24 MISC. PUBLICATION 4 98, U. S. DEPT. OF AGRICULTURE 



use of too much heat and inadequate circulation. When the offending 

 condition is corrected "gas burn" does not occur. 



The browning caused by too low humidity in the coloring room can 

 be distinguished from that which accompanies aging of the fruit in 

 storage by the roughened, papery appearance of the surface of the 

 rind and by the fact that affected areas are not sunken. Areas show- 

 ing the blemish known as brown stain (p. 21) do not develop until 

 after shipment or storage and are neither sunken nor roughened. 



Brown spotting in the coloring room can be reduced by maintaining 

 the relative humidity at 90 to 92 percent or above during the ethylene 

 treatment. 



Another kind of coloring-room injury is the more rapid develop- 

 ment of stem-end rot in gassed fruit. However, this is due not so 

 much to the effect of the ethylene as to the more rapid aging brought 

 about by improper operation of the coloring rooms. It can be pre- 

 vented to some extent by maintaining a moderate circulation of air 

 in the coloring room throughout the coloring period and not allowing 

 the temperature to go above 85° F. Best results from the ethylene 

 treatment are obtained when the temperature is maintained between 

 80° and 85°, which markedly checks blue mold decay (p. 21). 



CREASING 



Creasing is a condition found in mature and overmature oranges 

 and is characterized by narrow sunken furrows or grooves in the rind, 

 usually less than 14 inch wide and from y 2 to 2 inches long (pi. 14, J.). 

 These may extend both longitudinally and crosswise and in severe 

 cases may run together to produce large areas of bumpy rind. In 

 small creases the color of the sunken skin is normal, but in larger 

 ones it may be yellowish green to gray. On fruits that have been 

 subjected to hot solutions, such as those often used in the "color 

 added'' treatment, creases become more apparent, the sunken rind 

 often becoming water-soaked or cracked. Sinking of the rind in the 

 creases is due to weakness in the underlying spongy portion. If a 

 thin paring is made so that the tissue bearing the oil cells and yellow 

 color is removed from the crease, it can be seen that the albedo is 

 thin or cracked and pulled apart (pi. 14, B). 



In California oranges mild creasing is not considered a serious de- 

 fect because the rind is pliable and few of the fruits crack open from 

 pressure during packing and shipping. Florida fruit, however, has 

 a thinner and more brittle rind so that creased areas split easily 

 in tight packs and open the way for blue and green mold rots. The 

 cause of creasing is not known. Except in fruit subjected to hot 

 solutions or too tightly packed, very little if any increase in amount 

 or severity of creasing has been observed in transit. 



(See 4-3, 96.) 



EXANTHEMA ( AMMONIATION ) 



OCCURRENCE, SYMPTOMS, AND EFFECTS 



Exanthema is a nonparasitic disease of the fruit, leaves, and twigs 

 of all commercial Citrus species. It occurs in practically all the 

 citrus-growing regions of the world but in the United States is most 

 common and most serious on oranges in Florida. 



