Minigrafting of Shoots, Roots, Inverted Roots, and Somatic Embryos for Rescue of in vitro Citrus Regenerants

Abstract

Minigrafting was used for rescue of tissue culture regenerants of the following four species of Citrus: sour orange (C. aurantium L. `AA CNR 31'), sweet orange [C. sinensis (L.) Osb. `Valencia Late'], lemon [C. limon (L.) Burm. `Femminello Comune'] and mandarin (C. deliciosa Tenore `Tardivo di Ciaculli'). The grafting was carried out with different scion types including shoots, roots, inverted roots and somatic embryos. This material was obtained in vitro from embryogenic style-derived callus. Seedlings of open-pollinated sour orange (C. aurantium L.), Cleopatra mandarin (C. reshni Hort. ex Tan.) and `Troyer' citrange [C. sinensis Osb. × Poncirus trifoliata (L.) Raf.] were used as rootstocks. Minigrafting of shoots, roots, inverted roots and embryos regenerated in vitro allowed successful rescue of these four species. Percentages of successful minigrafts ranged from 100% (shoots) to 2.5% (inverted roots). The probability of successful graft unions increased with the age of the rootstock. The final mean canopy leaf area (120 days after grafting) ranged from 5.2 cm2 (`Tardivo di Ciaculli' mandarin grafted on 6-month-old Cleopatra mandarin) to 157.9 cm2 (`Valencia Late' sweet orange grafted on 18-month-old Cleopatra mandarin). In this work we examined some of the variables which influenced minigrafting and we determined the efficacy of this method for rescue of in vitro regenerants of Citrus. This method is also suggested as a technique to produce a high percentage of viable plants from in vitro regenerants difficult to root.