Occurrence and importance
Black end, or hard end, of the fruits of pear occurs in many of the pear-growing sections of the Pacific Coast States. The disease is frequently found on the Bartlett variety. Anjou, Winter Nelis, Comice, Easter Beurre, Clairgeau, and probably other varieties also, are affected. Fruits with black end are culled out rather carefully during grading and packing, consequently, severe forms of the trouble are not often seen on the market.
Symptoms
The first symptoms of black end become evident when fruits are 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 1/4 to 1/2 inch (see photos); on some it covers half the surface of the fruit.
The discoloration usually does not extend deep into the flesh, sometimes it affects only the skin. Less seriously affected fruits 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 fruits, 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.
Another disease that is frequently associated with black end is cork spot (see Pears, Cork Spot). Both disorders are often found on the same tree.
Causal factors
Black end of pear is a physiological disease associated with trees grown on Japanese pear (Pyrus serotina Rehd.) rootstocks. The disorder is believed to be caused by water imbalance in the trees, apparently due to a restricted root system. Excessive subsoil moisture in the spring damages feeder roots, and uneven irrigation during the growing season also favors the development of black end.
Control measures
French rootstocks (Pyrus communis L.) should be used, and a uniform supply of irrigation water should be provided. Since it is impossible to cull all of the fruits with black end symptoms, fruits should not be picked from trees exhibiting black end symptoms.
