Low magnesium content in potato tubers associated with mass loss during storage

Potatoes are an important crop in the Sandveld and Kouebokkeveld regions of South Africa, and one of the challenges in effective potato production is maintaining quality post-harvest. In order to identify tuber characteristics that may be used to predict keeping quality of potatoes from the sandy soils of these regions, tuber, soil, and water samples were taken from different growers who planted the cultivar Sifra. Sampling started in January 2016 and ended in July 2017. Skinning potential, determined by thumb rubbing, chemical composition, and specific gravity (SG) were evaluated one day after hand harvesting. Undamaged tubers were kept at room temperature for 42 days whereafter mass loss and firmness were evaluated. Pearson correlations and Partial Least Squares Regression (PLS-R) were done to investigate the association between tuber quality characteristics and tuber, soil and water cations. Tuber firmness after storage showed a high positive correlation with tuber magnesium (Mg) levels, and was associated with reduced skinning potentials and lower mass loss percentages. Tubers with Mg levels lower than 0.13% had high skinning potentials with mass loss percentages higher than 4.5% during storage. Irrigation with water rich in sodium (Na) tended to limit mass loss, possibly due to the associated high levels of Mg in those water sources.