Submitted to: Journal American Society Hortscience
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/14/2008
Publication Date: 8/1/2008
Citation: Harrison Jr, H.F., Mitchell, T.R., Peterson, J.K., Wechter, W.P., Majetich, G.R. 2008. Caffeoylquinic Acids in Storage Roots of Sixteen Sweetpotato Genotypes. Journal American Society Hortscience. 133(4):492-500. Interpretive Summary: Caffeoyl quinic acid compounds (CQA’s) are found in many plant species and help protect plants against attack by diseases and insects. They also have nutritional value in the human diet, because they act as antioxidants and are thought to prevent many chronic health problems. CQA contents were determined in the storage roots (potatoes) of 16 sweetpotato varieties. The highest sweetpotato variety contained over 60 times as much CQA’s as the lowest variety. The CQA’s inhibited millet seedling, fungus and bacterial growth in laboratory tests; this suggests that they protect roots against attack by pathogens. These findings indicate that the CQA content of sweetpotato could be increased through selection and plant breeding. Increasing CQA content in sweetpotato has two potential benefits. The compounds help protect sweetpotato roots against bacteria and fungi that attack the roots and cause rotting. They are also beneficial in the diet, and increasing CQA’s could increase sweetpotato nutritional quality.
Technical Abstract: The contents of chlorogenic acid and the 3,4-, 3,5- and 4,5- isomers of dicaffeoylquinic acid (DCQA) in the storage root tissues of sixteen sweetpotato genotypes were determined. Averaged over genotypes, the contents of the four compounds were highest in the cortex, intermediate in the stele and lowest in the periderm. Chlorogenic acid contents ranged from 826 to 7274 µg/g in cortex and from 171 to 4326 µg/g in stele. The 3,5-DCQA isomer comprised over 80% of total DCQA and contents of 3,5-DCQA were similar to chlorogenic acid contents in cortex and stele tissues. Among the 16 genotypes, total DCQA contents ranged from 0 to 1775 µg/g dry weight in periderm tissue, 883 to 8764 µg/g in cortex tissue, and 187 to 4768 µg/g in stele tissue. The large differences found in a small germplasm collection suggest that selecting or breeding sweetpotato genotypes with high caffeoylquinic acid content is possible. The four caffeoylquinic acid compounds comprised over 3% of the dry weight of storage roots of the sweetpotato relative, I. pandurata, which may be useful as a source for the compounds. The effect of the DCQA’s isolated from sweetpotato tissue and caffeic and chlorogenic acid standards were tested in proso millet (Panicum milliaceum L.), Fusarium solani, and bacterial growth bioassays. Caffeic acid, chlorogenic acid and 3,5-DCQA were most inhibitory in millet and F. solani bioassays, but 3,5-DCQA was the only compound that did not inhibit bacterial growth. Their activity in bioassays suggests that the DCQA’s contribute to the allelopathic potential and resistance to root diseases of some sweetpotato clones.