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NOTE ON AMERICAN GOOSEBERRY MILDEW. 



By M. A. BAILEY, B.A. 



John Innes Horticultural Institution. 



During the last four years a large number of seedling gooseberries 

 have been raised here each season in the course of an experimental 

 study of the inheritance of disease-resistance and other characters in 

 this group*. 



Many of these seedlings are crosses between English and American 

 types and, as such, are either partly or wholly immune to American 

 Gooseberry Mildew, but the majority were obtained by the self- 

 pollination of various English varieties. The following observations 

 on the incidence of disease refer solely to the latter class. 



The first batch of seedlings raised — about a thousand plants — 

 were pricked out in the open (Plot A) on May 6th, 1912. They remained 

 free from disease till about the end of June. On August 25th and 

 subsequent days a careful examination of the individual plants was 

 made, and the intensity of infection and relative position of the bushes 

 noted. This examination showed that about 40 % of the plants were 

 infected with mildew, the intensity of the attack varying from "slight" 

 to "very severe." Infected bushes were found in all parts of the plot, 

 and a tendency to occur in groups suggested that the primary infection 

 was sporadic but widespread in its distribution. 



The manner in which this primary infection took place is not known 

 but it is possible that it was connected with the presence during the 

 previous year of two infected gooseberry bushes in a rather distant 

 portion of the grounds. These two bushes were destroyed in September, 

 1911, but by that time some of the perithecia would have already fallen, 

 and ascospores from these may have produced the infection in 1912. 



In cases of slight infection the mildew was found chiefly on the 

 underside of the young leaves, and frequently occurred high up on the 



* In this work I have had the collaboration first of Mr W. O Backhouse and. subse- 

 quently, of Mr J. W. Lesley. 



