RELATIVE susceptibility OF CITRUS FRUITS AND 
HYBRIDS TO CLADOSPORIUM CITRI MASSEE ‘ 
By G. I/. VnvtmR, formerly Plant Pathologist, Alabama Agricultural Experiment 
Station, and Agent, Bureau of Plant Industry, United States Department of Agri¬ 
culture, and W. J. FrEderich, formerly Assistant Pathologist, Bureau of Plant 
Industry, United States Department of Agriculture 
INTRODUCTION 
During the course of citrus-canker investigations by the authors in 
Alabama, only one other Citrus disease has appeared naturally with 
any frequency. This disease is citrus scab, caused by Cladosporium 
citri Massee (5).^ 
So far as the writers are aware, no one has ever attempted to make 
any extensive observations to determine the relative susceptibility of 
Citrus plants to scab. All reports so far published on this subject have 
been based on occasional field observations of commercial varieties. A 
summary of the scattered literature reveals the fact that, with a few 
exceptions, the Citrus plants mentioned as subject to scab by all writers 
can be arranged into three groups, according to their susceptibility, as 
follows: 
1. Severely attacked. 
Sour orange. 
Rough lemon. 
Lemon. 
2. Moderately attacked. 
Satsuma and other mandarin oranges. 
Lime (^, p. 82). 
Grapefruit. 
Trifoliate orange (2, p, 244), 
3. Rarely attacked. 
Some few varieties of sweet orange (j; 7; d, p. 113)^ 
Observations on the amount of scab were made by the authors at 
times during the growing season over a period of four years on a repre¬ 
sentative lot of Citrus plants growing under approximately the same 
conditions in the canker isolation field near Loxley, Ala. They were 
made in connection with the authors' citrus-canker work, accounts of 
which have appeared (5, 4). In these publications, the type, age, 
and number of plants grown are given in some detail. Owing to the 
fact that only few of the plants were large enough to set and bear fruit, 
the degree of susceptibility to scab of the various plants is based on the 
amount of scab present on the leaves and angular wood. 
* Accepted for publication Jan. 29, 1923. Published with the approval of the Director of the Alabama 
Agricultural Experiment Station. This paper is based on cooperative investigations between the Ofi&ce 
of Crop Physiology and Breeding Investigations, Bureau of Plant Industry, United States Department 
of Agriculture, and the Department of Plant Pathology, Alabama Agricultural Experiment Station. 
2 Reference is made by number (italic) to “Eiterature cited,” p. 959. 
Journal of Agricultural Research, 
Washington, D. C. 
afa 
43325-23-—6 
(9SS) 
Vol. XXIV, No. It 
June r6, 1923 
Key No. Ala.-S 
