July IS, 1920 Relative Susceptibility to Citrus-Canker 357 



All three plants (CPB 1668A) in the isolation field have been snccessfully infected. 

 Spots are limited to the leaves. No twig or stem cankers have developed. Judging 

 from the type of spot produced and the leaf texture, this hybrid will prove rather 

 susceptible. 

 Orangequat {Citrus sinensis, Hartley mandarin, X ForhmMa margarita, oval 



kumquat). On Poncims trifoliata. 



The one plant (CPB 50312) in the isolation field was easily infected. A few twig 

 and stem cankers have appeared. Judging from the leaf texture and type of spot, 

 it may prove susceptible. 

 Clemelo {Citrus nobilis, Clementine orange, X C . grandis , gTapeimit) . On Povcirus 



trifoliata. 



Both the plants in the greenhouse (CPB 49006, 49012, 49013. 49025, and 4903S) and 

 those in the field (CPB 49029, 49032 , and 49049) have been easily infected. From 50 to 

 100 per cent leaf infection with some defoliation has occurred. Most of the plants in 

 the greenhouse have large, girdling stem cankers. The spots in all cases resemble 

 those on grapefruit. The clemelos (PI. 67, B, at left) are as susceptible as grapefruit 

 and therefore can not be considered promising. 

 Siamelo {Ciirtis nobilis, King of Siam orange, X C. grandis, grapefruit). Seedlings 



and on C. grandis. 



The behavior of the siamelos (PI. 67, A) (CPB 47255B, 51588, 51598, 59852, S2G07N2, 

 52013S9, and 5202iA5)in the greenhouse, and 50320, 52007N2, 52007B3, and 51947 

 in the field, toward canker is about like that of the clemelos. However, they are 

 not quite as susceptible, in that less twig and stem infections occurred. 

 Satsumelo {Citrus nobilis var. tinshiti, Satsuma, X C. grandis, grapefruit.) On Pon- 



cirus trifoliata and C. grandis. 



Many numbers of this hybrid have b^en tested in the field (CPB 50304) and green- 

 house (CPB 50304, 52009A2, 52009G 5, 52011, and 52011G 4). Thus far, the satsu- 

 melos react to citrus-canker in the same manner and extent as the siamelos (PI. 67, B, 

 center) . 



Siamor {Citrus nobilis, King of Siam orange, X C. sinensis. (CPB 52029E 2, seed- 

 ling), III. 



The plant included in the greenhouse experiment has proved to be extremely sus- 

 ceptible to canker. Heavy defoliation and severe stem cankers occiured soon after 

 inoculation. Leaf texture and the type of spot are identical with those of grapefruit. 

 The plant is likewise as susceptible. 

 Tangelo {Citrus nobilis var. deliciosa, tangerine, X C- grandis, Florida grapefruit). 



Seedlings, and on C. grandis. 



Besides the Thornton (CPB Iv7i5, and 11034 greenhouse and L714B field) and Samp- 

 son (CPB Iy789A and 7664 greenhouse, and 7664 and 11037 field) tangelos, which are now 

 being grown to a small extent in Florida, about a dozen numbers (CPB 1230, 1257A, L16, 

 7161, 7675C, 1191, 1348A, 1262B, 40971A, 52018C2, and 52018E2 in the greenhouse and 

 CPB 52016E4 in the field) were tested. Plants of all numbers have been infected. 

 From 20 to 100 per cent leaf infection has occurred in the greenhouse. Twigs and 

 stem infections have not been general but are rather the exception than the rule. 

 In the field, canker has been limited to the foliage. The spots in all cases resemble 

 those on grapefruit. Careful observations have shown that those plants (PI. 68, B) 

 with leaves resembling the tangerine are more resistant than the numbers with grape- 

 fruit leaves. For the present the tangelos can be considered somewhat promising 

 but not quite so resistant as the Satsuma. 



