PSEUDOMONAS CITRI, THE CAUSE OF CITRUS CANKER 



[a preliminary report] 



By Clara H. Hasse, 



Scientific Assistant, Fruit-Disease Investigations, 



Bureau of Plant Industry 



During the summer of 1914 reports of the rapid spread of Citrus 

 canker and the severe injury caused by this new Citrus disease were 

 received by the Bureau of Plant Industry from orange and grapefruit 

 growers in Florida, Texas, and Mississippi. It soon became evident that 

 this disease was one of unusual virulence, which made the investigation 

 of its cause a matter of urgent importance. From the reports of various 

 investigators it appears that Citrus canker was known and recognized as 

 a new disease before any specimens were received by this Bureau.^ The 

 first specimens received by the Bureau consisted of fruits, leaves, and 

 twigs of grapefruit and showed cankers in every stage of development, 

 from the youngest infections, which were scarcely more than a millimeter 

 in diameter, to the large corky forms, as much as 5 mm. in diameter. 

 A careful microscopic study was made of some of the youngest cankers, 

 and the presence of bacteria was immediately detected. Bacteria were 

 found in fresh sections and have been demonstrated in a large number 

 of stained sections, as represented in the accompanying illustration (PI. 

 IX, fig. I). 



Numerous plate cultures were made from fresh specimens of cankers 

 received at different times, and an organism was isolated which has been 

 proved to be pathogenic to grapefruit seedlings. 



Due attention has been given to all the rules governing bacteriological 

 technique, and every precaution has been observed in making the inocu- 

 lations. The inoculations were made on young, healthy, vigorously 

 growing grapefruit seedlings, which were kept in the laboratory because 

 the highly infectious nature of the disease made it impossible to carry on 

 the experiments in the Department greenhouses. Pure cultures of the 

 organism were mixed with sterile distilled water, and the suspension 

 thus obtained was placed upon the upper and the under leaf surfaces 

 by means of a sterile pipette in such a manner that the leaves were, for a 

 short time at least, covered with a film of the inoculating fluid. The 

 main stem and branches were treated in the same way. In some cases 

 the leaves and stems were punctured with a sterile needle, but this is not 



1 Stevens, H. E. Citrus canker. A preliminary bulletin. Fla. Ajrr. Exp. Sta. Bui. liz, p. 113-118. 

 fig. 44-46. Mar., 1914. 



Berger, E. W., Stevens, H. E., and Stirling, Frank. Citrus canker. II. Fla. Agr. Exp. Sta. Bui. 124, 

 p. 27-53, fig- 7-14- Oct., 1914. 



Edgerton, C. W. Citrus canker. La. Agr. Exp. Sta. Bui. 150, 10 p. Oct.. 1914- 



Wolf, F. A., and Massey, A. B. Citrus canker. Ala. Agr. Exp. Sta. Circ . 27. P- 97-ioi. 'Mus- May. 1914- 



Journal of Agricultural Research, ° ' ' 



Dept. of Agriculture, Washington, D. C. , ^P*"- 'S. 'S'S 



G — ^45 



(97) 



