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The results from these tests clearly demonstrated that the 

 CO2 pretreatment can delay softening of 'Mcintosh' in CA storage. 

 At every location, treating them with 121 CO2 for 2 weeks produced 

 apples that were 1 to 2 lbs firmer than untreated CA samples after 

 4 to 6 months in storage. However, the effect gradually wore off; 

 after a week at room temperature these differences had largely dis- 

 appeared, and after 7 to 8 months of storage even the fruit right 

 cut of storage showed only small differences. Nevertheless, 

 these differences would be well worth the treatment if no problems 

 arose from the treatment. 



But there are problems! Both external COo injury (a scald- 

 like burn) and internal CO2 injury (a form of internal breakdown) 

 developed. The extent of these injuries was variable among loca- 

 tions; external injury occurred everywhere except in Michigan, and 

 internal injury was distinct only in British Columbia. However, 

 the problems were sometimes overwhelming; in British Columbia, 431 

 of the fruit had external injury, and 53% had internal injury, and 

 in New York 30 to 351 of the apples had external injury. In Massa- 

 chusetts, we've found the extent of injury to vary from year to 

 year, sometimes not occurring at all and in other years occurring 

 to a serious extent. We also find different samples varying great- 

 ly in the amount of injury that they develop from the same treat- 

 ment. Just as it was obvious in these tests that the CO2 treat- 

 ment can delay softening of 'Mcintosh', it was also obvious that 

 the treatment has the potential of causing very serious damage to 

 the stored apples. 



What about other factors that might influence results? We 

 found that increasing the CO2 level from 12% up to 15% resulted 

 in a bit more fruit firmness after storage, and that increasing 

 treatment time from 2 weeks to as much as 6 weeks did likewise. 

 However, both of these modifications increased the amount of CO2 

 injury as well as increasing firmness of the apples. Harvesting 

 the fruit 1 week earlier than peak time increased treatment bene- 

 fit, but again it also increased the amount of injury. Harvesting 

 1 week later than peak time reduced benefit from the treatment. 

 Treating the apples at 32°F rather than at 38° reduced both bene- 

 fit and injury. In tests in New York, treatment was begun when 

 the apples were still warm (55°) and they were cooled to 38° dur- 

 ing the 2-week treatment; the CO2 treatment was of no value in de- 

 laying softening of these warm fruit. In Michigan, apples were 

 kept at 70°F for a week, or at 32° for 1 or 2 weeks, before they 

 were treated; any delay reduced treatment benefit, and 1 week at 

 70° eliminated any benefit. The O2 level and the humidity in the 

 storage during the CO2 treatment had no effect on the delay in 

 softening brought about by the CO2 pretreatment. 



It was rather clear from the results of these tests that rais- 

 ing the CO2 level to 12% for 2 weeks at the beginning of CA storage 

 has no magic effect on the apples; it simply slows down their rate 

 of ripening even more than CA alone does. Anything that increases 



