Micropropagation of Juglans regia L

Micropropagation of Juglans regia and hybrids may either be initiated from zygotic embryos, shoots, branches or adult plant scions (Leslie & McGranahan, 1992). Like several other woody species, walnut tree explants obtained from embryonic tissues are easily established in vitro and multiplied by direct organogenesis; however, this often happens with little early care. Explants obtained during the fruit production phase can also be multiplied this way (Leslie & McGranahan, 1992). The experience with Juglans regia cv. Chandler shows that individuals reproduced in vitro by culture of nodal segments have earlier fruit production as compared with those obtained by traditional grafting techniques, besides presenting a stronger rooting system and avoiding incompatibility between rootstock and scions (Hasey et al., 2001; López, 2001).

The major problem associated with in vitro introduction of walnut mature material is the endogenous bacterial contamination and phenolic compound exudation. However, the use of renewed material from consecutive pruning or macrografting allows us to develop shoot tips with high growth rates (Claudot et al., 1992; Leslie & McGranahan, 1992), a practice that could reduce such problem in later phases of the culture. The use of annual growth shoot tips (Leslie & McGranahan, 1992), meristems (Meynier, 1984) as well as tips obtained from epicormic sprouts appear to be the best alternatives for introduction of explants from field to in vitro conditions (Heile-Sudholt et al., 1986).