BOTANICAL, 

 GAi^DEri 



JOIM£ OF AGMmiAL ISEARCH 



Vol. XIX Washington, D. C, July 15, 1920 No. 8 



RELATIVE SUSCEPTIBILITY TO CITRUS-CANKER OF 

 DIFFERENT SPECIES AND HYBRIDS OF THE GENUS 

 CITRUS, INCLUDING THE Vi^ILD RELATIVES ' 



By George L. Peltier, Plant Pathologist, Alabama Agricultural Experiment Station, 

 and Agent, Bureau of Plant Indiistry, United States Department of Agriculture, 

 and William J. Frederick, Assistant Pathologist, Bureau of Plant Industry, United 

 States Department of Agriculture ' 



INTRODUCTION 



In a preliminary report {6y the senior author briefly described the 

 results obtained under greenhouse conditions for a period of six months 

 on the susceptibility and resistance to citrus-canker of a number of 

 plants including some of the wild relatives, Citrus fruits, and hybrids of 

 the genus Citrus. Since that time the plants reported on have been 

 under close observation; a third experiment has been started, and many 

 inoculations have been made in the isolation field in southern Alabama 

 during the summers of 1917, 1918, and 1919. Many more plants have 

 been successfully inoculated; others have proved to be extremely sus- 

 ceptible; while some of those tested still show considerable resistance. 

 The results obtained up to November i, 191 9, are described in this report. 



EXPERIMENTAL METHODS 



In the greenhouse, the methods used and the conditions governing 

 the inoculations described in the preliminary report were closely fol- 

 lowed. The same strain of the organism was used and was applied in the 



' Published with the approval of the Director of the Alabama Agricultural Experiment Station. The 

 paper is based upon cooperative investigations between the Office of Crop Physiology and Breeding Investi- 

 gations, Bureau of Plant Industry, United States Department of Agriculture, and the Department of 

 Plant Pathology, Alabama Agricultural Experiment Station. 



' The writers wish to acknowledge their indebtedness to Dr. K. F. Kellerman, Associate Chief, Bureau 

 of Plant Industry, United States Department of Agriculture; to Mr. W. T. Swingle, Physiologist in Charge, 

 Crop Physiology and Breeding Investigations; to Mr. T. R. Robinson, Physiologist of the same office, for 

 their cooperation and many helpful suggestions; and to Dr. O. F. E. Winberg, of the Alabama State 

 Board of Horticulture, for valuable assistance and suggestions in the field work. 



' Reference is made by number (italic) to "Literature cited," pp. 361-362. 



]pumal of Agricultural Research, Vol. XIX. No. 8 



Washington, D. C. July 15, 1920 



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