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Abstract
Changes in surface characteristics of the adaxial and abaxial cuticular membranes of expanding ‘Red-haven’ peach [Prunus persica (L.) Batsch] leaves were followed and related to wettability and to retention and penetration of foliar-applied compounds. Epicuticular wax deposition increased with leaf development until full expansion, the maximum being 50 to 65 μg cm−2. Although wax fine-structure was not prominent on expanding leaves, localized areas of crystalline wax occurred on both surfaces of fully expanded leaves. The 2 surfaces differed markedly in the composition of the epicuticular wax. Although triterpenoid acids, alkanes and primary alcohols were present on both surfaces, sterols and esters were predominant on the adaxial surface. Marked changes in composition occurred with leaf age. The contact angles formed by aqueous droplets on the adaxial surface increased with leaf development and attained the highest value only after full leaf expansion; on the abaxial surface the contact angle increased sharply and approached a maximum at 70 to 80% full expansion. Retention of aqueous solutions decreased with leaf expansion. Permeability of the cuticular membrane, as indexed by transpirational loss and penetration of 14C-NAA (naphthaleneacetic acid), decreased progressively with increasing leaf age. These findings are discussed in relation to spray application and penetration of foliar-applied chemicals.