Building a replacement sour orange rootstock: Somatic hybridization of selected mandarin plus pummelo combinations

Sour orange has been a premier citrus rootstock worldwide due to its ability to perform on challenging soils and to produce and hold high-quality fruit. However, increasingly widespread quick-decline isolates of citrus tristeza virus (CTV) have destroyed entire industries on sour orange in some countries, and are in the process of destroying millions of trees on sour orange in Florida. CTV also threatens other citrus locations, planted heavy to sour orange, including Texas and Mexico. An acceptable alternative rootstock to replace sour orange is in high demand but has yet to be developed. Molecular analyses have recently determined that sour orange is probably a hybrid of pummelo and mandarin. We report the production of 12 new mandarin + pummelo somatic hybrids produced by protoplast fusion from selected superior mandarin and pummelo parents, in efforts to develop a suitable replacement sour-orange-like rootstock that is resistant to CTV-induced quick decline. Somatic hybrids from all 12 parental combinations were confirmed by a combination of leaf morphology, flow cytometry, and RAPID analyses (for nuclear hybridity). These new mandarin + pummelo somatic hybrids are being propagated by rooted cuttings as necessary to conduct quick-decline resistance assays and to assess horticultural performance in replicated field trials.