Aug. 26, 1918 
Susceptibility and, Resistance to Citrus-Canker 
349 
The spots (PI. 53, B) vary in numbers per leaf from one to many. They are small 
to large (2-3 mm) (PI. 53 B, E), light to dark brown, raised, somewhat spreading, 
and corky, breaking through to the upper surface to form a slightly raised spreading 
spot. The oily outline is distinct, while the yellow zone varies in width. This 
description characterizes the spots on all the citranges. All are typical of those 
found on the Poncirus trifoliata. 
With the exception of the Willits citranges, the following citranges tested showed 
approximately the same degree of susceptibility as the Colman: Cunningham (CPB 
7665k Morton (CPB 771A (PI. 50, E) and 761AC); Rusk (CPB 7956, 11030, and 44980); 
Rustic (CPB 7934A); Sanford (CPB 7963); Savage (CPB 7961); citranges (CPB 1416 
43480, and 4349 1 )- 
Citrange, Willits (CPB 7897, seedlings), I, II. 
These plants (14 inches) have been in fine shape throughout the experiments and 
have retained their foliage. The leaves have held their dark-green color. While 
Citrus-canker is fairly well distributed over the foliage, it is the only citrange that^ 
gives promise of showing any resistance to canker. 
The citranges as a whole, with the possible exception of Willits, are 
equally susceptible to Citrus-canker, and no doubt under field condi¬ 
tions they will probably show about the same susceptibility as Poncirus 
trifoliata. This is to be expected since it is known that both parents 
of the citranges are quite susceptible to canker. 
The character of the spots are similar on all the plants and resemble 
those produced on Poncirus trifoliata. As all the leaves of the hybrids 
are trifoliate and of the same texture as those of the trifoliate orange, 
naturally the same type of spot would occur. 
Citrumelo (C. grandis, Bowen grapefruit, X Poncirus trifoliata). (CPB 4493, 4554, 
4564, seedlings), I, II, I, II, and I. 
The plants (9 to 16 inches) varied a great deal in their condition for infection. 
On the whole, considerable new growth developed, and as a consequence Citrus-canker 
appeared early in the experiments and spread rapidly to the young and mature leaves. 
Spots are present on the leaves, twigs, and thorns, and have caused considerable 
defoliation on one or two plants. Apparently as susceptible as either parent, grape¬ 
fruit or trifoliate orange. 
The spots (PI. 53, A) are numerous, medium to large, light to dark brown, raised, 
spreading, and corky, breaking through to the upper surface to form a slightly raised, 
corky and spreading spot. The oily outline is distinct, and the yellow zone varies 
in width. The spots resemble to some extent those found on both parents, but are 
not typical of either. 
Citradia (Poncirus trifoliata X C. Auraniium, sour orange). (CPB 50850, seedlings), 
I, II. 
The plants (ro inches) have been in only fair shape for infection, although new 
growth developed once during the experiment. Citrus-canker appeared shortly after 
inoculation at the punctures but spread slowly to the healthy foliage. However, 
new infections were noted at each monthly reading. Apparently the plants are quite 
susceptible but not as much so as either parent. No doubt this hybrid will prove as 
susceptible to Citrus-canker as the parents when more vigorous plants are inoculated. 
The spots are few, small to large, light to dark biown, slightly raised, compact, 
with little cork, breaking through the upper surface to form a compact spot. The 
oily outline is distinct, and the yellow zone varies in width. The spots are more or 
less typical of those found on Poncirus trifoliata. 
