Thiamin addition to soil increases potato tuber thiamin content under greenhouse conditions

Thiamin is essential for human health, but humans do not synthesize it and must consume it through regular dietary intake. Plants synthesize thiamin in photosynthetic tissues to support various primary metabolic pathways. In addition, plants can also absorb thiamin from the soil. Interestingly, plant growth can be improved by supplying exogenous thiamin, but this effect has not been investigated in potato (<i>Solanum tuberosum</i>). Here, we report the effect of soil thiamin amendment on yield and tissue thiamin content of three potato varieties grown in a greenhouse. We watered plants with different concentrations of thiamin on a weekly basis from emergence until harvest. Under optimal growth conditions, thiamin supplementation did not affect tuber yield, regardless of soil type. Thiamin accumulated up to 58, six and three times in roots, tubers and stems, respectively, of plants grown in soil supplemented with thiamin compared to control plants, while leaf thiamin content did not significantly change. Quantitative polymerase chain reaction analysis showed that soil thiamin supplementation had no or little effect on the expression of two key thiamin biosynthesis genes in leaves. Our results indicate that increasing soil thiamin concentration does not improve potato yield under optimal growth conditions at the greenhouse scale. However, increased yield at field-scale under stress conditions remains to be tested. Intriguingly, the accumulation of thiamin in potato tubers suggests that soil thiamin supplementation may be a viable strategy for biofortification.