Induction of apple scald by anaerobiosis has similar characteristics to naturally occurring superficial scald in 'Granny Smith' apple fruit

Scald, which can be induced by anaerobiosis (N-2-induced), may involve similar physiological and biochemical mechanisms to those which contribute to naturally occurring superficial scald. To investigate this hypothesis, Granny Smith apples were harvested weekly from four orchards and stored in air for 16 weeks at 0 degrees C, before being ventilated with N-2 for up to 4 days, or held in air at 20 degrees C. Following N-2 treatment, scald developed within a few minutes of transfer to air and its severity was positively correlated with duration of N-2 treatment. Susceptibility to induction of scald with N-2 decreased through the harvest season and increased with length of refrigerated storage. Following N-2 treatment, the levels of alpha-farnesene, conjugated triene (CTH) and OD200 (Abs(200)) were significantly lower than in fruit held continuously in air. This effect was more apparent in the early than late harvest fruit. RNA gel blot analysis of polyphenol oxidase (PPO) was conducted on selected samples. Expression of PPO was very low while fruit were held in N-2, suggesting that the regulation of PPO gene expression is dependent on oxygen. Once fruit were removed to air, browning occurred almost immediately, too rapidly for the initial development of browning symptoms in scald to be attributed to increased PPO gene expression. We conclude that anaerobically induced scald development has similar characteristics of naturally occurring superficial scald and in both cases elevated PPO gene expression may not be associated with the initial development of symptoms. (C) 1999 Published by Elsevier Science B.V. All rights reserved.