Survey of Tuber pH Variation in Potato (Solanum) Species

Variation in tuber pH has been previously reported in cultivated potato and shown to be associated with economic traits. We here report a broad survey of potato germplasm for tuber pH, including wild Solanum species. Cultivar pH ranged from about 5.5 to 6.2, while six wild species were significantly lower. Solanum microdontum had the lowest pH average of the wild species examined at 5.17 with the lowest observed reading of 4.99. This species also exhibited a strong environmental effect, in which field tubers (5.28) were much lower than greenhouse tubers (5.63). Long storage generally did not have a significant effect on wild species tubers, except for S. jamesii, which reduced from 5.78 to 5.54. Various types of sampling were tested. Skins were generally lower than flesh, with a high correlation between the tissues. Samples that were frozen, cooked, or reconstituted from dried powder had different absolute pH values, but these were highly correlated, so germplasm would be ranked for pH similarly regardless of method. Although not tested here, physiological links between pH and economic traits like disease resistance, nutrition and tuber quality are plausible. If so, pH testing might serve as a rapid and inexpensive screening tool in breeding programs. The association of pH and useful traits might also provide clues for exploring underlying genetic and physiological mechanisms in potatoes.