Toxic Ipomeamarone accumulation in healthy parts of Sweetpotato (Ipomoea batatas L. Lam) storage roots upon infection by Rhizopus stolonifer

Abstract

Furanoterpenoid accumulation in response to microbial attack in rotting sweetpotatoes has long been linked to deaths and lung edema of cattle in the world. However, it is not known whether furanoterpenoid ipomeamarone accumulates in the healthy-looking parts of infected sweetpotato storage roots. This is critical for effective utilization as animal feed and assessment of the potential negative impact on human health. Therefore, we first identified the fungus from infected sweetpotatoes as a Rhizopus stolonifer strain and then used it to infect healthy sweetpotato storage roots for characterization of furanoterpenoid content. Ipomeamarone and its precursor, dehydroipomeamarone, were identified through spectroscopic analyses, and detected in all samples and controls at varying concentrations. Ipomeamarone concentration was at toxic levels in healthy-looking parts of some samples. Our study provides fundamental information on furanoterpenoids in relation to high levels reported that could subsequently affect cattle on consumption and high ipomeamarone levels in healthy-looking parts.

Figure 1

Furanoterpenoids in sweetpotatoes: ipomeamarone, 1; dehydroipomeamarone, 2; 4-ipomeanol, 3; and 1,4-ipomeadiol, 4.

Figure 2

HPLC profile of the furanoterpenoid mix isolated from column chromatography with ipomeamarone and dehydroipomeamarone indicated as 16.43 min and 11.52 min, respectively.

Figure 3

Representative GC–MS total ion chromatogram of purified furanoterpenoids: ipomeamarone, 1; and dehydroipomeamarone, 2.

Figure 4

Controlled infection of sweetpotato samples by Rhizopus stolonifer that enabled ipomeamarone analysis of 1 cm slices for Kemb (A, B) and Naspot (C, D) cultivar samples.