Cuticle Development and Surface Morphology of Olive Leaves with Reference to Penetration of Foliar-applied Chemicals1

Surface morphology and development of the cuticle of olive ( Olea europaea L, cv. Manzanillo) leaves were studied in relation to some factors (wetting, retention) that influence absorption of foliar-applied substances. Cuticle deposition occurred at a uniform rate during leaf development, then ceased at full expansion. The total weight of the cuticular membrane per unit surface area remained constant during leaf expansion. The weight of the cuticular membrane of the adaxial epidermis was about 1.4 mg/cm 2 and in μ g/cm 2 the principal constituents were: epicuticular wax, 243; cutin, 886; cuticular wax, 272. The thickness of the cuticle was greater on the adaxial (11.5 μ m) than on the abaxial surface (4.5 μ m), and both surfaces were covered with large (130 μ m diameter) peltate trichomes, their number being greater on the abaxial surface (143/mm 2 vs. 18/mm 2 ). Stomata were present only on the abaxial surface (470/mm 2 ). The large number of trichomes contributed significantly to the effective surface area of the leaf, which was about 3 times greater for the abaxial than for the adaxial surface. No epicuticular wax fine-structure was observed. Both surfaces were difficult to wet. The advancing contact angle formed by distilled water was 106° for the adaxial and 125° for the abaxial surface. Retention as indexed by dipping leaves in distilled water was 0.34 μ l/cm 2 . When sprayed, maximum retention was 31.3 and 36.9 μl/cm 2 by the adaxial and abaxial surfaces, respectively.