20 MISC. PUBLICATION 498, U. S. DEPT. OF AGRICULTURE 



They occur in all parts of the world where these fruits are grown and 

 may attack them in the packing house, in transit, in storage, and on 

 the market. They are not often found on fruit hanging on the tree, 

 except after mechanical injuries. Green mold rot is much more prev- 

 alent than blue mold rot. 



Both rots first become apparent to casual examination as soft, 

 watery, decolorized spots in the rind, about one-fourth to one-half inch 

 in diameter. These constitute the so-called pinhole rot ; under favor- 

 able conditions they enlarge to spots V/ 2 to 2 inches in diameter within 

 24 to 36 hours and are then sometimes known as blister rot. Soon 

 after this stage is reached the mold begins to appear on the surface 

 of the decaying areas. 



In green mold rot the older portion of the fungus growth has an 

 olive-green color but is usually surrounded by a broad zone of white 

 mycelium, ahead of which is an indefinite band of softened rind 

 (pi. 6, B). In blue mold rot the fungus growth is blue, almost up to 

 its edge, and there is a definite band of water-soaked rind just ahead of 

 the mycelium (pi. 6, C). The surface of the green mold growth is 

 wrinkled, and that of the blue mold growth is powdery or velvety. 

 Blue mold sporulates on the surface and also in the flesh, sometimes 

 clear to the center of the fruit. Green mold sporulates only on the 

 surface. The wrappers adhere closely to fruits rotted by green mold 

 but not to those rotted by blue mold. 



CAUSAL FACTORS 



Most of the damage from these rots takes place after the fruit leaves 

 the producing region, although it frequently seems to be correlated 

 with weather conditions prevailing at time of harvesting and packing. 

 Fruit picked before or just after warm wet weather often suffers 

 severely later from the rots; the same is true of fruit picked during 

 fairly dry weather but held in the packing house and packed out while 

 still damp during rainy or foggy, warm weather. 

 . The chief factor, however, that favors the development of these rots 

 is mechanical injury of some kind, since both causal fungi enter readily 

 at such injuries. Skin breaks may result from careless harvesting and 

 packing methods, from too high a bulge on the packed boxes, from 

 rough handling in transit, or from shifting and breakage caused by 

 improper stowing of the load. However caused, they are always a 

 source of danger to the fruit. Blue mold is also able to grow through 

 the uninjured skin of citrus fruit and for that reason is often called 

 the blue contact mold. 



The amount of rot that develops after fruit is removed from a car 

 or a storage room depends largely on what stage is reached before that 

 time. If, when the rot is sorted out, most of it is found to be in the 

 early or pinhole stage, there probably are other spots in still earlier 

 stages that will soon make another culling necessary; but if most of it 

 is so far advanced as to show the mold and the green or blue color, 

 there is probably little danger that more rot will develop unless the 

 rest of the fruit was carelessly handled and became contaminated with 

 spores during the sorting process. 



The third important factor influencing the development of these 

 rots is temperature. At 75° F. both molds make their best growth. At 



