MARKET DISEASES OF FRUITS AND VEGETABLES 57 



Black End 



occurrence and symptoms 



Black end, or hard end, of pear occurs in many of the pear- 

 growing sections of the Pacific Coast States. The disease is fre- 

 quently found on the Bartlett variety. Anjou, Winter Nelis, 

 Cornice, Easter Beurre, Clairgeau, and probably other varieties 

 also are affected. Black end fruits are culled out rather carefully 

 during grading and packing, and consequently severe forms of 

 the trouble are not often seen on the market. 



The first symptoms of black end become evident when the 

 fruit is a third to half grown as an apparent protrusion of the 

 calyx due to the retarded development of the tissues around it. 

 Another symptom is the enlargement of the calyx opening. At 

 this time the epidermis over the affected portion appears tight 

 and shiny. As the disease progresses, the calyx lobes turn black, 

 the tissues surrounding the calyx opening become hard, and a 

 brownish discoloration begins to form. This discoloration may 

 appear at first in separate spots, which later coalesce; in other 

 instances a large area may be completely and uniformly discolored 

 from the beginning. The final color of the affected tissues is 

 black. Cracks sometimes 1 inch or more in length may appear 

 in the blackened areas. On many specimens the discoloration is 

 confined to an area extending from the calyx for only y& to % 

 inch (pi. 12, A y B) ; on some it covers half the surface of the 

 fruit. 



The discoloration usually does not extend deep into the flesh 

 and sometimes affects only the skin. Less seriously affected fruit 

 may not be discolored at all but have hard, gritty flesh around 

 the calyx and a pointed or peaked appearance that characterizes 

 typical black end fruits. The affected part of a fruit is likely 

 to be lighter green in color than healthy fruit, until it is fully 

 ripe. Mildly affected fruits are more common in market channels 

 than fruits severely affected with black end, since the latter can 

 be more completely eliminated in grading. Black end does not 

 develop or spread in storage or in transit. 



CAUSE 



Black end of pear is a psysiological disease ; that is, no bacteria 

 or fungi are found associated with it. The disease is found on 

 fruit from trees grown on Japanese (Pyrus pyrifolia (Burm.) 

 Nakai; synonym: P. serotina Rend.) and certain other oriental 

 rootstocks; hence the conclusion has been drawn that this kind 

 of rootstock is in some way the principal cause of the disease. 

 There is strong evidence that excessive subsoil moisture in the 

 spring and other abnormal moisture conditions in the soil or a 

 shallow-lying hardpan favor the development of black end on 

 fruit from trees on these rootstocks. 



CONTROL MEASURES 



Control measures that have been suggested are (1) use of 

 French rootstock (Pyrus communis) and (2) ample subsoil 

 drainage and ample soil moisture. 



(See S3, 63, 96, 139.) 



