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Title: SWEETPOTATO STORAGE ROOT PHENOLICS INHIBIT IN VITRO GROWTH OF ERWINIA CHRYSANTHEMI

Author
item Harrison Jr, Howard
item Peterson, Joseph
item Snook, Maurice

Submitted to: Allelopathy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2005
Publication Date: 1/2/2006
Citation: Harrison Jr, H.F., Peterson, J.K., Snook, M.E. 2006. Sweetpotato storage root phenolics inhibit in vitro growth of erwinia chrysanthemi. Allelopathy Journal. 17(l):81-88.

Interpretive Summary: Erwinia chrysanthemi causes bacterial stem and root rot of sweetpotato in the field and post-harvest storage root rot. Bacterial rot has become more widespread in recent years to the point that it is now a major problem for sweetpotato growers. Some sweetpotato varieties are resistant to bacterial rot; however, the mechanism of resistance is not understood. Phenolic compounds that occur at high levels in storage root periderm and cortex tissues of some sweetpotato varieties were tested to determine their effect on the bacterial rot pathogen. The simple phenolics caffeic acid and p-coumaric acid inhibited the growth of bacteria when added to nutrient agar at concentrations similar to contents found in some sweetpotato storage roots. This suggests that caffeic and p-coumaric acids protect sweetpotato against bacterial rot, and sweetpotato varieties that contain high levels of these compounds may be resistant to the disease. If further research establishes a direct link between phenolic acids and bacterial rot resistance, then measuring phenolic acid content could be a useful way to rapidly identify rot resistant lines.

Technical Abstract: Contents of the major phenolic components of sweetpotato roots of 14 genetically diverse sweetpotato clones ranged from 0.22 to 8.25 mg/g dry weight in periderm tissue and from 2.16 to 9.26 mg/g dry weight in cortex tissue. Caffeic acid, chlorogenic acid, and three isomers of dicaffeoyl quinic acid comprised 92 and 96 % of the phenolics in periderm and cortex, respectively. Scopoletin and its glycoside scopolin were the only other phenolics found at high levels. Caffeic and p-coumaric acid (a component of sweetpotato latex), reduced Erwinia chrysanthemi growth by over 90 % when they were included at 2 mg/ml in a nutrient broth. Chlorogenic acid caused only moderate inhibition, and scopoletin was not inhibitory. This evidence suggests that constituent levels of caffeic acid may function to protect sweetpotato storage roots against bacterial rots.