July IS. I9J0 Relative Susceptibility to Citrus-Canker 355 



of the King of Siam orange with Poncirus trifoliata. In the field, CPB numbers 

 40175 A, 49720, 49721, 49722, 49724, and 49726 (cross between King of Siam orange and 

 Poncirus trifoliata), 49624, 49625, 49629, 49644, 49663, and 49644 (cross between Clemen- 

 tine orange and P. trifoliata), 49686, 49688, 49695, 49699, and 49712 (cross between 

 Oneco tangerine and P. trifoliata), 49732, 49735, 49737. 49746, and 49748 (cross be- 

 tween a tangerine and P. trifoliata) were tested. 



Some individual variation in susceptibility due to the condition of the plants oc- 

 curred in the greenhouse. However, all plants proved susceptible. From 30 to 100 

 per cent leaf infection, with some defoliation, was observed on the majority of the 

 plants. Some scattering twig infections occurred on all but one number. Rather 

 large, girdling spots on the old wood were found on several of the plants. 



In the isolation field, all the plants have been successfully infected. An abun- 

 dance of spots occurred not only on the leaves but on the twigs, branches, and old 

 wood. No differences were noted in the susceptibility of the plants having different 

 Citrus nobilis varieties as one parent. The Poncirus trifoliata blood predominates, 

 in that all the leaves of the above numbers are like this plant and all have the same 

 leaf texture. All the citrandarins (PI. 65, E) are about as susceptible as their parent, 

 P. trifoliata. 

 Citrunshu {Citrus nobilis var. unshiii, Satsuma, X Poncirus trifoliata). Seedlings 



and on P. trifoliata. 



These plants are very similar to the citrandarins, and their behavior towards citrus- 

 canker is likewise the same. Of the nine numbers (CPB 51102, 49607, 49608, 49611, 

 49615, 49616, 49619, 49620, and 49623) tested in the field, all proved equally suscep- 

 tible. Leaf infection was common, and some stem cankers were present. They are 

 more resistant than the citrandarins, although further tests may show them to be as 

 susceptible. The type of spot produced on all these plants is identical to those on 

 Poncirus trifoliata. 

 Cicitrange {Poncirus trifoliata X Colman citrange, and P. trifoliata X Sanford cit- 



range). (CPB 48290 and 48316A, seedlings), I, II, and I, II, III. 



These plants have shown considerable susceptibility to canker throughout the 

 course of the inoculation experiments; in fact, one plant was killed by canker, while 

 the others have been severely attacked. Without question, the cicitranges (PI. 

 65, F) are equally as susceptible as Poncirus trifoliata. 

 Citrangedin (a citrange X Citrus mitis, calamondin). Seedlings and on Poncirus 



trifoliata. 



All plants in the greenhouse (CPB 48045) and isolation field (CPB 50485, 50486, 

 50493, 50495, 50500, and 50501) have been successfully infected. The spots are 

 rather small and scattering on the leaves. Few twig and stem cankers have been 

 observed. The spots are not typical of those produced on the citranges but resemble 

 more those on Citrus mitis. The fact that these plants are more resistant to canker 

 and that the spots themselves are not similar to those on the citranges can be traced 

 back primarily to a difference in the leaf texture of the two hybrids. The citrangedins 

 are more susceptible than C. mitis, but they are more resistant than the citranges. 

 While the leaves still retain their trifoliate character, the size, shape, and texture of 

 the leaflets are different. They are also a darker graen, and apparently mattu-e 

 faster than the leaves of the citranges. 

 Citrangarin (Sanford citrange X Citrus nobilis var. deliciosa, Oneco tangerine). 



Seedlings. 



A plant (CPB 48776) of this hybrid was tested in the isolation field and has been 

 successfully infected with a few scattering spots resembling those on Satsuma. While 

 the leaves of this plant are trifoliate, they have a texture similar to that of the 

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