July IS, 1920 Relative Susceptibility to Citrus-Canker 351 



All the plants of this group tested in the isolation field have been successfully 

 inoculated. The following numbers were represented: CPB 11196 Narute, CPB 

 1 1 164 Temple, CPB 11028 South Carolina, CPB 11 198 Japanese No. i, and CPB 

 11199 Japanese No. 2. The spots in all cases resembled those found on grapefruit. 



In susceptibility this group ranks just above the citrons in that twig and stem 

 infections are of more general occurrence. Lee (j) has obser\'ed that the Mediter- 

 ranean varieties are less susceptible than the others. This fact has also been pointed 

 out by other investigators. 

 Citrus nobilis Lour. King of Siam (^CPB 2105, seedlings), I, III. "Naranjita" (?) 



(CPB 7830, seedlings), II, III, var. dcliciosa Swingle. Tangarine (CPB 11195, seed- 

 lings), I, III. Cleopatra tangerine (CPB 11338, seedlings), I, II, III, var. unskiu 



Swingle. Satsuma (on Poncirus irifoliata Alabama), II, III. 



Twig infection, consisting of small, unruptured, scattering spots, is limited to one 

 piant (Naranjita) of this group. The spots (PI. 63, B, at left) on the leaves are small 

 to medium-sized, and, as a rule, rather scattering. The King of Siam orange is 

 apparently the most susceptible. The Satsuma plants are the most resistant. 



The spots (PI. 63, B) found on the plants of the Citrus nobilis group are very 

 characteristic, resembling to some extent those produced on kumquats. They are 

 of medium size, dark, raised, compact, mostly unruptured, with a distinctly oily 

 outline and some yellow zone. Ruptured spots are only slightly corky. 



Recent investigations by Tanaka (9) and Scott {8) show that there are a number of 

 distinct strains of Satsuma in Japan, of which three have been found in Alabama. 

 Experiments are now under way to determine the relative susceptibility and resistance 

 of these strains under field conditions. Successful inoculations have been made in 

 the field on Satsuma (PI. 64) and the Cleopatra tangerine. However, these plants are 

 not easily attacked, canker being limited to the foliage. 



All the plants tested in this group are very resistant. The writers believe that under 

 field conditions suitable for Satsuma culttu-e, and with no interplanting of susceptible 

 varieties, this orange can be grown with little or no loss from canker even when the 

 disease is prevalent. From the results so far obtained all the plants of the Citrus 

 nobilis group can be placed in this class. In the investigations on susceptibility and 

 resistance any variety showing as much resistance to canker as the Satsuma has been 

 classed as promising. 

 Citrus mitis Blanco. Calamondin orange (CPB 11265, 44305, and 7065 seedlings), 



I, 11,1 11^ iii^ and 1,1 11,1 iii^ in f^^i^^ j^j^^ j^^g, and 1919. 



Scattering stem infections and some defoliation have occurred on two of the seven 

 plants tested. From 20 to 90 per cent of the foliage of the other plants have small to 

 large, scattering spots. 



The spots (PI. 63, E) are altogether characteristic, and for the most part are unrup- 

 tured. They are round, raised, compact, and oily, somewhat like the spots described 

 for kumquat. When ruptured the spots are flat and have very little cork. 



In the field canker is limited to the foliage, and the plants are more resistant than 

 Satsuma. Lee (j) also finds that in the open Citrus mitis is truly resistant, and he 

 thinks that it is apparently more so than Satsuma. 

 Citrus sp. Kansu (Yuzu) orange (CPB 11242, seedlings), I,' II, III, in field, 1918 



and 1919. 



The Kansu orange, collected by Mr. Frank N. Meyer in north China several years 

 ago, is considered by Dr. T. Tanaka^ to be the same as the well-known "Yuzu "used 

 in Japan for many years as a stock. 



Under both field and greenhouse conditions the plants have proved resistant. 

 Apparently the leaves are quite easily infected, but the spots rarely increase in size, 



> Included in experiments of March ai, 1918. ' The data are uiipublished. 



