Somatic hybridisation for improvement of citrus rootstock: production of five new combinations with potential for improved disease resistance

The development of biotechnological tools such as protoplast fusion has provided a means of bypassing natural barriers related to reproductive biology of citrus found in conventional breeding systems. We report the production of 4 interspecific somatic hybrids, Cleopatra mandarin + Volkamer lemon, Ruby Blood sweet orange + Volkamer lemon, Rohde Red Valencia sweet orange + Volkamer lemon, and Rangpur lime + Sunki mandarin, and 1 intergeneric somatic hybrid, Valencia sweet orange + Fortunella obovata (Tanaka), which may be included and evaluated in rootstock improvement programs. Protoplasts were isolated from embryogenic calli and seedling leaves, and chemically fused with polyethylene glycol. Plants were regenerated via somatic embryogenesis and somatic hybridisation was confirmed by foliar morphology, cytological and DNA (RAPD) analyses. Somatic hybrids may combine required rootstock characteristics such as tolerance to citrus blight, tristeza virus, and Phytophthora, and have potential for control of tree size due to polyploidy.