Skin spots on ‘Cripps Pink’ and ‘Elstar’ apples are identical

Abstract

Brown spots have recently been reported on the surfaces of ‘Cripps Pink’ apples, grown in Marsillargues, France. Preliminary observations suggest the symptoms on ‘Cripps Pink’ apples resemble those reported earlier on ‘Elstar’ apples and then referred to as ‘Elstar skin spots’. Elstar skin spots occur particularly in coastal production areas of northern Europe, and in rainy seasons. The objective of this study was to establish more definitively whether the skin spots observed on ‘Cripps Pink’ are identical to those reported on ‘Elstar’. Hence, the morphological and anatomical characteristics of ‘Cripps Pink’ skin spots were assessed in more detail. The skin spots on ‘Cripps Pink’ develop on the non-blush side of the fruit. High resolution scanning light microscopy revealed a network of cuticular microcracks in both symptomatic and non-symptomatic regions of an affected fruit. When fruits with microcracks were dipped in a 1:1 chloroform:methanol mixture, the width and depth of the microcracks increased, indicating that the microcracks had previously been partially filled with wax. The microcracks on a symptomatic surface were wider and deeper than those on a non-symptomatic surface. After the cuticular wax had been extracted (as above), the microcracks on the symptomatic surface were found to be partially infiltrated with the fluorescent dye acridine orange; but not so the microcracks on a non-symptomatic surface. The fruit skin of symptomatic apples had a higher rate of water loss than that of non-symptomatic apples. Microscopy revealed that the epidermal and some of the hypodermal cells beneath the microcracks within a symptomatic area were brown and their cell walls lignified. We infer from these observations that the skin spots on ‘Cripps Pink’ are identical to the well-known skin spots on ‘Elstar’ apples.