14 CIRCULAR 7 6 5. U. S. DEPARTMENT OF AGRICULTURE 



fruits. When the cultures were removed from the ozonized chamber 

 after 3 weeks' exposure, they resumed their usual rapid rate of growth. 

 Haines (14) found that ozone in concentrations greater than 200 

 p. p. m. was needed to sterilize bacteria in a vegetative state on nutrient 

 agar. Thus, it is concluded that once the growth of these micro- 

 organisms has become established, high concentrations of ozone are 

 required to kill them. 



EFFECT OF OZONE ON THE DEVELOPMENT OF 

 FRUIT DECAY 



In the course of harvesting and packing apples, the fruit is exposed 

 to inoculation by various fungi, some of which cause decay. An im- 

 portant phase of the present investigation, therefore, was to determine 

 the effect of ozone on the infection and subsequent development of 

 decay in apples. In order to obtain comparative data, large numbers 

 of apples were inoculated artificially with Penicillium expansum and 

 Phial opho id malorum (Kidd and Beaum.) McColloch and subsequent 

 decay development was observed. The natural decay development on 

 the regular apple pack was also observed. 



Fruit Inoculated With Penicillium Expansum 



Sound apples were wounded on two opposite sides or on three areas 

 by means of a cork with four pins protruding one-fourth of an inch. 

 The apples were then dipped in an aqueous sp::re suspension to which 

 a small amount of a commercial wetting agent had been added. The 

 spore suspension was made by scrubbing four agar slants of PeniciTlium 

 expansum into 6 liters of tap water. After being dipped the fruit 

 was allowed to dry and was placed in the storage rooms in open, paper- 

 lined boxes. 



Ozonization failed to prevent germination of spores lodged in the 

 wounds and to stop subsequent decay, although at a concentration of 

 3.25 p. p. m. ozone injured the fruit. As a matter of fact, in some 

 instances a higher percentage of inoculated wounds developed into 

 actively decaying areas on the ozonized fruit than on the nonozonized. 

 as shown in table 6 for Rome Beauty apples. After 30 days of storage 

 at 31° F. and 5 days at 70°, 90.6 percent of the inoculations on the 

 ozonized (3.25 p. p. m.) fruit were actively decaying as compared 

 with 62.5 percent of those on the nonozonized fruit. In another lot 

 which was held for 63 days at 31° and for 3 days at 70°, 76 percent 

 of the inoculations had developed into decayed areas on the ozonized 

 fruit and 48.2 percent on the nonozonized fruit. Thus, it appears 

 that instead of preventing penicillium decay ozone may stimulate its 

 development. Similar results have been observed by other investi- 

 gators (1. 3, 18) . working with different micro-organisms. A possible 

 explanation is that the wounded tissue was damaged further by the 

 ozone, giving very favorable conditions for fungus invasion. Another 

 explanation that has been given is acclimatization of the organism to 

 ozone (16. 18) . However, Ewell ( /) was unable to confirm acclimati- 

 zation of mold to ozone; and observations after a season of ozonization 

 of the regular commercial pack do not support this contention. 



