4 MISC. PUBLICATIOiT 16 8, U.S. DEPT. OF AGEICULTURE 



APPLES 



ALTERNARIA ROT 



{Alternaria sp.) 



Alternaria rot occurs almost wholly on stored apples, but has been 

 reported as attacking apples and pears on the tree in Colorado. It 

 is most frequently found on apples held in common storage, but even 

 on them it seldom causes much loss. 



On apples from the Northwest, Alternaria rot occurs in three 

 fairly distinct types, one of which, found so far only on apples in 

 cold storage, is characterized by rather small, firm, slightly sunken 

 areas which may be brown around the edges, but are covered for the 

 most part by a rough, black crust (pi. 1, E). The second type 

 occurs on apples in cold storage and also develops from the black- 

 crust type after apples are removed from storage. It is character- 

 ized by firm, slightly sunken, rotten areas which are most commonly 

 dark brown to black, but may occasionally be light yellowish brown 

 to almost gray. The third type is found as a black rot on areas of 

 apple skin that have been weakened by scald. A similar rot is pro- 

 duced, however, by the fungus Cladosporium-^ and it is not safe to 

 attempt to distinguish between the two without laboratory study. 

 For all practical purposes in inspection, both Alternaria and Clado- 

 sporium rots can be described simply as " a black rot." So far as 

 Imown, both rots develop 'under the same conditions and neither is 

 able to spread from one apple to another to such an extent as to make 

 it commercially important. 



Alternaria rot is perhaps most frequently found following scald, 

 soft scald, arsenical injury at the calyx, and as a rot at the core, 

 especially in apples showing severe codling-moth injury. On apples 

 from the eastern part of the United States it sometimes occurs in 

 the form of a sunken ring of brown, diseased tissue half an inch or 

 more in width close around the stem. 



Alternaria rot can be distinguished from other rots of north- 

 western apples by a uniform brown or black coior; that is, by the 

 absence of a " bullseye " appearance. On eastern apples it can be 

 distinguished from black rot by the absence of pycnidia and of 

 alternating zones of light and dark brown in affected skin, and from 

 bitter rot by the absence of concentrically arranged pink or cream- 

 colored spore masses. If aerial mycelium develops, it is dark colored. 



The fungus occurs in orchards on plant debris. It apparently 

 gains entrance into the fruit through breaks in the skin, or through 

 areas of the skin that have been killed by physiological diseases such 

 as scald or by chemical injury. Control of the Alternaria rot must 

 therefore depend chiefly on careful handling during the process of 

 picking, washing, and packing, and the prevention of skin diseases 

 and injuries which open the way for rot infection. {17^ ^22, S9, 62^ 100^ 

 1S6, 137, 195, 205, 235.) 



