Effects of Low Temperature, Ripening, 

 and Light on Scald Susceptibility of 

 Apples at Harvest 



Cynthia L. Harden* and William J. Bramlage 



Department of Plant and Soil Sciences, University of Massachusetts 



*Present address: Pennsylvania State University, 



Fruit Research Laboratory, Biglerville, PA. 



Many factors influence scald susceptibility 

 of apples, including cultivar, orchard locality, 

 weather, harvest maturity, and storage condi- 

 tions. For example, Cortland and Delicious are 

 very susceptible, Mcintosh is moderately sus- 

 ceptible, and Empire and Gala seldom if ever 

 develop scald. Also, it has long been recognized 

 that fruit generally become less susceptible as 

 they become more mature. Among weather 

 conditions, preharvest temperature is espe- 

 cially important, with cool temperatures before 

 harvest reducing scald susceptibility. Another 

 potentially significant factor is light, since scald 

 is usually more prevalent on the green (shaded) 

 portion of a fruit than on the red (sunlit) portion, 

 and frmt from the interior of the tree usually are 

 more susceptible than ones from the exterior. 



We have been attempting to predict scald 

 susceptibility from preharvest temperature 

 records, using hours below 50°F as our tempera- 

 ture indicator. In attempting to apply such a 

 predictor to orchard conditions, however, it is 

 important to understand how much some of the 

 other key factors contribute to changes in scald 

 susceptibility, for if they are major contributors, 

 they must also be included in a predictor system 

 to avoid potential errors in predictions. 



Consequently, we conducted a three-year 

 study (1988 through 1990) of the effects of 

 preharvest hours below 50°F, fruit maturity, 

 and light intensity on scald susceptibility of 

 Cortland and Delicious apples grown at the 

 University of Massachusetts Horticultural Re- 

 search Center, Belchertown. 



Three experiments were conducted. In the 

 first, both Cortland and Delicious were har- 

 vested at three or four weekly intervals in each 

 year, and stored at 32°F for 20 weeks, with scald 

 being evaluated after an additional seven days 

 at room temperature. Preharvest temperatures 

 were recorded continuously in an enclosed shel- 

 ter in the orchard, so hours below 50°F after 

 August 1 could be counted at each harvest date. 

 Fruit maturity at harvest was measured both by 

 internal ethylene content of the fruit and by 

 their average starch score, obtained by staining 

 10 fruit per sample with an iodine-potassium 

 iodide solution and comparing their stain inten- 

 sity to standard charts, with one indicating 

 complete staining (very immature) and nine 

 indicating no staining (very mature). With each 

 succeeding harvest date, fruit were more ma- 

 ture, as shown by increasing starch index and 

 increasing internal ethylene content (Table 1). 

 In all but one instance, however, fruit from each 

 succeeding harvest date also had experienced 

 more hours below SO'F, so later harvest repre- 

 sented a combination of both riper fruit and 

 more preharvest exposure to cool temperatures. 



After 20 weeks at 32°F plus one week at room 

 temperature, scald development was quite vari- 

 able among samples (Table 1). In general, scald 

 decreased with later harvest but there were 

 exceptions; for example, scald did not decrease 

 from the September 15 to the September 22 

 harvests in 1989 on Cortland. Also, scald sus- 

 ceptibility on corresponding dates in different 

 years was not always comparable; for example. 



Fruit Notes, Summer, 1994 



