CHANGES IN CUTICULAR COMPOUNDS OF DEVELOPING PECAN LEAVES

Leaf surface compounds of pecan [Carya illinoensis (Wangenh.) C. Koch] were analyzed with regard to developmental stage and to susceptibilit y to infection by Cladosporium caryigenum (Ell. et Lang. Gottwald). Im mature and mature leaves of two resistant ('Elliott' and 'Sumner') and two susceptible ('Wichita' and 'Schley') cultivars were extracted wit h methylene chloride, Extracts were separated by silicic acid chromato graphy into polar and nonpolar fractions, Constituents of each fractio n were subsequently separated by gas chromatography and were identifie d by gas chromatography-mass spectroscopy. Leaf surface constituents c haracterized included long-chain aliphatic hydrocarbons, aliphatic wax esters, triterpenoid constituents, aliphatic alcohols, fatty acids, a nd diacyl glycerides. The predominant surface compounds on immature le aves were lipids such as fatty acids, fatty alcohols, and glycerides. On mature leaves, lipids declined and aliphatic hydrocarbons and trite rpenoids became predominant leaf surface constituents. The changes wer e observed for all cultivars, regardless of genotypic response to C. c aryigenum. Thus, we conclude that cuticular chemicals change dramatica lly during leaf maturation but do not correlate with resistance to sca b disease common to certain pecan cultivars.