IN VITRO MICROGRAFTING OF THE ALMOND CULTIVARS TEXAS, FERRASTAR AND NONPAREIL

A successful micrografting technique for the almond cultivars (cvs) Texas, Ferrastar and Nonpareil was developed using in vitro germinated seedlings as rootstocks and axenic shoot cultures established from mature tree sources as microscions. In vitro germinated seedlings, which developed 14 days after culturing in the modified Murashige and Skoog (MS) medium, were decapitated and used as rootstock. Shoot culture initiation from three almond cvs (Texas, Ferrastar and Nonpareil') was successfully achieved by culturing mature shoot tips from forced nodal buds, about 4-6 mm, on a modified MS medium containing I mg.L-1 benzyl adenin (BA). Slit micrografting on epicotyl and on hypocotyls were equally successful (83.3 % to 100 %). Grafting success was dependent on the rootstock type and lenght of the scion. Grafting success varied between 83.33 % and 100 % depending on the cultivar, when the scion contained I, 2, and 3 nodes. When almond scions, about 1.5 cm long, were micrografted on germinated seedling and cultured on proliferation medium (PM), the mean shoot length was 19.84 mm, 16.50 mm, 26.93 mm for the cvs Texas, Ferrastar and Nonpareil respectively Micro grafts could be easily cultured on a hormone-free semi-solid MS medium and were potted out after 4 to 6 weeks of culture growth. Rooted micrografted plantlets were successfully acclimatized and transferred to potting mix with 100 % survival. Although low percentages of variation were obtained in tested cvs (3.70 %, 6.25 % and 10.2 % in Texas, Ferrastar and Nonpareil'), molecular analysis showed that the developed micrografting technique produces genetically stable plantlets, at least up to 6 months of sub-culturing in cvs Ferrastar and Nonpareil. The described micrografting technique could be used for rejuvenation of shoot explants of mature elite almond cultivars and it also has potential use in the commercial production of other almond cultivars. Biotechnol. & Biotechnol. Eq. 2013, 27(1), 3493-3501