Growth Rate and Surface Wetness are Critical Factors in Microcracking, Loss of Water Vapour and Russeting of the Apple Fruit Surface

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Abstract

The study was carried out at the Leibniz Universität Hannover Germany. The objectives were to quantify microcracking of the cuticle, fruit surface permeability and fruit surface russeting in apple (Malus x domestica Borkh. Cultivar ‘Pinova’). Samples were obtained from the experimental orchards of the Leibniz Universität Hannover Germany. Selected portion of the fruit surface was exposed to1-(2-chloro-4-piridinyl)-3-phenylurea (CPPU) solution (20 ml l^-1) or liquid water for two days and 12 days, respectively. After the termination of each treatment, assessment of the indices above-mentioned was carried out four times. Microcracking of the fruit surface was quantified using acridine orange infiltration. Permeability was quantified by water loss using excised epidermal segments (ES). Calibrated photographs of the russeted fruit were taken and russeted area quantified by image analysis using Cell P^. At 21 days after full bloom (DAFB), acridine orange (AO) infiltrated area of the CPPU treated and moisture treated surface of the fruit were respectively 4-folds (8 %) and 8-folds (8 %) more than that of the untreated surface (2 % and 1 % respectively). Permeability of CPPU treated and moisture treated surface of the fruit were respectively 15 x 10^-5 m s^-1 and 40 x 10^-5 m s^-1 when compared to the untreated surface (10 x 10^-5 m s^-1 and 10 x 10^-5 m s^-1 respectively) at 21 DAFB. There was 10 % (10.3 ± 2.6) and 37 % (37.1 ± 7.3) russeting when the fruit surface was treated with CPPU and moisture respectively at 21 DAFB. Therefore, both factors are critical in microcracking, loss of water vapour and russeting of the apple fruit surface.