The cuticular membrane (CM) covers all aboveground, primary surfaces of terrestrial plants. It serves as a protective barrier against water loss, infection with pathogens, and mechanical damage. Maintaining these functions throughout development requires an intact CM. This is a particular challenge for the CM on fruit that often are characterized by continuous surface expansion until maturity. Recent investigations in sweet cherry (Prunus avium L.) established that the CM is markedly strained during stage III [“final swell” (Lilleland and Newsome, 1934)] of fruit development, which is characterized by a rapid increase in fruit mass and, hence, surface area in the absence of CM deposition (Knoche et al., 2004). Furthermore, the resulting strain of the CM is closely and positively related to frequency and severity of microscopic cracks in the CM (Knoche and Peschel, 2006). Cracks impair the barrier function of the CM and serve as entry ports for fruit rot pathogens, including Botrytis cinerea Pers. and Monilinia laxa (Aderh. & Ruhland) Honey 1945 (Borve et al., 2000).
European plum belongs to the stone fruit group and its drupe has the same double-sigmoidal growth pattern as that of the sweet cherry. It therefore may be hypothesized that in plum, CM deposition does not keep pace with fruit surface expansion and that this causes strain and microcracking of the CM. The objective of our study was to test this hypothesis. We focused on time courses of change in 1) fruit mass, 2) deposition of the CM, 3) strain, and 4) formation of microcracks in the CM of developing fruit of european plum.
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