i?6 DISEASES OF CULTIVATED PLANTS 



Apple rot. This disease probably occurs wherever apples 

 are cultivated; it is also found on wild crabs, causing the 

 well-known sunken patches, the flesh of which has a very 

 bitter taste, hence the term < bitter rot ' used in the United 

 States, where the disease is rampant. In 1900 it was 

 estimated that the loss to the apple crop from bitter rot 

 amounted to 10,000,000 dollars for that year. The fungus 

 concerned is Glomerella rufo-maculans (Spauld. and Schrenk) 

 with its conidial form Gloeosporium rufo-maculans (Spauld. 

 and Schrenk), perhaps better known as Gloeosporium 



FIG. 45. Glomerella rufo-maculans. i, apple 

 with conidial form of fungus ; 2, the apex of a 

 conidial form of the fungus ; the conidia are escap- 

 ing as a mucilaginous tendril ; 3, section through 

 conidial form of fruit ; 4, conidiophores bearing 

 conidia. Figs. 2-4 mag. 



fructigenum (Berk.). To the grower the fungus is most 

 obvious on the fruit, which at first appears as a faint, light 

 brown speck under the skin of the apple. These spots 

 gradually increase in size, become darker brown in colour, 

 and the surface of the diseased spot gradually sinks below 

 the general level of the surface of the fruit. At a later stage 

 minute black points, usually arranged in concentric circles, 

 appear on the brown spots. These are the Gloeosporium 

 condition of the fungus. The conidia are protruded from 

 under the cuticle in the form of sticky tendrils, and form a 



