354 Journal of Agricultural Research voi. xix. no. s 



SUSCEPTIBILITY OF CITRUS HYBRIDS 



Faustrime* {Citrus aurantifolia, West Indian lime, X Microcitrus australasica) . (CPB 



49819, 49823, and 49835, cuttings), II; II and III. 

 Faustrimon [Citrus limonia, lemon, X Microcitrus australasica). (CPB 49841, 49843, 



and 49844, cuttings), II; II and III. 

 Faustrimedin (O'/rwj miiis, calamondin, X Microcitrus azistralasica). (CPB 47431, 

 cuttings), I, III, in field, 1918. 



From 30 to 90 per cent of the foliage of these plants is infected with scattering 

 spots (PI. 63, A). Some defoliation from canker has taken place. Thorn, twig, and 

 stem cankers are common (PI. 63, A). The spots are similar to those found on Micro- 

 citrus australasica, except that they are larger and more ruptured. The spots on the 

 twigs and stem are of a girdling nature. The last number has been tested in the 

 field with positive results on the foliage only. These hybrids are more susceptible 

 than M. australasica. 

 Citr&nge (Poncirtis trifoliata, X Citrus sinensis) . Seedlings. 



Two or more plants of each number of the following citranges have been given a 

 thorough test in both the greenhouse and the field: Colman (CPB 7896 and 772 AC), 

 Rusk (CPB 7956, 1 1030, 7895, and 716), Rustic (CPB 7934 A), Sanford (CPB 7963 and 

 1423 AB), Savage (CPB 7961 and 1423 AB), Willits (CPB 7897 B, 7960, and 777 AB), 

 Etonia (CPB 749 AB), and citranges (CPB 1425 AB, 1416, 43931, 43480, and 43434). 



The percentage of leaf infection has varied from 10 to 100 per cent, depending on 

 the condition of the plant. The majority showed over 50 per cent of infected leaves. 

 Defoliation of the leaves due to canker was common. Large girdling spots have 

 appeared on the stems of most of the plants. The spots (PI. 63, D) on the leaves and 

 twigs are similar to those produced on Poncirus trifoliata. 



While some variations have occurred in the susceptibility of the different numbers, 

 the results as a whole show that all the citranges (PI. 65, B) are equally as susceptible 

 as Poncirus trifoliata (PI. 65, B). Thus none of the citranges tested are of any promise 

 in the search for a resistant stock. 

 Citnunelo {Citrus grandis, Bowen grapefruit, X Poncirus trifoliata). (CPB 4493, 



4554, 4564, and 4475, seedlings), I, II; I, II (2 plants); I and I, III. 



Almost 100 per cent leaf infection, with some defoliation, occurred on all the plants. 

 The spots (PI. 63, D) are large, scattering to many, and resemble those produced on 

 Poncirus trifoliata except in size. Girdling spots of various sizes occurred on most 

 of the plants, not only on the twigs and branches but even on the old wood. 



The citrumelos (PI. 65, C) are even more susceptible than Poncirus trifoliata and, 

 therefore, are of no economic value from the standpoint of their behavior to citrus- 

 canker. 



Citradia {Poncirus trifoliata, X Citrus aurantium, sour orange). (CPB 50850, seed- 

 lings), I, II. 



While from 40 to 80 per cent of the leaves have been infected with small, scattering, 

 typical spots, no spots have been produced on the twigs or branches. Apparently, the 

 citradia (PI. 65, D) is a slower grower than the rest of the Poncirus trifoliata hybrids. 

 The susceptibility of these plants, however, is sufficient to bar them from fvulher tests. 

 Citrandarin {Citrus nobilis X Poncirus trifoliata). Seedlings. 



In the greenhouse, plants of the following numbers have been given a thorough trial. 

 CPB 40210, 40303, 40315, 40368 B, and 48529. All of these numbers are hybrids 



* The hybrids were supplied by ^Ir. Walter T. Swingle, who informs me that they were labeled with the 

 aboratory names, for the most part still unpublished. Citrange, limequat, and tangelo have been pub- 

 lished, but citnmshu, cicitrange, citrumelo, citradia, citrandarin, faustrime, faustrimon, faustrimedin, 

 citrangedin, citrangarin, citranguma, citrangequat, limelo, bigaraldin, orangelo, orangequat, clemelo, 

 siamelc^ satsumelo, siamor, calarin, and calashu are tentative laboratory names that may not be used 

 in the reports which taay later be issued concerning hybrids. Many hybrids which in this paper are 

 given separate names will in later reports be group>ed under some one name. 



