Tuber Oxalic Acid Content and Ploidy Levels in Oca (Oxalis tuberosa) Use-Categories

Oxalis tuberosa Molina (“oca”) is a tuber crop cultivated for subsistence in the Andean region. Oca is an octoploid (2n = 8x = 64; x = 8) with an incompletely resolved evolutionary history. Oca is divided into two folk use-categories: those that are eaten baked or boiled after post-harvest “sweetening” in the sun and those that are reserved for processing into a storable dried food product called khaya. To test a potential biochemical basis for the cultural use-categories, we quantified oxalic acid in tubers from each use-category from both Quechua- and Aymara-speaking communities. Surprisingly, only a small proportion of the ocas reserved for khaya have significantly higher concentrations of oxalic acid, and these comprised some, but not all, ocas of a single folk cultivar, called p’osqo, apparently endemic to Cusco Department, Peru. Flow cytometry and SSR genotyping revealed that the ocas with elevated levels of oxalic acid are tetraploid.