STRAWBERRY LEAF-SPOT 
There are at least two leaf-spot diseases of strawberries, but the one 
to which this name is applied is by far the most prevalent and injurious. 
SYMPTOMS 
The lesions on the leaves are most numerous and conspicuous, but the 
petioles and fruit-pedicles are often affected. In the material provided, 
OBSERVE :-— 
1. The spots on the upper side of the leaf, ranging in size from 
mere pink flecks to areas almost one centimeter in diameter. The large 
spots always have white centers and pink or brick-red margins. 
2. That some of the spots have coalesced to form larger lesions: 
which may cover a large part of the leaf-area. 
3. The character of the under surface of the spots as compared 
with the upper surface. To what extent are the veins affected? 
4. The elongated spots on the leaf-petioles and on the fruit- 
pedicles; the white centers of the lesions, which are very conspicuous. 
Are they surrounded by red margins as in the leaf? 
5. The small and dried berries on the diseased pedicles. One 
or two berries may develop normally before the food supply is cut off, 
after which the others shrivel and are worthless. 
‘ Make DRAWINGS to show the symptoms on the different parts of the 
ost. 
Compare these symptoms with those of the Marssonia leaf-spot on 
strawberry. 
ETIOLOGY 
The pathogene causing this disease is an ascomycetous fungus, Mycos- 
phaerella Fragariae (Tulasne) Lindau, belonging to the family Mycos- 
phaerellaceae of the order Sphaeriales. 
Life-history. 
The Primary Cycle is initiated by the ascospores of the sexual stage 
found in the dead leaves on the ground. These ascospores, while still in 
the fruit-body, germinate sending out a long germtube which pushes out 
through the mouth of the perithecium and produces a conidium at the tip. 
(See Cornell Bul. 15: 178-180.) Make a diagrammatic DRAWING to show 
production of primary conidia. 
Pathogenesis. The conidium is blown to a young leaf where it pro- 
duces a germtube that directly penetrates the upper epidermis and invades 
the tissues beneath. 
Cut out a diseased spot with the scalpel, and include a margin of the 
healthy tissue. Place the small piece in the casserole with a dropperfull 
of potassium hydroxide solution, and boil over a microburner for half a 
minute. Rinse two or three times with water, then mount and OBSERVE :— 
6. The browned or blackened appearance of the diseased area 
in contrast to that of the healthy tissue immediately adjoining it. 
7. The mycelium ramifying all the diseased tissue; its color, 
width, septation and branching. Does it extend into the tissues which 
still contain chlorophyl? 
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