JOIML OF ACMIMIRAL RESEARCH 



Vol. XII Washington, D. C, January 21, 191 8 No. 3 



IRRIGATION EXPERIMENTS ON APPLE-SPOT DISEASES^ 



By Charles Brooks, Pathologist, and D. F. Fisher, Assistant Pathologist, Bureau 

 of Plant Industry, United States Department of Agriculture 



THE PROBLEM 



The present paper deals with the effects of soil-water supply upon 

 bitter-pit, Jonathan-spot, and certain other nonparasitic spot diseases 

 of the apple (Mains sylvestris). It also includes notes upon the relation 

 of the time of picking to the development of apple-spots in storage. 



BITTER-PIT 



HISTORICAL REVIEW 



Bitter-pit was first described by Wortmann {22) ^ under the name 

 "Siippen." It has been frequently discussed in the publications of the 

 State Experiment Stations under the name "Bald win -spot" and was 

 referred to in the Nineteenth and Twentieth Reports of the New Hamp- 

 shire Experiment Station as "fruitpit." Lewis (8) and Allen (7) appar- 

 ently used the term "fruitpit" to refer to the troubles discussed later 

 in this paper under the name "cork," and McAlpine (9-12) apparently 

 included cork and also drouthspot under the name "bitter-pit." 



Various explanations have been offered as to the cause and nature of 

 bitter-pit. Wortmann (22) reported that the disease was due to abnor- 

 mal transpiration conditions and that varieties of apples in which the 

 water was conducted most readily from the deeply seated cells to replace 

 that lost by transpiration were least susceptible. 



Sorauer (19, p. 80) thought that the pits were produced by rupturing 

 of the cells during the process of swelling. In a later publication {20, p. 

 116-169) he stated that the disease was worst on porous dry soils and 

 suggested that the pits were produced by an overrapid maturing of 

 certain cell groups resulting from the checking effect of drouth upon the 

 accumulation of organic material. 



Evans (5) reported that the disease was due to a bursting of cells in 

 the apple tissue that resulted from the sudden checking of transpiration 

 at night while the root action of the tree remained vigorous. 



' Studies on Fruit Rots and Spots: III. 



2 Reference is made by number (italic) to "Literature cited," p. 136-137. 



Journal of Agricultural Research, Vol. XII, No. 3 



Washington, D. C. Jan. 21, 1918 



Iv Key No. G-133 



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