BITTER ROT OF APPLES 
Although bitter rot is known to occur on many different plants, it is of 
preéminent importance on the apple in the southern and central states. 
It is practically unknown in northeastern United States. It has been 
estimated that American growers of this fruit lose from bitter rot in some 
years ten million dollars. For the most part the disease has been called 
bitter rot, but the names anthracnose and ripe rot have been used. 
SYMPTOMS 
The disease affects the fruit and the bark of limbs and twigs. Leaves 
never show the lesions. 
On the fruit. Spots on the apple ordinarily appear in July and August, 
although they may be seen as early as June and as late as October. Lesions 
at first appear as a light-brown discoloration beneath the skin. They are 
very small but soon enlarge and become firm in texture and circular in 
outline. When the lesions are three millimeters or more in diameter, 
the surface is distinctly sunken. Usually each fruit shows only a few 
spots, but in cases of severe infection more than a thousand separate 
lesions may occur. In cases like the latter very few if any of the spots 
increase in size, but instead, after reaching a diameter of about two milli- 
meters, cease enlarging and appear as brown raised blisters. Study the 
specimen in the jar and OBSERVE :— 
1. The stage of development of the affected apple. At what 
stage, green or ripe, was the fruit affected?) Make an outline DRAWING 
of the apple. : 
2. The spots on the fruit; their size, color, distribution, appear- 
ance (sunken or raised). Estimate the number. Draw lesions on the 
apple already outlined. Have any of the many spots enlarged? If so, 
show relative size in the sketch. See illustration photograph and Jour. 
Agr. Research 4, pl. VII, fig. 1. 
In more typical cases of bitter rot only a few spots occur on each fruit. 
(See Pl. Ind. Bur. Bul. 98, pl. I and VI.) These spread rapidly, involving 
the entire fruit in a short time. Ripe apples have been inoculated with 
pure cultures of the fungus and placed in an incubator at 30° C. One or 
more specimens are provided for each student. Study the apples with the 
following POINTS as a guide. 
3. The size of the spot; its form, and color. Note any other 
characters exhibited. 
4. Do you find any evidence of the fruiting bodies of the patho- 
gene on the surface of the lesions? If so, note their distribution, color, 
and relation to the tissues of the apple (sunken or superficial ?). 
5. Study the following figures so far as available:—PIl. Ind. Bur. 
Bul. 44, pl. I, II, IV, and VI; Pl. Ind. Bur. Bul. 93, pl. I and VI; Illinois. 
Bul. 118, pl. III] and VIII. Read the legend in each case. 
Make a DRAWING to bring out the points observed. copy a figure: 
such as is shown in Pl. Ind. Bur. Bul. 44, pl. II. 
Cut the artificially infected apple longitudinally into halves (do not use 
the razor) NOTE:— 
6. Taste of the rotten flesh. Is it bitter? Examine Pl. Ind. Bur. 
Bul. 44:17, fig. 2-3. Make a prawinc to show the lesion internally, its 
depth and shape. 
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