MARKET DISEASES OF FRUITS AND VEGETABLES 59 



sickening odor. In late stages the color becomes brownish or 

 black, and in severe cases rapid break-down and browning of the 

 entire fruit occur. The internal condition is often associated 

 with a discoloration of the skin resembling scald. 



Core break-down is classed as a market or storage disease of 

 pear, but its time of occurrence depends largely upon the ma- 

 turity of the fruit at the time of picking. Tests have shown that 

 fruit harvested after its best picking time is much more likely 

 to become seriously affected in storage or on the market. 



(See 52, 53, 86, 103.) 



Freezing Injury 



When pears of the Bartlett and Anjou varieties are exposed 

 for long periods to temperatures only slightly below freezing, 

 they develop, a condition that is fairly definite in its symptoms. 

 In all cases the affected specimens have a glassy, water-soaked 

 appearance externally (pi. 14, E). When such fruits are cut, 

 the water-soaked condition is seen to be confined to certain por- 

 tions of the flesh. Usually it is found just beneath the skin and 

 involves several layers of cells. It may occur also within the core 

 area. The remaining flesh is usually dry and pithy (pi. 14, F) ; and 

 in cases of severe injury it may be badly cracked, so that there 

 are numerous open spaces. Freezing injury should not be con- 

 fused with old-age break-down (pi. 14, C). 



Pears showing the symptoms just described often remain in 

 an unchanged state for several weeks. They seem to be rather 

 resistant to decay and do not undergo normal break-down from 

 overmaturity, but they are inedible and have no commercial value. 



The injury has been found to develop slightly in 4 weeks and 

 to become severe in 6 weeks in pears held at a temperature of 

 27° F., which is slightly below their freezing point. 



(See 55.) 



Gray Mold Rot 



Gray mold rot (pi. 13, C, D) is one of the most serious storage 

 diseases of pear. The term "gray mold" is descriptive of the 

 gray mycelium that appears on the fruit in the late stages of 

 decay. The disease is also known as cluster rot and as nest rot 

 because a large number of affected fruits are frequently found 

 at one location in the package. The fungus mycelium grows from 

 one pear to another in such a manner that it holds the rotting 

 fruits together. It is often possible by careful examination to trace 

 the infection of large clusters of pears to a single initially infected 

 pear. Gray mold rot is darker brown than blue mold rot, and the 

 affected tissue is relatively much firmer. It usually has a sour 

 smell. 



The causal fungi (Botrytis spp.) are widely distributed and 

 live upon a large number of hosts. They are present on decaying 

 matter in the orchard, a circumstance that probably is respon- 

 sible for much of the infection found in stored fruit. Infection 

 frequently takes place through the stem, starting at the free end. 

 Diseased stems become soft and spongy and in advanced stages 

 of the decay can be crumbled between the fingers. When pears 

 for storage are not packed immediately after picking, special 



