Factors affecting shoot multiplication and rooting of walnut (Juglans regia L.) in vitro

Abstract

Juglans regia is one of the most important nut crops rich in oil, protein and vitamins, and its high value timber is used for furniture, veneer and gunstock production. However, the propagation of J. regia is strongly dependent on the genotype. Slow in vitro growth results in low propagation rates and difficulties are encountered using conventional rooting methods. Embryo axes dissected from mature nuts were used as primary explants for establishing shoot cultures. The growth of walnut shoot cultures was compared on media differing in nutrient formulation (Rugini olive medium and DKW medium), concentrations of 6-benzyladenine (BA) (2.2-8.8 µM), solid and liquid medium and indole-3-butyric acid (IBA) concentration (4-20 µM). During the 21 days culture passage the Rugini medium gave significantly higher fresh mass and numbers of axillary shoots than DKW medium. The best BA concentration for J. regia explants was 2.2 µM BA. The results also indicated that solid medium (7 g L-1 agar) was better than liquid medium for shoot proliferation. The optimal IBA concentration in the induction medium for rooting of microcuttings was 12 µM IBA applied for 5 days in darkness before transfer to root expression media. There was no significant difference among two root expression media (¼ DKW + Vermiculite and ¼ MS + Vermiculite) in rooting of microcuttings after 21 days. The acclimatization of rooted microcuttings was difficult because the tendency to dessicate of plantlets and because of the occurrence of diseases due to high humidity in the greenhouse. Nevertheless, 80% of the J. regia plantlets were successfully established in the greenhouse.