FURTHER DATA ON THE SUSCEPTIBILITY OF RUTA- 

 CEOUS PLANTS TO CITRUS-CANKERS 



By H. Atherton Lee 



Assistant Pathologist, Fruit-Disease Investigations, Bureau of Plant Industry, United 

 States Department of Agriculture 



INTRODUCTION 



In the present paper results are given of field observations and inocu- 

 lations with Pseudomonas citri upon plants belonging to genera more 

 or less related to Citrus. These results show a wide range of hosts for 

 Citrus-canker, and the possibility of lesions upon plants other than 

 Citrus spp. serving as sources of new infection becomes emphasized in 

 Citrus-canker eradication work. 



In the present investigation the findings of Jehle ^ as to the suscep- 

 tibility of Chalcas (Murraya) exotica Millsp., were corroborated and 23 

 other species representing 20 genera of the Rutaceae were studied. 



It seems inadvisable to present the inoculation data here, since over 

 2,000 innoculations were made. Table I presents the data in a very much 

 condensed form, and the illustrations show a few of the positive results. 

 To anyone interested the complete inoculation data are available at 

 the Bureau of Plant Industry, Washington, D. C. The inoculations and 

 the controls were dried as herbarium specimens and will also be available 

 for examination. 



In making the inoculations an infusion of the organism was painted 

 upon the leaf blade, midrib, petiole, or stem, as the case might be, with 

 a small camel's-hair brush, and then the tissue was punctured through 

 the coating of infusion with a needle. The inoculated twig was main- 

 tained in a moist condition by wrapping it in paraffin paper, including 



1 The investigations here outlined have been carried on largely at the Lamao Experiment Station of the 

 Division of Plant Industry of the Philippine Bureau of Agriculture. Thanks are due to Mr. A. M. Burton, 

 former Chief , and to Mr. S. Apostol, present Chief of this Division, as well as to Mr. F. G. Galang, Superin- 

 tendent of the Lamao station. The Citrus coDection of the College of Agriculture at Los Banos was also 

 placed at the use of the writer through the courtesy of Dr. C. F. Baker, Dean of the College. 



Many of the plants studied, belonging to genera closely related to Citrus are growing in the experimental 

 plots of Mr. W. T. Swingle, Physiologist in Charge of Crop Physiology and Breeding Investigations, Bureau 

 of Plant Industry, United States Department of Agriculture, for use in the breeding of canker-resistant 

 Citrus fruits and canker-resistant stocks. Permission to use this material has greatly facilitated the work. 

 Thanks are also due to Mr. Swingle for many helpful suggestions. Many plants related to Citrus grow wild 

 in the Philippine Islands. Prof. E. D. Merrill, Botanist of the Bureau of Science, made helpful suggestions 

 as to such plants and identified many of them. His help has been of the greatest value, and is hereby 

 gratefully acknowledged. 



It would have been difficult, if not impossible, to carry on this work without the extensive laboratory 

 facilities of the Bureau of Science so freely made available through the courtesy of Dr. A. J. Cox, Director. 



2 Jehle, R. A. susceptibility op non-oTrus plants to bacterium citri. In Phytopathology, v. 

 7, no. s, P- 339-344. 3 fJK- i9»7. 



Journal of Agricultural Research, Vol. XV, No. i 



Washington, D. C. Dec. 23, 1918 



at Key No. G-170 



