358 Journal of Agricultural Research voi. xix, no. s 



Calarin {Citrus mitis, calamondin, X C. nobilis var. deliciosa, tangerine). On 

 Poncirus trifoliata. 



The one plant (CPB 50314) tested proved to be easily infected in the field. How- 

 ever, no twig or stem spots have been observed. Further trials are necessary before 

 the susceptibility of the plant can be definitely judged. 



CaX&shw {Citrus mitis , calamondin, X C. nobilis var. unshiu, Satsuma.) On Pon- 

 cirus trifoliata. 



The plant (CPB 50309) in the isolation field has reacted to canker in about the same 

 degree as the calarin. 



Among the numerous crosses of Citrus fruits made by Mr. Swingle 

 Poncirus trifoliata was used as one parent in the hope of obtaining hy- 

 brids more resistant to low temperatures than the ordinary Citrus fruits. 

 Thus, P. trifoliata has been crossed with sweet orange, sour orange, 

 grapefruit, King of Siam orange, tangerine, Clementine orange, Satsuma, 

 and citrange. While all of the resulting hybrids have proved to be 

 quite resistant to low temperatures they are equally as susceptible to 

 citrus-canker as P. trifoliata; in fact, the citrumelos are even more so. 

 The hybrids all resemble P. trifoliata in size, shape, and texture of leaves, 

 so that the more or less resistant mandarin group has had no influence 

 on the character or resistance of the hybrid. Thus, it can be safely 

 predicted that all crosses with P. trifoliata will yield a hardy hybrid 

 resembling P. trifoliata and equally susceptible. 



On the other hand, the citranges, while equally as susceptible as 

 Poncirus trifoliata, when crossed with calamondin, tangerine, Satsuma, 

 and kumquat, yield hybrids which are hardy and at the same time 

 resistant to citrus-canker. In fact, the citrangequat is even more resist- 

 ant than the kumquats themselves, in spite of the fact that it is a rather 

 rank and rapid grower. The citrangarins and citranguma, while not as 

 resistant as the citrangequat, are decidedly more resistant than the 

 citrandarin and citrunshu, the corresponding hybrids with P. trifoliata. 



These hybrids, while still retaining the trifoliate character of Ponci- 

 rus trifoliata, are more like the resistant parent in texture of the leaves. 

 In the case of the citranguma and citrangequats there is also a tendency 

 for the leaves to revert to a single leaf. Thus, any plant resistant to 

 canker when crossed with the citranges will be hardy and resistant, or 

 even more so than the original resistant parent, as shown by the be- 

 havior of the citrangequat, even though the citranges are equally as 

 susceptible to canker as P. trifoliata. 



The limequat and the orangequat, while more resistant than the lime 

 or orange, are not as resistant to canker as the kumquat. The leaves 

 resemble those of lime and orange, respectively, in size and shape, but the 

 leaf texture resembles more that of the kumquat. The citrangequat is 

 much more resistant to canker that the two hybrids named above, in spite 

 of the fact that the citrange is much more susceptible than either the 

 lime or orange. 



