956 
Journal of Agricultural Research voi. xxiv. No. n 
RELATIVE susceptibility TO SCAB 
With the exception of Poncirus trifoliata (L.) Raf., all the wild relatives 
of Citrus so far grown in the isolation field are nonsusceptible to scab. 
With this exception, scab appears to be strictly limited to Citrus fruits 
and their hybrids. In this respect it differs from citrus-canker, which 
can attack a large number of Rutaceous plants. 
In Table I an attempt has been made to list the majority of Citrus 
fruits and their hybrids grown in the isolation field, and to indicate 
the average relative susceptibility of these plants to scab, as has been 
observed at times over a period of four years under various conditions. 
The relative susceptibility of the various species and varieties to scab 
as given in the table is tentative. Many plants are quite susceptible 
to scab in the early spring when the first growth pushes out, while no 
scab appears on the foliage of the second or succeeding growths. Some 
plants, on the other hand, present a more or less scabby appearance during 
the whole season. Whether the plants placed under the first heading 
are nonsusceptible in a strict sense, only direct inoculations will ‘^how. 
Table i. —Relative susceptibility of Citrus fruits and hybrids to scab 
Genus and species. 
Scab 
not ob¬ 
served. 
Slightly 
suscep¬ 
tible. 
Suscep- 
tib:e. 
Very 
suscep¬ 
tible. 
X 
X 
Citrus hyslrix, round leaf form. 
X 
C. hystrix, pointed leaf form. 
X 
Citrus sp., Ichang lemon. 
X 
C. grandis, grapefruit seedlings. 
X 
Duncan. 
X 
Sullivan.. 
X 
Shaddock, Fla. 
X 
Pummelo, Hirado Buntan. 
X 
Chinese, Orangedale.. 
X 
Marks. 
•X 
Indian, Roeding. 
X 
Siamese. 
X 
C. sinensis, orange, navel.•.. 
X 
Temple. 
X 
Japanese No. i. 
X 
Japanese No. 2 .. 
X 
Sekkan... 
X 
Pan Van... 
X 
Tankan... 
X 
C. nobilis, orange. King. 
X 
C. nobilis var. deliciosa, tangerine, Cleopatra. 
X 
C. fiohilis var. unxhiuj Satsuma. .. 
X 
C. mitis- Calamondin. 
X 
Citrus sp. Kanzu. 
X 
Citrus sp. Natsu-mikan. 
X ■ 
Citrus sp. orange, Naranja. 
X 
Citrus sp. orange, Narute. 
X 
Citrange (^P. trifolioto X C. sinenses') . 
X 
X 
Citrandarin (^P. trifoliata X C- nobilis) . 
X 
X 
Citrunshu (i^, trifoliata X C. nobilis var. unshiu) ... 
X 
Citrangeguat (citrange X Fortunella margariia) . 
X 
Citranguma (citrange X C. nobilis var. unshiu) . 
X 
Citrangarin (citrange X C. nobilis var. deliciosa) .'.. 
X 
Citrangedin (citrange X C. mitis) .. 
X 
X 
LimeQuat (C. aurantifolia X F. margarita) .. 
X 
Bigaraldin (C. aurantium X C. mitis) . 
X 
Orangelo (C*. sinensis X C. grandis) . 
X 
Oranguma (C. sinensis X C. nobilis var. unshiu) . 
X 
Orangef(Uat (C. xinpttt.vix V F. 'm.n.rgarifn') . 
X 
X 
Satstunelo (C. nobilis var. unshiu X C. grandis) . 
X 
X 
Clemelo (C. nobilis var. deliciosa X C. grandis) . 
X 
Siamelo (C. nobilis X C. grandis) . 
X 
Tangelo (C. nobilis var. deliciosa X C, grandis) . 
X 
Siamor (C. nobilis X C. sinensis) . 
X 
Sopomaldin (C. grandis X C. mitis).. . 
X 
Calashu (C. mitis X C. nobilis var. unshiu) . 
X 
Citraldin (P fjrifnliqin '>( 'nj.jfi^) . 
X 
Calarin (C. 'm.il.iv V C. nnhili^ var dpl-irincn') . 
X 
False hybrids . 
X 
X 
