Freezing Tolerance and Growth Characteristics of USDA Intergeneric Citrus Hybrids US 119 and Selection 17-11

Abstract

Two USDA intergeneric, hybrid citrus scions, US 119 {[Citrus paradisi Mac. `Duncan' × Poncirus trifoliata (L.) Raf.] × C. sinensis Osb. `Succory'} and selection 17-11 {C. grandis US 145 × [Citrus paradisi Mac. `Duncan' × P. trifoliata (L.) Raf.]} on `Swingle' citrumelo (C. paradisi × P. trifoliata) rootstocks were examined for freeze hardiness traits (4 years) and general growth characteristics (2 years). Hardiness was compared with that of `Hamlin' orange [C. sinensis (L.) Osb.] and satsuma mandarin (C. unshiu Marc) from Fall 1993 to Spring 1997. As expected, US 119 and 17-11 were both hardier than `Hamlin' orange as determined by leaf disc electrolyte leakage (EL). Both showed freezing tolerance similar to that of satsuma mandarin, but 17-11 was significantly hardier than satsuma or US 119 at several times during the 4-year study. Trunk diameter and tree height were similar for US 119 and selection 17-11.