Bulletin 229, Diseases of Citrus in Florida


 On the Fruit:-Fruits injured by frost show certain external
and internal effects, depending upon the extent of the injury.
These may range all the way from a slight spotting of the rind
to complete destruction of the fruit, the latter occurring when
the fruit is frozen almost or entirely solid. Of the three types
of citrus fruits extensively grown in Florida for the market,
namely oranges, grapefruit, and tangerines, the fruit of the
latter is the first to be affected by frost and suffers the most
severely. Oranges freeze
more slowly than tanger-
ines and more rapidly than
grapefruit and the after-
effect is greater than it is
in the latter.
 One of the most conspic-
uous external effects of
frost is the appearance of
spots produced by oil lib-
erated from the rind dur-
ing the process of freezing.
Such spots are character-
ized by the tissue between
the oil-bearing cells becom-
ing sunken and later turn-
ing brown as the fruit re- Fig. 84.-Section through frozen orange,
 showing hesperidin crystals, appear-
 mains on the tree. The ex- ing as white specks in the pulp on the
 tent of the oil spotting, left side and the abnormally thicken-
 ed rind. From "The Cultivation of
 however, is not always an Citrus Fruits" by H. Harold Hume.
 indication of the degree of By permission of The Macmillan
 freezing, since not all fruits Company.
 on the same tree will show the same degree of injury from spot-
 ting and some types of fruit do not develop the spotting readily
 even when severely injured internally. Grapefruit and lemons
 appear to show it more readily than oranges, and tangerines less
 than oranges. When freezing is more severe, watery patches of
 considerable size may appear, especially on lemon fruits. Even
 when the tissues are not badly killed or injured, however, fruit
 affected by frost is rendered susceptible to the invasion of blue
 and green molds and other fungi which, ordinarily, would not
 readily enter sound, uninjured fruit.
 Other than the formation of ice crystals within the fruit, the