Core breakdown seems to be more serious in districts having cool growing seasons than in hot ones, but it occurs in all pear growing sections. Most varieties of pears are subject to the disease. Clairgeau, Clapp Favorite, Early Harvest, Guyot, Jargonnelle, Le Conte, Madeleine, and Sudduth have been reported susceptible under New York conditions. Of the varieties grown in the Northwest, Bartlett, Bosc, Comice, and Clapp Favorite have been found most susceptible.
Various names have been applied to the disease by different authors; among these are internal breakdown, core rot, and brown heart. As the names imply, the disease is characterized by softening and browning of tissues in the region of the core (see photos). The breakdown may be closely confined to the core or may extend to surrounding flesh. Sometimes the softening is most pronounced in a zone about halfway between the center and the outside of the pear. In the early stage the affected tissues are soft and watery, and in any stage they have a disagreeable, sickening odor. In late stages the color becomes brownish or black, and in severe cases rapid breakdown and browning of the entire fruit occurs. The internal condition is often associated with a discoloration of the skin resembling senescent scald.
Core breakdown is classed as a market or storage disease of pears, but its time of occurrence depends largely upon the maturity of the fruits at the time of picking. Tests have shown that fruits harvested after optimum maturity are much more susceptible to core breakdown both in storage and on the market. The specific cause of core breakdown in pears is not known. The assumption is that pears harvested after optimum maturity are unable to slow their life processes enough for successful storage at 30° to 31 °F. Abnormal metabolism follows, and serious breakdown can occur in storage or after the pears are removed to ripen at 65° to 70 °F. Late-harvested, susceptible pears show an increase in carbon dioxide in the tissues around the core area until the onset of core breakdown. Such fruits produce an abnormally high amount of acetaldehyde until core breakdown is in an advanced stage. Although these byproducts of metabolism accompany core breakdown, no claim has been made that they are the cause of the disorder.
Pear core breakdown, Anjou
Pear core breakdown, Bartlett
Brown core of oriental pear (natural senescence)