutrition

Calcium plays a major role in plant growth and development and in the maintenance and modulation of various cell functions, especially related to membrane structure and function and to cell wall structure. Calcium stabilizes cell membranes by bridging polar head groups of phospholipids at the membrane surface. Calcium is also an integral part of the cell wall where it provides stable intra-molecular linkages between pectin molecules, resulting in cell wall rigidity. A change in the cytosolic calcium concentration is also known to provide a cellular signal that regulates metabolism and mediates plant responses to stresses. Calcium deficiency is pervasive among fruit and tuber crops because calcium moves with water in the xylem and very little water moves to fruit and tuber tissues as compared to leaves. The water potential gradient within the potato plant favors xylem transport to the foliage since tubers are surrounded by moist soil. As a result, the calcium concentration is much higher in foliage than in the tuber. In our early work, we demonstrated that water and calcium taken up by the main root system bypass the tubers and are delivered to the above-ground portion of the plant, and roots arising from the stolons and tubers supply calcium to the tubers. Tuber calcium concentration can therefore be increased by selectively feeding tubers with calcium nutrients during tuber bulking period. The discovery of tuber roots has led to the development of a new concept in potato nutrition. We have demonstrated that in-season fertilization with calcium increases tuber calcium and lowers incidence of physiological disorders such as internal brown spot, hollow heart, and bruising. Localized tissue calcium deficiencies are implicated as mechanisms initializing cell death and tissue necrosis leading to internal brown spot and hollow heart in potatoes. There is also strong evidence for reducing storage rot by increasing tuber calcium. Finally, tuber calcium is important for the health of the sprout and of the tuber skin.