CHARACTERIZATION AND QUANTITATION OF HEXADECYL, OCTADECYL, AND EICOSYL ESTERS OF P-COUMARIC ACID IN THE VINE AND ROOT LATEX OF SWEET-POTATO[IPOMOEA-BATATAS (L) LAM]

Methanol extracts of vine latex of four cultivars of sweetpotato [Ipom oea batatas (L.) Lam.] were analyzed for their chemical phenolic compo sition by reversed-phase HPLC. Major components were identified as hex adecyl, octadecyl, and eicosyl p-coumarates by an evaluation of data f rom UV spectra, hydrolysis, synthesis, and GC/MS of their trimethylsil yl derivatives. Both Z- and E-isomers of the phenolic acid were found, with the latter predominating. Trace quantities of hexadecyl (Z)- and (E)-ferulates were also identified in ester concentrates. Levels of o ctadecyl (E)-p-coumarate ranged from 0.7% fresh weight in cv. Resisto to almost 2% in cv. Jewel, while the hexadecyl ester levels were only 1/4 to 1/3 these values. Levels of the Z-esters were 1/10 to 1/20 of t he levels of the corresponding E-isomers. Levels of the esters in cv. Jewel sweetpotato root latex were 2-10-fold the levels in the vine lat ex, while the ratio of E-esters to Z-esters was found to be 7-14-fold. The concentration of Z-esters among the sweetpotato cultivars tested correlated closely with the leaf feeding index for the sweetpotato wee vil (Cylas formicarius) (R(2): C-20 = 0.96; C-18 = 0.98; C-16 = 0.71). The results indicate a possible relationship between latex chemistry and insect resistance that might be exploited via plant breeding.