CHEMICAL AND ENZYMATIC INVESTIGATION OF THE LEAF CUTICLE OF PEAR GENOTYPES DIFFERING IN RESISTANCE TO PEAR PSYLLA

The composition and structure of dewaxed cuticular membranes of three genotypes of pear (Pyrus spp.) leaves differing in resistance to attac k by pear psylla (Cacopsylla pyricola Forester) were studied by chemic al and enzymatic hydrolysis. The amount of chloroform/methanol-soluble material obtained after hydrolysis by methanolic KOH (indicative of l eaf cuticle thickness) was inversely proportional to the relative degr ee of insect resistance. HPLC and GC/MS analyses were used to identify and quantify the fatty acids and phenolics present in the extracts. T he major cutin monomer of all three genotypes was 10,16-dihydroxyhexad ecanoic acid. Enzymatic hydrolysis with three commercial lipases and a cutinase isolated from Nectria haematococca indicated that there were structural differences among the dewaxed cuticular membranes of the p ear genotypes.