Diane M. Varga

Using accumulated cold units to predict the development of superficial scald disorder on ‘d’Anjou’ pears during cold storage

Summary Superficial scald disorder was studied in ‘d’Anjou’ pears (Pyrus communis L.) from 14 orchards at different elevations in the Hood River valley of Oregon, USA, during 1996, 1997, 1998, and 1999. At each orchard, the accumulated cold units (ACU) were calculated as the total number of hours, in the previous 42.d prior to the first date of commercial harvest, during which time the temperature was 10˚C or lower. Fruit was harvested on the first day of commercial maturity, based on a flesh firmness of 64.5.±2.1 Newtons. Following various lengths of cold storage at 1˚C, the pears developed symptoms of superficial scald disorder after 7.d of ripening at 20˚C regardless of elevation ofgrowing origin. The term “DIS(10%)” was standardized for each orchard block, and was defined as the number of days fruit was held in air storage at ±1˚C, after which 10% of the fruit showed scald symptoms following 7.d of ripening at 20˚C. DIS(10%) was plotted against each corresponding ACU. Regression analyses were conductedas the following functions: 1) linear; 2) exponential; 3) natural logarithmic; 4) power law; and 5) polynomial. The power law function was the best fit of the regression: DIS(10%) = 62.3827.*.ACU0.0003700350037; (R2.=.0.0003700320037;***). Therefore, this equation could be used to predict scald development in ‘d’Anjou’ pears during cold storage.